Page 7.2
PROGRAMMABLE RESISTOR MODULES 40-290/291
pickering
SECTION 7 - MAINTENANCE INFORMATION
6½ Digit DMM
V,Ω+
I+
V,Ω-
I-
40-290/291 Programmable
Resistor Module
R offset
R
Figure 7.1 - Calibration of the 40-290/291 using a DMM with 4-wire resistance measurement
CALIBRATION
The 40-290 and 40-291 have no user adjustable components. In most applications regular calibration is not required;
however for applications where a routine calibration is required for a system we suggest the following functional test
for the module.
The 40-290/291 should be tested with a 6.5 digit DMM or better. The user must use 4 terminal resistance
measurement to avoid the introduction of errors due to leads.
For each channel of the 40-290/291 connect the 4 wires to the connector as shown in Figure 7.1. For automated
systems a multiplexer can be used provided the 4 wire measurement system is maintained.
The test principals for the 40-291 are the same as for 40-290, from this point the procedure just refers to 40-290
models.
The procedure is given for the standard modules only; custom modules use the same procedure but must apply
individual limits that reflect the accuracy of the resistors fitted and the resolution.
To test the module, launch the module soft front panel.
Close all the relays in the selected channel and measure the residual path resistance, note the result (from now
referred to as PATH).
With the channel still set to the minimum resistance use the DMM offset facility to set the reading to ZERO.
For each resistor in the chain close all the relays except for the resistor to be measured
Example:
For R1 close all except the relay in parallel with R1, for R2 close all the relays except the relay in
parallel with R2
Record each result for each resistor in the channel. For the tables the results are identified by the resistor number
in each channel
Example:
For 8 bit channels each channel will have 9 measurement results consisting of one PATH result and
8 resistors numbered R1 to R8.
