Scaling Non-Linear Input

I’m using a RMC75E-AA2. It’s my understanding that scaling is handled by Pressure Scale (Pr/V) F12:0 and Pressure Offset (Pr) F12:1. This assumes that the input is linear.

Is it possible to have a lookup table for scaling non-linear input?

Although it is not possible to scale non-linear inputs, it may still be possible to make non-linear applications work by using the mathematical expressions in RMCTools.

These types of applications require two parts:

  • Calculate the Target Pressure
    With the expressions in RMCTools, you can calculate what the target pressure needs to be so that the pressure will be correct. For example, if you want the pressure to be 1000, you may calculate that you need to command the target pressure to be 1058. Then, you can send a pressure command with a requested pressure of 1058, and the true requested pressure will be 1000.

Continuously calculate the scaled pressure
With the expressions in RMCTools, you can make a user program that continuously calculates the true scaled pressure. You can put the result in a variable, and monitor that variable. You can do this for both the Target Pressure and Actual Pressure.

With these two steps, you can correctly determine the target pressure, and you can monitor the scaled target and actual pressure. That’s usually all you need for basic pressure control. If you need to do custom profiles, this method may not be enough.