RS Logix 500 Math (Dew Point)

Hi,

I am looking for a formula or even better the ladder logic for a Micrologix 1500 (RS Logix 500) using Temperature (Fahrenheit) and RH to calculate Dew Point.

I have had problems with this in the past and I don't know if it was my logic or my formula, but I scrapped the whole mess.

Any Help or Guidance is appreciated.

Regards,

Kirk

Google How to calculate dewpoint. Info abounds.

Yes, but you have sights like www. ajdesigner.com/phphumidity/dewpoint_equation_dewpoint_termperature.php which gives you a easy formaula, but doesn't evene give you an acuate dewpoint conversion on its own page. Or ehow.dot com which gives you something for dewpoint over 50 %
OR some formula that refers to log functions which I am not sure the Micrologix 1500 support. I was hoping someone had a formula or logic that had already tackled all these problems and has been tested to work.

I fought thru these problems on a previous occaion with nothing to show but a headache and lost hours.

kirk

I would use this formula along with a look-up table and a simple linear interpolator to calculate ln(RH). I know you can do indirect addressing with the 1500. This may get a little squirrelly at very low relative humidity (<3 or so). But if that is an issue you can overload points in that region (change your index increment below a certain RH).

Keith