Metrohm 791 VA Detector - Manual (Page 40)

4 Maintenance – Malfunctions
791 VA Detector
34
4.4 Instrument test with the dummy cell
The correct functioning of the 791 VA Detector can be checked with the
included 6.2813.020 Dummy cell. Several simple checks can be carried
out with this extremely simplified electrical simulation of a detector cell.
Fig. 9 shows the construction of the dummy cell. The checks described
below can be carried out with the recording instrument which is con-
nected (chart recorder, integrator, PC data recording program) or, for
precise measurements, with a voltmeter which is connected to analog
outputs 22 and 23. The dummy cell is connected to the corresponding
cable instead of the electrode. Each test can be carried out separately.
The settings of any operating elements which are not mentioned are ir-
relevant.
1%
AE 10 M Ω
10 Ω
1 µF
WE
RE
Fig. 9: Circuit of 6.2813.020 Dummy Cell
4.4.1 Check of "meas" and "damp" commutators and of current
amplifier offset
1 Set digital switch 11 U
pol
to +1000 mV.
1 0 0 +
2 Set adjusting knob 8 to 0.1 µ A.
4
5
1
10
50
1
5
0,1
0,5 100
10
0,5
0,1
3 Set potentiometer 9 I
comp
abs. to 0.
0.02 nA
Icomp