Section 3: Connections Model 6517B Electrometer Reference Manual
3-4 6517B-901-01 Rev. C / August 2015
Adding a resistor and two diodes (1N3595), as shown in the following figure, provides considerable
extra protection. The resistor must be large enough to limit the current through the diodes to 10 mA or
less. It must also be large enough to withstand the supply voltage. The protection circuit should be
enclosed in a light-tight conductive shield.
This same protection circuit is useful when measuring the insulation resistance of films or high-
voltage cables. Without such added protection, a pinhole or other defect could cause an arc,
damaging the electrometer input.
Figure 13: Capacitor test circuit with protection
Connection methods
High-resistance meter connections
The Model 6517B uses the force voltage measure current (FVMI) configuration to measure
resistance. From the known voltage and measured current, the resistance is calculated (R = V/I) and
displayed.
The resistance to be measured is connected to the center conductor of the INPUT triaxial connector
and the V SOURCE OUT HI binding post as shown in the following figure. This configuration
assumes that V-source LO is internally connected to ammeter LO through the METER-CONNECT
option of the CONFIGURE V-SOURCE menu structure.
The maximum common-mode voltage (the voltage between V-source/ Electrometer LO and
chassis ground) is 500 V
peak
. Exceeding this value may create a shock hazard.
Figure 14: Force voltage measure current - basic connections
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