Electronic – Reasons for strain gauge drift

I'm testing a load cell where the result drifts over time.

By weighing it down with a known weight over night, the result crept up by 10% in 18 hours. It's a completely linear increase, with consistent variations due to noise.

I'm using a HBM QuantumX MX840B and two pairs of strain gauges that form a full bridge. The cable has been perfectly still during the test. The strain gauges are 120 ohm and it's been set at a 5V exitation voltage. The load cell is of stainless steel and is quite massive, so I would assume heat dissipation shouldn't be too big of an issue, but I don't know.

Temperature is reasonably stable (it's indoor) and the full wheatstrone bridge would compensate for change, something we also tested with a heat gun.

I'll re-mount the strain gauges on the load cell and see if it gets better, but I'm not sure as to why it drifts, and especially in such a linear way, and advice would be helpful.

Edit: This is what I'm going to do in order to re-mount it properly, please give me input as to where your experience differs from this.

Physical installation of strain gauge:

• Remove all strain gauges

• Clean with isopropanol

• Prepare the area with rough grinder if need be

• Sand down to 320 grit with electric sander or grinder flappy disks

• Slightly roughen the texture with a courser paper to increase adhesion

• Clean with isopropanol again Put a small amount of HBM Z70 cyanoacrylate glue

• Push the strain gauge down with my thumb Cover with suitable material (silicone or similar)

Results from load cell overnight testing:

This is from testing the first cell over night, it dips considerably.

This is from the second cell, it has a much smaller variation. It makes a huge dip in the morning, something we have seen before. This is because the test lab has eight huge halogen lamps in the ceiling that draws a big current when starting, I'm certain those affect the results. What is concerning is that it does not recover back to it's previous state.