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, luxmeters etc.
Analog inputs on Neuron and Axon
The functionality of AIs on Neuron and Axon is different on Group 1 and Group 2/3 and on 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 on 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 2-wire method
- measuring of resistance 0-2kOhm via more precise 3-wire method
Changing between modes depends on the software you are using, please follow the relevant tutorial.
Measuring voltage
Measuring current
Measuring resistance
Analog inputs on Unipi 1.1
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 resistor
For reading temperature between 200-3800R (-200°C/+800°C), a 1K resistor should be used to ensure the voltage will not exceed 10V.
The value at the AI is calculated using the following formula
R_sens (200) = 12V/969.7 + 200)*969.7 = 9.948V
R_sens (3800) = 12V/(969.7+3800)*969.7 = 2.439V
When the -200°C temperature is measured, a 9.948V voltage is present on the AI, while with the +800°C temperature the AI voltage will be 2.439V. To verify those values, please check the documentation of your sensor.
Please keep in mind the ability of UniPi 1.1's architecture to precisely measure voltage is limited at voltages below and including 0.05V. For our showcase sensor, the resulting deviation could be up to +-50°C. If a more precise measurement is required, change the R_ref value accordingly.
If the R_sens value does not match the requirement, you need to change the R_ref setting. The R_ref value is calculated using this formula
Rx = (R_ref*12K8)/(R_ref+12K2)
When setting the R_ref, please ensure that at maximum/minimum resistance the voltage at AI+ will not exceed 10V or decrease below 0V.
