The difference between sensor and transducer
Both sensor and transducer are translated as sensors, but the former is a physical sensor and the latter is a structural sensor. For example, a photoresistor is a physical sensor, and an illuminance sensor made of a photoresistor is a structural sensor. But they are all photoelectric sensors or photoelectric sensors.
The Sensor converts physical signals into electrical signals, mainly pressure, flow, liquid level, etc. Of course, some discrete signals such as proximity switches may also be included. The Transducer function is to re-convert the measured value into a transform that becomes a signal acceptable to the system. This may still be somewhat difficult to understand. For example, there is a need in the field to convert the temperature signal into a 4~20mA standard current signal. We have a thermocouple sensor in hand, a transducer, connected to them, so that the sensor converts the temperature signal into an mV signal, and the transducer converts the mV signal into a current signal, and the Analog Input module of the system can accept and process it.
There is one more word to note: the transmitter. First, a physical quantity (such as atmospheric pressure) is sensed, then transduce (becomes an electrical signal), and then it can be transmitted to other components. So the transmitter must be some kind of transducer, and the transducer must be some kind of sensor. For example, water quantity sensors and pressure sensors, because the physical quantity is usually transmitted to other parts, so the transmitter is used more. If the signal of the sensor passes through other intermediate parts to realize signal transmission, then the transducer is used, and the LVDT linear variable difference is used. The sensor, whose function is simply to turn the distance into an electrical signal, so use a transducer. The sensor is rare in the manual, and very few sensors really only function as a sensor, but do nothing else.
The meaning of sensor classification
Sensors can be categorized according to different perspectives: principle, purpose, type of output signal, material used, and process. The classification of sensors into physical sensors and structural sensors is of practical significance, as the technical fields of interest in the research of physical and structural sensors are quite different. This scientific classification is much more important than the distinction between resistive and resistive sensors, the difference between capacitive and capacitive sensors, and the difference between inductive and inductive sensors.
The classification of the sensor should not be too fine. For example, the piezoelectric sensor is a self-generating sensor. The magnetoelectric sensor based on electromagnetic induction is also a self-generating sensor. If the photoelectric sensor is understood as such, the photoresistor does not belong. This column is self-generating sensor type. Similarly, the Hall sensor does not belong to a magnetoelectric sensor of magnetoelectricity and belongs to a sensor that senses a magnetic field. The classification of sensors into parametric (energy controlled) and generator (energy conversion) sensors is of theoretical significance.