Gents,

I make progress with the speed sensor.
My logger is designed for sensor from 0 – 200 (160 mph)
A sensor for 0 – 200 km/h (160mph) has a accuracy from 5 % below 80 km/h (50 mph). And when this is the full scale value, then it’s +/- 10 km/h. These instrument are no more actual, maybe on that worldwide site we all talk about.
When I make the instrument myself I can define the values myself and try to get a better instrument.

The pressure difference of the pitot tube is low, especially at low speeds.
144 km/h = 90 mph , the pressure difference is 100 mm water column so 4 “ water column.
But a speed of 72 km / h = 45 mph , gives a pressure difference 25 mm wc , 1 “ wc.
With 36 km/h = 23 mph, the pressure difference is 6,25 mm wc, , ¼ “ wc, so very low.

When you want to measure with high accuracy it is important to bring down the max speed to measure, so calibrated range will be for my instrument 0 – 100 km/h is 62 mph.
Maximum pressure difference will be about 50 mm wc is 20 “ wc

My Robbe bordcomputer will do the calculation (root extracting)
Biggest problem is the drift with low temperatures
So in the winter I put the whole test array in the snow, easier than the refrigerator.
Results are good already, maybe I can show you a simple test rapport in the coming days.

Today I did reach a zero drift from less than 1 % full scale for 0 – 100 km/h (62 mph) between the warm and cold condition, a difference from about 20 degrees C is 36 degrees Fahrenheit see picture 1.
On a normal flying day the temperature is nearly constant and I always do zero adjustment so this will do.

The range is global calibrated but that’s easy to complete. Most important is to get a stabile instrument with less drift depending from temperature, supply voltage and so on.
Next action is to compress the circuit to usable proportions, just I show in picture 2, the transmitter of the TF Taurus.
Picture 3, of course Hanna Poes is always highly interested.

I will keep you informed.

Cees