Re : Thermocouple measurment with PCI 6220 + external SCB-68

[Nico_las]

Hello,

I am currently trying to test an installation using a thermcouple, plugged on an SCB-68, itself by cable on a 6220 card into a pc. The aim after check test, will be to put this thermocouple in a constant temperature bath to check during measurments if this one is has a problem and pause labview. But before 😞 ...

... I have some problems to measure a correct temperature.

To make test, i use MAX. I have find some tutorial like these below but i think i have missed something. There are no reason that my thermocouple ; who give me correct temperature with an other device ; tell me 25°-27°C when the lab is at 18.5-19°C. I want to use the internal CJC.

Read tutorial and documentation :

Max tutorial : http://www.ni.com/getting-started/set-up-hardware/data-acquisition/thermocouples

To setup SCB-68 : http://www.ni.com/pdf/manuals/371745c.pdf

CJC setup SCB-68 : http://digital.ni.com/public.nsf/allkb/96B996BAD82A84E9862570690066B03F

and a youtube video.

I have tried different channel on my card. I have tested, i think, different type of config (single-ended or differential) because MAX doesn't ask it and if i have understand my SCB-68, it depend on the switch on it.

I have put integer in the selection menu, i suppose, to use the internal thermistance of the SCB-68.

Do you think i have make correct test but it's just the 'calibration' to make (tab in MAX).

If i test all the SCB-68 channel, why MAX tell me that in the connexion tab : the channel 1 to 7 are between two channel (CH1 with CH8 - ; CH2 with CH9 etc) and 8 to 15 are between corresponding CH and ground (CH8 with AIGND ; CH9 with AIGND etc) with the same SCB-68 switch setup ? Mean that 1 to 7 are in differential and 8 to 15 in single-ended ?

I hope my english is understable and i give you enough informations. I hope someone will clear my interrogations about this SCB-68 with these thermocouples.

Accordingly 🙂

Nicolas

[karine_huyge]

Hello,

SCB68 has switches to be configured depending on the type of thermocouple you're using. Have you checked this?

Details could be found on page 5, 6 of this document: http://www.ni.com/pdf/manuals/371745c.pdf

Some more infos are available here:

Why Is the Temperature Sensor on My SCB-68 Reading an Incorrect Value? :

http://digital.ni.com/public.nsf/allkb/073d7dbb0497d51386256caf0077a1f0

or in the advanced user manual of the SCB68: http://www.ni.com/pdf/manuals/372551a.pdf

Karine

[Nico_las]

Thanks for your answer.

I have read these documents, that's why I think I have missed something concerning these switches. I will look deeper into this way. According to you, and I think too, it will be working easely.

I didn't found and searched the fuse topic because mine looks good. I will test the thermistance, may be damaged.

Nicolas

[Nico_las]

After some tests, the fuse is ok. Same thing for the internal thermistance of the SCB-68. I use the MAX protocole : measure voltage and use a personnal scale to convert ; it's give me the correct temperature(+1°C). If I put my hand in the thermistance to warm it, temperature climb.

Some details of the configuration :

Swithes are in differential mode (S5, S4 up and S3 down, S2 and S1 left)

I put my thermcouple between two channels (CH1, positive ; CH9, negative)

CJC : integer on max

In the property of the PCI 6220, accessory : SCB-68, configuration : CJC activated in the SCB-68 configuration

DAQmx tash, new Task, thermocouple, ai1

Temperature of the thermocouple still wrong.