Rockwell Automation 1761 MicroLogix 1000 Programmable Controllers - Manual (Page 394)

Preface MicroLogix 1000 Programmable Controllers User Manual
F–2
Calibrating an Analog Input Channel
The following procedure can be adapted to all analog inputs; current or voltage.
For this example, the 1761-L20BWA-5A with a 4 mA to 20 mA input is used. The
overall error for the MicroLogix 1000 is guaranteed to be not more than
±
0.525 at
25
_C.
The overall error of
±
0.525% at 20 mA equates to
±
164 LSB of error, or a code
range of 31043 to 31371. Any value in this range is returned by an analog input
channel at 20 mA. The expected nominal value at 20 mA is 31207. After
performing a software calibration, the overall error is reduced to 5 LSB (0.018%), or
a code range of 31202 to 31212.
The graph shown below shows the linear relationship between the input value and
the resulting scaled value. The values in this graph are from the example program.
Scaled
Value
Input Value
20 mA = 31207
(scale Hi)
4 mA = 6241
(scale low)
Low Value from card Hi Value from card
6292 31352
Scaled Value vs. Input Value