Title of Invention	"DEVICE FOR CONTROLLED OF TEMPERATURE BYPASS"
Abstract	The present invention relates to a device for control of temperature bypass mechanisms. More particularly, the present invention relates to a device for controlling bypass of auto-mode in controlled temperature environments such as air-conditioned railway coaches, air-conditioned buses, auditoria and other such locations. The present invention also relates to thermostat capable of implementing a method for controlled bypass of the auto-mode in railway AC coaches, relay management and interlocking technique to achieve said controlled bypass and smart selection of mode using a microcontroller based switch panel. [Figure 2]

Title of Invention

"DEVICE FOR CONTROLLED OF TEMPERATURE BYPASS"

Abstract

The present invention relates to a device for control of temperature bypass mechanisms. More particularly, the present invention relates to a device for controlling bypass of auto-mode in controlled temperature environments such as air-conditioned railway coaches, air-conditioned buses, auditoria and other such locations. The present invention also relates to thermostat capable of implementing a method for controlled bypass of the auto-mode in railway AC coaches, relay management and interlocking technique to achieve said controlled bypass and smart selection of mode using a microcontroller based switch panel. [Figure 2]

Full Text	DEVICE AND METHOD FOR CONTROLLED TEMPERATURE BYPASS FIELD OF THE INVENTION The present invention relates to a device for control of temperature bypass mechanisms. More particularly, the present invention relates to a device for controlling bypass of auto-mode in controlled temperature environments such as air-conditioned railway coaches, air-conditioned buses, auditoria and other such locations. The present invention also relates to thermostat capable of implementing a method for controlled bypass of the auto-mode in railway AC coaches, relay management and interlocking technique to achieve said controlled bypass and smart selection of mode using a microcontroller based switch panel. The invention generally relates to industrial controls and specifically a temperature controller capable of implementing an interlocking technique for controlled bypass of auto mode in railway AC coaches. The invention also discloses a method for relay interlocking within the thermostat and control interlocking within the control panel for implementation of this controlled bypass. BACKGROUND OF THE INVENTION Air conditioned railway coaches use solid-state temperature controllers with determinate technical specifications prescribed by various regulatory authorities. For example, in India, the governing specification is RDSO/SPEC/PE/0025 rev 0 Amendment No. 3, prescribed by the Railways Designs and Standards Organisation. The thermostat forms a part of the control panel for the air conditioning system in a railway coach. The thermostat conventionally used in railway air-conditioned coaches consists of the following: 1. Sensor: senses temperature at the return air grill and transmits the same to the controller using an analog or digital signal. A sensor when used along with a conditioning circuit at the sensor end is known as a sensor module. 2. Display: An LCD/ LED display that shows the temperature of air as sensed by the sensor. 3. Heating relay(s): An electromechanical or Solid State Device that switches on/off the contactor switchgear devices that drives the heaters. 4. Cooling Relay(s): An electromechanical or Solid State Device that switches on/off the contactor switchgear devices that drives the compressors. 5. DISP Key: The thermostat can consist of a single or multiple keys. Presently the thermostat has just one DISP key with multiple functions. Pressing the key activates the display that starts showing the temperature. Long pressing key unlocks the system and pressing the same key when the system is unlocked, changes the temperature setting from low to high or vice versa. 6. Long pressing the DISP switch on the keypad results in the system getting unlocked for temperature setting. Once unlocked, the temperature setting can be changed only by the use of this switch. 7. LED's: For indicating the state of the heating relay, cooling relay, temperature setting (low and high), Fault condition, Power supply status. 8. Power supply: The SMPS power supply that steps down the 110V Ac/Dc power supply as it exists in AC control panel to working (12V) for the electronic circuits. 9. Microcontroller: The brain of the thermostat, which takes the sensor input, converts it into a digital read-out and takes control actions. This is the device that actuates relays and display and various LED's. 10. Controller Module: An electronic circuit consisting of all the above components except the sensor/ sensor Module is known as controller module. 11. Temperature Controller: All the above parts along with the connectors, interconnecting cables and associated circuit are known as temperature controller. Figure 1 is a schematic circuit diagram of a conventional thermostat used in railway air conditioned coaches. It is further possible to enhance the temperature controller by adding additional keys and additional software algorithms to achieve the following: a. The user can set the temperature of the thermostat according to convenience in certain predefined steps or as a continuous gradient. b. The thermostat can be interfaced with an external temperature selector switch that may work on analogue or digital signals or a potential divider circuit to set the temperature for the thermostat. c. Add additional sensors/ sensor Modules to the system to achieve various operational objectives. The prior art circuit shown in Figure 1 incorporates several safety interlocks. Specifically, the interlocks Airvane relay, HP and LP cutouts are built into the system when these interlocks have a truth status (that is their status is all OK), phase is available at common terminal of RSW3. The following interlocks are critical for the AC plant: 1. Manual cooling bypass selection: The cooling circuit is switched on directly bypassing the thermostat's control interlocks. 2. Manual heating bypass selection: The cooling circuit is switched on directly bypassing the thermostats control interlocks. 3. Auto Mode: The manual interlocks are bypassed and all control switching of the cooling and heating circuit is done through the thermostats heating and cooling pilot relays (inter-locks) 4. Vent Mode: Neither cooling, nor heating will be switched on. Only the fan of the AC plant will be switched on and thermostat's control circuit will be bypassed. The switching of the cooling and heating circuit in any of the above-mentioned selections is done through several interlocks that follow thereafter. The prior art circuit suffers from several disadvantages which are listed hereinafter: The control wiring of the control panel is such that the thermostat can be bypassed very easily with the turn of a switch, called the bypass switch. This switch, as it is being put to use presently, is a single pole-four position switch or similar. By turning this switch known as RSW3 in the RDSO control wiring, the user can simply select between Auto, Manual Cooling, Manual Heating, Or Vent control modes. The RSW3 switch is also known as the bypass switch as it provisions the bypass modes. The bypass switch is an important element. For example, if the thermostat fails, the bypass switch is used to switch on the heating and cooling of the AC plant, instead of through the cooling and heating relays of the thermostat. Similarly, if the thermostat is operational, but the temperature is not adequately maintained due to any number of reasons, the coach attendant or technician, can, for a certain time period, convert the system from auto-mode to manual heating or cooling by bypassing the thermostats and letting the AC plant run without any temperature control. The bypass switch is often prone to misuse. The coach attendant/technician may fail to remove the switch from bypass mode into auto-mode. As a result, the air conditioning plant may operate without any temperature control for a prolonged period of time resulting in over-chill or over-heat and cause passenger discomfort and also result in a high load on the system. The margin for human error in terms of the coach attendant/technician simply forgetting to convert the system from manual to controlled mode by undoing the bypass despite the thermostats being in working state is also high. Bypassing the thermostat leads to following problems: 1. Stress and damage to the AC plant's compressors due to long running time without getting switched off. 2. Potential fire hazards if manual heating is left switched on unattended for extended hours. 3. Discomfort to passengers due to over-heating and over-cooling. Problem Statement 2: Electrically noisy environments The problem of common mode noise in electrical circuits. Some of the coaches in Indian Railways are being run on inverters where the problem of common mode noise has been found to exist. This problem results in incorrect firing of feedback circuits specifically opto-couplers in case they are not shielded against common mode noise. Incorrect firing of feedback circuits used in the control results in incorrect operation of the unit. Another significant problem in air conditioned environments such as railway AC coaches is that of electrical fast transients, surges and spikes in the circuit. For example, air-conditioned railway coaches, particularly those running on invertors are known to be electrically noisy. The noise persists on two levels: 1. Negatively affects feedback circuits: 2. Disturbs/Corrupts analog/digital signals from the sensor to the controller. Switching of inductive loads like compressors generates spikes and surges in the electrical circuits. Control wires running close to these electrical circuits are generally known to pick up these induced transients that ultimately sink through the control circuits, in the process degrading or damaging them. The currently used thermostats fitted on Indian Railway Coaches use analogue sensor/sensor modules connected to controller through an interconnecting cable that carries a sensor signal to the controller. The inventor's model developed earlier uses digital Rs485 based communication between the sensor and the controller. If EFT are conducted/ induced on the sensor cable, they sink through the electronic circuits of the controller, which can potentially damage them. OBJECTS OF THE INVENTION The primary object of the invention is to provide a device and a method for temperature controlled bypass which obviates the problems of the prior art circuits discussed above. It is another object of the invention to provide a device for permitting bypass of an airconditioning system which allows bypass by the coach attendant or an authorized personnel, whether the thermostat is functioning in OK status or the thermostat is dysfunctional. It is a further object of the invention to provide a device and method for controlled temperature bypass in air conditioned environments wherein a direct bypass of the automatic control circuit is enabled in case the thermostat is not functioning and has a defect in the power supply or the sensor or the controller, thereby allowing the AC Plant (heating and cooling) to come on when bypass is selected manually. It is another object of the invention to provide a device and method for controlled temperature bypass in an airconditioned environment where even if the thermostat is functioning and has still been bypassed through manual selection or manual cooling, the thermostat is enabled to take over control of the plant from the bypass circuit automatically on expiry of a predetermined period of time and continue switching of heating and cooling relays even if the selector switch is not returned to Auto mode and stays at manual cooling/ heating mode. It is another object of the invention to provide a device and method for controlled temperature bypass wherein even if the thermostat is be switched off either due to power supply failure or deliberate human interference, the thermostat allows bypass circuit routed through a Rotary switch to activate the cooling and heating contactors in response to user selection of manual cooling or manual heating. It is another object of the invention to provide a device and method for temperature controlled bypass which is functional in all forms of airconditioning environments irrespective of the surrounding electrical noise. SUMMARY OF THE INVENTION The present invention provides a device for controlled temperature bypass for airconditioned environments. The device of the invention provides a circuit which solves the problems associated with the prior art and is described in detail below. Accordingly, the present invention provides a device for controlled temperature bypass in an airconditioned environment, the device comprising a control means connected at one end to a relay control means and at another end to at least two isolation means, the isolation means being connected individually to a neutral input through a common line and to a heating relay and a cooling relay through dedicated separate lines, the heating relay consisting of a first set of bypass heating relay and a bypass cooling relay, and a second set of cooling relay and a heating relay, the relay sets being in turn connected to a cooling contactor and a heating contactor respectively and thereby to a second neutral input, a selector switch being provided connected to a heat bypass and a cool bypass at two points and to auto mode and a vent fan at the other two points, enabling selection from heat bypass, cool bypass, vent fan and auto mode. In one embodiment of the invention, the control means is a microcontroller. In another embodiment of the invention, each isolation means consists of an opto-coupler. In another embodiment of the invention, a smart relay interlock is used coupled with a feedback loop into the device. In another embodiment of the invention, bypass rotary switches are provided interfaced with the control means to provide digital or analog inputs into the device. In another embodiment of the invention, the inputs are galvanically isolated from the control circuit. In another embodiment of the invention, the controller is provided with heating and cooling switches which are interlocked. In another embodiment of the invention, at least one timer means is provided to time duration of bypass on receipt of a signal from the isolation device to the control means, said at least one timer means being a heat timer means or a cool timer means. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Figure 1 is a circuit diagram of a prior art wiring circuit. Figure 2 is a control circuit according to one embodiment of the present invention. Figure 3 is a circuit diagram of a controlled bypass wiring schema for RMPU railway AC coaches with HR-CR hardwired interlocking through HR relay using 4 SPDT Pilot switching devices. Figure 4 is a circuit diagram of a controlled bypass wiring schema for RMPU railway AC coaches with HR-CR hardwired interlocking through CR relay using 4 SPDT Pilot switching devices. Figure 5 is a circuit diagram of a controlled bypass wiring schema for RMPU railway AC coaches without hardwired HR-CR interlocking using 4 SPDT Pilot switching devices. Figure 6 is a circuit diagram of a controlled bypass wiring schema for RMPU railway AC coaches with HR-CR hardwired interlocking through HR relay using 2 DPDT Pilot switching devices. Figure 7 is a circuit diagram of a controlled bypass wiring schema for RMPU railway AC coaches with HR-CR hardwired interlocking through CR relay using 2DPDT switching devices. Figure 8 is a circuit diagram of a controlled bypass wiring schema for RMPU railway AC coaches without hardwired HR-CR interlocking using 2 DPDT switching devices. DETAILED DESCRIPTION OF THE INVENTION The present invention uses a novel circuitry to filter out common mode noise or uses optocouplers with inbuilt common mode noise shield. Digital communication is used between sensor and controller using an RS485 transceiver IC and Modbus protocol. The RS485 transceiver is isolated from the processor for a minimum of 1.5Kv using optocouplers and i-couplers. Thus, any EFT on the sensor cable is isolated from the control circuits of the sensor module and the controller module. An SMPS with two isolated outputs is used to drive the controller module and the sensor module. The isolation transformer is also used to provide an isolated supply from the sensor module. Thus, the controller module and the sensor module are protected from transients on the interconnecting cable. As explained above, it is one of the objects of the invention to provide a method by which bypass of the system can be allowed by the coach attendant/technician irrespective of whether the thermostat is functioning or is dysfunctional. Other objectives include permitting a direct bypass by the thermostat of the automatic control circuit and allowing the AC plant to resume or start function when bypass is selected manually in case the thermostat is dysfunctional. In the event the thermostat is not defective and has still been bypassed through manual selection or manual cooling, the thermostat should be enabled to take over control of the plant from the bypass circuit automatically at the expiry of a predefined time period and continue the switching of the cooling and heating relay even if the selector switch is not returned to Auto mode and stays at manual cooling/ heating mode. Similarly, when the thermostat is be switched off due to either power supply failure or deliberate human intervention, it should still allow bypass circuit routed through the Rotary switch to activate the cooling and heating contactors in response to user selection of manual cooling or manual heating. The above objectives are achieved by using a smart relay interlocking technique coupled with a feedback loop into the system. The system is a microcontroller based system and the embedded software conducts the algorithms for achieving the objectives mentioned above. The microcontroller in addition to the bypass algorithms also has embedded on its software the logics required for temperature control of the AC plant. The present invention will now be described with reference to the accompanying drawings, which are non-limiting of the scope of the invention. The modified control circuit diagram of the invention is shown in Fig 2. The hardware and software of the electronic thermostat is modified to include controlled bypass manifest itself on the thermostat. As can be seen from Fig. 2, the circuit consists of a microcontroller connected to a relay driver at one end and connected at another end to at least two isolation devices marked as opto-inputs. The isolation devices (opto-inputs) are in turn connected individually to a neutral input through a common line. The opto-inputs are also connected through separate lines to heating and cooling relay respectively. The relay driver drives a set of two relays - each set consisting of one heating and one cooling relay (Kl and K3; K2 and K4). The first set (Kl and K2) are bypass relays for heating and cooling respectively. The relay sets are in turn connected to a cooling contactor and a heating contactor respectively and thereby to a second neutral input. A selector switch is provided connected to a heat bypass and a cool bypass at two points and to auto mode and a vent fan at the other two points. Thus, the selector switch can select from heat bypass, cool bypass, vent fan and auto mode. The device of the invention envisages disconnecting manual cooling and manual heating control signal wires (connecting the bypass switch to the cooling and heating contactors) from the heating and cooling contactors and routing them through the enhanced thermostat. Enhanced thermostat implies thermostat with added hardware and embedded software to execute new algorithms. The device and method of the invention will be described in greater detail below with reference to Fig. 3 to Fig. 8. Turning now to Figures 3 to 5, the bypass heating circuit is activated when manual heating (position 5 of Selector Switch) is selected on selector switch. The thermostat receives the signal through the corresponding isolation device, marked "opto input". The heating SPDT pilot switching devices "Relay HR" and "Relay_HR_BP" are switched off, irrespective of the temperature at the sensor. This makes the Phase available through the NC contact of "Relay_HR_BP" to the heating contactor, switching on the heating circuit of the AC plant. When the controller receives a signal through the isolation device that manual heating has been selected on the selector switch, a software timer is started that times the "miration of the bypass. This timer is referred to as timer_heat_bypass in the figures and herein and this state of the controller is referred to as heating bypass state. At the expiry of the predefined time limit of bypass, the thermostat starts switching the heating pilot switching device RelayHRBP to actuate/ deactivate the heating circuit. The RelayHR is kept in off state. However, the status,of the RelayHR does not affect the circuit. When the sensor temperature falls below the pre-set cut-in temperature the heating switching device Relay_HR_BP is switched off, bringing Phase to the NC contact and thus activating the heating bypass circuit. When the temperature goes above the predefined cut-off temperature, Relay_HR_BP is switched on, deactivating the bypass heating circuit. When the system is on Auto Mode however, the relay logic is inversed. When the sensor temperature falls below the pre-set cut-in temperature the heating switching device Relay_HR is switched on, bringing Phase to the NO contact and thus activating the heating bypass circuit. When the temperature goes above the predefined cut-off temperature, Relay_HR is switched off, deactivating the bypass heating circuit. The bypass cooling circuit is activated when manual cooling (position 4 of Selector Switch) is selected on selector switch. The thermostat receives the signal through the corresponding isolation device, marked "opto input". The cooling SPDT pilot switching devices "Relay CR" and "Relay_CR_BP" in figures 3, 4 and 5 are switched off, irrespective of the temperature at the sensor. This makes the Phase available through the NC contact of "RelayCRBP" to the cooling contactor, switching on the cooling circuit of the AC plant. When the controller receives a signal through the isolation device that manual cooling has been selected on the selector switch, it starts a software timer that times the duration of the bypass. This timer is being referred to as timer_cool_bypass in the figures and herein and this state of the controller is referred to as cooling bypass state. At the expiry of the predefined time limit of bypass, the thermostat starts switching the cooling pilot switching device Relay_CR_BP to actuate/ deactivate the cooling circuit. The Relay_CR is kept in off state, its status however does not make a difference on the circuit. When the sensor temperature falls below the pre-set cut-in temperature the cooling switching device Relay_CR_BP is switched off, bringing Phase to the NC contact and thus activating the cooling bypass circuit. When the temperature goes above the predefined cutoff temperature, Relay_CR_BP is switched on, deactivating the bypass cooling circuit. When the system is on Auto Mode however, the relay logic is inversed. When the sensor temperature goes above the pre-set cut-in temperature the cooling switching device Relay_CR is switched on, bringing Phase to the NO contact and thus activating the cooling bypass circuit. When the temperature goes below the predefined cut-off temperature, Relay_CR is switched off, deactivating the bypass coohng circuit. In Figs. 3 and 4, the heating and cooling pilot switching devices in the controller are further optionally interlocked. They can also be not interlocked as shown in Fig. 5. Interlocking as shown in Figs. 3 and 4 has an added advantage of providing additional switching safety as it disallows the cooling and heating circuit to switch on together. Turning now Figs. 6 to 8, bypass rotary switch contacts pertaining to "manual cool" and "manual heat" (marked 4 and 5 on rotary switch in Fig. 6-8 and in Fig. 1) are interfaced with the temperature controller as two digital or analog inputs into the system. These inputs are additionally galvanically isolated from the control circuit. Galvanic isolation can be bypassed for a non-isolated connection to the microcontroller also. These inputs will indicate to the controller whether the coach attendant has put the unit under manual cooling/ manual heating. Additional (optional) inputs for auto and vent mode can also be taken into the system. The bypass cooling circuit is now actuated through switches devices in the controller. These switches devices can be 2 SPDT relays as in Figs. 6-8 or a single DPDT switch. As shown in Figs. 6-8, the bypass cooling circuit is activated when manual cooling (position 4 of Selector Switch) is selected on selector switch. The thermostat receives the signal through the corresponding isolation device, marked "opto input". The cooling DPDT pilot switching device, irrespective of the temperature at the sensor is switched off. This makes the Phase available at the coohng contactor, switching on the cooling circuit of the AC plant. When the controller receives the signal through the isolation device that manual cooling has been selected on the selector switch, it starts a software timer to time the duration of the bypass. This timer is being referred to as timer_cool_bypass in this document. This state of the controller is referred to as cooling bypass state. At the expiry of the predefined time limit of bypass, the thermostat starts switching the cooling pilot switching device to actuate/ deactivate the cooling circuit. When the sensor temperature exceeds the pre-set cut-in temperature the cooling switching device is switched off, activating the cooling bypass circuit. When the temperature falls below the predefined cutoff temperature, the cooling switching device is switched on, deactivating the bypass cooling circuit. When the system is on Auto Mode however, the relay logic is inversed. When the sensor temperature goes above the pre-set cut-in temperature the cooling pilot switching device is switched on, bringing Phase to the NO contact and thus activating the cooling bypass circuit. When the temperature goes below the predefined cut-off temperature, cooling pilot switching device is switched off, deactivating the bypass cooling circuit. The bypass heating circuit is activated when manual heating (position 5 of Selector Switch) is selected on selector switch. The thermostat receives the signal through the corresponding isolation device, marked "opto input". The heating DPDT pilot switching device, irrespective of the temperature at the sensor is switched off. This makes the Phase available at the heating contactor, switching on the heating circuit of the AC plant. When the controller receives the signal through the isolation device that manual heating has been selected on the selector switch, it starts a software timer that times the duration of the bypass. This timer is being referred to as timer_heat_bypass in this document. This state of the controller is referred to as heating bypass state. At the expiry of the predefined time limit of bypass, the thermostat starts switching the heating pilot switching device to actuate/ deactivate the heating circuit. When the sensor temperature falls below the pre-set cut-in temperature the heating switching device is switched off, activating the heating bypass circuit. When the temperature goes above the predefined cutoff temperature, the heating switching device is switched on, deactivating the bypass heating circuit. When the system is on Auto Mode however, the relay logic is inversed. When the sensor temperature falls below the pre-set cut-in temperature the heating pilot switching device is switched on, bringing Phase to the NO contact and thus activating the heating bypass circuit. When the temperature goes above the predefined cut-off temperature, the heating pilot switching device is switched off, deactivating the bypass heating circuit. The heating and cooling pilot switching devices in the controller can further be interlocked as shown in Fig. 6 and 7 or not interlocked as shown in Fig. 8. Interlocking has the added advantage of providing additional switching safety as it disallows the cooling and heating circuit to switch on together. The Heating Bypass Circuit and the Cooling Bypass circuit in Figs. 3-8 are routed through a NC contact of the pilot switching devices. The advantage of using the NC contact is that in case the controller fails and the user puts the system into the bypass mode, the rest/ de-energized state of the relay being NC contact the phase signal from the bypass switch will still find a conductive path to the heating/cooling circuit allowing the system to switch on. Thus, the user is allowed to manually activate the cooling or heating bypass circuits even when the power supply of the controller units failed. Thus the thermostat becomes the governing devices for manual as well as auto modes except when the power supply of the unit has failed. In all Figs. 3-8, when the timer_heat_bypass or timer_cool_bypass reach their predefined limits, the controller will over ride the manual bypass bringing the system to controlled state (by energizing the relays) subject to following conditions: a. The thermostat in itself is not defective and incapable of taking corrective actions. b. The sensor of the thermostat is not defective. The problems of the prior art of electrically noisy environments and other problems discussed above including misuse of the bypass are overcome in the following manner. The problem of electrical noise due to use of invertors to run railway airconditioned coaches results in incorrect firing of feedback circuits specifically opto-couplers in case they are not shielded against common mode noise. Incorrect firing of feedback circuits used in the control results in incorrect operation of the unit. Further an AC coach, specifically those running on Invertors are known to be electrically noisy. The effects of common and differential mode noise exist on two levels: 1. Negatively affects feedback circuits: 2. Disturbs/Corrupts analog/digital signals from the sensor to the controller. Switching of inductive loads like compressors generates spikes and surges in the electrical circuits. Control wires running close to these electrical circuits are generally known to pick up these induced transients that ultimately sink through the control circuits, in the process degrading or damaging them. The currently used thermostats in Indian Railway Coaches have analogue sensor/ sensor modules connected to controller through an interconnecting cable that carries the sensor signal to the controller. If EFT are conducted/ induced on the sensor cable, they sink through the electronic circuits of the controller, which can potentially cause damage. The present invention overcomes this problem by isolating the controller from fast transients. The problem of feedback circuits misfiring due to common mode noise is overcome by using circuitry to filter out the common mode noise or by using optocouplers with inbuilt common mode noise shield. Examples of such optocouplers include HCPL2232. Other makes of optocouplers with similar characteristics are also available. The problem of how to isolate transients on the sensor cable is overcome by using digital communication between the sensor and the controller using an RS485 transceiver IC and Modbus protocol. In the present invention, the RS485 transceiver line is isolated from the control circuits. The RS485 line is isolated from the processor for a minimum of 1.5kv with the help of optocouplers/ icouplers. Any EFT on the sensor cable thus is isolated from the control circuits of the sensor module and the controller module. An SMPS with two isolated outputs is used to drive the controller module and the sensor module. Isolation transformer, of which Max7850 is an example, is also used for making an isolated supply for the sensor module. Thus the controller module and the sensor module are protected from transients on the interconnecting cable. The inventive step in the present invention resides inter alia, in 1. The method by which the control pilot switching devices are interlocked. 2. Taking the feedback to the controller. 3. Use of galvanic isolation techniques and the interface between the sensor module and the controller module. 4. Software handling in the controller whereby the logical switching of the interlocked relays is controlled. 5. Software handling of the thermostat's switching back to normal mode with all due checks on the health of the thermostat. The above permits the following to take place: 1. Controlled bypass permission instead of total bypass permission from the controller. 2. Total bypass in case the controller or the sensor is defective as then all relays will be off. 3. Operation of feedback circuits in electrically noisy environment of Railways. 4. Protection against transients on the sensor cable connecting the module to the controller. We claim: 1. A device for controlled temperature bypass in an airconditioned environment, the device comprising a control means connected at one end to a relay control means and at another end to at least two isolation means, the isolation means being connected individually to a neutral input through a common line and to a heating relay and a cooling relay through dedicated separate lines, the heating relay consisting of a first set of bypass heating relay and a bypass cooling relay, and a second set of cooling relay and a heating relay, the relay sets being in turn connected to a cooling contactor and a heating contactor respectively and thereby to a second neutral input, a selector switch being provided connected to a heat bypass and a cool bypass at two points and to auto mode and a vent fan at the other two points, enabling selection from heat bypass, cool bypass, vent fan and auto mode. 2. A device as claimed in claim 1 wherein the control means is a microcontroller. 3. A device as claimed in claim 1 and 2 wherein each isolation means consists of an opto-coupler. 4. A device as claimed in claims 1 to 3 wherein a smart relay interlock is used coupled with a feedback loop into the device. 5. A device as claimed in claim 1 to 4 wherein bypass rotary switches are provided interfaced with the control means to provide digital or analog inputs into the device. 6. A device as claimed in any preceding claim wherein the inputs are galvanically isolated from the control circuit. 7. A device as claimed in any preceding claim wherein the controller is provided with heating and cooling switches which are interlocked. 8. A device as claimed in any preceding claim wherein at least one timer means is provided to time duration of bypass on receipt of a signal from the isolation device to the control means, said at least one timer means being a heat timer means or a cool timer means. 9. A device for controlled temperature bypass substantially as described hereinbefore and with reference to the accompanying drawings. 10. A method for controlled temperature bypass substantially as described hereinbefore and with reference to the accompanying drawings.

Full Text

DEVICE AND METHOD FOR CONTROLLED TEMPERATURE BYPASS FIELD OF THE INVENTION
The present invention relates to a device for control of temperature bypass mechanisms. More particularly, the present invention relates to a device for controlling bypass of auto-mode in controlled temperature environments such as air-conditioned railway coaches, air-conditioned buses, auditoria and other such locations. The present invention also relates to thermostat capable of implementing a method for controlled bypass of the auto-mode in railway AC coaches, relay management and interlocking technique to achieve said controlled bypass and smart selection of mode using a microcontroller based switch panel.
The invention generally relates to industrial controls and specifically a temperature controller capable of implementing an interlocking technique for controlled bypass of auto mode in railway AC coaches. The invention also discloses a method for relay interlocking within the thermostat and control interlocking within the control panel for implementation of this controlled bypass. BACKGROUND OF THE INVENTION
Air conditioned railway coaches use solid-state temperature controllers with determinate technical specifications prescribed by various regulatory authorities. For example, in India, the governing specification is RDSO/SPEC/PE/0025 rev 0 Amendment No. 3, prescribed by the Railways Designs and Standards Organisation.
The thermostat forms a part of the control panel for the air conditioning system in a railway coach. The thermostat conventionally used in railway air-conditioned coaches consists of the following:
1. Sensor: senses temperature at the return air grill and transmits the same to the controller using an analog or digital signal. A sensor when used along with a conditioning circuit at the sensor end is known as a sensor module.
2. Display: An LCD/ LED display that shows the temperature of air as sensed by the sensor.
3. Heating relay(s): An electromechanical or Solid State Device that switches on/off the contactor switchgear devices that drives the heaters.
4. Cooling Relay(s): An electromechanical or Solid State Device that switches on/off the contactor switchgear devices that drives the compressors.
5. DISP Key: The thermostat can consist of a single or multiple keys. Presently the thermostat has just one DISP key with multiple functions. Pressing the key activates the
display that starts showing the temperature. Long pressing key unlocks the system and pressing the same key when the system is unlocked, changes the temperature setting from low to high or vice versa.
6. Long pressing the DISP switch on the keypad results in the system getting unlocked for temperature setting. Once unlocked, the temperature setting can be changed only by the use of this switch.
7. LED's: For indicating the state of the heating relay, cooling relay, temperature setting (low and high), Fault condition, Power supply status.
8. Power supply: The SMPS power supply that steps down the 110V Ac/Dc power supply as it exists in AC control panel to working (12V) for the electronic circuits.
9. Microcontroller: The brain of the thermostat, which takes the sensor input, converts it into a digital read-out and takes control actions. This is the device that actuates relays and display and various LED's.
10. Controller Module: An electronic circuit consisting of all the above components except the sensor/ sensor Module is known as controller module.
11. Temperature Controller: All the above parts along with the connectors, interconnecting cables and associated circuit are known as temperature controller.
Figure 1 is a schematic circuit diagram of a conventional thermostat used in railway air conditioned coaches. It is further possible to enhance the temperature controller by adding additional keys and additional software algorithms to achieve the following:
a. The user can set the temperature of the thermostat according to convenience in certain
predefined steps or as a continuous gradient.
b. The thermostat can be interfaced with an external temperature selector switch that may
work on analogue or digital signals or a potential divider circuit to set the temperature
for the thermostat.
c. Add additional sensors/ sensor Modules to the system to achieve various operational
objectives.
The prior art circuit shown in Figure 1 incorporates several safety interlocks. Specifically, the interlocks Airvane relay, HP and LP cutouts are built into the system when these interlocks have a truth status (that is their status is all OK), phase is available at common terminal of RSW3. The following interlocks are critical for the AC plant: 1. Manual cooling bypass selection: The cooling circuit is switched on directly bypassing the thermostat's control interlocks.
2. Manual heating bypass selection: The cooling circuit is switched on directly bypassing the thermostats control interlocks.
3. Auto Mode: The manual interlocks are bypassed and all control switching of the cooling and heating circuit is done through the thermostats heating and cooling pilot relays (inter-locks)
4. Vent Mode: Neither cooling, nor heating will be switched on. Only the fan of the AC plant will be switched on and thermostat's control circuit will be bypassed.
The switching of the cooling and heating circuit in any of the above-mentioned selections is done through several interlocks that follow thereafter.
The prior art circuit suffers from several disadvantages which are listed hereinafter:
The control wiring of the control panel is such that the thermostat can be bypassed very easily with the turn of a switch, called the bypass switch. This switch, as it is being put to use presently, is a single pole-four position switch or similar. By turning this switch known as RSW3 in the RDSO control wiring, the user can simply select between Auto, Manual Cooling, Manual Heating, Or Vent control modes. The RSW3 switch is also known as the bypass switch as it provisions the bypass modes.
The bypass switch is an important element. For example, if the thermostat fails, the bypass switch is used to switch on the heating and cooling of the AC plant, instead of through the cooling and heating relays of the thermostat. Similarly, if the thermostat is operational, but the temperature is not adequately maintained due to any number of reasons, the coach attendant or technician, can, for a certain time period, convert the system from auto-mode to manual heating or cooling by bypassing the thermostats and letting the AC plant run without any temperature control.
The bypass switch is often prone to misuse. The coach attendant/technician may fail to remove the switch from bypass mode into auto-mode. As a result, the air conditioning plant may operate without any temperature control for a prolonged period of time resulting in over-chill or over-heat and cause passenger discomfort and also result in a high load on the system. The margin for human error in terms of the coach attendant/technician simply forgetting to convert the system from manual to controlled mode by undoing the bypass despite the thermostats being in working state is also high. Bypassing the thermostat leads to following problems:
1. Stress and damage to the AC plant's compressors due to long running time without getting switched off.
2. Potential fire hazards if manual heating is left switched on unattended for extended
hours. 3. Discomfort to passengers due to over-heating and over-cooling. Problem Statement 2: Electrically noisy environments
The problem of common mode noise in electrical circuits.
Some of the coaches in Indian Railways are being run on inverters where the problem of common mode noise has been found to exist. This problem results in incorrect firing of feedback circuits specifically opto-couplers in case they are not shielded against common mode noise. Incorrect firing of feedback circuits used in the control results in incorrect operation of the unit.
Another significant problem in air conditioned environments such as railway AC coaches is that of electrical fast transients, surges and spikes in the circuit. For example, air-conditioned railway coaches, particularly those running on invertors are known to be electrically noisy. The noise persists on two levels:
1. Negatively affects feedback circuits:
2. Disturbs/Corrupts analog/digital signals from the sensor to the controller. Switching of inductive loads like compressors generates spikes and surges in the
electrical circuits. Control wires running close to these electrical circuits are generally known to pick up these induced transients that ultimately sink through the control circuits, in the process degrading or damaging them.
The currently used thermostats fitted on Indian Railway Coaches use analogue sensor/sensor modules connected to controller through an interconnecting cable that carries a sensor signal to the controller. The inventor's model developed earlier uses digital Rs485 based communication between the sensor and the controller. If EFT are conducted/ induced on the sensor cable, they sink through the electronic circuits of the controller, which can potentially damage them. OBJECTS OF THE INVENTION
The primary object of the invention is to provide a device and a method for temperature controlled bypass which obviates the problems of the prior art circuits discussed above.
It is another object of the invention to provide a device for permitting bypass of an airconditioning system which allows bypass by the coach attendant or an authorized
personnel, whether the thermostat is functioning in OK status or the thermostat is dysfunctional.
It is a further object of the invention to provide a device and method for controlled temperature bypass in air conditioned environments wherein a direct bypass of the automatic control circuit is enabled in case the thermostat is not functioning and has a defect in the power supply or the sensor or the controller, thereby allowing the AC Plant (heating and cooling) to come on when bypass is selected manually.
It is another object of the invention to provide a device and method for controlled temperature bypass in an airconditioned environment where even if the thermostat is functioning and has still been bypassed through manual selection or manual cooling, the thermostat is enabled to take over control of the plant from the bypass circuit automatically on expiry of a predetermined period of time and continue switching of heating and cooling relays even if the selector switch is not returned to Auto mode and stays at manual cooling/ heating mode.
It is another object of the invention to provide a device and method for controlled temperature bypass wherein even if the thermostat is be switched off either due to power supply failure or deliberate human interference, the thermostat allows bypass circuit routed through a Rotary switch to activate the cooling and heating contactors in response to user selection of manual cooling or manual heating.
It is another object of the invention to provide a device and method for temperature controlled bypass which is functional in all forms of airconditioning environments irrespective of the surrounding electrical noise. SUMMARY OF THE INVENTION
The present invention provides a device for controlled temperature bypass for airconditioned environments. The device of the invention provides a circuit which solves the problems associated with the prior art and is described in detail below.
Accordingly, the present invention provides a device for controlled temperature bypass in an airconditioned environment, the device comprising a control means connected at one end to a relay control means and at another end to at least two isolation means, the isolation means being connected individually to a neutral input through a common line and to a heating relay and a cooling relay through dedicated separate lines, the heating relay consisting of a first set of bypass heating relay and a bypass cooling relay, and a second set of cooling relay and a heating relay, the relay sets being in turn connected to a cooling contactor and a heating contactor respectively and thereby to a second neutral input, a
selector switch being provided connected to a heat bypass and a cool bypass at two points and to auto mode and a vent fan at the other two points, enabling selection from heat bypass, cool bypass, vent fan and auto mode.
In one embodiment of the invention, the control means is a microcontroller.
In another embodiment of the invention, each isolation means consists of an opto-coupler.
In another embodiment of the invention, a smart relay interlock is used coupled with a feedback loop into the device.
In another embodiment of the invention, bypass rotary switches are provided interfaced with the control means to provide digital or analog inputs into the device.
In another embodiment of the invention, the inputs are galvanically isolated from the control circuit.
In another embodiment of the invention, the controller is provided with heating and cooling switches which are interlocked.
In another embodiment of the invention, at least one timer means is provided to time duration of bypass on receipt of a signal from the isolation device to the control means, said at least one timer means being a heat timer means or a cool timer means. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 is a circuit diagram of a prior art wiring circuit.
Figure 2 is a control circuit according to one embodiment of the present invention.
Figure 3 is a circuit diagram of a controlled bypass wiring schema for RMPU railway AC coaches with HR-CR hardwired interlocking through HR relay using 4 SPDT Pilot switching devices.
Figure 4 is a circuit diagram of a controlled bypass wiring schema for RMPU railway AC coaches with HR-CR hardwired interlocking through CR relay using 4 SPDT Pilot switching devices.
Figure 5 is a circuit diagram of a controlled bypass wiring schema for RMPU railway AC coaches without hardwired HR-CR interlocking using 4 SPDT Pilot switching devices.
Figure 6 is a circuit diagram of a controlled bypass wiring schema for RMPU railway AC coaches with HR-CR hardwired interlocking through HR relay using 2 DPDT Pilot switching devices.
Figure 7 is a circuit diagram of a controlled bypass wiring schema for RMPU railway AC coaches with HR-CR hardwired interlocking through CR relay using 2DPDT switching devices.
Figure 8 is a circuit diagram of a controlled bypass wiring schema for RMPU railway AC coaches without hardwired HR-CR interlocking using 2 DPDT switching devices. DETAILED DESCRIPTION OF THE INVENTION
The present invention uses a novel circuitry to filter out common mode noise or uses optocouplers with inbuilt common mode noise shield. Digital communication is used between sensor and controller using an RS485 transceiver IC and Modbus protocol. The RS485 transceiver is isolated from the processor for a minimum of 1.5Kv using optocouplers and i-couplers. Thus, any EFT on the sensor cable is isolated from the control circuits of the sensor module and the controller module. An SMPS with two isolated outputs is used to drive the controller module and the sensor module. The isolation transformer is also used to provide an isolated supply from the sensor module. Thus, the controller module and the sensor module are protected from transients on the interconnecting cable.
As explained above, it is one of the objects of the invention to provide a method by which bypass of the system can be allowed by the coach attendant/technician irrespective of whether the thermostat is functioning or is dysfunctional. Other objectives include permitting a direct bypass by the thermostat of the automatic control circuit and allowing the AC plant to resume or start function when bypass is selected manually in case the thermostat is dysfunctional. In the event the thermostat is not defective and has still been bypassed through manual selection or manual cooling, the thermostat should be enabled to take over control of the plant from the bypass circuit automatically at the expiry of a predefined time period and continue the switching of the cooling and heating relay even if the selector switch is not returned to Auto mode and stays at manual cooling/ heating mode. Similarly, when the thermostat is be switched off due to either power supply failure or deliberate human intervention, it should still allow bypass circuit routed through the Rotary switch to activate the cooling and heating contactors in response to user selection of manual cooling or manual heating.
The above objectives are achieved by using a smart relay interlocking technique coupled with a feedback loop into the system. The system is a microcontroller based system and the embedded software conducts the algorithms for achieving the objectives
mentioned above. The microcontroller in addition to the bypass algorithms also has embedded on its software the logics required for temperature control of the AC plant.
The present invention will now be described with reference to the accompanying drawings, which are non-limiting of the scope of the invention.
The modified control circuit diagram of the invention is shown in Fig 2. The hardware and software of the electronic thermostat is modified to include controlled bypass manifest itself on the thermostat.
As can be seen from Fig. 2, the circuit consists of a microcontroller connected to a relay driver at one end and connected at another end to at least two isolation devices marked as opto-inputs. The isolation devices (opto-inputs) are in turn connected individually to a neutral input through a common line. The opto-inputs are also connected through separate lines to heating and cooling relay respectively. The relay driver drives a set of two relays - each set consisting of one heating and one cooling relay (Kl and K3; K2 and K4). The first set (Kl and K2) are bypass relays for heating and cooling respectively. The relay sets are in turn connected to a cooling contactor and a heating contactor respectively and thereby to a second neutral input. A selector switch is provided connected to a heat bypass and a cool bypass at two points and to auto mode and a vent fan at the other two points. Thus, the selector switch can select from heat bypass, cool bypass, vent fan and auto mode.
The device of the invention envisages disconnecting manual cooling and manual heating control signal wires (connecting the bypass switch to the cooling and heating contactors) from the heating and cooling contactors and routing them through the enhanced thermostat. Enhanced thermostat implies thermostat with added hardware and embedded software to execute new algorithms. The device and method of the invention will be described in greater detail below with reference to Fig. 3 to Fig. 8.
Turning now to Figures 3 to 5, the bypass heating circuit is activated when manual heating (position 5 of Selector Switch) is selected on selector switch. The thermostat receives the signal through the corresponding isolation device, marked "opto input". The heating SPDT pilot switching devices "Relay HR" and "Relay_HR_BP" are switched off, irrespective of the temperature at the sensor. This makes the Phase available through the NC contact of "Relay_HR_BP" to the heating contactor, switching on the heating circuit of the AC plant.
When the controller receives a signal through the isolation device that manual heating has been selected on the selector switch, a software timer is started that times the
"miration of the bypass. This timer is referred to as timer_heat_bypass in the figures and herein and this state of the controller is referred to as heating bypass state. At the expiry of the predefined time limit of bypass, the thermostat starts switching the heating pilot switching device RelayHRBP to actuate/ deactivate the heating circuit. The RelayHR is kept in off state. However, the status,of the RelayHR does not affect the circuit. When the sensor temperature falls below the pre-set cut-in temperature the heating switching device Relay_HR_BP is switched off, bringing Phase to the NC contact and thus activating the heating bypass circuit. When the temperature goes above the predefined cut-off temperature, Relay_HR_BP is switched on, deactivating the bypass heating circuit.
When the system is on Auto Mode however, the relay logic is inversed. When the sensor temperature falls below the pre-set cut-in temperature the heating switching device Relay_HR is switched on, bringing Phase to the NO contact and thus activating the heating bypass circuit. When the temperature goes above the predefined cut-off temperature, Relay_HR is switched off, deactivating the bypass heating circuit.
The bypass cooling circuit is activated when manual cooling (position 4 of Selector Switch) is selected on selector switch. The thermostat receives the signal through the corresponding isolation device, marked "opto input". The cooling SPDT pilot switching devices "Relay CR" and "Relay_CR_BP" in figures 3, 4 and 5 are switched off, irrespective of the temperature at the sensor. This makes the Phase available through the NC contact of "RelayCRBP" to the cooling contactor, switching on the cooling circuit of the AC plant.
When the controller receives a signal through the isolation device that manual cooling has been selected on the selector switch, it starts a software timer that times the duration of the bypass. This timer is being referred to as timer_cool_bypass in the figures and herein and this state of the controller is referred to as cooling bypass state. At the expiry of the predefined time limit of bypass, the thermostat starts switching the cooling pilot switching device Relay_CR_BP to actuate/ deactivate the cooling circuit. The Relay_CR is kept in off state, its status however does not make a difference on the circuit. When the sensor temperature falls below the pre-set cut-in temperature the cooling switching device Relay_CR_BP is switched off, bringing Phase to the NC contact and thus activating the cooling bypass circuit. When the temperature goes above the predefined cutoff temperature, Relay_CR_BP is switched on, deactivating the bypass cooling circuit.
When the system is on Auto Mode however, the relay logic is inversed. When the sensor temperature goes above the pre-set cut-in temperature the cooling switching device
Relay_CR is switched on, bringing Phase to the NO contact and thus activating the cooling bypass circuit. When the temperature goes below the predefined cut-off temperature, Relay_CR is switched off, deactivating the bypass coohng circuit.
In Figs. 3 and 4, the heating and cooling pilot switching devices in the controller are further optionally interlocked. They can also be not interlocked as shown in Fig. 5. Interlocking as shown in Figs. 3 and 4 has an added advantage of providing additional switching safety as it disallows the cooling and heating circuit to switch on together.
Turning now Figs. 6 to 8, bypass rotary switch contacts pertaining to "manual cool" and "manual heat" (marked 4 and 5 on rotary switch in Fig. 6-8 and in Fig. 1) are interfaced with the temperature controller as two digital or analog inputs into the system. These inputs are additionally galvanically isolated from the control circuit. Galvanic isolation can be bypassed for a non-isolated connection to the microcontroller also. These inputs will indicate to the controller whether the coach attendant has put the unit under manual cooling/ manual heating. Additional (optional) inputs for auto and vent mode can also be taken into the system.
The bypass cooling circuit is now actuated through switches devices in the controller. These switches devices can be 2 SPDT relays as in Figs. 6-8 or a single DPDT switch.
As shown in Figs. 6-8, the bypass cooling circuit is activated when manual cooling (position 4 of Selector Switch) is selected on selector switch. The thermostat receives the signal through the corresponding isolation device, marked "opto input". The cooling DPDT pilot switching device, irrespective of the temperature at the sensor is switched off. This makes the Phase available at the coohng contactor, switching on the cooling circuit of the AC plant. When the controller receives the signal through the isolation device that manual cooling has been selected on the selector switch, it starts a software timer to time the duration of the bypass. This timer is being referred to as timer_cool_bypass in this document. This state of the controller is referred to as cooling bypass state. At the expiry of the predefined time limit of bypass, the thermostat starts switching the cooling pilot switching device to actuate/ deactivate the cooling circuit. When the sensor temperature exceeds the pre-set cut-in temperature the cooling switching device is switched off, activating the cooling bypass circuit. When the temperature falls below the predefined cutoff temperature, the cooling switching device is switched on, deactivating the bypass cooling circuit.
When the system is on Auto Mode however, the relay logic is inversed. When the sensor temperature goes above the pre-set cut-in temperature the cooling pilot switching device is switched on, bringing Phase to the NO contact and thus activating the cooling bypass circuit. When the temperature goes below the predefined cut-off temperature, cooling pilot switching device is switched off, deactivating the bypass cooling circuit.
The bypass heating circuit is activated when manual heating (position 5 of Selector Switch) is selected on selector switch. The thermostat receives the signal through the corresponding isolation device, marked "opto input". The heating DPDT pilot switching device, irrespective of the temperature at the sensor is switched off. This makes the Phase available at the heating contactor, switching on the heating circuit of the AC plant.
When the controller receives the signal through the isolation device that manual heating has been selected on the selector switch, it starts a software timer that times the duration of the bypass. This timer is being referred to as timer_heat_bypass in this document. This state of the controller is referred to as heating bypass state. At the expiry of the predefined time limit of bypass, the thermostat starts switching the heating pilot switching device to actuate/ deactivate the heating circuit. When the sensor temperature falls below the pre-set cut-in temperature the heating switching device is switched off, activating the heating bypass circuit. When the temperature goes above the predefined cutoff temperature, the heating switching device is switched on, deactivating the bypass heating circuit.
When the system is on Auto Mode however, the relay logic is inversed. When the sensor temperature falls below the pre-set cut-in temperature the heating pilot switching device is switched on, bringing Phase to the NO contact and thus activating the heating bypass circuit. When the temperature goes above the predefined cut-off temperature, the heating pilot switching device is switched off, deactivating the bypass heating circuit.
The heating and cooling pilot switching devices in the controller can further be interlocked as shown in Fig. 6 and 7 or not interlocked as shown in Fig. 8. Interlocking has the added advantage of providing additional switching safety as it disallows the cooling and heating circuit to switch on together.
The Heating Bypass Circuit and the Cooling Bypass circuit in Figs. 3-8 are routed through a NC contact of the pilot switching devices. The advantage of using the NC contact is that in case the controller fails and the user puts the system into the bypass mode, the rest/ de-energized state of the relay being NC contact the phase signal from the bypass
switch will still find a conductive path to the heating/cooling circuit allowing the system to switch on.
Thus, the user is allowed to manually activate the cooling or heating bypass circuits even when the power supply of the controller units failed. Thus the thermostat becomes the governing devices for manual as well as auto modes except when the power supply of the unit has failed. In all Figs. 3-8, when the timer_heat_bypass or timer_cool_bypass reach their predefined limits, the controller will over ride the manual bypass bringing the system to controlled state (by energizing the relays) subject to following conditions:
a. The thermostat in itself is not defective and incapable of taking corrective actions.
b. The sensor of the thermostat is not defective.
The problems of the prior art of electrically noisy environments and other problems discussed above including misuse of the bypass are overcome in the following manner.
The problem of electrical noise due to use of invertors to run railway airconditioned coaches results in incorrect firing of feedback circuits specifically opto-couplers in case they are not shielded against common mode noise. Incorrect firing of feedback circuits used in the control results in incorrect operation of the unit.
Further an AC coach, specifically those running on Invertors are known to be electrically noisy. The effects of common and differential mode noise exist on two levels:
1. Negatively affects feedback circuits:
2. Disturbs/Corrupts analog/digital signals from the sensor to the controller. Switching of inductive loads like compressors generates spikes and surges in the
electrical circuits. Control wires running close to these electrical circuits are generally known to pick up these induced transients that ultimately sink through the control circuits, in the process degrading or damaging them.
The currently used thermostats in Indian Railway Coaches have analogue sensor/ sensor modules connected to controller through an interconnecting cable that carries the sensor signal to the controller. If EFT are conducted/ induced on the sensor cable, they sink through the electronic circuits of the controller, which can potentially cause damage. The present invention overcomes this problem by isolating the controller from fast transients.
The problem of feedback circuits misfiring due to common mode noise is overcome by using circuitry to filter out the common mode noise or by using optocouplers with inbuilt common mode noise shield. Examples of such optocouplers include HCPL2232. Other makes of optocouplers with similar characteristics are also available.
The problem of how to isolate transients on the sensor cable is overcome by using digital communication between the sensor and the controller using an RS485 transceiver IC and Modbus protocol. In the present invention, the RS485 transceiver line is isolated from the control circuits.
The RS485 line is isolated from the processor for a minimum of 1.5kv with the help of optocouplers/ icouplers. Any EFT on the sensor cable thus is isolated from the control circuits of the sensor module and the controller module. An SMPS with two isolated outputs is used to drive the controller module and the sensor module. Isolation transformer, of which Max7850 is an example, is also used for making an isolated supply for the sensor module. Thus the controller module and the sensor module are protected from transients on the interconnecting cable. The inventive step in the present invention resides inter alia, in
1. The method by which the control pilot switching devices are interlocked.
2. Taking the feedback to the controller.
3. Use of galvanic isolation techniques and the interface between the sensor module and the controller module.
4. Software handling in the controller whereby the logical switching of the interlocked relays is controlled.
5. Software handling of the thermostat's switching back to normal mode with all due checks on the health of the thermostat.
The above permits the following to take place:
1. Controlled bypass permission instead of total bypass permission from the controller.
2. Total bypass in case the controller or the sensor is defective as then all relays will be off.
3. Operation of feedback circuits in electrically noisy environment of Railways.
4. Protection against transients on the sensor cable connecting the module to the controller.

We claim:
1. A device for controlled temperature bypass in an airconditioned environment, the device comprising a control means connected at one end to a relay control means and at another end to at least two isolation means, the isolation means being connected individually to a neutral input through a common line and to a heating relay and a cooling relay through dedicated separate lines, the heating relay consisting of a first set of bypass heating relay and a bypass cooling relay, and a second set of cooling relay and a heating relay, the relay sets being in turn connected to a cooling contactor and a heating contactor respectively and thereby to a second neutral input, a selector switch being provided connected to a heat bypass and a cool bypass at two points and to auto mode and a vent fan at the other two points, enabling selection from heat bypass, cool bypass, vent fan and auto mode.
2. A device as claimed in claim 1 wherein the control means is a microcontroller.
3. A device as claimed in claim 1 and 2 wherein each isolation means consists of an opto-coupler.
4. A device as claimed in claims 1 to 3 wherein a smart relay interlock is used coupled with a feedback loop into the device.
5. A device as claimed in claim 1 to 4 wherein bypass rotary switches are provided interfaced with the control means to provide digital or analog inputs into the device.
6. A device as claimed in any preceding claim wherein the inputs are galvanically isolated from the control circuit.
7. A device as claimed in any preceding claim wherein the controller is provided with heating and cooling switches which are interlocked.
8. A device as claimed in any preceding claim wherein at least one timer means is provided to time duration of bypass on receipt of a signal from the isolation device to the control means, said at least one timer means being a heat timer means or a cool timer means.
9. A device for controlled temperature bypass substantially as described hereinbefore and with reference to the accompanying drawings.
10. A method for controlled temperature bypass substantially as described hereinbefore and with reference to the accompanying drawings.

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=LGBt9BhLeu4X7XCoOzZEpg==&loc=+mN2fYxnTC4l0fUd8W4CAA==

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Patent Number

270498

Indian Patent Application Number

1391/DEL/2005

PG Journal Number

01/2016

Publication Date

01-Jan-2016

Grant Date

28-Dec-2015

Date of Filing

30-May-2005

Name of Patentee

PAWANDEEP VOHRA SINGH BAHL

Applicant Address

1-FF, ARAVALI SHOPPING COMPLEX, ALAKNANDA,NEW DELHI-110019, INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	PAWANDEEP V. SINGH BAHL	1-FF, ARAVALI SHOPPING COMPLEX, ALAKNANDA, NEW DELHI-110019, INDIA

PCT International Classification Number

F24F3/052

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA