An EC Labor measurement guide with manufacturer references and our own calculated example.
A controlled electrochemical experiment
In potentiostatic mode, the instrument controls the potential difference between the working and reference electrodes while measuring current. In galvanostatic mode, current is the controlled quantity and potential is the measured response.
Three electrodes, three roles
The reaction of interest takes place at the working electrode. The reference electrode provides a stable potential reference; the counter electrode completes the current path. Feedback allows the instrument to follow the setpoint.
Depending on the task, the experiment may include cyclic voltammetry, cycling or impedance measurement. BioLogic: how a potentiostat works.
What is controlled, and what limits that control?
Distinguish the controlled WE–RE potential in a three-electrode experiment from the complete WE–CE voltage. Compliance voltage is the output voltage limit: the instrument uses this available headroom to maintain the target. A small controlled potential can require a larger complete cell voltage. Reaching the output limit can prevent the setpoint from being maintained. BioLogic: what is compliance?.
A quotation stating “±10 V” therefore needs context. Ask which terminals the voltage refers to and at what current the limit applies. The resistor example below shows why these distinctions matter.
Original example: controlling 0.2 V requires a 10 V output
Consider an ideal, purely resistive dummy load. Two resistors, 100 Ω and 4900 Ω, are connected in series between WE and CE. RE senses their junction, with WE at the other end of the 100 Ω resistor. Assume that the reference input does not load the divider; there is no electrode polarisation or cable resistance. The following values are voltage and current magnitudes.
- A target of 0.2 V across 100 Ω requires I = 0.2 V / 100 Ω = 2 mA.
- Across the complete 5000 Ω load, this requires U = 2 mA × 5000 Ω = 10 V.
- A hypothetical instrument limited to 5 V output could produce at most 1 mA through this load. The controlled section would then see only 0.1 V, failing to reach the 0.2 V target.
- Prescribing 1 mA galvanostatically instead gives 0.1 V WE–RE and 5 V total in this ideal model. Operating at the limit leaves no headroom.
These values are not specifications of a BioLogic model. In a real cell, the counter-electrode reaction, electrolyte and geometry require separate evaluation of the necessary output. The practical lesson from this example is to accompany the target potential with estimates of current and total voltage.
Maximum current does not establish low-current accuracy
Current-range selection affects signal-to-noise ratio and the ability to follow rapid changes. A fixed range avoids switching; autoranging accommodates changing currents but can introduce acquisition gaps during range changes. Evaluate it against the timescale of the experiment. BioLogic: selecting a current range.
Original specification-reading example: suppose a fictional instrument allows an error of ±(0.1% of range + 0.05% of reading). Measuring 100 µA on the 10 mA range gives ±(10 + 0.05) µA, or ±10.05%. On the 1 mA range, the same formula gives ±1.05 µA, or ±1.05%. This excludes noise and other error contributions and does not describe an actual product’s accuracy.
When comparing quotations, calculate error at the expected signal and the range actually used. Do not substitute the number of decimal places on the display for an error estimate.
What requirements should guide instrument selection?
Our suggested specification checklist makes the intended experiment reviewable:
- Describe the cell, electrode roles and quantity to be controlled.
- State the smallest signal of interest and the largest expected current, including transients.
- Separate the WE–RE potential window, complete cell voltage and output headroom.
- List independent experiments that must run simultaneously; use that list to establish channel needs.
- For EIS, request confirmation of the required frequency, impedance and amplitude ranges for the actual configuration.
- Ask for an explicit breakdown of the base instrument, channel boards, options and boosters.
Write acceptance criteria for a trial before running it: allowable deviation between target and measured response, data to retain, and how an output-limit condition will be indicated. This ties the comparison to a concrete experiment.
What should you check when a curve looks unusual?
Our suggested troubleshooting order starts with connections and reference-electrode condition, then ranges, output limits and raw time-domain signals. Record whether the feature repeats at the same current, potential or range transition. Keep instrument and software configuration with the measurement so technical support has a reproducible starting point.
Related guides cover reference-electrode selection, iR compensation and EIS fundamentals. Use the instrument finder to shortlist configurations against your requirements.