On Thu, 19 May 2016 07:40:15 -0400 Bob Camp <kb...@n1k.org> wrote: > One advantage of doing all the compensation off of a single sensor is that > *if* there are cross effects and *if* you can characterize them, you can > correct them out. Put another way, if the pressure reading changes by > 0.01% per C, having a reasonable idea of the temperature of the sensor lets > you take care of that.
But munching everything into a single system makes the thing mathematically intractable. Seperating the values, compensating them for induced errors first and then using them is much easier and less errorprone. Also, composite sensors have higher uncertainties and drift then single sensors. Even more so: the integrated temperature sensors are intended for use with the main sensor as a compensation tool. The specs of the temperature sensor are good enough if the drift/hysteresis of the temperature sensor is less than the one of the main sensor. That you can read out the temperature sensors value is more a goody for those applications when a temperature sensor is needed but not high accuracy/precision required. What is usually a good approach is to use the temperature sensors on barometric and hygrometric sensors only for their temperature compensation. At most, use the temperature sensor for cross checking and detecting faults. For real temperature measurements, I would use a wirewond Pt sensor on a 24bit ADC with a stable reference. Temperature effects are by far the largest effects we have to deal with. Having a stable and reliable measurement system for temperature is not only worthwhile, but actually a requirement before you start compensating anything else. > Things like sensor drift and sensor hysteresis … that’s not quite so easy to > take care of. The only hope there is that they are small enough to be > neglected. The same issue with hysteresis is actually a big limit on > humidity compensation of some devices. They adsorb water vapor at a very > different rate than they desorb. > Modeling that can be really messy. Hysteresis can be properly modeled and compensated. The problem is, that the math behind it becomes nasty very quickly. Often just using a simple second order diff equation system and letting a Kalman filter estimate the parameters is easier than modeling a full memory system... under the condition that one can excite the system reliably and isolate/estimate the other effects well enough. Attila Kinali -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.