Float32 Log not working as expected
Hi All,
I have a problem again [noparse]:)[/noparse]
I have the following code:
There is a bit more after here but nothing that touches bAlt (which is where my problem is)
The code seems to go wrong with bAlt:=fl.Log(bAlt).
Measuring ground pressure, bPres ends up ~102.48 which is correct for where I am.
I have calculated all the steps manually, and in excel
bAlt:=fl.fDiv(bPres,101.325) gives 1.0113989637305699481865284974093
bAlt:=fl.Log(bAlt) gives wild numbers between 0.14 and 0.49, where it should be 0.0049225043228992493572043410264757
Can anyone throw in some suggestions?
Thanks!
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-Alec
My our page
I have a problem again [noparse]:)[/noparse]
I have the following code:
DAT bADC word 0 'barometric adc data bAlt long 0.0'ft bPres long 0.0 'kpa bGroundAlt long 0.0 'ft bPrevAlt long 0.0 'ft bVel long 0.0'ft/s Period long 200 'Calibration PRES_ALT_CONST long -6.8755856e-6 ... ... ... Pub do_pres_calcs(timechange) | bfADC,ftimechange bfADC:=fl.fFloat(bADC) ftimechange:=fl.fFloat(timechange) 'change time from ms to s for calcs ftimechange:=fl.fDiv(ftimechange,1000.0) bPrevAlt:=bAlt 'Pressure=((ADC/4096)+0.095)/0.009 bPres:=fl.fDiv(bfADC,4096.0) bPres:=fl.fAdd(bPres,0.095) bPres:=fl.fDiv(bPres,0.009) 'Altitude=(10^(LOG(Pressure/101.325)/5.2558797)-1)/(-6.8755856*(10^-6)) bAlt:=fl.fDiv(bPres,101.325) bAlt:=fl.Log(bAlt) bAlt:=fl.fDiv(bAlt,5.2558797) bAlt:=fl.Pow(10.0,bAlt) bAlt:=fl.fSub(bAlt,1.0) bAlt:=fl.fDiv(bAlt,PRES_ALT_CONST) 'alt in feet ... ... ...
There is a bit more after here but nothing that touches bAlt (which is where my problem is)
The code seems to go wrong with bAlt:=fl.Log(bAlt).
Measuring ground pressure, bPres ends up ~102.48 which is correct for where I am.
I have calculated all the steps manually, and in excel
bAlt:=fl.fDiv(bPres,101.325) gives 1.0113989637305699481865284974093
bAlt:=fl.Log(bAlt) gives wild numbers between 0.14 and 0.49, where it should be 0.0049225043228992493572043410264757
Can anyone throw in some suggestions?
Thanks!
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
-Alec
My our page
Comments
fl.Log10(bAlt)
instead of
fl.Log(bAlt) -- base e
But that would not explain the wildness. ??
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Tracy Allen
www.emesystems.com
Log10 gives similar results (still 0.xx rather than 0.00x).
The strange thing is, log (base e) works on my calc and also in excel
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-Alec
My our page
Righty, ive found a linear version of the same math which is ok but not ideal.
Id prefer not to use it as the log based result (when it works!) is more accurate.
Does anyone know who wrote Float32? or has anyone used fl.log sucessfully?
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-Alec
My our page