Figure 18-1 Test Resistor Construction - Keithley 6430 Instruction Manual

Test resistor construction
The 1TΩ and 10TΩ test resistors used to test the 2TΩ and 20TΩ resistance ranges should be
mounted in a shielded, guarded enclosure like the one shown in Figure 18-1. The resistors
should be properly characterized to the accuracy stated in Table 18-1 before use. Connect the
resistors terminals to the triax jack center conductor and outer shell. Connect the guard shield
to the triax jack inner ring.
WARNING
Figure 18-1
Test resistor
construction
Inner Ring
Verification limits
Most of the verification reading limits stated in this section have been calculated using only
the Model 6430 one-year accuracy specifications, and most reading limits do not include test
equipment uncertainty. (However, 1pA-100nA and 2GΩ-200GΩ range limits do include the
uncertainty of the Model 5156 Electrometer Calibration Standard.) If a particular measurement
falls outside the allowable range, recalculate new limits based both on Model 6430 specifica-
tions and corresponding test equipment specifications.
Example limits calculation
As an example of how verification limits are calculated, assume you are testing the 20V DC
source range using a 20V output value. Using the Model 6430 20V range one-year accuracy
specification of ±(0.02% of output + 2.4mV offset), the calculated output limits are:
Output limits = 20V ± [(20V × 0.02%) + 2.4mV]
Output limits = 20V ± (0.004 + 0.0024)
Output limits = 20V ± 0.0064V
Output limits = 19.9936V to 20.0064V
To avoid a shock hazard, do not connect guard to an exposed shield.
Center
Conductor
Triax Jack
Shell
Performance Verification
1TΩ or 10TΩ
Resistor
Guard
Shield
18-5