Error in measuring the temperature of a B Type thermocouple below 200 degrees

[nnarra]

In one of our applications,we are measuring temperature.We configured DAQ mx VI in AI Temperature,thermocouple.We are measuring temperature based on type and units as per the user configuration.For all thermocouple types except B Type,DAQ mx Read VI is giving correct values based on the range user configured.But,for B Type thermocouple,after 200 degrees to 300 degrees only,DAQ mx Read VI is giving correct values.If we source 0 degrees,DAQ mx Read VI is not giving any value.If we give 5 degrees to 90 degrees its showing temperature from 100 to 101 degrees.If we give 100 degrees,its showing 125 degrees.After 200 degrees only,DAQ mx Read VI is giving correct values.But range for a B Type thermocouple is -250 degrees to 1830 degrees.Is there any limitation in the measurement of temperature of a thermocouple of B Type?

Regards,
Naresh.N

[JÞB]

B Type thermocouple  range is 0-1700C.  here's a good referance http://www.omega.com/temperature/Z/pdf/z212-213.pdf

It looks like your DAQmx scale is based on flawed assumptions and may be using the incorrect range.  Rebuild your scale IAW the table above.

[AnalogKid2DigitalMan]

Type B is usually regarded for high temperatures. I bet NI's lookup table/compensation curve calculations start at 200 degrees.

Just a hunch.

-AK2DM

[kikiduu]

Hi Naresh,

Which hardware are you using? How are you applying voltage corresponding to temperature? What about CJC?

[nnarra]

Hi,

Hardware configuration is as follows,

SCXI 1000 Chassis

SCXI 1102 Thermocouple Amplifier

TC 2095

PCI 6250 

We are not applying voltage.We configured the physical channel as Analog Input ->Temperature->Thermocouple.So we are giving

thermocouple type,units,Max and Min Temperature values directly and CJC Source also built-in.And for testing,just using Calibrator,

we are giving Thermocouple type,degrees and we are appltying to SCXI,and we are monitoring temperature in DAQ mx Read VI directly. 

Regards,

Naresh.N 

[kikiduu]

Ok, so how much voltage are you applying to simulate voltage generated by a B-type thermocouple?

[nnarra]

Hi,

I am not applying voltage,i am directly giving temperature as an input to the SCXI using calibrator.

Regards,

Naresh.N 

[kikiduu]

So are you using a B-Type thermocouple and conected it to the calibrator? Have you checked whether the thermocouple is working correctly? One way of verifying it is to measure the voltage (instead of measuring as Temperature) and see whether it is actually varying with temperature.

[nnarra]

Hi,

We have not connected any thermocouple to the calibrator.In the calibrator itself,we can select thermocouple type and give input to SCXI either in mV or in degrees.