Xycom XVME-560, Руководство пользователя

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XVME-560 Manual
September, 1984
2 0
Test point 1 is to be offset nulled to within uV with a digital voltmeter
with at least 10 uV resolution. T e s t point 1 is the output of the
instrumentation amplifier which will go to the positive side of the
voltmeter.
Analog ground may be obtained from J15 and Jl6 and
connected to the negative side of the voltmeter. Potentiometer R18 is to
be adjusted until the output is nulled.
3
With the instrumentation amplifier nulled, it is necessary to perform
continuous conversions on channel 0 with a gain factor of eight. The
conversion result should be displayed on a CRT screen in hex format for
verification purposes.
By
applying
0
volts
+1/2 LSB to
channel
0,
the offset
potentiometer Rll
can
be adjusted until
the conversion result is toggling
equally between the two points described in Table 3-7 below.
Table 3-7. Calibration
Points
Unipolar
(Straight
Binary)
0 v + l/2 LSB FS. - 1 l/2 LSB
Transition Points Transition Points
OOOOH OOOlH
OFFEH OFFFH
Bipolar
(Offset Binary)
0800H 0801H
OFFEH OFFFH
Bipolar
(2's Complement
Offset Binary)
OOOOH
0001H
07FEH 07FFH
4
l
The gain is adjusted by removing
J15 and J 1 6 and then applying the full
scale voltage of that particular range minus
1 l/2
LSB
and adjusting R17
until toggling occurs between the points described in Table 3-7.
Field Calibration
In the field, the AIN may be calibrated without the use of a micro-voltmeter. This
method will not provide as accurate a calibration, but will be within +l LSB. There
-
are three steps involved in field calibration:
1)
Null the A/D.offset error.
2)
Null the instrumentation amplifier offset.
3)
Calibrate the gain.
The first step is to null the A/D offset error.
T
O do this, jumper J12 must be placed in
the “A” position. This grounds the gain. On a gain of eight, a reading of 0000H
(OSOOH
for offset binary) should be observed as a conversion result on channel 0.
Potentiometer
Rll can be adjusted until the zero reading is observed. Jumper
312
must then be placed back in the
"B"
position to allow the second step of field
calibration.
The second step is to null the instrumentation amplifier offset. This requires the input
to channel 0 to
be grounded. T
O do this, either jumper
J16
must be installed for
3-13