[aprssig] FindU Telemetry page - Help needed
steve at dimse.com
Fri Oct 10 15:02:25 CDT 2008
Let me guess, you learned using the new math... if it doesn't involve
apples or trains heading in opposite directions, you are lost ;-)
First, this is also a linear system, which means that the a is zero.
For a given change in the telemetered value, the measured parameter
changed the same amount, whether the parameter change is from 99 to
100 or 1 to 2.
Given it is linear, the formula is bx + c
You are right, the problem is easier without converting to F, so let's
do it in C first.
The way you wrote it is (with an extra set of parens added for clarity)
((tele + 4.7) * 1.9608 ) - 273.15
it is just algebra to put this in the form bx + c
distribute the multiplication
((tele x 1.9608) + (4.7 * 1.9608 )) - 273.15
4.7 * 1.9608 is 9.215, add this to the other constant -273.15
that makes the centigrade formula 1.9608 x + (-263.9)
b = 1.9608 c = -263.9
solving for x = 148 gives 26.3 degrees C, a reasonable room temp
so you want F?
F = (C * (9/5) ) + 32
We know C is 1.9608x - 263.9 and 9/5 is 1.8
F = ((1.9608x - 263.9) * 1.8) + 32
Just like above, you distribute the 1.8, and add the two constants to
get the b and c. This is left as an exercise for the reader. ;-)
On Oct 10, 2008, at 3:25 PM, Mark Cheavens wrote:
> I am trying to work with the telemetry page on FindU. I have a
> telemetry value that requires the attached math to make it display
> the way I want. I haven't figured out how to make the math work to
> get it to display correctly. Any help would be appreciated.
> Sample URL:
> I am reading telemetry parameter 1.
> I need to take the value (Currently sitting on my bench in an air
> conditioned room!) with a value of 148
> I would LIKE to have the value in Degrees F (I know that C would be
> So here is the formula:
> ((Telemetry + Correction Factor) X 1.9608 Sensor Multiplier - 273.15)
> * 5 / 9 - 32 = F
> For this install the correction factor is 4.7.
> 1.9608 is the sensor multiplier (Constant)
> The rest if just the basic math...
> OR ((148-4.7)*1.9608-273.15)*9/5+32=TempF
> I don't understand how the a= b= and c= can get me there!
> Any help would be appreciated!
> (I have figured out the easy linear ones in the past - Like this same
> one for voltage -
> (FYI - This is the output of an OpenTracker+ being used in an outdoor
> solar only radio site (Emergency Clinic) to record interior
> temperature for the batteries and battery voltage. - I do have it on
> the status line, but I don't like the resolution, and would like to
> plot it like I have done for the voltage) http://map.findu.com/purg
> aprssig mailing list
> aprssig at lists.tapr.org
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