number entry to control a pid

stu · Mar 31, 2009

hi i have a ML1200 (ab) plc how can i use a number entry display to enter the setpoint in a pid? the pid has an transducer to control the speed of a pump, the setpoint is in pressure please help

bwiring · Mar 31, 2009

If your data entry device does not support writing directly to the pid file you could wtire it to a "n" file then use a move instruction to move it to the pid file.

stu · Mar 31, 2009

hi say i am using a pid (pd10.0) to add the setpoint from the hmi to the pid do i instruct it pd10.0/sp am i right ???

Ken Moore · Mar 31, 2009

First question: Do you now have a functioning PID loop?
2. Do you have a means of entering the setpoint?
3. If question 1 is a yes, can you post a snippet of the PID setup?

This is pretty straight forward, but there a lots of details, and posting your PID setup will allow us to assist you, without having to play 20 questions.

Ken

stu · Mar 31, 2009

at the moment i am starting to write the program, i have not got the pid set up yet. i have got a entry on the hmi for the pid but i need to address it? is it like addressing a timer by putting eg /dn on the end but instead use a sp(setpoint on the end of the instruction)

Roy Matson · Mar 31, 2009

You don't say what software you are using. For RSLogix 5000 I create a tag Loop#_SP. In my function block program I select the tag and connect it to the PID function.
You are correct though, you can probably address it directly
Roy

stu · Mar 31, 2009

sorry i thought micrologix 1200 could only be programmed by rslogix 500. (i am new to plcs)thanks stu

Roy Matson · Mar 31, 2009

Stu,
You may be right, I don't claim to be an expert on AB products, it's just that I have been using 5000 lately.
I don't have 500 at the moment.
Roy

stu · Mar 31, 2009

ok, thank you for your help.
stu

Brownhat · Mar 31, 2009

Stu,

You were right, RSLogix 500 is the only software for programming the Micrologix 1200. In order to answer your original question, what are you using for the operator interface?

stu · Mar 31, 2009

hi the hmi i am using is automation direct 8" screen EA7-T8C

widelto · Mar 31, 2009

PID Example

Stu:
This is an example of PID for a ML1200, in this case the setpoint is taken from N7:3 ( Thermocouple Type J range), in my example this value is entered thru a PV300, your case is the same but different brand.
Observe the scale for PID and observe where the scaled value is written.
PV data is scaled for PID also (I:1.0)

number entry to control a pid

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