4.1.8.1.3 Resistance temperature detectors
Resistance temperature detectors (RTDs) are manufactured from metals whose resistance increases with
temperature.
SOMANET servo drives can directly measure the voltage or resistance so RTDs like KTY84-130 and PT1000 can
be directly attached.
A wide range of RTD sensors can be measured by the temperature sensor input (SOMANET Circulo only) or
analog inputs.
Note
This application note is focused on RTDs.
4.1.8.2 Pull-up resistor selection
For measuring the temperature using an RTD, the sensor’s voltage needs to be adjusted to a specific
temperature range by adding a pull-up resistor.
The analog input can be configured to read the input voltage or input resistance. Subitem 0x2038:3 defines
the value of the pull-up resistor. Two modes for measuring the analog input value can be distinguished:
Pull-up resistor (0x2038:3) = 0
The measured value will be the exact value of the analog input voltage.
0 = 0 volts and 4096 = full scale (according to the full scale voltage of the analog input)
Pull-up resistor (0x2038:3) > 0
In this mode, the firmware will calculate the resistor value (in Ω) connected to the input terminals. This
feature is useful when using RTD sensors or another resistive sensor.
Note
RTDs with a minimum of 3 Ω resistance change per °C result in an acceptable accuracy.
According to the curves below, PT1000 and KTY-130 are good fitting sensors, both sensors are almost linear
in the desired range.
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