AD DL06 - math with negative numbers.

bmil

Member
Join Date
Dec 2007
Location
Pa
Posts
3
The current project involves resetting boiler temp higher with a drop in outdoor temp. This makes the slope negative. I have the y=mx+b thing down OK. The math I need to accomplish is "boiler setpoint = (-1.09)(outdoor air temp) + 180". The schedule works on paper. I have the AI module set up to use BCD values and the input values are accurate as they are displayed in the data view as well as on the LCD panel on the PLC. Any help with this will be appreciated.
 
Instead of deriving a negative from the Outdoor Air Temp and adding it to 180 I derived the positive amount and subtracted it from 180. I did the math in 'REAL' with the appropriat4e conversions.

LD (Outdoor Air Temp)
BIN
BTOR
MUL R1.09
OUTD V2000 (as a temp)
LDR 180.0
SUBR V2000
RTOB
BCD
OUT V2002 (Boiler Set Point)
 
Thank you for the quick reply. I will put the code in try it. Am I correct that you simply rearranged the equation to avoid the negative multiply?
 
I can find no MULR or SUBR in the DL06 instruction set. There must be a way to get the values into real format, manipulate them, and put them back to BCD but I have not found it. Otherwise, your solution would work.
 
There must be a way to get the values into real format,

In Bernie's post he used BTOR this is - Binary to Real Number Conversion Box
Then he works the numbers, then you can conveert it back
 
Yes BMIL, I just rearranged the equation. I was going to cover the other question in the next post but GIT and Eric jumped in. The RTOB then BCD converts the REAL answer back to BCD in case that's how you want the format.
 

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