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How to set external reference junction for two measure cards

Question asked by Skoti84 on Mar 5, 2019

I use 34970A connected to computer via rs232. 

I have two measurment cards inserted:

slot 100 34908A -  8 K-type thermocouple connected

slot 300 34902A - 16 K-type thermocuples connected


I use benchlink link dataloger 3 to configure and view data.


All thermocouples hot ends are connected to accurate heat source (250 degrees Celsius)


I noticed that when the internal reference junction source is set far all channels there is difference between channels 100+ and 300+ about 2,5 degrees. I used external thermometer to measure temperature near screw connectors on the cards. Next i set measured temperature as a fixed reference junction for all channels. Now temperatures are almost equal. I noticed that probably the card 300 shows incorrect indications using the internal junction. So i decided to use external PT100 sensor connected to 100 card  chanel 01 to work as external reference junction. PT100 is mounted in gap between 100 and 300 card (in 200 slot place).


Now I have problem with configuration in benchlink. I set 101 channel as 2 wire RTD and rest channels  as temperature measurment K type with advanced option: external reference junction. When i try to download configuration to instrument i get a message Incorrectly configured ref channel. When program is downloading status bar appear, error occurs when chanel 301 or 302 is downloaded. When i change 301 as internal reference junction i can download configuration without problems. There is also no problem if i set configuration manually (on control panel) without benchlink but then i will get the same error when trying to download data from the device.