[time-nuts] HP5065A environmental sensitivities

[Bob Camp]

Hi

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. 

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. 

Bob

> On May 19, 2016, at 1:49 AM, Attila Kinali <attila at kinali.ch> wrote:
> 
> On Thu, 19 May 2016 06:33:38 +0200
> "Björn Gabrielsson" <bg at lysator.liu.se> wrote:
> 
> 
>> What are time-nuts using for monitoring the environment?
> 
> The Sensirion SHT21 has become the gold standard silicon based
> humidity sensor over the past years. Even though it's quite old
> (IIRC close to 10 years) it has performance metrics that still
> rival modern sensors. Its rather "large" package with the 1mm
> pitch makes it one of the easier to solder sensors as well.
> It's only drawback is its relatively large price of €6
> 
> As for barometric sensors, the ones by Measurment Specialities
> are quite good. The MS5607-02BA03 for example does a resolution
> of 2.4Pa with a long term stability of 100Pa/a.
> There is also the MS5611-01BA03 which offers 1.2Pa resolution,
> but also doubles the price and I am not so sure whether that
> tiny bit more resolution is more than just noise.
> 
> A little advice: If you want to measure pressure with high precision,
> you should think about temperature stabilizing the sensor.
> 
> The same is true for humidity, but does not work as well, as temperature
> stabilization (aka heating) changes the relative humidity and thus
> the measurement value depends quite a bit on how the air around the
> sensor flows.
> 
> Also, provide good and low noise power to the sensors. These are
> precision instruments with high resolution ADCs. To work properly
> they need a clean power source.
> 
>> I have been playing a little with the Bosch BME280 - doing air pressure,
>> temp and relative humidity in a small form factor. Easy to interface to
>> Raspberry Pi or Arduino.
> 
> The only Bosch sensor i've ever used was a BMA250 acceleration sensor.
> It worked reasonably well, but i've never evaluated it for precision
> or accuracy. But at least it looks like Bosch does not exagerate
> in their datasheets.
> 
> 
> 			Attila Kinali
> -- 
> Reading can seriously damage your ignorance.
> 		-- unknown
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