How it's made a variometer


Q: What are the parameters that measure the quality of a variometer? 
A: From an "electronic" point of view there are two factors that have an effect on the quality of a vario: sensitivity and response time. The first is the measurement of the smallest change in vertical speed that the vario is able to detect. The response time is the time required for the variometer to notice a change. One major difficulty encountered in the design of such an instrument comes from the fact that these two factors are competing with each other, because with the same sensor and electronic circuit for reading the signal, I can, within certain limits, increase the sensitivity to the expense of response time, or vice versa 

Q: I understand (better, I think that I understand) that the fluctuations of the sensor can be reduced, but at the expense of a slower response. 
A: Exactly. 

Q: This means that the electronic components is not sufficient, because the same components must also have an optimal setting? 
A: Of course it is necessary to start from a very good components. But it is even more important to aim at an optimal goal and achieve it through proper planning. The component placing on the board, the assembly and the shielding are all essential factors to avoid "noise" and interference. 

Q: But what is then the resolution at which you can measure altitude?
A: In theory you can achieve resolutions of a millimeter, but this have no sense in practice. The fluctuations we are talking about lead to variations much larger than a millimeter: it would be like trying to measure with an accuracy of one millimeter the height of the sea near the shore when the waves rise and fall. The fluctuations can be reduced by acquiring several times the signal and making an average of the measured values, but this has a significant negative impact on response time of the vario. 

Q: What do you mean by "noise"? 
A: It 'a very important factor, in electronics. The noise is the set of unwanted signals in voltage or electric current, that overlap with the useful signal transmitted or processed. The difference between a great variometer and a lesser one resides in part on the quality of the electronic components and the project, so that the noise is already at the start as low as possible, and in the other part in the ability to "manage" and reduce noise. The noise in the altitude (pressure) measurements is further amplified when such measurements are processed to obtain the vertical speed. A big problem. 
Roughly speaking, if you want to get a reliable reading of the variometer with an error of + / - 0.1 m/s with a response time of one second, the "noise" rms (rms = root mean square) of the barometer should be less than 0.05 m in one second. 

Q: So we can say that from your project put into practice on C-Pilot PRO, the resolution is estimated at plus or minus in 10 centimeters per second?
A: Noooo! Much less! 

Q: even on a very small tool such as Compass Beepper? 
A: The C-Pilot PRO is a bit 'better, but the Beeper is very close.

Team Compass