GE DigitalFlo XGM868i, Service Manual

Page: 12 / 80

Chapter 1. Calibration
4 DigitalFlow™ XGM868i Service Manual
1.3.4 Testing Output Linearity (cont.)
Table 1 lists the expected ammeter readings at various % Full Scale settings, for both 4-20 mA and 0-20 mA scales.
Refer to this table to verify the accuracy of the ammeter readings taken above.
If the linearity test readings are not within 5

A of the values listed in Table 1, check the accuracy and wiring of the
ammeter. Then, repeat the low and high end calibrations. If the analog output still does not pass the linearity test,
contact the factory for assistance.
10. Scroll to EXIT and press [Enter] to return to the Cal menu. Then choose another output to calibrate or press
[Escape]
to leave the CALIB menu.
This completes calibration of the Slot 0 analog outputs. Proceed to the appropriate section to calibrate additional
inputs/outputs.
1.4 Calibrating Analog Inputs
Analog inputs may be added to the Model XGM868i by installing an appropriate option card in
Slot 1
. This option card
contains two or four analog inputs, which are designated as A, B, C and D. Both the zero-point and full-scale values for
each input must be calibrated.
Calibration of the analog inputs requires the use of a calibrated current source. If an independent calibrated current
source is not available, one of the
Slot 0
analog outputs may be used for the calibration. During the analog input
calibration, the Slot 0 analog output will supply the low reference, high reference, 4 mA and
20 mA signals at the appropriate times.
IMPORTANT: If a
Slot 0
analog output will be used to calibrate the analog inputs, the
Slot 0
analog output calibration
procedure must be completed first.
Table 1: Expected Ammeter Readings
% Full Scale 4-20 mA Scale* 0-20 mA Scale*
0 4.000 0.000
10 5.600 2.000
20 7.200 4.000
30 8.800 6.000
40 10.400 8.000
50 12.000 10.000
60 13.600 12.000
70 15.200 14.000
80 16.800 16.000
90 18.400 18.000
100 20.000 20.000
* all ammeter readings should be ±0.005 mA