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Description of several common industrial control signals

In industrial automation control, various concepts such as switch quantity, digital quantity, analog quantity, discrete quantity, and pulse quantity are often encountered, and people are easily confused with these concepts in practical applications. The various concepts are listed as follows


It generally refers to the "on" and "off" states of the contacts. Generally, "0" or "1" is also used in computer equipment to represent the state of the switch. Switch is divided into active switch signal and passive switch signal, active switch signal refers to the state of "on" and "off" is a signal with power supply, it can also be called wet contact, passive switch The quantity signal refers to the signal without power supply in the state of "on" and "off", which is generally called dry contact.
(Wet contact: active switch; has 2 states with electricity and no electricity; there is a polarity between the 2 contacts, which cannot be reversed;)


Many people confuse digital with switch and also with analog. Digital quantities are discrete physical quantities in time and quantity, and the signals they represent are digital signals. A digital quantity is a signal composed of 0 and 1, which is encoded to form a regular signal, and the quantized analog quantity is a digital quantity.


The concept of analog quantity corresponds to digital quantity, but after quantization, it can be converted into digital quantity. An analog quantity is a physical quantity that is continuous in time and quantity, and the signal it represents is an analog signal. Any value of the analog quantity in the continuous change process is a specific and meaningful physical quantity, such as temperature, voltage, current and so on.

Discrete quantity:

The discrete quantity is the physical quantity obtained by discretizing the analog quantity. That is, it is impossible for any instrument to have a completely accurate representation of the analog quantity, because they all have a sampling period, during which the value of the physical quantity is unchanged, while the actual analog quantity changes. of. In this way, the analog quantity is discretized and becomes a discrete quantity

Pulse volume:

The pulse quantity is the signal quantity in which the instantaneous voltage or current jumps from a certain value to another value. After quantization, its constant change is a digital quantity. If it changes from 0 to a fixed value and remains unchanged, it is a switching quantity.