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GFK-0825F Chapter 8 Datagrams 8-31
8
Field Recalibration
The 16 Point Grouped Analog Input module is calibrated at the factory. It can also be recalibrated
from the host, to adapt to different conditions. Calibration data consists of two sets of values for each
channel. One value is provided to the module during calibration. The other value is a corresponding
A/D sample value for that current that is determined by the module. One pair of values represents a
low value (typically 4mA) and the other represents a high value (typically 20mA).
Recalibration, if needed, is done as described below.
1. Connect a known current to each of the channels.
2. (Optional) Place the module in warmup mode by sending the warmup command from the host.
3. Send the calibration command from the host. The calibration command specifies the channel to
calibrate and the current being supplied to the channel's input. There is a calibrate command
for a high point and one for a low point.
4. The module samples the channel and calculates the nominal value using the default calibration
data. The module reads the number of samples specified in the command (1 to 65535) and
calculates the average. It then stores the current value and the sample average and recalculates
the scaling constants for the channel.
5. The module returns status information about the recalibration to the BIU.
Message Content for Storing New Calibration to Field Area
Byte Value Description
70Reserved
80Reserved
9 3 Code to store to field area
10 - 20 0 Reserved
Message Content for Reverting to Factory Calibration
Byte Value Description
70Reserved
80Reserved
9 4 Code to revert to factory calibration
10 - 20 0 Reserved
Message Content for Putting Module in Warmup Mode
Byte Value Description
70Reserved
80Reserved
9 5 Code to put module in warmup mode
10 - 20 0 Reserved