Troubleshooting Your Gamry Potentiostat

Introduction

The Calibration Cell is a printed-circuit board used for calibration and troubleshooting of your Gamry Instruments potentiostat, and is supplied with every Gamry Instruments potentiostat. Each potentiostat also comes with an AC dummy cell. If your instrument was manufactured before May 2018, you have a Universal Dummy Cell (UDC x) instead.

Figure 1. (Top) Typical Calibration Cell—but resistance value varies with the model of instrument;
(Bottom) older Universal Dummy Cell, or UDC 4.

The Calibration Cell has large and small jacks on the front of the board, to connect to the appropriate potentiostat.

The UDC 4 has two sides, equipped with tabs, labeled Calibration and EIS Dummy Cell. The tabs are marked with labels corresponding to the leads on a Gamry Instruments Cell Cable. The Calibration side on the UDC 4 is a 2000 Ω precision resistor (with some protection components). Its value is typically between 1.994 kΩ and 2.006 kΩ.   

As the name implies, the UDC 4 is the fourth revision of the Universal Dummy Cell. Do not use the UDC 1 (labeled Universal Dummy Cell) to calibrate a PCI4, Series G, or Reference Family potentiostat. Using a UDC 2 or UDC 3 is OK. Some Universal Dummy Cells include a DC Dummy Cell. The DC Dummy Cell was removed from the UDC 4.

Calibration

If you suspect that your Gamry Instruments potentiostat is misbehaving, the first step is to calibrate it.

Connect the potentiostat Using the Calibration Cell

Connect the correct colors of the cell cable to the correctly labeled receptacles on the Calibration Cell. Place the Calibration Cell inside the Calibration Shield included with your potentiostat.  This is very important because of the high sensitivity of the potentiostat.

Connect the Potentiostat Using the Older UDC

Connect the cell cable to the appropriate tabs on the Calibration side of the UDC 4. Place the UDC 4 inside the Calibration Shield included with your potentiostat.  This is very important because of the high sensitivity of the potentiostat.

Run the Calibration Software

Run the calibration by opening the Gamry Instruments Framework™ software and clicking Experiment > Utilities > Calibrate Instrument. 

When you select Calibrate Instrument, you have a choice of a DC Calibration, an AC Calibration, or Both.

If your Potentiostat is not connected to an ECM8 Multiplexer, then select Both.

If you are using an ECM8 Multiplexer with your Potentiostat, then calibration is a two-step process: 

1. Perform the DC Calibration with the ECM8 Multiplexer disconnected from your Potentiostat. 

2. Perform the AC Calibration with the ECM8 Multiplexer connected to your potentiostat. In this case, you must set a Multiplexer channel to connect to the Calibration Cell or UDC4: click Experiment > Named > Script >Multiplexer Set.exp and click the radio button for the channel you wish to use.

If you are using a Reference™ 600, 600+, 620, 3000, or  3000 AE potentiostat, AND you have more than one cell cable, be aware that the EIS capability of a potentiostat is affected by the length of the cell cable. DC measurements, in general, are not affected by the length of the cell cable. For the best EIS measurements, you’d like to calibrate the potentiostat using each cell cable. The Reference 600/600+/620/3000/3000 AE is a smart instrument and it knows which cell cable is connected, so you can run the “AC only” calibration for each cell cable. The calibration data for each cell cable is saved in the instrument and used whenever that cable is used in an EIS measurement.

Of all the components of a potentiostat, the Cell Cable is the one that is constantly being flexed and exposed to corrosive environments, and so is often the first component to fail. Be sure to check the integrity of your Gamry Cell Cable, as explained in our Technical Note outlining the process.

DC Low I Calibration

When you click Experiment > Utilities in the Framework software, note an entry called DC Low I Calibration. This is a special calibration procedure used to ensure that ultralow DC currents are measured as accurately as possible. This procedure is recommended for users of the Gamry Instruments Physical Electrochemistry Software and the Reference 600/600+/620 potentiostat.

You can also use the Calibration Cell or Calibration circuit in the UDC 4 to test for proper operation of your potentiostat. 

Test the Potentiostat with the Calibration Cell

Using Chronoamperometry in the Physical Electrochemistry software or Polarization Resistance in the DC Corrosion software, apply ±1 volt to the Calibration Cell resistor. The resistance of that resistor is given on the front label on the Calibration Cell. The current should equal that calculated by Ohm’s Law, I = E/R. At 1 V using, for example, the 2 kΩ Calibration Cell, the current should be 500 µA (1 V/2000 Ω = 5 × 10^–4 A). Values for the calibration cell are

Test the Potentiostat with the UDC 4

Using Chronoamperometry in the Physical Electrochemistry software or Polarization Resistance in the DC Corrosion software, apply ±1 volt to the 2000 Ω UDC 4 Calibration resistor. The current should equal that given by Ohm’s Law, I = E/R. At 1 V, for example, the current should be 500 µA (1 V/2000 Ω = 5 × 10^–4 A). 

You can also do scanning experiments with the 2000 Ω resistor, such as Polarization Resistance or Cyclic Voltammetry. For these tests, the current-voltage curve should be perfectly linear and the data should obey Ohm’s Law.

Checking the EIS Performance of Your Potentiostat

The EIS Dummy Cell on the UDC 4 is a simplified Randles cell. A circuit diagram of the EIS cell (Fig. 2) and a typical spectrum of the cell in Bode format (Fig. 3) are provided below. In “electrochemistry-speak,” Rp is 3000 Ω, Cdl is 1 µF, and Ru is 200 Ω.

Figure 2. Circuit schematic for the UDC 4.

Figure 3. Bode plot of the Dummy Cell’s EIS response.

A visual examination of the spectrum is usually sufficient to determine if your EIS system is working. Most instrument malfunctions either prevent recording of the spectrum or cause gross errors that dramatically change the shape of the curve.

If you want a numerical confirmation of the system’s performance, fit the Dummy Cell’s spectrum to the Randles model in the Echem Analyst™. The calculated values should be:

R_p = 2.95 kΩ to 3.07 kΩ
R_u = 196 Ω to 204 Ω
C_f = 0.90 µF to 1.10 µF

 

Technical Note Rev. 2.1 9/11/2019 © Copyright 1990–2019 Gamry Instruments, Inc.  

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