OMC-042 / 043 / 044 Data loggers
Users
’ manual
page 100
*) An accuracy of 0.5° is possible when step 1 to 3 are taken with care.
*) Using a thermistor is not recommended for Lithium powered data loggers as it draws a 1.5mA current
continuously. On the next page this example is continued with screenshots of the data logger’s
configuration menu.
Note: Because of power consumption we recommend to use PT1000 thermistors only. Before you can
measure temperature with a PT1000 you have to perform the following calibration/configuration steps:
1) Use a 10M potentiometer to do a 2 point user calibration of the potentiometer input.
2) Determine the reference resistance.
a) Choose a reference resistor of about 1k and connect it between the potentiometer Vref (3.3V)
at connector X1 pin 8 and the potentiometer input X1.7.
b) With an accurate multi meter measure the current between potentiometer input X1.7 and GND
X1.6.
c) Calculate the total reference resistance Rref by dividing 3.3V (Vref) by the measured current.
3) connect a PT1000 between the potentiometer input X1.7 and GND X1.6
4) Create a calculated channel to calculate the resistance of the PT1000 by entering the following
equation: (:PM*Rref)/(100-:PM)
Where Rref is the value determined at step 2 and PM the parameter code of the potentiometer input.
5) Create a calculated channel (TPT) to calculate the temperature of the PT1000 by entering the
following equation: (:RPT-1000)/3.84
Where 1000 is the resistance of the PT1000 at 0°C and RPT the parameter code of the calculated
resistance channel.