Hi CK,

   I suspect that there might be two causes for the drift you are
observing. One possibility is the self-heating of the polysilicon
resistor as you pass a current through it to measure its resistance
(this is what most multimeters do to measure resistance: they flow a
small current through the resistor and measure the voltage drop across
it). Since the TCR of polysilicon resistors is large, the small
temperature change that the multimeter current causes will change its
resistance. The other possible cause is the drift in your multimeter.

   To fix the first problem, try to use a better multimeter which uses a
smaller current for its measurements. If this is not possible, try to
apply a fixed voltage across the resistor (instead of flowing a current
through it) and measure the current. If you use a voltage source, the
self-heating will be limited due to the negative feedback in the system
and after a while you should be able to read a fixed number for the
resistance.

   To fix the second problem, the only thing that comes to my mind
(except for replacing the multimeter) is letting the multimeter be on
for a long time (~24hrs) before you take your measurements,

   Good luck,
   Behraad


> Hello, Community,
>
> I am having problem with my piezoresistors.  As soon as I touch them with
> miltimeter probes(via two-point method), they drift upwards at a rate about
> 0.1 ohm every seconds.  as you can predict, with a large gain, small drift
> can cause big calibration errors.
>
> Does anyone know the most likely source?
> Is it electromagnetic noise?
> Is it motion?
> Is it localized temperature variation?
> Are the resistors leaky?
>
> Here is a follow-up question, is there anyway to compensate or correct this
> for pressure sensing?