Arduino to control modulating belimo actuator

Other Hardware General Electronics
1

I’d like to build myself a new modulating maple syrup draw off system.
I currently have one now that uses a PID controller. It is very slow to react and calculates so many variables that it does not work very well amd fluctuates the temp a lot.
I’d like to keep it simple.
Basically what it needs to do is

-Have a display that shows current real time temp in 000.0 format. Using a Rtd pt100 probe.

  • show an adjustable by button set point on the display that is the goal temperarure.
  • send a 4-20ma signal to the actuator that is relevent to how high or low the temperature is above the set point within 1 degree

For example. If the set point is 219.0 F and the temp hits 219.1 the valve will open 10% if it goes up to 219.2 it will open 20% etc. with the valve being open 100% at 1 degree above set temp.
Once the temp is detected as going down the valve will start to close by 10% as the temp goes down every 0.1 degree.

This is possible with a regular PID controller. But the parameters are hard to dial in. The controllers track time and a whole bunch of other variables and are not very user friendly.
I’d like to only have to worry about setting the set point and that’s it.

I have worked with arduino before but just for simple projects. Never done actual coding for them so I’d need help with that.
Wonder if anyone out there could give me a hand with this.

2

Can't you use your PID controller with the I & D terms set to zero?
Sure this can be done with an arduino, but if you already have the control hardware, it's probably easier that way.

3

Setting the I and D parameters to 0 would achieve the same thing on a PID controller ?

4

If you want to do this with a PT100 and for example an Arduino Uno Rev3 You may want to start by giving this a read. Then some basic Arduino code can be found here.

Once you get things working I would calibrate your measurement plane, especially since you want to work from 0.1 degree changes. Obviously you will need to modify a basic code sample to meet your needs.

Ron

5

With proportional control only, the controller will stabilize below setpoint, you need some integral control to force it to setpoint.
With a PT100 @ 220F, 0.1° difference is only 0.02Ω.
PT!00 table

6

Right now on my PID the settings are

P = 2
I= 4
D = 0

Would it be better and do more like I’d like if I set it to
P = 1
I = 0.5
D= 0

7

How precise does the temperature have to be and can you guarantee that the temperature is the same across the evaporator.

Thanks... Tom... :grinning: :+1: :coffee: :australia:

8

The temperature of the rest of the evaporator is not important.
The Set temp is when the syrup is done and has to be taken off rhe evaporator by a valve. The liquid levels are set to stay even throughout the evaporator so whatever comes out as hot goes in to replace it as cold sap. So when the 219 syrup is drawn off then colder sap comes in behind it and cools the temp down.

9

You seemed concerned about the integral time, so I suggested removing it. If you need the I term, then you'll have the same problem with an Arduino.

10

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