Analog inputs

Analog inputs (AI) are for measuring analog values such as DC voltage, current and resistance. These values are produced by sensors which indicate multiple states such as thermometers, tensometers, distance meters, lux meters etc.

The functionality of AIs on Neuron and Axon is different on Group 1 and Group 2/3 and Neuron extensions.

On Group 1, the analog input is capable of:

  • measuring 0-10V DC
  • measuring 0-20mA DC

The Group 1 is also capable of measuring the resistance, but this is achievable with Analog output.

On Group 2 and 3 and the Neuron extensions, the analog input is capable of:

  • measuring 0-10V DC
  • measuring 0-2.5V DC with higher precision
  • measuring of 0-20mA DC
  • measuring of resistance 0-100kOhm via a 2-wire method
  • measuring of resistance 0-2kOhm via a more precise 3-wire method

Changing between modes depends on the software you are using, please follow the relevant tutorial.

The Unipi 1.1 has two analog inputs and they are only capable of measuring voltage in a range of 0-10V DC.

Measuring resistance

To measure resistance from the Unipi 1.1's AI (ie. by using PT1000 thermal probes), it is necessary to add a resistor according to the following scheme.

 R_sens = the sensor itself
 R_ref = the reference resistor

There is also a input resistor inside of the AI with the value:

 R_ai = 12200ohm

For R_sens >= 200ohm, use R_ref = 1k. For R_sens < 200ohm, use R_ref = 10k

The value at the AI is calculated from the voltage you read from the AI (V_ai)

           Vcc - V_ai     R_ref * R_ai
 R_sens = ------------ * --------------
              V_ai        R_ref + R_ai
              

The Vcc is the applied voltage (12V in the picture above).