Rockwell Automation 1761 MicroLogix 1000 Programmable Controllers - Manual (Page 396)

Preface MicroLogix 1000 Programmable Controllers User Manual
F–4
Example Ladder Diagram
The following ladder diagram uses 3 internal bits to perform the calibration
procedure. CAL_LO_ENABLE causes the ladder to capture the 4 mA calibration
value and CAL_HI_ENABLE causes the ladder to capture the 20 mA calibration
value. CALIBRATE causes the ladder diagram to scale the hi and low values to the
nominal values, which provides the slope and offset values used to calibrate the
analog input channel.
Once the calibration procedure is complete, set the CONVERSION ENABLE bit to
a “1”. The calibration numbers can then be used to scale the raw analog data. The
corrected analog input data will be placed in memory location
ANALOG_SCALED.
The following symbols are used in this example:
CAL_LO_ENABLE = B3/500
CAL_HI_ENABLE = B3/501
CALIBRATE = B3/502
CONVERSION ENABLE = B3/503
ANALOG_IN = I:0.4
LO_CAL_VALUE = N7:90
HI_CAL_VALUE = N7:91
CAL_SPAN = N7:92
SCALE_HI = N7:93
SCALE_LOW = N7:94
SCALE_SPAN = N7:95
SLOPE_X10K = N7:97
OFFSET = N7:100
ANALOG_SCALED = N7:101