Overview of Calibrate Instrument

Calibrate Instrument is used to measure and correct for drifts in potentiostat circuitry. Gamry Instruments’ potentiostats are precision instruments not subject to large drifts. However, occasional recalibration by a user can improve instrument accuracy.

Additional information including instructions for calibrating specific instruments is found at: https://www.gamry.com/support/documentation-downloads/.

NOTE: Gamry Instruments’ potentiostats make extensive use of software calibration. Some of the calibration data is recorded at the factory. These Factory Cal data cannot be measured and replaced at a user’s facility. Other calibration data are called User Cal data. These are the data that are measured and replaced during the calibration routines described here. Gamry Instruments has a System Assurance program that allows you to update your Factory Calibration data. Contact your local Gamry representative for more information.

Potentiostat recalibration is only required infrequently. Recalibrate your potentiostat under the following circumstances:

• It has been at least one year since your last calibration.
• After your potentiostat has been serviced.
• If you notice breaks or discontinuities in the data-curves recorded with your system.
• If the system is being run in an environment that is very different from the previous operating environment. For example, if the potentiostat was calibrated at 18°C and you are now operating it at 30°C, you should recalibrate.
• When you change to different cell cables.

You should calibrate using the cell cable used in testing. It is is connected to a resistive “dummy” cell which is placed within a faraday cage. A suitable dummy cell ships with every Gamry potentiostat. Always calibrate using the dummy cell supplied with your instrument or a replacement dummy cell of the same type. Contact your local Gamry Instruments sales representative or e-mail techsupport@gamry.com if you do not have your dummy cell.

NOTE: Gamry’s dummy cells are carefully designed for optimum DC and AC performance. We strongly advise against use of a different dummy cell or resistor in calibration. AC Calibration is particularly sensitive to poor dummy cell choices.

NOTE: AC Calibration constants depend upon particular cables. An instrument that is used with both a 60 cm cable and a 150 cm cable will have two separate AC calibration tables. When you run an experiment, the potentiostat determines the type of cable connected and the appropriate corrections are applied. For this reason, you should recalibrate whenever a new type of cable is connected.

Calibration data are stored within the instrument. You do not need to recalibrate when a potentiostat is moved from one computer to another.

Calibration is typically divided into three sections: DC Calibration, DC Tests, and AC Calibration.

• DC Calibration corrects for offset errors in the measurement and application of signals.
• DC Tests are run during DC calibration as a check of basic system operation. A DC voltage and current are applied to the dummy cell, and the resulting current and voltage are measured. Gross system problems (e.g., a broken lead in the cell cable) always cause a failure in the DC Tests. Calibration’s DC Tests do not ensure an instrument is within its accuracy specification.
• AC Calibration is only applicable to some models of Gamry potentiostats. Other models use AC Calibration constants determined at Gamry’s factory. In these models, AC calibration does not normally drift, so user AC calibration in the field is not required. If AC Calibration is unavailable, selecting it in the Calibration menu is okay. The system displays a dialog box informing you AC calibration is not required. Gamry has a System Assurance program that allows you to update old AC Factory Calibration data. Contact your local Gamry representative for more information.

Instruments are always calibrated using the Framework Calibrate Instrument command. The calibration constants are applied in all Gamry applications, including user applications developed using the Gamry Toolkit.