Allen-Bradley MicroLogix 1200, User Manual, Page: 44 / 144

Publication 1762-UM002A-EN-P - July 2002
3-14 Module Data, Status, and Channel Configuration
The cut-off frequency for each channel is defined by its filter
frequency selection. Choose a filter frequency so that your fastest
changing signal is below that of the filter’s cut-off frequency. The
cut-off frequency should not be confused with the update time. The
cut-off frequency relates to how the digital filter attenuates frequency
components of the input signal. The update time defines the rate at
which an input channel is scanned and its channel data word is
updated.
Selecting Enable/Disable Cyclic Calibration (Word 4, Bit 0)
Cyclic calibration functions to reduce offset and gain drift errors due
to temperature changes within the module. By setting word 4, bit 0 to
0, you can configure the module to perform calibration on all enabled
channels. Setting this bit to 1 disables cyclic calibration.
You can program the calibration cycle to occur whenever you desire
for systems that allow modifications to the state of this bit via the
ladder program. When the calibration function is enabled (bit = 0), a
calibration cycle occurs once for all enabled channels. If the function
remains enabled, a calibration cycle occurs every five minutes
thereafter. The calibration cycle of each enabled channel is staggered
over several module scan cycles within the five minute period to limit
impact on the system response speed.
See Effects of Autocalibration on Module Update Time on page 3-34.
Determining Effective
Resolution and Range
The effective resolution for an input channel depends upon the filter
frequency selected for that channel. The following graphs provide the
effective resolution for each of the range selections at the six available
frequencies. These graphs do not include the affects of unfiltered
input noise. Choose the frequency that most closely matches your
requirements.