Formula

siggibald · Feb 20, 2015

hi

how do you write this formula

in the Expressions in CPT --- rslogix 500

siggibald · Feb 20, 2015

siggibald said:
hi

how do you write this formula

in the Expressions in CPT --- rslogix 500

(243.12*(ln(rh/100)+((17.62*t)/(243.12+t))/(17.62-(ln(rh/100)+((17.62*T)/(243.12+t))) ????

jstolaruk · Feb 20, 2015

better to continue the original thread
thread is here

hint (replace "/" with "|"), not sure about the log functions

Timbert · Feb 20, 2015

siggibald said:
(243.12*(ln(rh/100)+((17.62*t)/(243.12+t))/(17.62-(ln(rh/100)+((17.62*T)/(243.12+t))) ????

I got:

(243.12*(LN(RH/100)+((17.62*T)/(243.12+T)))/(17.62-(LN(RH/100)+((17.62*T)/(243.12+T)))))

Doug-P · Feb 20, 2015

Just saying

Since everything inside the curly braces is identical, solve for this quantity once and use the result in both numerator and denominator. This will save processing time.

Lancie1 · Feb 20, 2015

Using Doug's idea, it would look like the attached rungs (assuming you have a PLC with the LN function, such as the SLC 5/03 with OS302 or higher, 5/04, 5/05, or ML 1400).

shooter · Feb 21, 2015

or use another function

realolman · Feb 21, 2015

another just saying

I don't know if it's me or what, but I had some trouble already with CPT. I don't think (2+2) is the same thing as ( 2 + 2 ) ... it seems like it wants the spaces. It won't allow you to pick the existing tags... you have to type everything out... I think I'd sooner just use a couple math instructions

Formula

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