Stanford Research Systems SIM983, Operation And Service Manual

Page: 50 / 74

4 – 2 Performance Verification
4.1 Verifying the DC Accuracy
The gain and the o
ff
set of the SIM983 Scaling Amplifier are calibrated
at the factory. Besides self-calibration, there are no user-adjustable
calibration settings.
4.1.1 Getting ready
To verify the DC performance of the SIM983, one needs a DC signal
source (able to output either polarity) and, as a minimum, a volt-
meter accurate to
± 500
µ
V or better. Two voltmeters with matched
calibration are most convenient, such as two channels of the Stanford
Research Systems’ SIM970 Quad DVM. The SIM928 Isolated Voltage
Source is recommended as the calibrator; however, the wiper of a
potentiometer connected to a power supply can be a simpler if less
convenient solution. The DC source must be quiet. If the verification
is done with only one voltmeter, cables have to be connected and
disconnected between measurements, so the voltage source must be
stable within the voltmeter’s accuracy. No such stability is required
if two voltmeters are used.
1. Warm up the SIM983 for at least 2 hours.
2. If the voltmeter requires a warmup of a certain duration prior to
establishing its accuracy specifications, or an autocalibration,
be certain to complete these.
3. Perform an autocalibration of the SIM983 as specified in Sec-
tion 2.2.
In order to perform the measurements, connect the output of the volt-
age source to the input of the amplifier and to Voltmeter 1. Connect
the output of the SIM983 to Voltmeter 2. If using only one voltmeter,
use it to alternately measure the DC source voltage and the output
voltage of the SIM983.
4.1.2 Interpreting the accuracy specifications
Gain and o
ff
set errors specified in the table on Page vi contribute to
the overall output error. The error in V
out
=
G × ( V
in
+
V
ofs
) is
δ
V
out
= δ
G × ( V
in
+
V
ofs
)
+
G ×
δ
V
ofs
.
The gain error
δ
G
and the o
ff
set error
δ
V
ofs
both have temperature-
dependent contributions, mentioned in the specification table under
“Stability”.
SIM983 Scaling Amplifier