surface thermal resistance

WZCM, WZPM surface thermal resistance is made of special material and can contact thermometer closely. Compared with the general axial thermal resistance, it can measure temperature more accurate and rapid. It is applicable to measure bearing temperature, or other parts of the face.

Surface temperature sensors are components for measuring surface temperatures in the aerospace, aerospace, energy, chemical, textile and other fields of scientific research and production. The surface temperature sensor is a special surface thermometer. Generally, the dedicated surface temperature sensor is a sheet-like shape with extremely thin thickness. It is divided into surface thermal resistance and surface thermocouple induction sensor according to the requirement of measuring temperature.

There are a lot of surface temperature test problems in aviation, aerospace, energy, chemical, textile and other research and production. But the environmental condition, the temperature sensor and the measured surface interact with each other to form a complex system. Various factors directly or indirectly affect the accuracy of the surface temperature. Therefore, surface temperature measurement is a frequently needed but difficult to measure.

If the use of the usual shape of the temperature sensor (such as needle-like, spherical, cylindrical, etc.), will be due to the shape of the sensor heat conduction interference caused by the original temperature field measurement error.

Therefore, for the surface temperature of the precise measurement should use a dedicated surface thermometer. In other words, a thermometer with a dedicated surface temperature sensor should be used to accurately measure the surface temperature.

In general, a dedicated surface temperature sensor is a sheet-like profile having an extremely thin thickness.

Choose a method

In order to accurately measure the surface temperature, it is recommended to use a special surface temperature sensor.

By looking at the various sensor types and technical specifications, it is clear that the most significant difference between the surface thermal resistance and the surface thermocouple sensor sensor. In some applications (such as those involving temporary non-critical measurements at moderate temperatures), both types are sufficient, and only the price is the determining factor. In general, thermocouples have a wider operating temperature range and faster response speed, and the price is slightly lower.

The surface thermocouple is much structurally strong and is not affected by the strain caused by the installation material or method. They have the inherent characteristics of simple design, so that the cost is low. All thermocouple surface sensors have the ability to work at a much higher temperature than the surface thermal resistance sensor and to respond more quickly. However, the thermocouple sensor generates a low voltage signal that may require additional amplification, which is a disadvantage in an environment where electrical noise is high.

Unlike surface thermocouple sensors, surface thermal resistance sensors do not require reference points, ice baths, or temperature compensation circuits. These sensors have very low thermal mass, thus providing true surface temperature measurements as well as response times up to 50 ms. Platinum sensor is recognized as a precision temperature measurement sensor, it can be -190 ℃ ~ 660 ℃ temperature range to define the international temperature scale (ITS-90). The main reason for choosing platinum thermometer as the primary criterion is that its resistance temperature parameter has excellent stability and repeatability. Surface thermal resistance of the signal output size is 50 to 200 times the output of the thermocouple. This means that temperature measurements can often be done using standard instruments.

Precautions

It is common practice to immerse the sensor contained in the protective tube in the controlled fluid or in a known environment, and the surface temperature measurement requires that the sensor be placed outside the container where the environmental conditions may have an effect on the measurement results. In addition, the surface profile, the surface of the thermal performance and the sensor and the measurement object between the conductive path and other factors will also affect the integrity of the output signal. At the same time, the sensor selection and installation technology will also affect the performance of the measurement system. Surface temperature measurement is widely used and is useful for assessing conditions that can not be touched. The types of sensors used and the installation techniques are also varied. Selection should be based on factors such as range, accuracy, reliability and sensitivity of the material in contact with the measuring element, as well as the thickness and flexibility of the sensor and the heat exchange with the measurement object and the surrounding environment.

When using a surface sensor, note the following two most important rules

1) When installing a surface sensor, the highest thermal contact and the minimum mechanical stress are obtained. The RdF sensor is easy to install correctly.

2) The surface sensor must be insulated or isolated so that its temperature is as close as possible to the surface temperature. This is controlled by the user.

In order to illustrate these problems, Figure 1 shows a typical surface temperature sensor. The sensor in this example is mounted on the pipe that conveys the fluid. The closest point of the sensor that can be installed with the fluid is the outer wall of the pipe. If the fluid flow is sufficient and the temperature fluctuation is not severe, the outer wall temperature will be very close to the temperature of the fluid.

The sensor can only measure its own temperature and must try to make the surface temperature equal to the sensor temperature. This can be achieved by arranging an insulating layer on the sensor to reduce the environmental impact and by selecting a mounting method that provides good thermal contact between the surface and the sensor.

The chosen sensor mounting method is important because a large thermal mismatch of the thermal expansion coefficient may cause strain in the wire-type resistance temperature sensor, although good thermal contact is required. This strain will produce a change in resistance that may be misinterpreted as a change in temperature. When installing resistors and thermocouple sensors, the lead should be in contact with the sensing surface for a length so as to reduce the heat transfer effect of the sensing wires or junctions.

installation method

The first step in installing the surface sensor of Shanghai Automation Instrumentation Co., Ltd. is to determine the installation method. Some rigid surface temperature sensors provide mechanical mounting, but in most cases, a binder is required. When choosing an adhesive, consider the following:

1. Is the expected operating temperature range suitable for the adhesive considered?

2. Is the thermal expansion coefficient of the sensor, surface and adhesive similar?

3. Is the coating of the adhesive compatible with the installation method? For example, if the adhesive needs to be cured at a higher temperature, this would be a problem in the case of long-range installation.

4. Is the adhesive installed for permanent or temporary installation?

There are several types of adhesives used to install the sensor:

1) epoxy resin adhesive

Such adhesives may be provided in a variety of forms, including liquids, pastes, films and powders, and when two-component adhesives are commonly used, the two components must be mixed before use. The curing time is from 5 minutes at room temperature up to several hours at higher temperatures. Most epoxy adhesives are added to the matrix resin so that they are suitable for filling the gap or coating on the sensor.

2) cyanoacrylate adhesive

These adhesives are ultra fast curable adhesives. They are cured at room temperature in 10 to 60 seconds. Their use is limited by temperature and humidity. Since most cyanoacrylate-based adhesives do not contain fillers or have the ability to fill voids, the adhesive must be in close contact with each other.

3) Silicone rubber adhesive

The advantage of silicone rubber adhesives is rubber elasticity, providing a resilient low stress bond between the sensor and the surface. They are available as a one-component or two-component paste, even in the form of double-sided tape, which can be instantly attached to the sensor and the surface. They have a very wide use temperature range. The paste-like silicone rubber adhesive requires a longer curing time, and if it is not cured at the desired temperature, the binder may be reversed.

4) Polyimide adhesive

There are several series of polymer adhesives that provide excellent adhesion and high temperature stability. However, they must be cured at carefully controlled temperatures and pressures. This makes the installation very difficult on site.

5) ceramic adhesive

The advantage of ceramic adhesives or binders is that they have a very high use temperature. They can be used in the form of paste, which added metal oxide filler, with an acid as a sticky material. They usually require a higher temperature to cure. After curing, the ceramic binder is generally hard, fragile and hygroscopic.

6) Solvent release type adhesive

Some of the more common and less expensive adhesives need to release the solvent from the resin material to form an adhesive layer. It should be noted that if the sensor is not permeable to the solvent, the adhesive will not cure properly. Care should be taken when selecting these adhesives. After selecting the adhesive, you must develop a step that can be used to consistently mount the sensor.