16 Rockwell Automation Publication 1756-RM011A-EN-P - June 2016
Chapter 3 Hardware Specifications and Considerations
Calibration
All 8-channel modules use precise analog components that maintain their
specifications over time. The modules are calibrated at the factory and
recalibration is not required.
If you want to calibrate an 8-channel module in 6-channel Emulation mode,
the calibration cannot be performed using the 6-channel module profile. The
recommended way to calibrate the 8-channel module would be to temporarily
relocate the module to a test bench, recalibrate it, and then return the module
to the desired slot.
If you have any program code to facilitate the calibration of a 6-channel
module, that code will no longer function. If you were to select the Calibration
tab of a 6-channel module, they would most likely get an error similar to
Figure 3
. This error will not harm the application.
Figure 3 - Module Error Message
RPI and RTS Values of
6-channel versus 8-channel
Modules
The rate at which all 6-channel modules send or receive data is determined by a
combination of RTS (Real-Time Sample) and RPI (Requested Packet
Interval). Depending on the settings of these two parameters, the 6-channel
module behaves a certain way when sending input data to the controller. When
an 8-channel module is in Emulation mode, inputs are sampled at the faster of
the configured RPI and RTS. This maintains the fastest production time for
the user, but can change the exact sampling behavior depending on precise user
configuration. Adjustments would need to be made to the RPI or RPS to
maintain exact data update rates if this change occurred.
For example, if you are using a 1756-IF6I with the RPI set to 25 ms and the
RTS set to 50 ms, the IF6I scans and changes the actual input data at the 50 ms
RTS rate. The 1756-IF8I examines the 25 ms RPI and the 50 ms RTS and
scans the inputs using the faster of the two, which in this case, would be 25 ms.
Therefore the 6-channel module was scanning the inputs at a 50 ms rate, but
the 8-channel module is scanning inputs at a 25 ms rate. It is up to the user to
determine if any adjustments in RTS and RPI are needed. In most cases, no
changes are necessary. However, if analog input data is being supplied to a
sensitive PID loop, you can make adjustments to accommodate.
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