Calculated values

[svego]

what is the best way to set formula and use it many times in our aplication...

For example...

I found somewhere formula to calculate DEW point from temperature and relative humidity from many sensors..

X= 1-(0.01*RH)
K= Tc-(14.55+0.114*Tc)*X-((2.5+0.007*Tc)*X)^3- (15.9+0.117*Tc)*X^14
 

[AzeoTech]

Do you want to apply this to a bunch of channels?  In that case, you should use a Conversion.  Replace the variable that should get the channel value with the word Value.

But I'm guessing that since you are calcing this from two channels you probably can't do that.  In that case, create a sequence that returns the result, something like:

function CalcDewPoint(Tc, Rh)

return( Tc-(14.55+0.114*Tc)*( 1-(0.01*RH) )-((2.5+0.007*Tc)*( 1-(0.01*RH) ))^3- (15.9+0.117*Tc)*( 1-(0.01*RH) )^14

Note how I replaced X with the calc.  This is faster than doing it in two lines.  Once you've created this sequence, you can calc dew point by doing:

calcDewPoint(x,y)

If you want to trend dewpoint (or log it), you probably will want to create a channel to hold the value and calculate it at some interval, then use the Event on RH or Tc to call your function and then use AddValue() on the dew point channel to stick the result into the channel.

[svego]

Hi,

 

Can you correct me where is problem here ?

temco_temp[0] and temco_hum[0] are values that must be calculated in function

[AzeoTech]

I'd have to see the doc.  Can you post it? But one thing: you really should name the sequence the same as the what you put in the function prototype.  Meaning, name the sequence CalcDewPoint.

[svego]

you have ctl file...Page name is DEW_point...

KucnaSCADA_8_2016.ctl

[AzeoTech]

The function works fine for me.  I just went to the command alert and typed:

? dew_point(1,2)

I'm guessing that when you call the function one, or both, of the channels are empty and don't have values yet.

[svego]

I was my mistake..I called function inside sequence, CalcDewPoint(Tc, Rh), so it must be sequence name like DEW_point(temco_temp[0],temco_hum[0]) in my example..

pls, see screens...

now it works, calculations should be OK

 

[AzeoTech]

Yes, that is why I suggest naming the sequence the same as the function prototype in the sequence.  Its more for your benefit than DAQFactory's.  DAQFactory doesn't really use the name in the function prototype except inside classes.