Method 1
This method strictly uses the RTD coefficient and assumes a proportional relationship between impedance
and temperature. The equation for this is given in the following equation.
Tc = (R – R
0
) / (
α
* 100)
Where Tc = Temperature in deg C
R
0
= 100
Ω
α
= 0.00385
Below is an example program for using Method 1 that could run on the RIO-4712x.
#MAIN
REM set Analog inputs 0-5 to 0-5V inputs
AQ 0,3
AQ 1,3
AQ 2,3
AQ 3,3
AQ 4,3
AQ 5,3
AT0;'set initial time reference
#Calc
REM calculate resistance of RTD
r0 = (1000*@AN[0])/21
r1 = (1000*@AN[1])/21
r2 = (1000*@AN[2])/21
r3 = (1000*@AN[3])/21
r4 = (1000*@AN[4])/21
r5 = (1000*@AN[5])/21
REM calculate deg C
Tc0 = (r0-100)/0.385
Tc1 = (r1-100)/0.385
Tc2 = (r2-100)/0.385
Tc3 = (r3-100)/0.385
Tc4 = (r4-100)/
0.385
Tc5 = (r5-100)/0.385
REM calculate deg F (not required)
Tf0 = ((9*Tc0)/5)+32
Tf1 = ((9*Tc1)/5)+32
Tf2 = ((9*Tc2)/5)+32
Tf3 = ((9*Tc3)/5)+32
Tf4 = ((9*Tc4)/5)+32
Tf5 = ((9*Tc5)/5)+32
AT-100;'wait 100 ms from last time reference
JP#Calc
This method provides a relatively accurate temperature reading with a simple and straight-forward
calculation. A limitation with this method is that it uses an idealized relationship between the impedance of
an RTD and the temperature of the RTD. In reality, the relationship between impedance and temperature is
not linear, so if higher precision is required from the temperature reading, the following Method should be
used.
RIO-47xxx
A1 – SCB-48206
●
95
