Hello,
We have a circuit that amplifies the output from a 350 Ohm Wheatstone bridge Load cell and then sends that amplified value to a Delta-sigma ADC. It generally works quite well but occasionally we find a INA131 with an unstable output. The output will "jump" and hold a new value with no associated input change. The offsets are not permanent: different values are produced for short periods of time (a few seconds to a few tens of seconds). Not every part shows the same offset magnitude.
The latest example we have jumps within a 500uV window at room temp with the inputs shorted and 4V of commom mode voltage applied. The output will change quickly, in a second or two, and then hold for 30 or more seconds and then abruptly swing again to a new level. Changing the InAmp solves the problem. Other INA131's will jitter a few tens of uV but will not show large jumps. The problematic parts have come from different production lots.
The load cell is excited with 8V from an LDO. The InAmp is powered from this same LDO, The value at VREF is 1.98V and is stable.
Any ideas as to what might be causing this behavior?
Regards,
Carmine
