Hi,

Wondering the real difference between digital and analog I/O? Which one I should use and when?

Thanks.

Digital input signals are used to represent items that only have two (2) states, such as... ON (binary 1) or OFF (binary 0) states. Similarly, Digital output signals are used to control items that again only have two states, such as.. START or STOP a device.

So, a digital signal is something like telling if a door is open or not.

Analog signals are variable, they have multiple states. Analog input signals can represent such items as temperature or level or rate of flow. Analog output signals are also variable and can be used for such things as opening a valve to a desired position.

Then, an analog signal is something like telling how much the door is open (or closed).

In our day to day life, we mainly do analog measurements and all analog signals includes the digital ones like a door is 0%=closed or 100%=open. However, digital signals are more suitable for computers (PC/PLC, etc).

An analog signal can only be read by an analog I/O, but a digital one can use both analog or digital I/Os. There is sometime a possibilities to convert an analog signal into a series of digital ones. Because, in practice, you never connect a digital signal to an analog I/O because the analog I/Os are way more expensive than digital ones.

So for a rule of thumb,

• Whenever possible use a digital I/O, since it’s cheap.

• In other case, use an analog I/O if the option to convert the signal in a series of digital signals isn’t possible.

It was very helpful. Thanks for the answer. 

Digital input signals are used to represent items that only have two (2) states, such as... ON (binary 1) or OFF (binary 0) states. Similarly, Digital output signals are used to control items that again only have two states, such as.. START or STOP a device.-- As per your explanation that means  both the digital i/p and  digital o/p is same , because digital signal is only understand the binary , so the binary means 0 and 1. Suppose if I want to open a door or close the door through the automation software then we can use digital output and at the same time if i want to close the door and open the door through the automation software then also we can use digital input, because both the off and on if i consider as door close and door open. Could you please explain more with a proper example so that it can be better for me to understand 

Analog signals are variable, they have multiple states. Analog input signals can represent such items as temperature or level or rate of flow. Analog output signals are also variable and can be used for such things as opening a valve to a desired position.. -- Could you please give the few example so that i can understand the difference between the digital signal and analog signal and their uses in automation 

Waiting for your reply