Classification of ifm temperature sensors

According to the measurement method, it can be divided into two categories: touch type and non-touch type.

1. Touch type

The detection part of the touch temperature sensor has an outstanding touch with the measured target, also known as a thermometer.

The thermometer reaches thermal equilibrium by conduction or convection, so that the thermometer's indication directly represents the temperature of the measured target.

Generally, the measurement accuracy is high. Within a certain scale of temperature measurement, the thermometer can also measure the temperature distribution inside the object. However, for moving bodies, small targets or targets with small heat capacity, large measurement errors will be generated, and commonly used thermometers include bimetal thermometers, glass liquid thermometers, pressure thermometers, resistance thermometers, thermistors and thermocouples. They are widely used in the industrial, agricultural, commercial and other sectors. These thermometers are also often used in everyday life.

2. Non-touch

Its sensitive element does not touch the measured target, also known as non-touch temperature measurement appearance. This appearance can be used to measure the surface temperature of moving objects, small targets, and targets with small heat capacity or agile (transient) temperature changes, as well as the temperature distribution of the temperature field.

The commonly used non-touch temperature measurement surface is based on the basic law of blackbody radiation, which is called the radiation temperature measurement surface. All kinds of radiation temperature measurement methods can only measure the corresponding photometric temperature, radiation temperature or colorimetric temperature. As long as the temperature measured on a black body (an object that absorbs all radiation and does not reflect light) is the true temperature. If the true temperature of an object is to be determined, it is necessary to correct the apparent emissivity of the data. The surface emissivity of the data not only depends on the temperature and wavelength, but also depends on the surface condition, coating film and microscopic arrangement, so it is difficult to measure.

The advantage of non-touch temperature sensors is that the upper limit of measurement is not limited by the temperature resistance of the temperature sensing element, so there is no limit to the highest measurable temperature in principle.

Classification of ifm temperature sensors

Classification of ifm temperature sensors

According to the sensor data and the characteristics of electronic components, it is divided into two categories: thermal resistance and thermocouple.

1. Thermal resistance

Thermistors are made of semiconductor materials, and most of them have a negative temperature coefficient, that is, the resistance decreases with the addition of temperature.

Temperature changes can create large resistance changes, so it is the most sensitive temperature sensor. However, the linearity of thermistors is extremely poor and has a lot to do with the production process.

Thermistors also have their own measurement techniques. The advantage of the thermistor is its small size, it stabilizes quickly and does not form a thermal load. However, it is also very unrobust, and high currents will form self-heating. Since a thermistor is a resistive device, any current source will generate heat on it due to power. The power is equal to the product of the square of the current and the resistance. Therefore, it is necessary to use a small current source. If a thermistor is exposed to high heat, it will cause permanent damage.

2. Thermocouples

Thermocouples are the most commonly used temperature sensors in temperature measurement. Its main advantages are a wide temperature scale and a variety of atmospheric environments, and it is robust, inexpensive, does not require power supply, and is also the most cheap. Thermocouples are simple and versatile temperature sensors, but thermocouples are not suitable for high-precision measurement and use.

According to the form of the output signal of the temperature sensor, it can be roughly divided into three categories: digital temperature sensor, logic output temperature sensor, and analog temperature sensor.

1. Digital temperature sensor

It uses a digital temperature sensor produced by silicon process, and its PTAT structure is selected, which has the best temperature-dependent outstanding output characteristics.

2. Logic output temperature sensor

In many uses, we do not need to measure the temperature value strictly, only care about whether the temperature exceeds a set scale, once the temperature exceeds the specified scale, then send an alarm signal, start or turn off the fan, air conditioner, heater or other control equipment, at this moment you can choose the logic output temperature sensor

3. Analog temperature sensor

Analog temperature sensors, such as thermocouples, thermistors, and RTDS, monitor the temperature with poor linearity in some temperature scales and require cold-junction compensation or lead compensation; The thermal inertia is large and the response time is slow. Compared with the integrated analog temperature sensor, it has the advantages of high sensitivity, good linearity, and fast response speed, and it also integrates the drive circuit, signal processing circuit, and necessary logic control circuit on a single chip, which has the advantages of small practical size and easy operation. Common analog temperature sensors are LM3911, LM335, LM45, AD22103 voltage output type, and AD590 current output type.

Classification of ifm temperature sensors

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