VXI VT1422A - Manual (Page 476)

474 VT1529A/B Verification & Calibration Appendix C
Test V-7: Shunt Cal
Resistor Port
Description
This test verifies the operation of the switches associated with the front panel
Shunt Cal Resistor port. The operation of these switches can be verified by
observing the changes in the bridge output voltage when external shunt
calibration is disabled and enabled.
A 1 k
Ω external shunt resistor is connected to the Shunt Cal Resistor port
and the Dummy Load is attached. The 350
Ω bridge completion resistor path
is configured. With the external shunt disabled, the bridge output voltage
should be:
V
sense
= V
excitation
* (10 / (10 + 7.5 + .350) - 0.5)
With V
excitation
= 5.0 V, the expected value of V
sense
is 0.301120 V.
With the external shunt enabled, the bridge output voltage should be:
V
sense
= V
excitation
* (10 / (10 + 7.5 + R) - 0.5)
Where R equals the parallel combination of the 350
Ω resistor and the 1 kΩ
external shunt or 259.26
Ω. Again, with V
EXCITATION
= 5.0 V, the expected
value of V
sense
is 0.315433 V.
Note that the actual measurements will vary based on the actual resistor
values in the dummy load, so these values should be considered approximate
when running this test.
Setup
The VT1529A/B must be connected to the VT1422A through the VT1539A
SCP. The Dummy Load must be connected to the channel(s) being tested.
The Voltage Source must be connected to the appropriate channel bank
terminals of the Bridge Excitation input on the VT1529A/B.
The signal path through the VT1529A/B is highlighted in Figure C-5.
Procedure
If necessary, send the *CAL? query to the VT1422A (required if more than
8 hours has elapsed since the last *CAL? command). The expected return
value is “+0”.
Set the Voltage Source to 5.000 V.
Configure the VT1529A/B for 350
Ω quarter-bridge operation using the
SENS:FUNC:STR:Q350 (@<ch_list>) command. Disable shunt
calibration by sending the OUTP:SHUNt OFF,(@<ch_list>) command.
Send the MEAS:VOLT:UNStrained? (@<ch_list>) query to the VT1422A.
The expected return value is ~0.301 V on each channel. Now, configure
for external shunt using OUTP:SHUNt:SOURce EXTernal,(@<ch_list>).
For each channel (each must be tested separately), enable external shunt
calibration by sending the OUTP:SHUNt ON,(@<channel>) command.
Note: this turns off the shunt on the previous channel.
Send the MEAS:VOLT:UNStrained? (@<channel>) query to the
VT1422A. The expected return value is ~0.315 V on each channel.