im stuck..
im reading modbus tcp values, when temperature goes -1 and below the graph seems to go bananas at night. Im trying to find out the right formula to calculate negative values passed from the modbus tcp.. i tried
y=mx+c
where x is analog value, y is values stored as max/min value in holding register(16bit)
m=(Ymax-Ymin)/(Xmax-Xmin)
The sensor is a PT1000 and i base Xmax as Ymax.. in example.. PT1000tables at the internet shows me +50 at 1194ohm and -50 at 303ohm
(50--50)/(1194-303) => 100/891=0,11 (m)
and... here im stuck, not sure what to do... maybe my sensor is bad or my node-red settings are bad