Thermocouples, connected to AMUX-64T, read wrong temperature data.

[nattapol_stp@chula.com]

I'm using a AMUX-64T to multiplex voltage signal from thermocouples connected. The AMUX-64T deliver any signals to my DAQ card, AT-MIO-16-E. For the other side of thermocouples, they are directly and permanently attached to bare conductor which is short-circuited loop and holds at least 200 A AC-current or zero in cycle. I found that every temperature value showing on my monitor was strange data. It change all time. When I compare the temperatures on my monitor with on a digital multimeter, the difference is about at least 20 degree celsius. I would like to know how I should set any jumpers on AMUX-64T and what point of system should be connected to ground. Should I use single-end or differential signal?
How I use it?

[JoshuaP]

The user manual for the AMUX 64T is a good reference for connecting thermocouples. http://www.ni.com/pdf/manuals/320253c.pdf

It gives an example on how to connect a thermocouple on page 3-9.

With that being said I would recommend using your MIO device in Differential Mode. Leave Ch 0 unwired for the built in IC and set jumper W1. This will set up your cold junction compensation. Next, connect your thermocouple to Ch 1 and Ch 33. You will also need to connect a bias resistor from Ch 33 to GND. Refer to KB 2068B2WE, http://digital.ni.com/public.nsf/websearch/2ACDAC0C7737FBC886256934004EEEC9?OpenDocument on why to connect the bias resistor.

Here is a LabVIEW example program that shows how to convert the CJC and thermocouple to degrees.

Joshua

[mohamed ameur]

if you use the differential signal, the AMUX-64T has a capter ( sensor) for the ambiant temperature.

look at the page number 2-3 of the the user manual of the AMUX-64T. you must set the jumper W1 for temperature sensor selected.