Analogue Sensor With 4 To 20Ma Output; Analogue Sensor With Thermistor - NetComm NTC-220 User Manual

Analogue Sensor with 4 to 20mA output

Another common type of sensor type is the 4-20mA current loop sensor. It provides a known current through a
fixed resistor, usually 250 ohms thus producing a voltage of 0v to 5V at the input. The sensor would require an
external power source which may or may not be the same as the unit itself. It will also require an external resistor.
The internal pull up resistor is not activated.

Analogue Sensor with Thermistor

Some sensors work by changing resistance due to a change, such as temperature, light etc. These may be wired up
to an external or internal power source and the resistance can be read into the analogue signal. This will require
some software calibration like scaling or offset to map the voltage received to the sensor resistor value. An
example below shows the internal pull-up voltage and 1K resistor activated. The voltage received depends on the
combination of resistors and the value of the resistance of the sensor itself.
NTC-220 – User Guide
UG01028 v1.2 March 2019
187 of 193
© NetComm Wireless 2019