Hello,
I've been working with a Labjack T7 with 4 CB37s connected by a Mux80 for a while now for thermocouple temperature readings, and I've been avoiding using differential pairs that span more than one CB37, such as those found in Differential Blocks 1, 3, and 4. These thermocouple readings have been accurate with little noise. However, recently I had to use Differential Block 2 due to the amount of thermocouples I've needed to add. Every signal connected in this block is extremely noisy, despite having set up every thermocouple I've used the same way. I am using type T thermocouples with a 113k Ohm resistor from every negative terminal to GND. If I switch the thermocouples to a block that has its differential pairs on a single CB37, the noise disappears.
I was wondering if there is any way to reduce the noise for differential channels that span two CB37s.
Thank you for your time and consideration!
.png%3Fitok=PHGBxf6M "EEV Blog Reviews LabJack T7-Pro & Software Tools")
.jpg%3Fitok=B1YcuDFK)
.png%3Fitok=Ybt-OlgU "LabJack + JEDI One Can Create a Powerful Distributed DAQ Ecosystem")
If you remove signals such that you just have 2 thermocouples connected, 1 to a single CB37 and 1 spanning that CB37 and another, do you see the same issue?
How about a basic noise test. Remove the 2 thermocouples and instead use a jumper wire to short the AIN+/AIN- to each other. Leave the 113k resistors in place to provide the ground reference. You can use LJM-Windows-AIN-Noise-Test.zip to get noise figures (effective RMS resolution):
http://files.labjack.com/utilities/