Definition and composition of sensors
Definition and composition of sensors
The definition of Transducer/Sensor in my country's national standard (GB7665-1987) is: "a device or device that can sense the prescribed measurement and convert it into a usable output signal according to a certain rule."
This definition has the following meanings: ①The sensor is a certain measuring device or part of a measuring device, which can complete part of the detection task;② Its input quantity is a certain measured quantity, which may be a physical quantity, or a chemical quantity, biomass, etc.;③ Its output is a certain physical quantity, which should be easy to convert, process, etc. This quantity can be gas, light, electrical physical quantity, but mainly electrical physical quantity;④ There is a corresponding relationship between output and input, and there should be a certain degree of accuracy.
Regarding sensors, there have been many names in our country, such as transmitter, transmitter, transmitter, transducer, etc. They have the same or similar connotations, so in recent years, they have gradually unified, and most of them have used the name sensor.Literally, it can be explained as follows: The function of the sensor is one-sensing two-transmission, that is, to sense the measured information and transmit it.
The sensor is generally composed of three parts: sensitive components, conversion components, and basic conversion circuits. The block diagram is shown in Figure 0-1.
Sensitive element: It is an element that directly senses the measured and outputs a certain physical quantity in a certain relationship with the measured.
Figure 0-2 is a schematic diagram of a gas pressure sensor. The lower half of the diaphragm 2 is fixedly connected to the body 1, and the upper half is connected to the magnetic core 4 by a connecting rod. The magnetic core 4 is placed in two inductive coils 3, and the latter is connected to the conversion circuit 5.The bellows here is a sensitive element, the outside of which is connected to the atmospheric pressure p, and the inside feels the measured pressure p.When P changes, it causes the upper half of the diaphragm to move, that is, the corresponding displacement is output.
Conversion element: The output of a sensitive element is its output, which converts the input into circuit parameters.In Figure 0-2, the conversion element is a variable inductance coil 3, which converts the input displacement into a change in inductance.
Basic conversion circuit: The above-mentioned inductance change is connected to the basic conversion circuit (referred to as the conversion circuit), and it can be converted into electrical output.The sensor only completes the basic conversion from the measured parameter to the electric quantity, and then inputs it to the measurement and control circuit for further conversion such as amplification, calculation, and processing to obtain the measured value or perform process control.
In fact, some sensors are simple, some are more complex, most are open-loop systems, and some are closed-loop systems with feedback.
The simplest sensor consists of a sensitive element (also a conversion element), which directly outputs electricity when it senses the measurement, such as thermocouples.As shown in Figure 0-3, two different metal materials A and B are connected at one end and placed in the measured temperature T, and the other end is the reference, and the temperature is T. , Then a temperature T and T will be generated in the loop. The relevant electromotive force, thus temperature measurement.
Some sensors are composed of sensitive components and conversion components.In the piezoelectric acceleration sensor shown in Figure 04, the mass m is a sensitive element and the piezoelectric sheet (block) is a conversion element.Since the output of the conversion element is already power, no conversion circuit is needed.
In some sensors, there is more than one conversion element, which requires several conversions
Sensitive components and conversion components are often installed together in structure, and the basic conversion circuit is also expected to be installed with them in order to reduce external influences. However, due to space constraints or other reasons, the basic conversion circuit is often installed in an electric box .Nevertheless, many sensors can only output electrical signals after passing through the conversion circuit, which determines that the conversion circuit is one of the components of the sensor.