Method and apparatus for providing stable voltage to analytical system
View Patent ↗An electrochemical cell has two terminals. One of the terminals is connected to a pulse-width-modulated (PWM) power supply and to a voltmeter. The other terminal is connected to circuitry capable of switching between amperometric and potentiometric measurement modes. A sequence of successive approximations permits selection of a PWM duty cycle giving rise to a desired voltage at the terminal connected with the power supply. In this way a stable excitation voltage is supplied to the cell even in the face of supply voltage instability or drift or instability in electronics coupled with the cell.
1. A method for use with a digitally controlled power supply and a reaction cell having first and second load electrodes and a liquid sample disposed between the load electrodes, the power supply coupled with the first load electrode to provide an excitation voltage to said first load electrode, a first signal line coupling the first load electrode with a first analog-to-digital converter, and a voltage sensor coupled with the second load electrode, the voltage sensor having a second signal line coupled to a second analog-to-digital converter, the method comprising the steps which follow in the order given:
making a first approximation to a digital control signal for the power supply;
measuring a first potential at the second load electrode by means of the second signal line;
making a second approximation to the digital control signal for the power supply, wherein the second approximation differs from the first approximation based on the difference between the first potential measured at the second load electrode and a target value;
measuring a second potential at the second load electrode by means of the second signal line;
making a third approximation to the digital control signal to the power supply, wherein the third approximation differs from the second approximation based on the difference between the second potential measured at the second load electrode and the target value and
measuring a measurement potential at the first load electrode by means of the first signal line, said measurement potential being used for analysis of the liquid sample.
2. The method of claim 1 wherein the power supply is a pulse-width-modulated power supply and the steps of making approximations to digital control signals each comprises making an approximation to a duty cycle for pulse-width-modulating the control signal.