Comparison block programming

Jbeard

Member
Join Date
May 2019
Location
Tn.
Posts
14
Hello all. Im new to place programming. I have Schneider electric plc's using twidosuite 2.33. I'm trying to write some ladder logic using comparison blocks with pt100 temperature sensors to turn on and off some cooling tower fans at a certain temperature. I can write the ladder logic part but I'm trying to figure out on the anolog input module what should I do for the settings on the pt100? Any ideas?
 
Never used twido but a quick look at the manual see below
An analog to discrete converter samples an input voltage from 0 to 10 V to a discrete
value from 0 to 1023. This value is stored in system word %IW0.0.1. The value is
linear through the entire range, so that each increment is approximately 20 mV (10
V/512). Once the system detects value 1023, the channel is considered saturated.

This was for a 0-10v but can assume the raw values are either 0-1023 or 0-2048 you could then scale this to 0-150 for 0c or what ever you need then do comparisons. As I say have never used twido but I have attached some code below done on Mitsubishi, It contains analog scale function, and how it is used
This one for historical reasons had to convert the integer values into reals and back again but if accuracy is not a problem you could just use integer maths
Note: I assume twido has the functions for the maths but in any case it should give you an idea. Once you have the analog values you can then compare them with say a set point and either switch something on or off including slug timers or dead bands to stop it oscillating, if you are going to control with analog output positioning I suggest using a PID block.
 

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