3 – 4
Performance Tests
non-inverting, Channel 3 inverting, and Channels 2 & 4 o
ff
is noted
as “
+
−
”. Measure the amplitude for each permutation, and
record the results (circle either RMS or peak-to-peak)
3.4
Calibration
Prior to beginning calibration, photocopy a blank version of the per-
formance test record (page 3 – 7 ).
3.4.1
Offset Adjustment
Calibration starts by disconnecting all inputs and resetting the elec-
tronic output o
ff
set calibration constants. This is accomplished by
issuing the remote commands:
CHAN 0,0
OFST 5, 128; OFST 6, 127
which set the electronic trim-DAC outputs to midpoint. Connect the
SIM980 output to the voltmeter, and adjust R245 to zero the voltage
reading.
After nulling R245, an unconditional autocalibration cycle should be
initiated. Issue the following remote commands:
ARMC FORCE; ACAL
to arm and start internal calibration. The autocalibration will com-
plete in approximately one minute (wait for relays to cease switching
for at least 10 seconds). The output voltage will fluctuate during cal-
ibration but settle to less than
±
20
µ
V.
Verify that the calibration words are within the valid range 1–254
by repeating the queries of section 3.3.2. Nominally, all calibration
words should be within the range 50–200; values of 0 or 255 indicate
that the o
ff
sets have shifted outside of the adjustable range and the
SIM980 may be damaged.
Input o
ff
set voltages should be measured directly by the procedure
of section 3.3.1. Except for short term drift, the calibration should
reduce input o
ff
set voltage errors to less than 10
µ
V. If the result is un-
satisfactory, adjustment of the calibration constant may be attempted
by manually issuing explicit
OFST
commands (see section 2.4.5).
Manually adjusted constants should di
ff
er only slightly (
±
1 count)
from the automatic result. Otherwise the module should be power-
cycled and the adjustment procedure should be repeated.
Record the final o
ff
set values, and final calibration words, on the
performance test record.
SIM980
Analog Summing Amplifier