The input and output types of PLC are divided into digital input and output, analog input and output, and high-speed pulse input and output.
You should know the digital analog quantity, the digital quantity is only 0 and 1 (the circuit is represented as on and off), the analog quantity is a current or voltage signal with a difference in size.
The digital input has only one transistor, and the output is divided into two types: transistor and relay. There are two types of transistor output: NPN and PNP. The difference is that the contact is connected to the positive pole when the NPN is turned on, and the electric shock is connected to the negative pole when the PNP is turned on. NPN is more common in European and American brand products, and PNP is more common in Asian products.
Do you know what a relay is? This thing can only output digital quantity, because it only has two states of on and off.
The difference between the transistor output and the relay output is: the transistor output current is small (driving capacity is 0.75A), while the relay output is large (about 2A, the large can reach 5A); the transistor output voltage is only 24VDC, and the relay is based on your wiring ; The response speed of the transistor is fast, the speed of the relay is slow; the number of transistor switches is almost unlimited, and the relay has a life limit (about 30W times).
Analog input and output have both voltage and current.
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