analog configuration

To configure the analog I/O module for the micrologix 1200, there are different options. Whats the difference between raw proportional configuration vs. scaled PID?

Pressing F1 on the Advanced Configuration Menu yeilds the following text (excerpted):

Data Format

Raw/Proportional Data - The value ... provides a -32,767 to +32767 full range for a +/- 10vdc user input.

Scaled for PID - The value at the controller is an integer with 0 representing the lower range and 16,383 representing the upper range.


RSLogix 500 - Copyright Rockwell Software 2000

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More simply:
If you are using Raw and there are 0V on the wire, the input register will have a value of 0. 10V will produce a signal of 32767.

If you are using PID and there are 0V on the wire, the input register will also have a value of 0, but 10V will produce a signal of 16383.

If you are going to use the PID instruction, then it can be handy to use the PID scaling, so you can reference the raw input as your Process Variable, instead of having to scale (via an SCP instruction) it to be in the 0 to 16383 range.

Otherwise, the Raw/Proportional setting gives you the highest resolution, which is typically the most desirable. Keep in mind that even though the PLC may be able to differentiate betweeen ¹⁰/₃₂₇₆₇th of a volt (=0.003 V), your transmitter may not be able to send out that fine a difference, especially in a noisy environment.