Micrologix 1400

Hi, I am using a potentiometer (set point) and temperature transmitter (process variable) (0-10V DC output and 0 degc to 50 deg c temperature range) as a PID input. Can someone please advice on scaling?

Thnx.

Look at the SCP instruction. I copied the following from the RS500 instruction help

Entering Parameters:
Input - Enter a value to be scaled. This can be a word address or an address of floating point data elements.

Input Min - Enter a minimum value for the input (low end of range). This value can be a word address, a long (double-word) address, an integer constant, floating point data element, or a floating point constant.

Input Max - Enter a maximum value for the input (high end of range). This value can be a word address, a long (double-word) address, an integer constant, floating point data element, or a floating point constant.

Scaled Min - Enter a minimum scaling value representing the low end of the range to which you want to scale the input. The scaling relationship is linear. The value can be a word address, a long (double-word) address, an integer constant, floating point data element, or a floating point constant.

Scaled Max - Enter a maximum scaling value representing the high end of the range to which you want to scale the input. The scaling relationship is linear. The value can be a word address, a long (double-word) address, an integer constant, floating point data element, or a floating point constant.

Output - Enter an address for the scaled value that is returned after the instruction is executed. This value can be a word address, a long (double-word) address or an address of floating point data elements. If any floating-point file types or floating-point constants are encountered in the above parameters, then the entire instruction is treated as floating point, and all immediate integer data values are converted to immediate floating-point data values.

Note: The input minimum, input maximum, scaled minimum, and scaled maximum are used to determine the slope and offset values. The input value can go outside of the specified input limits and no ordering is required. For example, the scaled output value will not necessarily be clamped between the scaled minimum and scaled maximum values.

You'll use the SCP for scaling the pot input for the setpoint. But for scaling the temp transmitter set your input configuraiton to "scaled for PID" and set the scaling in the PID configuration.
Double Click IO Configuration in the project tree. Then select that analog input module you are using. For each of the IO channels you will be using for your pot, your trasmitter, and your PID analog output configure the output range to the appropriate value and then set the data format to "Scaled for PID"



Scale the POT analgog input to 0 to 50 and put it in the PID setpoint. Program your PID instruction and click on setup. Configure the setpoint range from 0 to 50. Now your PV will automatically be scaled to match the setpoint range by the PID instruction.




There is a lot more to configuring the PID than just this however. You can download a manual describing all of the parameters and scaling for the ML PID instruction from the AB website
http://literature.rockwellautomation.com/idc/groups/literature/documents/rm/1763-rm001_-en-p.pdf