I. Introduction
In industrial automation and control systems, transmitters and sensors are both indispensable components. Although they each play important roles in the system, there are significant differences between them in terms of function, structure, and usage. This article aims to explore the differences between transmitters and sensors in depth to help readers better understand and apply these two key components.
II. Basic Overview of Sensors
Definition: A sensor is a device or apparatus capable of detecting a specified measured quantity and converting it into a usable signal according to a specific law. Typically consisting of a sensing element and a transducer, it detects information about the measured quantity and converts it into an electrical signal or other required form of output according to a specific law.
Classification: Sensors can be classified in various ways based on the physical quantity being measured and their operating principles. Common classification methods include categorization by the physical quantity being measured (e.g., temperature, pressure, flow rate, etc.) and by operating principle (e.g., electromagnetic, photoelectric, etc.).
Function: The primary function of a sensor is to convert non-electrical physical quantities into electrical signals to facilitate operations such as transmission, processing, storage, display, recording, and control. It serves as the first critical step in achieving automatic detection and automatic control.
III. Basic Overview of Transmitters
Definition: Transmitters evolved from sensors; any sensor capable of outputting a standard signal is referred to as a transmitter. A standard signal is one whose form and range of physical quantities comply with international standards. The primary function of a transmitter is to convert the non-standard electrical signal output by a sensor into a standard electrical signal, facilitating remote transmission and reception/processing by secondary instruments.
Classification: Transmitters can be classified into two types based on output signal type: current-output and voltage-output. Current-output transmitters function as constant-current sources and are suitable for long-distance transmission; voltage-output transmitters function as constant-voltage sources and are suitable for short-distance transmission and applications involving multiple instruments connected in parallel. Additionally, transmitters can be categorized into pneumatic and electric types based on the energy source used.
Operating Principle: Transmitters operate based on the principle of negative feedback and primarily consist of a measurement section, an amplifier, and a feedback section. The measurement section detects the measured variable and converts it into an input signal that can be accepted by the amplifier; the amplifier compares the input signal with the feedback signal and amplifies it; the feedback section converts the transmitter's output signal into a feedback signal and returns it to the input end.
IV. Differences Between Transmitters and Sensors
Functional Differences:
Sensor: Its primary function is to convert non-electrical physical quantities into electrical signals, thereby enabling signal detection and conversion.
Transmitter: Building upon the sensor, it converts non-standard electrical signals into standard electrical signals to facilitate remote transmission and reception/processing by secondary instruments.
Structural Differences:
Sensor: Typically consists of a sensing element and a conversion element, with a relatively simple structure.
Transmitter: In addition to the sensing element and conversion element found in a sensor, it includes complex circuit structures such as amplifiers and feedback sections.
Differences in Usage:
Sensor: Typically comes into direct contact with the measured object to acquire the raw signal.
Transmitter: Typically used in conjunction with a sensor, receiving the sensor's output signal and converting and processing it.
Differences in Signal Output:
Sensor: Outputs non-standard electrical signals, such as analog or digital signals.
Transmitter: Outputs standard electrical signals, such as a 4–20 mA current signal or a 1–5 V voltage signal.
Differences in Application Scenarios:
Sensor: Widely used in various measurement and control systems, such as for measuring physical quantities like temperature, pressure, and flow.
Transmitter: Typically used in situations where sensor signals need to be converted into standard signals for remote transmission and processing, such as in industrial automation and building automation systems.
V. Summary
Transmitters and sensors both play important roles in industrial automation and control systems. As the source of the signal, sensors convert non-electrical physical quantities into electrical signals; transmitters, building on the sensor's output, further convert non-standard electrical signals into standard electrical signals to facilitate remote transmission and reception/processing by secondary instruments. By thoroughly understanding the differences between the two and their application scenarios, we can better select and utilize these two key components to improve system stability and reliability.