Trouble with temp probe programing

I'm new to this rs5000 programming. I'm using a 1769-IF4 input module with a 837t temp probe and I'm not sure how to convert the 4-20ma data to temperature in vs21.11 rslogix program.

Welcome to the forum!

In the project tree down the left hand side, down toward the bottom, you'll find the hardware configuration. Right click on your 1769-IF4 and select properties. Here, you can configure your card and define the scaling values for each channel. You *could* just scale it right then and there - so set your low scale to 0 and your high scale to 100, and then 4-20mA becomes 0-100 degrees.

Doing it this simplistically, though, reduces your resolution. I prefer to scale each input so that 4mA=4000 and 20mA=20000. Makes it easy to see the mA reading at a glance, and gives me plenty of resolution.

Then, you just use standard math to scale it accordingly. Most programmers who work with analogs frequently will build an add-on instruction to scale analog values, so that you just have to plug in the low and high analog values (4000 and 20000), and the low and high scaled values (0 degrees and 100 degrees) and the calculation is all done internally. But you can just as easily do it directly in ladder logic using a CPT instruction, or even a series of discrete multiply/divide/add/subtract instructions.

Plenty of ways to skin this cat, have a go and if you get stuck post back with where you're up to!

What does the 4 to 20ma represent
4ma=???deg
20ma=???deg

How do you have the card configured (Input Data Format)
Raw Proportional Data ?
Engineering Units ?
Scaled for PID ?
Percent Range ?
See pdf

You can then use the following formula to rescale the raw data to the temperature range of your 4 to 20ma input.
See text

Edit: ASF types faster then I do.

ASF said:

Welcome to the forum!

In the project tree down the left hand side, down toward the bottom, you'll find the hardware configuration. Right click on your 1769-IF4 and select properties. Here, you can configure your card and define the scaling values for each channel. You *could* just scale it right then and there - so set your low scale to 0 and your high scale to 100, and then 4-20mA becomes 0-100 degrees.

Doing it this simplistically, though, reduces your resolution. I prefer to scale each input so that 4mA=4000 and 20mA=20000. Makes it easy to see the mA reading at a glance, and gives me plenty of resolution.

Then, you just use standard math to scale it accordingly. Most programmers who work with analogs frequently will build an add-on instruction to scale analog values, so that you just have to plug in the low and high analog values (4000 and 20000), and the low and high scaled values (0 degrees and 100 degrees) and the calculation is all done internally. But you can just as easily do it directly in ladder logic using a CPT instruction, or even a series of discrete multiply/divide/add/subtract instructions.

Plenty of ways to skin this cat, have a go and if you get stuck post back with where you're up to!

Click to expand...

The 1769-IF4 does not support on-board scaling like 1756 analog modules do. For the 1756 range, I don't know why you are against scaling on cards that support it, the output data is a REAL, so there is no loss of resolution.

Anyway, the output value scaling choices available for the 1768-IF4 are:-

Raw/Proportional (Default)
Engineering Units
Scaled for PID
PerCent Range

The attached table gives the Min and Max returned values for 4 to 20 mA, and you can see that the greatest "span", which gives the greatest resolution, is the default Raw/Propotional setting. But as stated already most people use the "Engineering Units" range....

For scaling that to your probes range, it is easiest to use a single instruction called SCP, which unfortunately doesn't exist in Logix5000, so you have to provide it yourself as an Add-On Instruction, or AOI.

You don't need to write your own SCP AOI, there is a perfectly good example in the "Samples" folder, "Add-On_Instruction_Samples.ACD" application, which you can just copy/paste into your application. See pictures...

Mickey said:

Edit: ASF types faster then I do.

Click to expand...

This is probably the only time that this has ever happened

ASF said:

This is probably the only time that this has ever happened

Click to expand...

I will blame it on a super bowl celebration.

We need a national holiday the day after.