Crimson 3 Output adjust

Hi everyone, new Crimson 3 user here.
Im trying to adjust an output 4-20 Ma signal automatically using the software and wondered what the best way to do this was?

Within the programme the user will select a target pressure, this pressure could fluctuate depending on a number of factors. Here is what I have so far (this programme is called on tick):

if (HotPressure > HotTargetPressure + 0.5)
{
PressureControlHot --;
if (HotPressure < HotTargetPressure - 0.5)
{
PressureControlHot ++;}
}

HotPressure is the input data to the HMI
HotTargetPressure is the user entered required pressure
PressureControlHot is the output signal controlling the pressure valve.
0.5 is the acceptable tolerance

Thanks

Is PressureControlHot a value sent to a PLC? Or are you using a Graphite Controller? or ??
That might help us know how to best help.

Hi Bullzi, I am using a graphite controller

Could you post your Crimson File? You will need to Zip it first. I would like to look at how you have everything set up.

Also can you describe your system? What is the 4-20ma output connected to? A valve? Temperature Controller?

The way you have your code set up, the program will "ratchet" up or down the output PressureControlHot every scan if you out of your +/-0.5 tolerance. So you will see your output got from 0% to 100% to 0% and back to 100% most of the time. How often and how extreme will depend on how big your system is and how long it will take for changes to take effect. If your output is going to a valve you will see the valve go full open and full close. The system will be very unstable and hard to tune.

You might be better off to use a PID loop to do this control.

Thanks for the reply again Bullzi

The 4-20Ma is controlling a valve. I had thought about using PID control but was trying to understand if there was a possible way of doing it without.

I have attached the ZIP file below. The code i have written to try and control the tolerance is so far only used on the hot constant loading user selection of the software.

I'm not into Crimson 3, but think I understand your challenge. You definitely should look into PID.

I looked at your Cimson DB but couldn't find where you were using that exact code. You have done a lot of nice work on the system by the way. I can tell you spent a lot of time on it.

What you have written may just work depending on how fast your system reacts. I still think that you will see the valve oscillate from closed to open to closed most of the time. But you can try it and see what happens.

The issue you have in trying to do control with a very basic algorithm like this is you don't have many good ways to make adjustments if the system doesn't work the way you want. PID gives you simple adjustments to tune the system.

Is there a reason you do not want to use PID? I know that you will need to add a PID module to the HMI but it may save you a lot of time and tuning headache in the long run.

It is up to you how to proceed. If you have some time to do some experimentation then I say try what you got and see what happens. It would be fun to see what happens. If you need to be up and running in short order then I wouldn't risk it. I would buy the PID module and go with that.

Just my $.02 but good luck either way!!

Thanks for the positive feedback, really appreciate it!
I haven't ruled out using a PID card and to be honest it's looking like I will end up using one, just wanted to see if there was a way around it really.

Next week I will be doing some real world testing with the system so will see how things pan out! My time scale is getting shorter with this too!
Thanks again for taking a look at it for me