datasheetdriftsensor
I am looking at the specs of tactile pressure sensor and I can't understand what this means:
"Drift: <3.3% per logarithmic time scale"
How should I understand this? Does this sensor drifts a lot or this is actual good. I am looking for cheap way for measuring wight changes over a long period of time.
Cheers Mitko.
The following is an example application circuit to power the heater for the solid state gas sensor:
,where V1 is our 5 V DC source, Rserial is a resistor, and RH is the heater on the gas sensor.
In this example we are using an Rserial value equal to our nominal powered heater resistance value. This means, by way of the maximum power transfer theorem, that most power will be transferred when the heater resistance is equal to the serial resistor, Rserial. If the heater resistance, Rh, varies in either direction from nominal the power dissipated in the heater will fall off quadratically.
The following graph shows when the simulation is run. The X-axis is the Rh value being swept from its minimum to its maximum operating resistance value. The plotted curve is showing the power dissipated by the heater resistor Rh as its value deviates.
Notice that even if the heater value resistance changes on us by +- 15%, the power dissipated in the heater resistor changes by only ~1%, thus maintaining a relatively constant temperature on the sensing element.
Aren't solid state gas sensors fun!
Edit1: If your budget allows it and you are going to be required to become proficient with these technologies, I find that this book has a lot of useful information about the history, characterization and performance of solid state gas sensors. The circuit applications presented in the book, however, are lacking.
I would use one of the Freescale sensors MPXV7002 http://uk.farnell.com/freescale-semiconductor/mpxv7002dp/sensor-pressure-dual-diff-0-02bar/dp/2080499
It says the response is 1.0 ms
However as @Nick Alexeev says... you need to know the expected pressure because I think you will break this one. On the plus side they do offer sensors for different ranges.
Best Answer
Tentative answer:
There may be some relaxation mechanism, the way a dent will appear in a carpet if you leave a chair leg sitting on it too long. This specification places an upper limit on the effect that will have on the reading.
So if you read 100N force after 1 second, the reading may have drifted by 5% or 5N (or less) after 10 seconds, 10N (or less) after 100 seconds, 15N after 1000 seconds and so on. (I am assuming they mean log(base 10) but the datasheet is not explicit on that point)
It's not obvious if there is a lower limit to this behaviour (i.e. 15% difference between 1ms and 1 second) but I would assume so, down to the 5 us specified settling time.
Another question is : does the same drift apply when you then remove the weight? (the chair leg depression disappears eventually after you move the chair). If I were contemplating this sensor the first thing I would do is get my hands on one and characterise it with actual measurements. It may be better than the spec, bearing in mind that future production may vary within these limits.
Whether this is good or bad depends on whether it meets your needs, and how well it compares with other sensor technologies within your budget.