그리고 analog quantity refers to the continuous change of the variable within a certain range. Note that it is a continuous change without interruption in the middle.
What does that mean?

Take the light switch as an example:
You press the switch once, the light turns on, press it again, the light turns off, and there is no operation during the period between the two presses of the switch, which is a broken change.
For another example, the pulse output IO is a kind of digital output IO, which can output an integer number of pulse signals, but cannot output 1.5 such pulse signals.
The above two examples are all about digital quantities. The continuously changing signals that can take any value within a certain range are analog quantities, such as input voltage signal, input current signal, input temperature signal, input pressure signal, etc. .

The common analog IO types are as follows:

1. -5V-+5V voltage analog input and output IO
2. -10V-+10V voltage analog input and output IO
3. 0V-+5V voltage analog input and output IO
4. 0V-+10V voltage analog input and output IO
5. 0-20mA current analog input and output IO
6. 4-20mA current analog input and output IO
7. Thermocouple analog input IO
8. Thermal resistance analog input IO and so on.