Temperature process Slc 5/04

Adam303 · Oct 6, 2009

Hi to all Again
I have a frezzer tunnel that used liquid nitrogen to freeze product.
I have to redesighn the tunnel because it looks like it came out of a junk yard. For the project we first wore not going to use a plc but now we came to a concusion we should.

I have most of the programing done but i'm stuck at few points.

For the Slc 500 7 slot rack i'm using the following:
slot o 5/04 processor
slot 1 1746-iv16 input module
slot 2 spare
slot 3 1746-ow16 output module
slot 4 spare
slot 5 1746-nio4i analog combination module
slot 6 1746-nr4 rtd module

The analog output 4-20 will be proportional to process temperatue and will drive a electronic to pneumatic controller. The controller than will have a proportional output of 3to 15 psig and will regulate a pneumatic valve that will open the liquid nitrogen.

The rtd will have two inputs (pt100) one for low temperature
limit (set At -280 F) The second will reed the process temperature.

Adam303 · Oct 6, 2009

The problem

Now i have to write a pid instruction but i'm not so sure how to adress it

In the pid intruction should the process veriable be the input of the 1746_NR4 module or should i take the output from NR4 (scaled from 0 to 16383) copy it to a inager and than place it to the process verible??

I also have to be able to write to the pid instruction to change the Sp set point.

Adam303 · Oct 6, 2009

Does any one have pdf file of a program using the hr4 rtd module and a pid instruction

val_99 · Oct 6, 2009

you should use 0-16383 scaled value of the temperature for PID instruction input (PV - process variable). PID output also will be scaled 0-16383 (if i'm not mistaken).

Adam303 · Oct 6, 2009

Adam303 said:
The problem

Now i have to write a pid instruction but i'm not so sure how to adress it

In the pid intruction should the process veriable be the input of the 1746_NR4 module or should i take the output from NR4 (scaled from 0 to 16383) copy it to a inager and than place it to the process verible??

I also have to be able to write to the pid instruction to change the Sp set point.

Pardon this it does not make any sense to me so how would it make any sense to any one eles.
let me clear this up.

IN the process verible I have to use scaled 0-16383 from the input of the 1476-nr4

Data transmitted from the module to the processor is called the input
image (for example, Channel Data Words and Channel Status Words).
Conversely, data transmitted from the processor to the module is
called the output image (for example, Channel Configuration Words

and Scaling Limit Words).

Adam303 · Oct 6, 2009

Ok so now I have the Process verible scaled for pid 0-16383
Since the pid control verible is also scaled 0-16383 how would I scale this to be a 4-20 output?????

Adam303 · Oct 6, 2009

attached file

curlyandshemp · Oct 6, 2009

Adam303 said:
attached file

This is way OT and not meant to be a putdown or any type of insult only an observation, but are you a Master Electrician over the age of 40?

You certainly spell like the Master Electrician we have on staff, a brilliant guy, but horrible with the command of the English language on paper.

val_99 · Oct 6, 2009

You don't have to scale 0-16383 output for 4-20mA. An output analog module does it.

Adam303 · Oct 6, 2009

so should i just address the control variable as an O:3.0 ??

Adam303 · Oct 6, 2009

curlyandshemp said:
This is way OT and not meant to be a putdown or any type of insult only an observation, but are you a Master Electrician over the age of 40?

You certainly spell like the Master Electrician we have on staff, a brilliant guy, but horrible with the command of the English language on paper.

Our core group is almost as large as any major company out there in the automation field

What can I Say ESL It is also sad that a specialist like you with a huge backgroung in automation can give such a huge feed back. But the only thing keeping me happy about this is that at some point in time You had the same knowledge as I do today.

OkiePC · Oct 7, 2009

For the current output:

0 digital = 0mA
3277 digital = 4.0mA = 3.0 psi
16384 digital = 20.0mA = 15.0 psi

I suggest you take the output of the PID and scale it to a floating point value that represents the engineering units (psi) of the final control element. That way you can verify your scaling throughout the controls.

You could then take the psi units and scale again to get the 4-20ma (3277-16384) or use the PID output directly and scale it.

Have a look at the SCP instruction (scale with parameters). It does all the work for you.

Paul

Adam303 · Oct 7, 2009

Thanks Paul

curlyandshemp · Oct 7, 2009

Adam303 said:
Our core group is almost as large as any major company out there in the automation field

What can I Say ESL It is also sad that a specialist like you with a huge backgroung in automation can give such a huge feed back. But the only thing keeping me happy about this is that at some point in time You had the same knowledge as I do today.

Like I said, I did not mean to offend, I just had a chuckle.

Also if you are using an air actuated proportional valve, ensure you have a Burkert style shut off valve upstream from the valve, and use an air solenoid to feed the I/P. One solenoid can be T'd for both and only actuated when you need the cooling. What this does is prevent any trickle cooling medium getting through when the process is not in use. Almost every 3 - 15psi controlled Jordan style proportional valve will eventually leak.

Temperature process Slc 5/04

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