Detailed explanations of common concepts in the field of industrial automation control

Abstract

The field of industrial automation control involves a vast array of measurement, control, and processing tasks, where concepts such as switch quantity, digital quantity, analog quantity, discrete quantity, and pulse quantity serve as foundational knowledge. This article will provide a detailed explanation of these concepts and explore their differences and connections, aiming to assist readers in better understanding the operational principles of industrial automation control systems.

1. Definition of Concepts

1.1 Switch Quantity

Switch quantity describes the "on" and "off" states of a contact, commonly found in computer equipment, represented by "0" or "1". Switch quantity is further subdivided into active switch quantity signals and passive switch quantity signals.

• Active switch quantity signals:Signals with power supply in the "on" and "off" states, also known as step signals, which in some cases resemble pulse quantity. Common signal voltages include 220VAC, 110VAC, 24VDC, 12VDC, etc.
• Passive switch quantity signals:Signals without power supply in the "on" and "off" states, often referred to as dry contacts. Through resistance testing, passive switch quantity signals exhibit a resistance value of either 0 or infinity.

1.2 Digital Quantity

Digital quantity is a physical quantity that exhibits discrete characteristics in both time and quantity, expressed in the form of digital signals. Digital quantity is composed of 0 and 1, and can be encoded to form regular signals. In fact, quantized analog quantity is digital quantity, and their conversion plays a crucial role in industrial control.

1.3 Analog Quantity

Compared to digital values, analog values are continuous physical quantities in terms of both time and quantity, and are expressed as analog signals. In the continuous changing process, each value of an analog quantity has a specific physical meaning, such as temperature, voltage, current, etc. Although analog values are inherently continuous, in practical applications, we often need to perform quantization processing on them to convert them into digital values for computer processing.

1.4 Discrete Quantity

A discrete quantity is a physical quantity obtained by discretizing an analog quantity. Since any instrument or device has a certain degree of error when representing analog quantities, it cannot accurately represent the actual value of the analog quantity. These devices usually have a sampling period during which the value of the physical quantity remains unchanged, while the actual analog quantity is continuously changing. This process of discretizing the analog quantity forms a discrete quantity, making it easier for us to process and analyze it.

1.5 Pulse Quantity

A pulse quantity describes a signal quantity in which the instantaneous voltage or current rapidly transitions from one value to another. In the quantization process, if the change in pulse quantity exhibits a regular sequence, it can be regarded as a digital quantity. When the pulse quantity transitions from 0 to a fixed value and remains unchanged, it is equivalent to a switch quantity.

2. Differences and Connections between Concepts

2.1 Analog Quantity and Digital Quantity

Analog quantity and digital quantity are the two most common data types in the field of industrial automation control. Analog quantity represents continuously changing physical quantities, while digital quantity represents discrete, countable physical quantities.

Differences between Analog Quantity and Digital Quantity:

• Continuity:Analog quantity is continuous, while digital quantity is discrete.
• Accuracy:Analog signals possess infinite precision, whereas digital signals have limited precision.
• Processing method:Analog signals require quantization before they can be recognized and processed by computers, whereas digital signals can be directly recognized and processed by computers.

Connection between analog and digital signals:

• Analog signals can be converted into digital signals through quantization.
• Digital signals can be converted into analog signals through an analog-to-digital converter.

2.2 Switching signals, digital signals, and pulse signals

Switching signals, digital signals, and pulse signals are all digital signals, and there are certain connections and differences between them.

Connection between switching signals, digital signals, and pulse signals:

• All three are digital signals and can be represented by "0" and "1".
• All three can form regular signals through encoding.

Difference between switching signals, digital signals, and pulse signals:

• Switching values only have two states, namely "on" and "off".
• Digital values can have an infinite number of states, but in practical applications, only a limited number of states are typically used.
• Pulse values are a special type of digital values, characterized by pulse width, pulse period, and other properties.

3. Practical Applications

In industrial automation control systems, concepts such as switching values, digital values, analog values, discrete values, and pulse values are widely used in various measurement, control, and processing stages.

• Switching valuesare applied to detect the motion state, position state, and working state of objects, such as travel switches, limit switches, liquid level switches, pressure switches, etc.
• Digital valuesare applied to counting, sorting, speed measurement, positioning, etc., such as photoelectric encoders, pulse sensors, Hall sensors, etc.
• Analog valuesare applied to measure temperature, pressure, flow rate, liquid level, etc., such as temperature sensors, pressure sensors, flow sensors, liquid level sensors, etc.
• Discrete valuesApplied to controlling the motion speed, positional accuracy, temperature accuracy, etc. of objects, such as PID controllers, frequency converters, servo motors, etc.
• Pulse quantityApplied to speed measurement, counting, positioning, etc., such as pulse generators, pulse counters, etc.

4. Summary

The concepts of switch quantity, digital quantity, analog quantity, discrete quantity, and pulse quantity are fundamental knowledge in the field of industrial automation control. Understanding these concepts is crucial for understanding and designing industrial automation control systems.

Appendix

• Glossary
  • Switch quantity:A physical quantity that describes the "on" and "off" states of a contact.
  • Digital quantity:A physical quantity that exhibits discrete characteristics in both time and quantity.
  • Analog quantity:Both time and quantity manifest as continuous physical quantities.
  • Discrete quantity:A physical quantity obtained by discretizing an analog quantity.
  • Pulse quantity:A signal quantity that describes the instantaneous voltage or current rapidly transitioning from one value to another.

• Frequently Asked Questions
  • Q:What is the difference between analog quantity and digital quantity?
  A: Analog quantity is continuous, while digital quantity is discrete. Analog quantity has infinite precision, while digital quantity has finite precision. Analog quantity needs to be quantized before it can be recognized and processed by a computer, while digital quantity can be directly recognized and processed by a computer.
  • Q:What is the difference between switch quantity, digital quantity, and pulse quantity?
  A: Switch quantity has only two states, namely "on" and "off". Digital quantity can have infinitely many states, but in practical applications, only a limited number of states are typically used. Pulse quantity is a special type of digital quantity, characterized by pulse width, pulse period, and other properties.
  • Q:What are some examples of these concepts in practical applications?
  A: Switching values are applied to detect the motion state, position state, working state, etc. of objects, such as travel switches, limit switches, liquid level switches, pressure switches, etc. Digital values are applied to counting, sorting, speed measurement, positioning, etc., such as photoelectric encoders, pulse sensors, Hall sensors, etc. Analog values are applied to measuring temperature, pressure, flow rate, liquid level, etc., such as temperature sensors, pressure sensors, flow sensors, liquid level sensors, etc. Discrete values are applied to controlling the motion speed, position accuracy, temperature accuracy, etc. of objects, such as PID controllers, frequency converters, servo motors, etc. Pulse values are applied to speed measurement, counting, positioning, etc., such as pulse generators, pulse counters, etc.