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 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.