noisy (+-100C temp spikes) readings with SCB-68 and T-type TC.

[jenya101]

I am getting very noisy readings of a T-type thermocouple with the SCB-68.  I was going to solder in a low pass filter and noticed there was already doides soldered in positions F and G for all channels.  It seems like these were installed at NI.  Can these be removed?  I have a picture I can email.

Thanks,

  -Jenya

[AnalogKid2DigitalMan]

I think those are not diodes, but actually zero ohm resistors. In the SCB's user manual, refer to CH4- Thermocouples, CH5- Adding Components and Appendix D- Circuit diagrams to aid in component selection and insertion.

Here's a link to the manual:

http://digital.ni.com/manuals.nsf/websearch/74C86ADEF0E4813F86256C84007CB3AB

You may also need to crank up the gain for the channel you are using to abtain accurate readings, these signals are quite small in amplitude.

Message Edited by AnalogKid2DigitalMan on 10-23-2006 09:52 AM

[jenya101]

Thanks for the response.  Is it possible to control the gain of the SCB-68?  I didn't see anything about gain control in the manual.

Thanks

[AnalogKid2DigitalMan]

The SCB is just a terminal block, the gain is set up by your Data Acquisition Hardware (DAQ). What is the model number for that?

[jenya101]

Hello, I am using the PCI-6023E.

Thanks

[AnalogKid2DigitalMan]

The 6023 can bee programmed for full scale inputs of +/-10V, +/-5V, +/-1V and +/-.1V. Suggest you try starting with 1 or .1 range.

Here's a link to the manual:

http://digital.ni.com/manuals.nsf/websearch/3628030C3760BC108625711400785056

[jenya101]

Thanks,

  I've already set the limits to -50C to +100C (-2.81 to 4.28mV).  Looks like the low pass filter may be the only option left for signal conditioning.  Can I remove the 0 ohm resistors in positions F and G to solder in the filter?  The filter requires that I use either F or G.  Should I remove both 0 ohm resistors or just one?

Thanks for the help.

[Kenn_N]

Jenya,

Thanks for contacting National Instruments.  That's right, you can remove the 0 ohm resistors.  The reference to the manual earlier in the post describes this.  I would reccomend you read through it. 

Regards,

[jenya101]

Thanks Kenn,

  I'll try it out.