A-B thermocouple or NI4 input card

[robb676]

What is the difference between a Allen Bradley NT4 and a NI4 input card? I am using a NI4 card for temp, but what is the difference? Do I need a CJC with the NI4?

 

[Mickey]

Your 1746-NT4 is a thermocouple or millivolt input card.

Your 1746-NI4 is a 4 channel voltage or current input card.

Do I need a CJC with the NI4?

no

What is connected to your 1746-NI4 if it's temp then there is probably a transmitter involved.


See links to the manuals below


http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1746-um007_-en-p.pdf

http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1746-um005_-en-p.pdf

 

[robb676]

Yes I know I need a transmitter for the NI4 which I have, but what is the dif in relation to the NT4? Does the NT4 have its own transmitter built in to it?

 

[Mickey]

You can connect a thermocouple directly to a 1746-NT4 card. Then configure it for the type of thermocouple you have. It will then give you a temperature value.

With the 1746-NI4 you will have to convert it's raw data to a temperature value
using math instructions or a scaling instruction. Advantage of the NI4 is you can use it for other inputs ( pressure,flow,level...) not just temperature.

 

[Mickey]

Does the NT4 have its own transmitter built in to it?

That's one way to look at it. The NT4 card converts a millivolt value to a temperature value based on how you setup the card. Each type of thermocouple has it's own millivolt response to a given temperature, see chart below for different type of thermocouple responses.

 

[robb676]

I have mine scaled to the transmitter range, is that correct or do I scale it to the thermocouple range?

 

[Mickey]

I have mine scaled to the transmitter range, is that correct or do I scale it to the thermocouple range?

Have what scaled?

You have mentioned two different cards which one are you using?

Can you post your .RSS file ( zip it first) tell us the type of thermocouple.
And range you want.

 

[Mickey]

If using a transmitter tell us how it is scaled ( e.g 4-20ma = 32 to 250 deg) or whatever.

Are you going to use this for control (PID)?

 

[robb676]

I'm using NI4, I'm using a K type thermocouple, and my transmitter is a 4-20ma, with a range of 0-600 degrees.

I set the min input to 3277 and the max input to 16384. when I set the scaled min to 0 I get a reading that is way off the current temp.


Is there some other math I have to add into this the get what I need?

What determines how it is scaled to?

 

[Mickey]

Based on the info provided see picture below for a typical scaling program.

Post your .RSS file and someone can take a look ( zip it first)

You might want to check the milliamp value to make sure the transmitter is giving you an accurate curent for a given temp.

 

[Mickey]

What determines how it is scaled to?

Not sure I completely understand the question.

Raw data from the card depends on the input. See picture below. Scaling depends on what the analog input represents. In your case you said 0-600 deg.

Is the card setup for current? Check it's dip switch.

 

[robb676]

that is exactly what I got, but isnt the f8:0 supposed to read me the temp or is there more math?

 

[Mickey]

that is exactly what I got, but isnt the f8:0 supposed to read me the temp or is there more math?

Yup it should be temp.

What are you getting?

What is the raw data value?

What is the milliamp value?

 

[robb676]

Still trying to figure out how to make a copy of the program, but it is EXACTLY the same as the you posted.

But for the output I am getting in the range of 0.90000 to 1.60000.
My transmitter is definitly a 4-20ma, I even looked it up to make sure at the manufactors sight.
My thermocouple is a K type for sure.

I did manage to get it real accurate when I put the scaled minimum to 80.6 then it would only be off a few 10ths in the whole range.

What else could it be? Maybe it is readindg celseis? (metric)

 

[Mickey]

Sounds like the scaling of your transmitter is not 0-600 deg F. I would double check it
if you have the equipment.
Also if you have a milliamp source then connect that to the PLC and check the PLC's response.

Maybe it is readindg celseis?

Could be.. 0- 600 deg C = 32-1112 deg F (change the Scaled min and scaled max to 32-1112 and see if that looks right, you can always change it back).