Allen-Bradley 1794-IT8, User Manual

Page: 49 / 76

6–7 Calibrating Your Module
Publication 1794-6.5.7 – April 1997
Gain Calibration
After completing the offset calibration, proceed with the gain
calibration.
1. Apply power to the module for 40 minutes before calibrating.
2. Connect 75.000mV across each input channel. Connect all high
signal terminals together and attach to the positive lead from the
precision voltage source. Connect all low signal terminals
together and attach to the negative lead.
3. After the connections stabilize, send a block transfer write to the
module to set the bit in the calibration mask that corresponds to
the channel to be calibrated to 1, and the hi/lo bit (bit 06 in write
word 0) to 1. (Set bits 08 through 15 in write word 0 if calibrating
all inputs at one time.)
4. Send another block transfer write to set the cal-clk bit (07 in write
word 0) to 1.
5. Monitor the cal-done bit (09 in read word 10). If the calibration is
successful, the cal-done bit will be set to 1. Verify that the bad-cal
bit (10 in read word 10) and the cal-range bit (08 in read word 10)
are not set (0).
6. Send another BTW to set the cal-clk bit (07 in write word 0) to 0.
7. Send another BTW to set the hi/lo bit (bit 06 in write word 0)
to 0.
8. Monitor the cal-done bit (09 in read word 10). The cal-done bit
will be reset to 0.
9. If individually calibrating channels, repeat steps 1 through 7 for
offset calibration on any additonal channels you want to calibrate.
10.Send a block transfer write to the module to clear all calibration
mask bits to 0.