E type thermocouple reading by 9211A

[techpia]

Dear all,

I am reading the E type thermocouple voltage signal using 9211A, and i am getting around 0.6mV when i grabbing the thermocouple with fingers.

I used to NIST ITS-90 table to calculated the temperature, and it gives only 10C...which doesn't make sense at all.

So, i am wondering 2 things.

1. what is the reference junction temperature for 9211A?

2. if the reference junction is not 0C, i cannot use NIST table. what is the converting equation from voltage to signal for E type thermocouple?

thanks.

[Henrik_Volkers]

If you know the CJ temperature, you can correct the EMF and use the ITS-90. 

Measure JC temp

Measure EMF

Calculate EMF of your TC @ CJ temp, add that (accordingly!) to the EMF measured and calculate the temperature with that new EMF

All this is done in the provided vi's

A good source for TC knowledge:
Manual on the use of thermocouples in temperature measurement,
ASTM PCN: 28-012093-40,
ISBN 0-8031-1466-4

(Page1): 'Regardless of how many facts are presented herein and regardless of the percentage retained,

                all will be for naught unless one simple important fact is kept firmly in mind.

                The thermocouple reports only what it "feels." This may or may not the temperature of interest'

Assuming a CJ temperature of 20°C you measured about 30°C , which seems reasonable (here I just added the CJ temp, but due to the nonlinearity of the TC EMF this is not the correct way!)

 

[Henrik_Volkers]

Type Ctrl-Space for Quick drop and search for the 'convert thermocouple reading.vi' 

[Seth_B.]

techpia,

Are you using this with NI-DAQmx or NI-DAQmx Base?  If you are using NI-DAQmx, could you try creating a thermocouple task in MAX (right-click the device » Create Task » Analog Input » Temperature » Thermocouple) and change the Thermocouple type to E and the CJC to "Built In" and see what you read?

Regards,

[ColeTrain]

Hello techpia,

Mirroring what Seth said, when you create a DAQmx task all of the CJC and conversions are done for you in the background.  If the temp still seems off (as can happen with thermocouples), you can calibrate your device with a  few reference temperatures to bring it back into range. Post back if you need any more help or tips!

[techpia]

thanks.

unfortunately, i don't know the CJ temp. that was one of my question. 

[techpia]

I am using NI-DAQmx Base...and i don't have labview to open vi file now.

I am trying to use simulink for temperature control using PID.

but i am still don't know how to convert the voltage to temperature.. 😞