Help for VM110

For school i’m using an NTC in combination with the velleman VM110 linked to my pc to measure temperatures. I’m using the analog input to measure the tension that is generated over a Wheatman-bridge with the NTC.
If I simply use a Fluke to measure the tension, I find the exact tension that is linked to the temperature I look. But as soon as I link the module to the place where I measured tension with the fluke the tension drops and I no longer can find the right temperature. I have already removed the jack’s and so the ground of my module is the same as the one of my circuit.

Can anyone help me??

Maybe you made some sort of short circuit when connecting the Wheatstone bridge circuit to the VM110.
You may try this kind of connection as in the image below. Connect it to both analog inputs and to the GND terminal of the VM110.
Read both analog channels (use ReadAnalogChannel or ReadAllAnalog function) and calculate the difference.

Remove jumpers SK2 and SK3 and adjust trimmer potentiometers ATT1 and ATT2 to max. position clockwise.

First of all I’d like to thank you for the quick reaction

This is the exact configuration as we use. The problem we detected is that the input impedance of our module finit is (non-ideal OPAMP). And that’s why we go from our normal 2.5V we measure with a Fluke to 1.9V.
A solution we found so far is to place two OpAmps with gain 1 between our module and our circuit.
But I keep thinking that we must be doing something wrong, that there has to be a way to only use the module to measure the tension.

If you look the circuit diagram of the module you’ll see that there are 100k ohm resistors from the input A1 and A2 to GND: RV1 and RV2.
You have to download the manual of the K8055. In the manual of the VM110 the circuit diagram seems to be missing.

By changing the RV1 and RV2 to 1Mega ohm (or 10 Mega ohm) you’ll get better results.

K8055 manual, see page 24: velleman.be/downloads/0/illu … k_rev3.pdf