analog scaling SCP

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#1

Hello! I don’t understand what values should I put in Input min and Input max in SCP block. Let’s say I have a pressure transmitter 0-10 bar that sends 0-20 mA and I want to read pressure value (in bar) on my PLC. Scaled min would be 0, Scaled max would be 10, but what should I put in Input min and Input max? 0 and 32 767 or 0 and 16 384. Can you explain the difference between those two when it comes to scaling. Are these raw values the same for every analog input card, or does it depend on the resolution (12 bit, … 15bit), analog signal (4-20mA, 0-20mA, -10/+10V…)

I think in Studio 5000 this is much clearer, as you can set up your own range that corresponds to 4-20 mA or any other signal

#2

Hi amina,

To get started, you need to determine the specifications of your input card. The documentation will tell you if it translates a 0-20mA input into 0 - 16384 OR 0 - 32767. This is different in various input cards.

Once you have that information, you should also confirm the scaling of the signal for your sensor. It should tell you (for example) that 0-10 bar is equivalent to 0-20mA OR it can be 4-20mA.

Once you have the two components above, you can build the parameters for the instruction. The input side is that the card specifies while the output is what the device specifies.

Note that the values must agree. It’s possible that your card has a 0-20mA input while the device specifies 4-20mA. In this case, you need to be careful on how you convert and interpret the data, as the 0-4mA range will be inaccurate.

Lastly, make sure that the input card is configured to what you’re expecting to scale. If you set the card to read a 0 - 16384 resolution and scale using 32767, your result will be inaccurate. On the same note, pay attention to scaling -10 to 10 VDC signals as I’ve seen multiple mistakes there.

Hope that helps, I’ll try and write up a better explanation and add to the article.

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