Title of Invention

"AN IMPROVED PH TRANSMITTER DEVICE FOR ON-LINE HIGH CURRENT APPLICATION"

Abstract

A pH tr ansmitter for on-line high current applications, that has a current output of 4 to 20mA, comprising of a pH sensor, electronic hardware circuits to process the sensor output, to compensate for pH variation with temperature, to calibrate the transmitter using buffers, and to provide current output corresponding to 0 to 14 pH, has been developed that has application to monitor and transport the pH signal over a large distance in chemical and electrochemical processes that involve high currents in industrial environment.

Full Text

This invention relates to an improved pH transmitter device for on-line high current applications. The present invention particularly relates to the improvements in or relating to a pH transmitter with 4 to 20 mA current output for on-line high current applications. The main usage of the device of the present invention is to monitor pH in chemical and electrochemical processes that involve high currents. The transmitter measures the pH and gives an output of 4 to 20 mA, corresponding to 0 to 14 pH. The device will be particularly useful where the pH data signal is to be transmitted over a long distance. More particularly, at industrial sites with significant interferences from electrical sources. Hitherto it has been proposed to develop pH meters and transmitters that work off-line or in processes that are not subjected to high currents. Reference may be made to G L Bodhe etal., Journal of Instrumentation Society, India, 30 (3) (2000) pages184 -193. They have developed a pH controller that has no built in transmitter and cannot be used to transport the signal and is not useful for on line monitoring of the process. Reference may also be made to Nayak etal., Journal of Instrumentation Society, India, 31 (2) (2001). They have developed a pH transmitter that cannot be used to monitor pH under high current applications. Reference may further be made to US patent no. 5,539,396: A remote monitoring system for instmmentation that is capable of measuring certain characteristics of a process such as a pH value includes an instrument for providing a measurement output signal which can be stored. A comparison circuit can compare the output signal with a predetermined value. A transmitter can transmit when the output signal exceeds the predetermined value, and a receiver can receive the output signal and convert it into a measured result. The instrumentation can be pulled from the receiver and the output signals can be encoded to identify a particular instrument with distinct transmission time periods available in a plurality of transmitting channels. They have developed a pH transmitter that cannot be used to monitor pH under high current applications. The main usage of the device of the present invention The transmitter measures the pH and gives an output of 4 to 20 mA, corresponding to 0 to 14 pH. The device will be particularly useful where the pH data signal is to be transmitted over a long distance. More particularly, at industrial sites with significant interferences from electrical sources. The main object of the present invention is to provide an improved pH transmitter device for on-line high current applications, that obviates the drawbacks as detailed above. Another object of the present invention is to provide an improved pH transmitter device for on-line high current applications, with 4 to 20 mA current output corresponding to 0 to 14pH. Yet another object of the present invention is to monitor pH in chemical and electrochemical processes that involve high currents. Still another object of the present invention is to provide a pH transmitter useful to transport the signal over long distances even in noisy industrial sites. The pH transmitter of the present invention is a novel device useful for online monitoring of pH under high current environment such as in chemical and electrochemical industrial processes and to transmit the signal over a long distance. The device of the present invention measures the pH and converts it in to current in the range of 4 to 20mA corresponding to 0 to 14pH. It essentially consists of an electrometer amplifier that interfaces the high impedance pH sensor to the electronic circuits. The transmitter has inbuilt provision to provide temperature compensation manually with the help of a precision potentiometer. Calibration of the device is done using pH buffers of known value. Two potentiometers have been provided to adjust the offset and slope separately while calibrating the device. In the drawing accompanying this specification figure 1 represents the block schematic of the pH transmitter for high current applications of the present invention. The device consists of an industrial grade combination electrode (1) to sense pH of the bath under study. The pH sensor electrode develops a negative voltage at zero pH, zero voltage at 7 pH and a positive voltage at 14 pH under temperature condition of 25° C. The electrode output is fed to an electrometer amplifier (2) that has very high input impedance so as to match the internal impedance of the pH sensor. Output of the electrometer amplifier is connected to a signal conditioning circuit (3). Manual temperature compensation is done using a precision potentiometer provided in temperature compensating circuit (4). The amplified and conditioned bipolar voltage output of the pH sensor is converted into a voltage of single polarity by an unipolar generator (5). Since in actual practice no pH electrode gives an output equal to its theoretical value, the electrode has to be calibrated with the device using buffers of known pH values. Two preset potentiometers have been provided in the calibration block (6) to adjust offset and slope respectively while calibrating the transmitter. Output of the unipolar generator is fed to a scaling amplifier (7) that amplifies the signal to a value suitable for the input to a voltage to current converter (8). The voltage to current converter (8) has two preset potentiometers to adjust the lower and higher current limits of the voltage to current converter which gives an output of 4 to 20 mA corresponding to 0 to 14 pH. The voltage to current converter output which is the pH signal is fed to a transmitter through a connector. The present invention relates to improvements in or relating to development of a pH transmitter for high current applicathich comprises of an electrometer amplifier to interface the industrial gracelectrode, signal conditioning and temperature compensation circuits, unipolar generator to convert the pH sensor output to a single polarity signal, calibration circuits with offset and slope adjustment potentiometers and a voltage to current converter that gives an output of 4 to 20mA corresponding to 0 to 14 pH. This output which corresponds to the pH value is transmitted via a transmitter. Accordingly the present invention provides an improved pH transmitter device for on line high current applications, which comprises an electrometer amplifier (2) capable of interfacing with a pH sensor (1), the signal output of the said electrometer amplifier (2) being connected to the input of a signal conditioning circuit (3) provided with temperature compensating circuit (4), the output of the said signal conditioning circuit (3) being the amplified and conditioned voltage output of the said pH sensor (1), the said output of the said signal conditioning circuit connected to an unipolar generator (5) having a calibration unit (6) consisting of two potentiometers for offset and slope adjustments, the unipolar voltage output is fed through a scaling amplifier (7) to a voltage to current converter (8) having two preset potentiometers capable of adjusting the lower and higher current limits of the voltage to current converter, the output current of the said voltage to current converter is fed to a transmitter for transport of the pH signal over a long distance. In an embodiment of the present invention, the electrometer amplifier (2) capable of interfacing with a pH sensor (1), has very high input impedance. In another embodiment of the present invention, the signal conditioning circuit (3) processes the electrometer amplifier output in such a way that it is free from unwanted harmonics. In yet another embodiment of the present invention the temperature compensation circuit (4) is capable of providing correction for variation of pH with temperature. In still another embodiment of the present invention the unipolar generator (5) converts the bipolar input to a voltage of single polarity. In still yet another embodiment of the present invention ihe calibration circuit (6) consists of two potentiometers for offset and slope adjustment separately while standardizing the device. In a further embodiment of the present invention the scaling amplifier (7) is capable of raising the output of the unipolar generator to a value suitable for the input to the voltage to current converter (8). In a still further embodiment of the present invention the voltage to current converter (8) provides a current output of 4 to 20 mA corresponding to 0 to 14pH. The novelty of the present invention resides in providing a pH transmitter for high current applications such as in chemical and eiectrochemical processes that involve high currents in industrial environment. The novel pH transmitter for online high current applications, that has a current output of 4 to 20mA corresponding to 0 to 14 pH, has been achieved by the inventive steps which essentially comprises providing in combination a pH sensor, electronic hardware circuits to process the sensor output, to compensate for pH variation with temperature, to calibrate the transmitter using buffers, and to provide current output capable of being fed to a transmitter for transport of the pH signal over a large distance. The details of the process steps to be followed while calibrating the pH transmitter of the present invention are given below: Before using the transmitter it has to be calibrated using pH buffers of known value. Normally used standard buffers are of value 4, 7 and 9.2 pH. When transmitter is to be used to monitor low pH values, it is calibrated using 4 and 7 pH buffers and to monitor high pH values calibration is done using 7 and 9.2 pH buffers. The pH transmitter is switched on connecting it to 230V line supply. Two buffer solutions of values 4 and 7 pH are taken in two clean beakers. The temperature of buffer solutions is measured and the temperature compensation adjustment is done to the match the measured value. The cleaned pH sensor is dipped in buffer solution of value 4 pH. The offset preset potentiometer is adjusted so that the pH value is exactly 4.00. The sensor is removed from the beaker, washed with distilled water, dried and dipped in the buffer of value 7pH. The slope preset potentiometer is adjusted so that the display reads exactly 7.00. If necessary the above procedure is repeated so that the display shows exact values of 4 and 7 pH when the sensor is dipped in buffers of respective values. While calibrating the transmitter its current output can also be tested using an external current meter having a resolution of ± 0.01mA. When the pH sensor is dipped in 4pH buffer the external meter should read 8.57± 0.01mA and when the sensor is dipped in 7 pH buffer the meter should read 12 ± 0.01mA. After the calibration and the current output are tested the pH transmitter of the present invention is ready for use. The foHowing examples are given by way of illustration of the pH transmitter of the present invention in actual use and therefore should not be construed to limit the scope of the present invention. The pH sensor developed an approximate voltage of - 413.7mV at zero pH, 0 mV at 7pH and +413.7mV at 14 pH under temperature condition of 25° C. Measurements were made using ammoniacal cupric chloride PCB etchant solutions at different current densities. In each of the examples given below, the following steps were followed for making the measurements. 1. Transmitter was connected to 230V supply and switched on. 2. It was calibrated using standard buffer solutions as described above. 3. The pH of the solutions to be tested was measured using a standard commercial pH meter. 4. The transmitter was used to measure the pH of same solutions under different currents and the transmitter output was noted. 5. The results were compared with the results obtained with the standard pH meter. Example -1 pH of the bath without application of current: 8.80 Applied current density 375A / m2 Theoretical value of current output 14.06mA Transmitter output observed 14.08mA Example - 2 pH of the bath without application of current: 8.80 Applied current density 750A/m2 Theoretical value of current output 14.06mA Transmitter output observed 14.07mA Example - 3 pH of the bath without application of current: 8.80 Applied current density 1500A'm2 Theoretical value of current output 14.06mA Transmitter output observed 14.10mA It is observed from the above examples that there is a very good agreement between the theoretical current output and the observed transmitter output and this confirms the satisfactory functioning of the pH transmitter of the present invention. The main advantages of the present invention are: 1. The transmitter can be used to monitor the pH on iine under high current applications. 2. Capable of monitoring pH in chemical and electrochemical processes that involve high currents. 3. It gives an output of 4 to 20mA corresponding to 0 to14 pH. 4. It is useful where the signal has to be transported over long distances even in noisy industrial sites. 5. Its operation is not affected by the interference from electrical sources. 6. The device is capable of computer interfacing. We claim: 1. An improved pH transmitter device for on line high current applications, which comprises an electrometer amplifier (2) capable of interfacing with a pH sensor (1), the signal output of the said electrometer amplifier (2) being connected to the input of a signal conditioning circuit (3) provided with temperature compensating circuit (4), the output of the said signal conditioning circuit (3) being the amplified and conditioned voltage output of the said pH sensor (1), the said output of the said signal conditioning circuit connected to an unipolar generator (5) having a calibration unit (6) consisting of two potentiometers for offset and slope adjustments, the unipolar voltage output is fed through a scaling amplifier (7) to a voltage to current converter (8) having two preset potentiometers capable of adjusting the lower and higher current limits of the voltage to current converter, the output current of the said voltage to current converter is feci to a transmitter for transport of the pH signal over a long distance. 2. An improved pH transmitter device as claimed in claim 1, wherein the electrometer amplifier (2) capable of interfacing with a pH sensor (1), has very high input impedance. 3. An improved pH transmitter device as claimed in claims 1-2, wherein the temperature compensating circuit (4) is capable of providing correction for variation of pH with temperature. 4. An improved pH transmitter device as claimed in claims 1-3, wherein the calibration unit (6) consists of two potentiometers for offset and slope adjustment separately while standardizing the device. 5. An improved pH transmitter device as claimed in claims 1-4, wherein the scaling amplifier (7) is capable of raising the output of the unipolar generator to a value suitable for the input to the voltage to current converter (8). 6. An improved pH transmitter device for on line high current applications, substantially as herein described with reference to the examples and drawing accompanying this specification.

Documents:

742-del-2003-abstract.pdf

742-del-2003-claims(cancelled).pdf

742-del-2003-claims.pdf

742-del-2003-complete specification(granted).pdf

742-del-2003-correspondence-others.pdf

742-del-2003-correspondence-po.pdf

742-del-2003-description (complete).pdf

742-del-2003-drawings.pdf

742-del-2003-form-1.pdf

742-del-2003-form-19.pdf

742-del-2003-form-2.pdf

742-del-2003-form-3.pdf