Usefulness of Thermocouple source/read meter. Studio 5000/Flex IO-IT8

[AutomationTechBrian]

I just finished wiring Flex IO in a cabinet, attaching the thermocouple wires removed from the old Eurotherm controller to the Flex IO, IT8 module (Type J thermocouples, white +, red -). I haven't done anything with the cold-junction yet. I'm just getting familiar with everything. I brought my CompactLogix L16 to get familiar with the IO modules (Ethernet communication), and started a test project (see pic.). Before I go any further, my thoughts are that I wish I had a source meter to confirm the values as I set up the scaling. I started looking into meters, and searched Google for recommendations, or at least comments or videos about using these meters. ...Not much to be found. I'm looking at:

Extech (now Flir) Model PRC20.... $530ish.
Fluke 714b......$1,800ish
or anything similar that makes sense.

Besides this project (about 30 heating zones total), I'll run into troubleshooting situation (maybe) a couple times a year where I'm trying to figure out if a thermocouple, the wiring, or the control device is bad. I've gotten by without a meter, but have thought about adding something like this to my tool collection (my own $).

Anyone have experience with setting up thermocouple cards like the Flex IO, IT8. Does a sourcing/reading meter make sense when setting configuring and testing? Thoughts?

 

[arpus4KM]

Having the right equipment to do a job makes sense if you need it to do the job.

having it because of a "Maybe this will happen" situation doesn't always.

if you can get the company or project money to fund it, then 100% get the one that reads and simulates the thermocouples you'll be using.

if you are funding it, ask yourself how many times you've ever needed one, or if it was just easier to swap a couple wires on some inputs and verify signal good/bad after the swap.

I would think the most use of a thermocouple sim/read device comes from people who are commissioning 1000s of thermocouples a year, and are making the money back 10 fold if they can detect an issue before an install.

 

[GaryS]

Where to start
I think what you are looking for is a calibrator or simulator. For thermocouple that’s challenging and expensive they are available. But I really don’t think you need one, if you want to test the thermocouple all you need is a good multi meter and cup of ice water and the conversion chart
Calibrators and simulators are generally used to check to see if the input is working correctly
And here again it is complicated.
But when you say that you haven’t done anything with the cold junction yet makes me think you really don’t understand what that is. Please do some research on how thermocouple input modules work to better understand what’s required.
On all thermocouple inputs they have a built in cold junction compensation as part of the module
As for scaling again no scaling is necessary as the mv signal from a thermocouple in not linear over the range of the thermocouple so scaling within the plc program will yield bad results. The input module it’s self will convert or scale the input signal to the out value. You just have to select the correct type in your setup.
A few things to keep in mind when dealing with thermocouples
I have run into many cases when this was missed and the resulting temperature reading were way off causing major problems in the production process.
You must use the correct thermocouple extension wire to connect the thermocouple to the input.
The extension wire must be connected correctly. If you short the extension wire together the temperature you read will be the temperature at the short.
You cannot use a standard copper terminal block to connect thermocouples that will cause a temperature offset. That’s where the cold junction compensation comes in but you need one for every junction and of course you also need to be able to read that junction temperature in and add it to the value read in.
in short as you can see here dealing with thermocouples can be complicated but must be done correctly if you expect good results
there are other things to consider when working with thermocouples as well
As a side note if you pass a dc current through a thermocouple it will generate heat on one lead and cold on the other solid state heaters/ coolers work that way

 

[arpus4KM]

As a side note if you pass a dc current through a thermocouple it will generate heat on one lead and cold on the other solid state heaters/ coolers work that way

This concept of reversing the in/out of something works with a lot of principles... the world is full of equalities on both ends of the equation

 

[AutomationTechBrian]

Ok, I've had some time to dig through manuals and try some experiments. I've worked with other temperature controllers, but not the IT8 Flex IO module. The manuals are so-so, with a lot of old information the isn't as relevant with my the Control Logix PLC (v34) and Ethernet com module. Some one else might search this topic, so here are a few high points before moving on...

First, the idea of a simulator/calibrator is in the manual... an older manual. (See Pic... Sorry the screen capture is so large, I'll do better next time.) After the results of my experiments, I know the TCs are all at the correct temps at room temperature. Looks like I don't *need* a calibrator, but I've put it on my list of things I might add in the future.

I'll make one more post with another picture so they load automatically if you're logged in.

 

[GaryS]

If I were looking for a Simulator / Calibrator I would check out https://in.omega.com/temperature/

 

[AutomationTechBrian]

The key was in the module configuration window in Studio 5000. The earlier instructions talked about scaling (yes, I know it's not linear, but that's the term they used in the manual). Once I clicked on this screen, I was half-way there (see pic.).

The next thing was installing the cold-junction wires. The manual assumes you know when you need them, and it seemed ambiguous about whether it was only needed for a calibration process (to be removed afterwards). The values without the cold-junction wires were too small to be correct. (ie, 250-ish (INT) which would be 25.0 degrees F.) So, I added the CJ wires, and they changed to around 730 (73.0 degrees F.). Just to be sure, one of the TCs is dangling in mid-air, showing about 67 degrees. I pinched it between my fingers for a couple of minutes and it changed to about 83 degrees. I think that's accurate enough for this process.

BTW... there were bad modules in the past. One guy said his temps were off about 135 degrees F. This *would* be an issue. Rockwell figured out there were bad modules and there was a notice written up. But that was over 10 years ago.

(Note: Sorry again... I made the picture small this time and lost the resolution.)

 

[AutomationTechBrian]

If I were looking for a Simulator / Calibrator I would check out https://in.omega.com/temperature/

It doesn't load from the link, but I know which one you're talking about. (probably wouldn't order it from India, though )

 

[AutomationTechBrian]

Here's one more visual for the next guy researching this topic. It points out the CJC wires connected to specific terminals. My thermocouple wires are Type J.

 

[GaryS]

As for Omega
They are a US based company and I think one of the best sources temperature measurement
I have been using them for years
This link should work I tested it.
Omega Engineering | Shop for Sensing, Monitoring and Control Solutions with Technical Expertise

You keep referring to the Cold Junction Compensation I check on the Input you are using it has it built in so you don’t need to do anything
The important thing to remember is to make sure you wire the thermocouple correctly us the correct extension wire, the correct connectors / terminal block in the field. I have seen this mistake many times

 

[AutomationTechBrian]

As for Omega... Yes, we did a lot of calibration labs with their equipment in school, about 15 years ago, so I'm familiar with them.

You keep referring to the Cold Junction Compensation I check on the Input you are using it has it built in so you don’t need to do anything
The important thing to remember is to make sure you wire the thermocouple correctly us the correct extension wire, the correct connectors / terminal block in the field. I have seen this mistake many times

I know exactly what you are talking about with the thermocouple extension wire... and the junction connections as well. This used to be a working machine, and it is an exactly the same machine I renovated and have been servicing for this customer since 2012. I'm just changing all of the temperature and pressure controllers to a Control Logix PLC that was included in another machine component of this newer machine (using Flex IO racks for the 3 different remote panels). It's just the Flex IO IT8 modules that I'm getting acquainted with.

I'm wrapped up until tomorrow, or I'd research the manual again tonight for clarification of the use of the CJC cables, which are provided in each module's box. There are also labels on the TB3T base for the CJC cable to be installed. You can see it in the last picture I posted. I just know the temps are *not* accurate unless they are used. Each cable controls 4 channels, and I installed them one at a time and saw the difference immediately.

The one possibility that still stands, is that I need to go through a calibration routine, with the CJC cables, and store the results somewhere in the module's control addresses. But it is obvious that they are absolutely needed to have accurate temperature results using the Type J thermocouples... I've proven it with my test.

Here is the manual I'm using. I'm logged in to Rockwell with my Tech Connect account, so I'm not sure if it is available to everyone.

https://literature.rockwellautomation.com/idc/groups/literature/documents/um/1794-um012_-en-p.pdf

 

[AutomationTechBrian]

I think I grabbed the wrong manual. That one doesn't include the IT8 module. ...but at this point, I have to set this aside until tomorrow.

 

[GaryS]

Actually the CJC is a external accessory that connects to the bottom TB 36,37,38 and another connects to 47,48,49
That would be a thermistor to feed the terminal temperature back into the module so it can calculate the correct thermocouple temperature follow the directions in them manual you should be fine
If you bought the module new from the factory it would already be calibrated so all you shoud need to do is connect the wires and program the plc

 

[danw]

A thermocouple calibration requires thermocouple wire between the calibrator and the thermocouple analog input.

The thermocouple calibrator I use does not have banana jacks for connecting the thermocouple wire, instead it has an integrated female connection jack that mates to a 2 prong mini thermocouple plug. Thermocouple plugs are color coded for the different Type thermocouples.

The thermocouple plugs and thermocouple wire were not supplied by the calibrator vendor. I had to buy a mini thermocouple plug and 10 feet of thermocouple wire for Types J, K and T that I commonly run into.

You should be aware that you have source the accessories yourself. I suspect that such is the case for most calibrator vendors.

I also have a mini 3-wire 100Pt RTD, probably only 0.025" in diameter that I fasten under a thermocouple connection screw terminal to measure the terminal temperature that the cold junction sensor should be reporting. That RTD value is what the CJ value is then calibrated to. I do the CJ calibration with an RTD because thermocouples have too much cumulative error to accurately measure CJ.

So my calibrator is both an RTD and a thermocouple calibrator.

 

[AutomationTechBrian]

Actually the CJC is a external accessory that connects to the bottom TB 36,37,38 and another connects to 47,48,49
That would be a thermistor to feed the terminal temperature back into the module so it can calculate the correct thermocouple temperature follow the directions in them manual you should be fine
If you bought the module new from the factory it would already be calibrated so all you shoud need to do is connect the wires and program the plc

Ok, great. Thanks!