B875–200 Configurable A/D Input, Calibration
(Original Document)
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General
The analog input module is calibrated at the factory prior to shipment. To ensure the module’s accuracy, the trim-pot should be calibrated regularly on a yearly interval.
The following tools and materials are needed to calibrate a configurable A/D input module:
NOTE: Calibration is not recommended for analog current, low bandwidth, 4—20 mA (AS–5B32001A) type input packs because of their reduced accuracy
Calibration of a given channel involves calibration of all eight channels of this module. There is no provision to calibrate a particular channel. Therefore, calibration can be performed with any one channel with any type of input pack. Calibration does require the calibration signals to pass through an input pack.
NOTE: If the particular input pack used in calibration is out of calibration, then all B875 modules calibrated with this input pack will be improperly calibrated.
Location of trim pot, diagram
Use the following procedure to calibrate the module. The input pack used in this procedure is used only as an example. A five-minute warm-up time is recommended prior to calibration.
Step
Action
1
To access both trim pots, remove two screws and label located on front panel of module, as shown on location of trim-pot diagram, above.
Note: The top trim-pot adjusts the total magnitude of the range (full scale). The bottom trim-pot adjusts the zero offset scale.
2
Open module handle to expose connectors and terminals.
3
Install an input pack in any channel, and connect an appropriate signal source to that channel. Refer to voltmeter connections diagram, below.
4
Apply input signal to selected channel which represents zero signal (zero volts when using analog, V input pack, low bandwidth, 0 to +10 V (AS--5B31003A). On programming panel observe input from B875 for selected channel. Adjust zero cal control (R29) as required to read 0000.
5
Apply input signal that results in output between 80 to 90% of full scale. Use 9.375 V if calibrating with an analog, V input pack, low bandwidth, 0 to +10 V (AS--5B31003A). Resultant reading should be set for 0F00 Hex, or 3840 decimal with full scale calibration control (R57).
6
Repeat previous two steps until readings are correct at both zero and near-full-scale points.
7
After calibration is complete, disconnect voltmeter, return connections to their original state, close module handle, and replace front label that covers trim-pot.
Voltmeter connections diagram