the trouble between the Temocouple and SCB-68 Box

[jilong2000@yahoo.com]

I messure the Tem. with Temocouple in one Terminal of SCB-68 (use DAQ ) ,at the same time I use another Terminal to messure a signal(Voltage)in a curcle.While V++ more than 15V the Temocouple show always overtemperature.But the two actions are seperated. This is a SCB-68 board.Why?Thans a lot.

[RIO-Todd]

Is the thermocouple reading correct without the other voltage signal connected? If so, then you might be running into cross-talk between channels. I would check the source impedances of your signals and see if decreasing the scan rate of your acquisition helps the problem. I have linked multiple documents below that discuss cross-talk (charge injection) and possible solutions to this problem. I hope this helps.

Data Acquisition: Troubleshooting Unexpected Voltages or Cross-talk in Analog Input Channels
http://digital.ni.com/public.nsf/websearch/B9BCDFD960C06B9186256A37007490CD?OpenDocument

Is Your Data Inaccurate Because of Instrumentation Amplifier Settling Time?
http://zone.ni.com/devzone/conceptd.nsf/webmain/B9B5D37A04C772B58625686500695C20?opendocument


How Do I Create a Buffer to Decrease the Source Impedance of My Analog Input Signal?
http://digital.ni.com/public.nsf/websearch/CF83426BC3AC514A86256C10005A4771?OpenDocument

Regards,

Todd D.