The distinction can be made based on their definitions
Sensor: The name "sensor" implies both transmission and sensing. Transmission refers to data transfer, while sensing refers to data perception. In reality, perception comes first, followed by conversion, and finally transmission. Therefore, transmission is the goal, conversion is the means, and perception is the foundation. The element that can sense the measured variable (temperature, pressure, level, flow rate) is called the sensing element, and the element that can convert the sensed variable into a non-standard electrical signal or other form of output signal is called the conversion element. Therefore, a sensor consists of a sensing element and a conversion element.
Transmitter: The name "transmitter" implies both transformation and transmission. Transformation comes first, followed by transmission. Transmission is the goal, and transformation is the foundation. The transformation section converts the non-standard electrical signal or other form of signal transmitted from the sensor into a standard electrical signal, such as 4-20mA or 1-5V, and then transmits the standard signal to the secondary instrument.
The distinction between sensors and transmitters can be based on their functions:
Sensors are the primary means of acquiring information in the natural and industrial fields. Sensor technology plays a crucial role in economic development and social progress. In modern industrial production, especially automated production, various sensors are used to monitor and control various parameters in the production process, ensuring equipment operates at its normal or optimal state and that products achieve the best quality.
Transmitters, on the other hand, detect process parameters and transmit the measured values as specific signals for display and adjustment. In automatic detection and control systems, they transform various process parameters, such as temperature, pressure, flow rate, liquid level, and composition, into standardized signals, which are then transmitted to controllers and indicating recorders for adjustment, indication, and recording.
Distinguishing between sensors and transmitters based on their components
A sensor generally consists of four parts: a sensing element, a conversion element, a conversion circuit, and an auxiliary power supply. The sensing element directly senses the measured quantity and outputs a physical quantity signal with a definite relationship to the measured quantity; the conversion element converts the physical quantity signal output by the sensing element into an electrical signal; the conversion circuit amplifies and modulates the electrical signal output by the conversion element; the conversion element and the conversion circuit require an auxiliary power supply.
A transmitter mainly consists of a measurement section, an amplifier, and a feedback section. The measurement section detects the measured variable x and converts it into an input signal Zi that can be accepted by the amplifier. The feedback section converts the transmitter's output signal y into a feedback signal Zf, which is then sent back to the input. Zi is algebraically compared with the zero-adjustment signal Zo and the feedback signal Zf, and the difference ε is amplified by the amplifier and converted into a standard output signal.
Distinguishing between sensors and transmitters based on the signals they acquire
Sensors output non-standard electrical signals or other forms of signals, which are weak non-standard signals.
Transmitters output standard electrical signals, and the output signal is strong. For long distances, standard current signals are used for transmission, while for short distances, standard voltage signals can be used.
Distinguishing between sensors and transmitters by their output:
Transmitters output standard electrical signals, such as 0-5V voltage or 4-20mA current.
Sensors output less standard signals, such as very weak electrical signals. A transmitter necessarily contains a sensor; it's essentially a sensor plus a power conversion device.
Distinguishing between sensors and transmitters by their wiring and power supply:
Sensors come in two-wire, three-wire, and four-wire configurations; some require an external power supply, while others do not.
Transmitters are generally two-wire, with the power supply and signal lines sharing the same wire. Transmitters are used to convert the energy of a system into the same or different forms of energy; the key word is "conversion." The name "transmitter" includes the words "conversion" and "transmission." Conversion is the transformation, and transmission is the delivery. In reality, transformation precedes delivery; therefore, delivery is the goal, and transformation is the foundation. The conversion section transforms non-standard electrical signals or other forms of signals transmitted from the sensor into standard electrical signals, such as 4-20mA or 1-5V, and then transmits the standard signals to the secondary instruments.
Pressure Transmitters
1. Wiring System and Power Supply: Sensors are available in two-wire, three-wire, and four-wire configurations; some require an external power supply, while others do not. Transmitters are generally two-wire, with the power supply and signal lines sharing the same wire.
2. Signal: Sensors output non-standard electrical signals or other forms of signals, which are weak. Transmitters output standard electrical signals, which are stronger. For long distances, standard current signals are used for transmission; for short distances, standard voltage signals can be used.
3. Primary and Secondary Instruments: Both transmitters and sensors are primary instruments. Primary instruments are used for signal acquisition and conversion, while secondary instruments receive signals acquired and converted by the primary instruments and can be used for display, control, alarm, and monitoring.
Integrating the sensor and transmitter into a single unit combines the functions of both primary and secondary instruments, creating what is known as an intelligent transmitter.
Sensors convert physical quantities such as pressure and flow rate into electrical signals, while transmitters output these electrical signals as standard current or voltage signals, typically 4-20mA and 1-5V. Sensors can convert signals according to a specific rule; when the sensor's output is a standard signal, it is a transmitter.
The following are the output signals of sensors and transmitters:
1. Current signal: 4-20mA, 0-20mA
2. Voltage signal: 0-5V, 1-5V, etc., and also mV signals
3. Resistance signal
4. Pulse signal When the above signal output is converted into a standard 4-20mA signal, it is called a transmitter.
Sensors are like your sensory system; pressure, temperature, and flow rate are all sensor types. Transmitters are like the nervous system connecting the sensory system to the brain; temperature transmitters, pressure transmitters, etc., convert voltage signals into current signals and transmit them to the processor.
The difference between sensors and transmitters lies in their output signals: sensors provide usable signals, while transmitters output signals conform to certain standards; most transmitters require sensors to function; and a sensor, when its signal is integrated to conform to a certain standard, is called a transmitter.
First, let's look at the origin of sensors: To obtain information from the outside world, people must rely on their sensory organs. However, relying solely on our own sensory organs is far from sufficient for studying natural phenomena and laws, as well as in production activities. To adapt to this situation, sensors are needed. Therefore, it can be said that sensors are an extension of human senses.
So when did transmitters appear? What is their relationship with sensors? How do we understand the difference between sensors and transmitters?
We know that a sensor is a general term for a device or apparatus that receives a specified measurand and converts it into a usable output signal according to a certain rule. It usually consists of a sensitive element and a conversion element. When the sensor's output is a specified standard signal, it is called a transmitter.
A transmitter is an instrument that converts non-standard electrical signals into standard electrical signals. A sensor, on the other hand, is a device that converts physical signals into electrical signals. While the term "physical signal" was commonly used in the past, it now encompasses other signals (divided into two main categories: physical sensors and chemical sensors). Primary instruments refer to field measuring instruments or base control instruments, while secondary instruments utilize signals from primary instruments to perform other functions, such as control and display.
A sensor converts non-electrical physical quantities, such as temperature, pressure, liquid level, material properties, and gas characteristics, into electrical signals, or directly transmits physical quantities, such as pressure and liquid level, to a transmitter. A transmitter amplifies the weak electrical signals acquired by the sensor for transmission or to activate control elements. Alternatively, it converts non-electrical inputs from the sensor into electrical signals and amplifies them for remote measurement and control. Analog signals can also be converted into digital signals as needed. Sensors and transmitters together constitute the monitoring signal source for automatic control. Different physical quantities require different sensors and corresponding transmitters.
Another type of transmitter does not convert physical quantities into electrical signals. For example, a "differential pressure transmitter" for boiler water level gauges transmits water from the lower part of the level sensor to the upper part of the transmitter's bellows via an instrument tube. The differential pressure across the bellows drives a mechanical amplification device to indicate the water level using a pointer-a remote instrument. Of course, transmitters can also convert analog electrical quantities into digital quantities. The above only explains the conceptual difference between sensors and transmitters.
