Stanford Research Systems SIM983, Operation And Service Manual

Page: 51 / 74

4.1 Verifying the DC Accuracy 4 – 3
4.1.2.1 Error budget
Consider, for example, a measurement with G
= +
13
.
30
,
V
in
=
6
.
192 V
,
and V
ofs
=
− 5
.
480 V
,
performed at a laboratory
temperature of
+
28
◦
C
.
1
The following are the worst-case contribu-
tions of the factors specified in the table on Page vi to the output
error:
Specification Contribution to Overall Error, V
Gain accuracy, ± 0
.
01 ± 0
.
01 × (6
.
192 − 5
.
480)
=
± 0
.
0071
Gain stability,
(28
◦
C − 23
◦
C) × ( ± 10 ppm
/
◦
C)
=
± 50 × 10
− 6
± 50 × 10
− 6
× (6
.
192 − 5
.
480)
=
± 0
.
0000
O
ff
set accuracy,
±
1 mV
±
200 ppm 13
.
30
×
(
±
0
.
001
±
200
×
10
− 6
×
(
−
5
.
480))
=
±
0
.
0279
O
ff
set stability,
(28
◦
C − 23
◦
C) × ( ± 20
µ
V
/
◦
C ± 20 ppm
/
◦
C)
=
± 100
µ
V ± 100 × 10
− 6
13
.
30 × ( ± 0
.
0001 ± 100 × 10
− 6
× ( − 5
.
480))
=
± 0
.
0086
Total
=
± 0
.
0436
The output of the instrument is therefore
V
out
=
13
.
30 × (6
.
192 V − 5
.
480 V) ± 0
.
0436 V
=
(9
.
47 ± 0
.
04) V
if the amplifier is performing within its specifications.
Consider another example, with G
=
− 0
.
19
,
V
in
=
− 3
.
954 V
,
and V
ofs
=
− 5
.
480 V
,
performed at a laboratory temperature of
+
23
◦
C
.
For | G |
<
1
,
the specified o
ff
set error term is referenced to the output,
according to Note 4 on Page vii. The worst-case error budget is
Specification Contribution to Overall Error, V
Gain accuracy, ± 0
.
01 ± 0
.
01 × ( − 3
.
954 − 5
.
480)
=
± 0
.
0943
O
ff
set accuracy, ± 1 mV ± 200 ppm ± 0
.
001 ± 200 × 10
− 6
× ( − 0
.
19) × ( − 3
.
954 − 5
.
480)
=
± 0
.
0014
Total
=
±
0
.
0957
The stability terms are zero because the test is taken at the calibration
temperature. The output of the SIM983 is therefore
V
out
=
− 0
.
19 × ( − 3
.
954 V − 5
.
480 V) ± 0
.
0957 V
=
(1
.
79 ± 0
.
10) V
if the unit is working according to the specifications.
When interpreting the results of a DC performance test of the SIM983,
always account for the voltmeter accuracy specifications.
4.1.2.2 Recalibration
If the module fails its DC accuracy specifications, return it to Stanford
Research Systems for a new calibration.
1
Note that the input voltage by itself, or the output voltage by itself, overloads
the amplifier at the chosen gain, but their combination does not.
SIM983 Scaling Amplifier