Hi all Im currently trying to use a a/d and a d/a on fx2n plc to turn on lights in a room when dark.Im using a ldr and a op amp and wheat stone bridge to convert the the change in light to a voltage.I know how to program the plc and a/d and d/a card but my problem is the scaling factor in the plc .I was asked to display the ouput from op amp on a display so im using sacda graph work32.My problem is that the lux or light which gives a change in resistance is not linear so when i try to compare counts in the plc to say voltage and display this on a screen im not sure how to approach this. there is a non linear realonship. This is where im stuck converting lux/counts to a voltage that is proportional to the change in light.Any guidance would be great.I had taught of tryinhg to implement chebychev in the plc to try and make it linear . but i think there is a better way as this will be diffcult to implement by math in the plc.I have graphed lux against resistans and the graph is in the shape of a L.Which has me thinking how can i make this linear.