76 DECADE user manual, edition 9
C H A P T E R 1 3
Dummy cell
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 trouble shooting
procedure.
The dummy consists of a resistor (R) of 300 MOhm and a capacitor (C) of
0.47 µF 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 about 2.67 nA. Slight differences as to 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 VT-03
flow cell in an ideal HPLC set-up.
The noise generated via the dummy should be less than 2 pA if the filter of
the controller is set to 0.1 second, provided that the dummy is within the fully
closed Faraday shield at the same position as the flow cell (see Table XIII for
settings). With a 1 second risetime the noise should be better than 1 pA.
Table XIII. Dummy cell test settings.
Parameter Setting
Cell potential
800 mV
Cell current
2.67 +/- 0.05 nA (read-out)
Oven
30 °C, stable
Risetime filter
0.1 s (or as specified)
Range
nA range, 0.1 nA/V
Output
Recorder, data acquisition at 1 V
The results of the dummy test must be comparable with the test sheet
supplied with your controller. If not, please consult your supplier.
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com