OBJECTIVE or GOAL
Perform the dummy cell test for the 2465 Electrochemical Detector. A successful dummy cell test confirms that the controller, including the cell cable, functions properly. If the result of the noise measurement with the dummy cell is within specs, the controller is excluded in a troubleshooting procedure.
- 2465 Electrochemical Detector
- Set all dummy cell test parameters to those shown in the following table:
2. Install the dummy flow cell by connecting the dummy leads to their respective, like-color connector leads.
3. Ensure that the temperature is stable at +30 ºC; a one-hour warmup is recommended.
4. From the main screen, press F5 to call up the diagnostic screen.
5. Press F2 to call up the noise test. A five-minute countdown takes place, while the cell current stabilizes, with the remaining time shown in the lower-right corner of the LCD.
6. After five minutes, the noise screen appears showing the calculated cell current value. The cell current should read 2.6 nA with the dummy cell installed.
7. The noise generated by the dummy cell should be no more than 20 mV, as measured at the output of the detector. NOTE: The display is a reference of the cell current. The true noise value is present on the analog output or can be read via the RS-232 serial output connected to an Empower workstation. The display does not show you the noise value. Look at these outputs to determine your noise peak.
8. Once finished, press F1 to revert to the diagnostics screen.
The dummy consists of a resistor (R) of 300 M and a capacitor (C) of 0.47 F in parallel. The current is measured over the resistor according to Ohm's law (V = I x R); hence, with a working potential of 800 mV the current drawn will be 2.67 nA. Slight differences from this (ideal) value are due to the tolerance of the resistor (± 1%). The capacitor functions as a "noise generator" and in fact resembles the capacitance of a well-functioning flow cell in an ideal HPLC setup.
The noise generated via the dummy should be less than 2 pA if the filter of the controller is set to 1 second, provided the dummy is within the fully closed Faraday shield at the same position as the flow cell.