# SLC 500 Analog card



## Tinker Hydro (Apr 6, 2010)

Wonderin if some one can tell me how to set-up a anolog card? I am using a 4-20 ma signal and I want to scale it to read from 0 - 110 degrees C. Is this possible? I am fairly new to the programming side. Can someone explain this to me please.


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## John Valdes (May 17, 2007)

So 4 Ma = 0c and 20 Ma = 110c right? Are you just displaying temp or are you heating and cooling?

The manual for the PLC will describe the analog card and how it is scaled for the application. To save yourself some time just call the vendor that sells you the PLC's and get one of their techs to walk you through it. Simple and fast. Its not a bad thing to call someone.


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## ElectricArcher (Feb 25, 2010)

This is very basic, you use the instruction SCP (Scale with Parameters). You will need an 1) "Input" - this can be word address or floating point data element(s) 2) "Input Min." - value of 3277. 3) "Input Max." - value of 16384. 4) "Scaled Min." - this value would be your 0 degrees C. 5) "Scaled Max." - this value would be your 110 degrees C. 6) then will get your output. As I stated before, this very basic and requires other fuctions. Use this instruction with the SLC 5/03, SLC 5/04 and SLC 5/05. You can find more information in Rockwell Automations site, look for SLC 500 Processors Documentation Reference Guide.


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## Tinker Hydro (Apr 6, 2010)

*please explain*

just wondering why you would use those numbers for the scale min and max? Why wouldnt you use 4000 min and 20000 max? Would i use for an input?? Also one last question is...how do you calibrate??These are temps. so if my calibrator says 86C but the input is reading 82C how do I change that. Can i use a simple math function?ADD function of 4C??

thanks


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## ElectricArcher (Feb 25, 2010)

As I mentioned before, this is a very basic explanation. Those are the numbers that a processer has to use, to convert a 4 to 20 mA Analog input signal to PID Variable. To explain why those numbers are needed would be very difficult and confusing in this forum, your going to have to get a "SLC 500 Instruction Set Reference Manual". With this manual you will get a very good understanding of all this numbers! As for the calibrating question I'm not clear on what your asking?


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## Tinker Hydro (Apr 6, 2010)

*Calibration*

What i am trying to say is: If i put a rtd in my dry well temp calibrator and it is set for 86C then I know the probe is seeing 86C. Sometimes the reading is not the same back at the PLC because of age of the probe, length of wire, etc. How can I make the input at the PLC show show 86C. Can you use a simple math add or sub function or is there another way? I guesss some people call it a offset.

thanks.


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## John Valdes (May 17, 2007)

CALL THE MAN. CALL THE MAN. When are you guys going to understand its not a sin to call for help. You could have been finished by now and have learned something while you where at it.


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## Tinker Hydro (Apr 6, 2010)

*support*

We dont have that kinda support where I live. can you help me out??


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## stars13bars2 (Jun 1, 2009)

If you are buying the AB at an authorized distributor they are required to have this support on staff. If you are buying from discount automation or black market then you supply your own support.


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## Tinker Hydro (Apr 6, 2010)

*help with offset please*



Tinker Hydro said:


> What i am trying to say is: If i put a rtd in my dry well temp calibrator and it is set for 86C then I know the probe is seeing 86C. Sometimes the reading is not the same back at the PLC because of age of the probe, length of wire, etc. How can I make the input at the PLC show show 86C. Can you use a simple math add or sub function or is there another way? I guesss some people call it a offset.
> 
> thanks.



can you help me with the offset issue please


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## ElectricArcher (Feb 25, 2010)

Your saying that sometimes, the reading is not the same back at the plc? And you want the input at the plc to be 86C? That is a different issue, because the input to the plc is changing. Your 4-20 mA is changing before your plc is getting it. If that is what you are saying.


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## MDShunk (Jan 7, 2007)

If your RTD is saying 82 when you actually have 86, my suggestion is to replace the RTD. It's not like they're a million dollars. Heck, certain RTD's are only 10 bucks. To simply "add 4" might not be true throughout the entire temperature range. Plus, who would want to reprogram the offset every time the RTD is replaced? Not me.


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## Seth (Apr 26, 2010)

Knowing what kind of card it is would help. 
If its an NI4 card, and you are using a 4-20mA signal then you must put in an offset Because the NI4 card is a 0-20mA card, when you have no signal coming from your transmitter (thermocouple, etc.) your input card is recieving 4mA or zero. Being as it is a 0-20mA card you have to ADD an offset. Usually the offset is 25% of your max reading that you are reading. For instance, if you have a load cell and it weighs 0-500lbs. When you add your offset in, you would enter 250 as your offset. 

Might I add, that the book on the NI4 card shows an example of it using the MUL, DDV, and ADD instruction to setup the card. And if you noticed in the ADD instruction they have a positive number. Since your using a 4-20mA signal, you will actually enter a negative number into source B of the ADD instruction.

I can give you a really simple way of setting up the card, if you would like. 
Instead of using the scale instruction that is.


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## Seth (Apr 26, 2010)

Heres a simple way to setup analog.

When using the DDV instruction, Source will be 16384 and Dest. N7:0


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