The difference between infrared temperature measurement and temperature sensor
Temperature sensors are mainly divided into contact and non-contact sensors. Contact temperature sensor: The detection part of the contact temperature sensor has good contact with the measured object, also known as a thermometer. Non-contact temperature sensor: Its sensitive element and the measured object are not in contact with each other, also known as non-contact temperature measuring instrument. This instrument can be used to measure the surface temperature of moving objects, small targets and objects with small heat capacity or rapid temperature changes (transient), and can also be used to measure the temperature distribution of the temperature field. The most commonly used non-contact thermometers are based on the basic law of black body radiation and are called radiation thermometers.
NTC and RTD high precision temperature sensor
Temperature sensor: Generally, the measurement accuracy is high. Within a certain temperature range, the thermometer can also measure the temperature distribution inside the object. However, for moving objects, small targets or objects with small heat capacity, large measurement errors will occur. Commonly used thermometers include bimetallic thermometers, glass liquid thermometers, pressure thermometers, resistance thermometers, thermistors, and thermocouples. They are widely used in industry, agriculture, commerce and other sectors. People also often use these thermometers in daily life. With the wide application of cryogenic technology in national defense engineering, space technology, metallurgy, electronics, food, medicine, petrochemical and other departments and the research of superconducting technology, cryogenic thermometers for measuring temperatures below 120K have been developed, such as cryogenic gas thermometers, steam Pressure thermometers, acoustic thermometers, paramagnetic salt thermometers, quantum thermometers, low temperature thermal resistance and low temperature thermocouples, etc. Cryogenic thermometers require small temperature sensing elements, high accuracy, good reproducibility and stability. The carburized glass thermal resistance made of porous high silica glass carburized and sintered is a kind of temperature sensing element of the low temperature thermometer, which can be used to measure the temperature in the range of 1.6 ~ 300K.
infrared temperature sensor
Infrared sensor: A sensor that uses the physical properties of infrared rays to measure. Infrared ray, also known as infrared light, has properties such as reflection, refraction, scattering, interference, and absorption. Any substance, as long as it has a certain temperature (higher than zero), can radiate infrared rays. The infrared sensor is not in direct contact with the measured object during measurement, so there is no friction, and it has the advantages of high sensitivity and fast response. The infrared sensor includes an optical system, a detection element and a conversion circuit. Optical systems can be divided into two types: transmissive and reflective according to their structure. The detection element can be divided into thermal detection element and photoelectric detection element according to the working principle. Thermistors are the most widely used thermal components. When the thermistor is exposed to infrared radiation, the temperature rises and the resistance changes (this change may be larger or smaller, because thermistors can be divided into positive temperature coefficient thermistors and negative temperature coefficient thermistors), It becomes an electrical signal output through a conversion circuit. Photosensitive elements are commonly used in photoelectric detection elements, usually made of materials such as lead sulfide, lead selenide, indium arsenide, antimony arsenide, mercury cadmium telluride ternary alloy, germanium and silicon doping.
Structure and Installation of Piezoelectric Acceleration Sensor
The structure of the commonly used piezoelectric acceleration sensor is divided into: a spring, a mass, a base, a piezoelectric element, and a clamping ring. The piezoelectric element-mass-spring system is mounted on a circular central pillar, which is connected to the base. This structure has a high resonant frequency. However, when the base is connected with the test object, if the base is deformed, it will directly affect the output of the vibration pickup. In addition, changes in the test object and ambient temperature will affect the piezoelectric element and cause changes in the preload, which can easily cause temperature drift. The piezo element is clamped to the triangular center post by a clamping ring. When the piezoelectric acceleration sensor senses axial vibration, the piezoelectric element bears shear stress. This structure has an excellent isolation effect on base deformation and temperature changes, and has a high resonance frequency and good linearity. The annular shear type has a simple structure and can be made into an extremely small accelerometer with high resonance frequency. The annular mass block is glued to the annular piezoelectric element mounted on the central pillar. Since the binder softens with increasing temperature, the maximum operating temperature is limited.
The upper limit frequency of the piezoelectric acceleration sensor depends on the resonance frequency in the amplitude-frequency curve. Generally, for piezoelectric acceleration sensors with small damping (z<=0.1), if the upper limit frequency is set to 1/3 of the resonance frequency, the amplitude can be guaranteed. The error is less than 1dB (ie 12%); if it is taken as 1/5 of the resonance frequency, the amplitude error is guaranteed to be less than 0.5dB (ie 6%), and the phase shift is less than 30. However, the resonant frequency is related to the fixed condition of the piezoelectric acceleration sensor. The amplitude-frequency curve given by the piezoelectric acceleration sensor when it leaves the factory is obtained under the fixed condition of rigid connection. The actual fixing method is often difficult to achieve a rigid connection, so the resonance frequency and the upper limit frequency of use will decrease. Among them, the use of steel bolts is a method to make the resonance frequency reach the factory resonance frequency. Do not screw all the bolts into the screw holes of the base, so as not to cause deformation of the base and affect the output of the piezoelectric acceleration sensor. Apply a layer of silicone grease to the mounting surface to increase connection reliability on uneven mounting surfaces. Insulation bolts and mica gaskets can be used to fix the piezoelectric acceleration sensor when insulation is required, but the gasket should be as thin as possible. Use a thin layer of wax to stick the piezoelectric acceleration sensor on the flat surface of the test piece, and it can also be used in low temperature (below 40°C) occasions. The hand-held probe vibration measurement method is particularly convenient to use in multi-point testing, but the measurement error is large and the repeatability is poor. The upper limit frequency is generally not higher than 1000Hz. The piezoelectric acceleration sensor is fixed with a special magnet, which is easy to use and is mostly used in low-frequency measurement. This method can also insulate the piezoelectric acceleration sensor from the test piece. Fixing methods with hard bonding bolts or adhesives are also commonly used. The resonant frequencies of a typical piezoelectric accelerometer using the above-mentioned various fixing methods are about: steel bolt fixing method 31kHz, mica gasket 28kHz, coated wax layer 29kHz, hand-held method 2kHz, magnet fixing method 7kHz.
Several Methods for Preliminary Judgment of Humidity Sensor Performance
In the case that the actual calibration of the humidity sensor is difficult, some simple methods can be used to judge and check the performance of the humidity sensor.
1. Consistency determination. Buy more than two humidity sensor products of the same type and the same manufacturer at a time. The more the more, the more the problem will be explained. Put them together and compare the detection output values. Under relatively stable conditions, observe the consistency of the test. For further testing, it can be recorded at intervals within 24 hours. Generally, there are three kinds of humidity and temperature conditions in a day, high, medium and low, so that the consistency and stability of the product can be observed more comprehensively, including temperature compensation characteristics.
2. Humidify the sensor by exhaling with your mouth or using other humidification methods, and observe its sensitivity, repeatability, performance of dehumidification and dehumidification, resolution, the highest range of the product, etc.
3. Test the product in both cases of opening and closing the box. Compare whether they are consistent and observe the thermal effect.
4. Test the product in high temperature state and low temperature state (according to the manual standard), and compare it with the record before the test under the normal state, check the temperature adaptability of the product, and observe the consistency of the product. The performance of the product must ultimately be based on the formal and complete testing methods of the quality inspection department. The saturated salt solution is used for calibration, and the product can also be used for comparison detection. The product should also be calibrated for a long time during long-term use in order to judge the quality of the humidity sensor more comprehensively.
