Guarded Operation - Keithley 5156 Instruction Manual

Guarded operation
Guarded connections are recommended for resistances 10GQ and abovc, and
only when using the Model 5156 as a resistance standard to test instruments that
measure resistance using the source current, mcasurc voltage resistance mcasurc-
ment method. Guarding is neither required nor recommended when used with
instruments that use the source voltage, measure current resistance measurement
method, such as the Model 65 I7 Electrometer.
Figure 2-8 shows guarded resistance connections. When making connections:
- Connect the Model 51 S6 OUTPUT jack to the instrument INPUT jack using
a suitable triax cable.
- Conncct the Model 48.51 BNC Shorting Plug to the BNC jack associated
with the desired resistance standard.
- Remove the link between the SHIELD and CHASSIS jacks.
- If instrument common is not connected to chassis ground, connect the
Model 5156 CHASSIS jack to the instrument common input terminal.
* If the test instrument does not automatically apply the guard signal to the
inner shield of the triax connecting cable, connect the Model 5156 SHIELD
jack to the guard or preamp output terminal of the test instrument.
WARNING
Hazardous voltage may be present on the Model 5156
SHIELD and OUTPUT jacks when using guarding.
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