Keithley 2750, Service Manual

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1-8 Performance Verification Model 2750 Multimeter/Switch System Service Manual
WARNING Observe the following safety precautions when performing these tests:
• Some of the procedures in this section may expose you to dangerous
voltages. Use standard safety precautions when such dangerous volt-
ages are encountered to avoid personal injury or death caused by elec-
tric shock.
• For the front panel terminals only, the maximum common-mode volt-
age (voltage between INPUT LO and chassis ground) is 500V peak.
Exceeding this value may cause a breakdown in insulation, creating a
shock hazard.
• For the plug-in modules, the maximum common-mode voltage (volt-
age between any plug-in module terminal and chassis ground) is listed
in the module’s specifications. Exceeding this value may cause a
breakdown in insulation, creating a shock hazard.
• When using the front panel terminals simultaneously with plug-in
modules, all cable insulation voltage ratings must equal or exceed the
maximum voltage applied to either the front panel terminals or the
plug-in module terminals.
Model 2750 verification
Perform these tests to verify accuracy using the Model 2750 front panel terminals.
Verifying DC voltage
Check DC voltage accuracy by applying accurate voltages from the DC voltage calibrator
to the Model 2750 INPUT jacks and verify that the displayed readings fall within speci-
fied limits.
CAUTION Do not exceed 1000V peak between front terminals INPUT HI and INPUT
LO because instrument damage may occur.
Follow these steps to verify DC voltage accuracy:
1. Connect the Model 2750 HI and LO INPUT jacks to the DC voltage calibrator as
shown in
Figure 1-1 . Make sure the INPUTS switch is set to the FRONT position.
NOTE Use shielded, low-thermal connections when testing the 100mV and 1V ranges
to avoid errors caused by noise or thermal effects. Connect the shield to the cal-
ibrator’s output LO terminal.