Electrochemical Control Systems And Methods
Methods for reducing response time of membrane based electrochemical cells. A probe correction factor is calculated based on a percent rate of change in probe signal with time. A staged correction may be applied such that as signal change gets smaller, the effect of the compensation is reduced to prevent over shoot on the calculated residual. Control systems and techniques can regulate or control operations of a water treatment system.
1 . A method of controlling a system, comprising:
detecting a step change in a process parameter of the system with a membrane-based electrochemical sensor;
estimating a residual value of the process parameter of the system based on the step change;
determining a correction factor based on the estimated residual value;
generating a first control signal based on the correction factor if the detected step change is within a first predetermined range;
determining a reduction factor if the step change is within a second predetermined range; and
generating a second control signal based on the correction factor and the reduction factor if the step change is within the second predetermined value.
2 . The method of claim 1 , wherein the process parameter corresponds to an oxidation reduction potential of water in the system.
3 . The method of claim 1 , wherein at least one of the first and second control signals is based on a difference between the estimated residual value of the process parameter and a set point.
4 . The method of claim 1 , wherein the correction factor is based on a rate of change of the value of the process parameter.
5 . The method of claim 1 , further comprising actuating a valve to adjust a value of the process parameter in the system based on at least one of the first and second control signals.
6 . The method of claim 1 , wherein the first control factor is applied when the detected step change is at least about 10%.
7 . The method of claim 6 , wherein the second control signal is applied when the detected step change is in a range of about 1% to about 10%.
8 . The method of claim 7 , wherein no control signal is generated when the detected step change is less than about 1%.
9 . A method of reducing response time of an electrochemical sensor, comprising:
measuring a first probe value;
measuring a second probe value after a predetermined time interval has elapsed;
determining a rate of signal change between the first and second probe values;
applying a first correction factor if the rate of signal change exceeds a threshold value; and
applying a second correction factor if the rate of signal change is below the threshold value.
10 . A water treatment system, comprising:
an electrochemical sensor disposed to measure an operating parameter of the water treatment system and generate a corresponding input signal;
a controller configured to receive the input signal, convert the input signal to a corrected input signal, and further configured to generate an output signal based on a difference between the corrected input signal and a set point value; and
an output device disposed to receive the output signal and adjust the operating parameter in the water treatment system based on the output signal.
11 . The system of claim 10 , wherein the operating parameter corresponds to an oxidation reduction potential of water in the water treatment system.
12 . The system of claim 10 , wherein the electrochemical sensor comprises a membrane covered electrode.
13 . The system of claim 12 , wherein the electrochemical sensor comprises a free or total chlorine probe.
14 . The system of claim 12 , wherein the electrochemical sensor comprises a redox probe.
15 . The system of claim 10 , wherein the output signal generated by the controller is based on a rate of change in the input signal.
16 . The system of claim 15 , wherein the output signal is reduced as a rate of change of input signal is reduced.
17 . The system of claim 16 , wherein the controller applies a reduction factor to the output signal if the rate of change of input signal is below a threshold value.
18 . The system of claim 10 , wherein the electrochemical sensor is characterized by a T90 response time of less than about 60 seconds.
19 . A membrane based electrochemical analyzer having a T90 response time of less than about 60 seconds.
20 . The electrochemical analyzer of claim 19 , configured to reduce an applied correction factor as the analyzer approaches a residual value.