adccommunitymod (AutomationDirect) asked a question.
Created Date: December 21,2015
Created By: steveola
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Greetings fellow travelers, I need to calculate relative humidity from two RTD's, (Dry Bulb and Wet Bulb) on a DL06 using inverse natural log. Is there any kind of math co-processor available for this platform? The formula looks like this in Excel: =100 * ((EXP(((16.78 * WB) - 116.9) / (WB + 237.3))) - ((101.325) * (DB - WB) * ((0.00066) * (1 + (0.00115 * WB))))) / (EXP(((16.78 *DB) - 116.9) / (DB + 237.3))) Right now I am using a Watlow EZ-Zone and putting the WB RTD onto it, and the PLC has the DB RTD attached so I am pushing a 0-20 mA at the EZ-Zone from the DL06, then letting the EZ-Zone calculate the %rh and pushing it as a 4-20 mA back at the DL06. It works, but I would much rather use an open RTD on the DL06 and calculate it on board to save $250 on the Watlow. Thank you for access to your collective smarts . . . Steve
Created Date: December 21,2015
Created by: ControlsGuy
You could also do a lookup table approach. It would need to be a 2D table. One axis could be DB temps, and for the other axis, I'd probably use DB-WB depression rather than WB, which should allow you to limit the size of the table better.
Precalculate the %RH values for all the table cells, then just fetch them at runtime.
Created Date: December 21,2015
Created by: steveola
Thanks, Controls Guy, appreciate the input.
Do-More looks like a brick PLC, at least the videos I was watching connect to a 205.
Do you have any experience with taking a 400 line DirectSoft project and converting it to "Do More? " Does it re-compile cleanly or do I have to re-write the project in the new format?
I'm using only 8 inputs, all 16 outputs, an analog in, an RTD in, a mA out, and analog VDC out, so I'm packed pretty solid on the DL06. I was originally a 205 guy, but the DL06 filled most project needs.
I'll call AD pre-sales tomorrow, but I wouldn't mind hearing your opinion. I have a lot of time in this particular project and a number in the field. The selling point would be data collection via network if some type of logging/displaying software is available.
Thanks again!
S
Created Date: December 21,2015
Created by: steveola
Greetings fellow travelers,
I need to calculate relative humidity from two RTD's, (Dry Bulb and Wet Bulb) on a DL06 using inverse natural log. Is there any kind of math co-processor available for this platform? The formula looks like this in Excel:
=100 * ((EXP(((16.78 * WB) - 116.9) / (WB + 237.3))) - ((101.325) * (DB - WB) * ((0.00066) * (1 + (0.00115 * WB))))) / (EXP(((16.78 *DB) - 116.9) / (DB + 237.3)))
Right now I am using a Watlow EZ-Zone and putting the WB RTD onto it, and the PLC has the DB RTD attached so I am pushing a 0-20 mA at the EZ-Zone from the DL06, then letting the EZ-Zone calculate the %rh and pushing it as a 4-20 mA back at the DL06.
It works, but I would much rather use an open RTD on the DL06 and calculate it on board to save $250 on the Watlow.
Thank you for access to your collective smarts . . .
Steve