Checking Potentiostat Bias and Counter Electrode Headroom

A potentiostat can have a correct programmed bias value while failing to maintain that potential at the connected electrochemical cell. The control amplifier must have enough voltage range to drive the counter electrode under the actual conditions. Check regulation at the electrodes rather than inferring it from a register setting.

Label electrode functions

Identify working, reference, and counter electrodes from the sensor documentation. Record the required bias polarity and magnitude between the specified electrodes. Do not assign connector pins by assuming that every three electrode sensor uses the same wiring convention.

The TI LMP91000 data sheet describes a potentiostat that adjusts the counter electrode voltage to maintain the required working to reference potential. Its programmable settings and voltage limits must be interpreted together with the cell’s requirements.

Review control headroom

Draw the internal or external reference levels used by the front end and the available supply range. Check the required working electrode level, reference electrode input range, and counter electrode output swing. A bias difference can be modest while one electrode approaches an amplifier’s rail.

Include the expected cell current and sensor impedance behavior. The voltage required to sustain the chosen potential may change with operating condition. If the control output reaches its limit, a reported current no longer necessarily represents operation at the intended bias.

Keep current measurement in range

Review transimpedance gain, output reference, and ADC range for both expected current directions where applicable. As an illustrative calculation, 5 microamps through a 100 kilohm feedback resistance produces a 0.5 V output change. The baseline and polarity determine whether that change fits within the available output and ADC range.

Do not increase gain merely to use more ADC codes without checking the maximum current and recovery from overload. Account for startup and exposure transitions separately from steady readings.

Verify the complete operating sequence

Use a sensor manufacturer approved test method or suitable cell model to examine the electronics before interpreting chemical measurements. Observe electrode potential, counter electrode output, current channel output, and startup settling. Confirm that the test model represents the behavior relevant to the question.

Save the sensor identity, wiring, bias settings, supply, gain, and measured electrode voltages. Identify periods when the control loop or current channel is outside its usable range and prevent those samples from appearing as ordinary measurements. Electrical verification establishes correct front end operation; sensor calibration and chemical selectivity remain separate requirements governed by the selected sensor and application.