German SUNDO sensors, SUNDO models, SUNDO prices

SUNDO sensors are sensors that can sense temperature and convert it into usable output signals. Temperature sensors are the core component of temperature measuring instruments and come in a wide variety. According to the measurement method, they can be divided into two major categories: contact and non-contact. According to sensor materials and electronic component characteristics, they are divided into resistance thermometers and thermocouples.

SUNDO sensor classification

1) Contact type: The sensing part of contact temperature sensors has good contact with the object being measured, also known as thermometers. Thermometers reach thermal equilibrium through conduction or convection, allowing the thermometer reading to directly indicate the temperature of the object being measured. Generally, the measurement accuracy is high. Within a certain temperature measurement range, thermometers can also measure the internal temperature distribution of objects. However, significant measurement errors occur for moving bodies, small targets, or objects with very small heat capacity. Commonly used thermometers include bimetallic thermometers, glass liquid thermometers, pressure thermometers, resistance thermometers, thermistors, and thermocouples. They are widely used in industrial, agricultural, commercial, and other sectors. These thermometers are also commonly used in daily life. With the widespread application of cryogenic technology in national defense engineering, space technology, metallurgy, electronics, food, medicine, petrochemicals, and research into superconducting technology, cryogenic thermometers for measuring temperatures below 120K have been developed, such as low-temperature gas thermometers, vapor pressure thermometers, acoustic thermometers, paramagnetic salt thermometers, quantum thermometers, low-temperature resistance thermometers, and low-temperature thermocouples. Cryogenic thermometers require sensing elements that are small in volume, highly accurate, and have good reproducibility and stability. Carburized glass resistance thermometers, made by carburizing and sintering porous high-silica oxygen glass, are a type of sensing element for cryogenic thermometers and can be used to measure temperatures in the range of 1.6 to 300K. 2) Non-contact type: Its sensitive element does not contact the object being measured, also known as non-contact temperature measuring instruments. This type of instrument can be used to measure the surface temperature of moving objects, small targets, objects with small heat capacity, or objects with rapid (transient) temperature changes, and can also be used to measure the temperature distribution of temperature fields. The most commonly used non-contact temperature measuring instruments are based on the basic laws of blackbody radiation and are called radiation thermometers. Radiation temperature measurement methods include the brightness method (see optical pyrometer), radiation method (see radiation pyrometer), and colorimetric method (see colorimetric thermometer). Various radiation temperature measurement methods can only measure the corresponding luminance temperature, radiation temperature, or colorimetric temperature. Only the temperature measured for a blackbody (an object that absorbs all radiation and reflects no light) is the true temperature. If the true temperature of an object is to be determined, correction for the material's surface emissivity is necessary. Material surface emissivity depends not only on temperature and wavelength but also on surface condition, coating, and microstructure, making precise measurement difficult. In automated production, radiation temperature measurement is often used to measure or control the surface temperature of certain objects, such as steel strip rolling temperature, roll temperature, forging temperature, and the temperature of various molten metals in smelting furnaces or crucibles in metallurgy. In these specific cases, measuring the surface emissivity of objects is quite difficult. For automatic measurement and control of solid surface temperature, additional mirrors can be used to form a blackbody cavity with the measured surface. The influence of additional radiation can increase the effective radiation and effective emissivity of the measured surface. By using the effective emissivity to correct the measured temperature via the instrument, the true temperature of the measured surface can ultimately be obtained. The most typical additional mirror is a hemispherical mirror. Diffuse radiation energy from the measured surface near the center of the sphere is reflected back to the surface by the hemispherical mirror, forming additional radiation, thereby increasing the effective emissivity. In the formula, ε is the material surface emissivity, and ρ is the reflectivity of the mirror. For radiation measurement of the true temperature of gas and liquid media, a method of inserting a heat-resistant material tube to a certain depth to form a blackbody cavity can be used. The effective emissivity of the cylindrical cavity after reaching thermal equilibrium with the medium is calculated. In automatic measurement and control, this value can be used to correct the measured cavity bottom temperature (i.e., medium temperature) to obtain the true temperature of the medium.

SUNDO sensor usage precautions

1) Errors introduced by improper installation: For example, the installation position and insertion depth of the thermocouple cannot reflect the true temperature of the furnace chamber. In other words, the thermocouple should not be installed too close to the door or heating elements, and the insertion depth should be at least 8 to 10 times the diameter of the protection tube; if the gap between the thermocouple protection tube and the wall is not filled with insulating material, heat escape from the furnace or intrusion of cold air may occur. Therefore, the gap between the thermocouple protection tube and the furnace wall hole should be blocked with insulating materials such as refractory clay or asbestos rope to prevent convection of hot and cold air from affecting the accuracy of temperature measurement; if the cold junction of the thermocouple is too close to the furnace body, the temperature may exceed 100℃; thermocouple installation should avoid strong magnetic and electric fields as much as possible, so thermocouples and power cables should not be installed in the same conduit to avoid introducing interference and causing errors; thermocouples should not be installed in areas where the measured medium flows minimally. When using a thermocouple to measure the temperature of gas in a pipe, the thermocouple must be installed against the flow direction and have full contact with the gas. 2) Errors introduced by deteriorated insulation: If the thermocouple insulation deteriorates, excessive dirt or salt residue on the protection tube and pull plate can cause poor insulation between the thermocouple poles and the furnace wall, which is more severe at high temperatures. This not only causes loss of thermoelectric potential but also introduces interference, and the resulting error can sometimes reach hundreds of degrees. 3) Errors introduced by thermal inertia: Due to the thermal inertia of the thermocouple, the instrument's indication lags behind changes in the measured temperature, an effect that is particularly prominent during rapid measurements. Therefore, thermocouples with thinner thermoelectrodes and smaller protection tube diameters should be used as much as possible. When the measurement environment permits, the protection tube can even be removed. Due to measurement lag, the amplitude of temperature fluctuations detected by the thermocouple is smaller than the amplitude of furnace temperature fluctuations. The greater the measurement lag, the smaller the amplitude of thermocouple fluctuations, and the greater the difference from the actual furnace temperature. When using thermocouples with large time constants for temperature measurement or control, although the temperature displayed by the instrument fluctuates very little, the actual furnace temperature may fluctuate significantly. To measure temperature accurately, thermocouples with small time constants should be selected. The time constant is inversely proportional to the heat transfer coefficient and directly proportional to the diameter of the thermocouple hot junction, material density, and specific heat. To reduce the time constant, besides increasing the heat transfer coefficient, the most effective method is to minimize the size of the hot junction. In use, materials with good thermal conductivity, thin-walled tubes, and small inner diameter protection sleeves are typically used. In more precise temperature measurements, bare-wire thermocouples without protection sleeves are used, but thermocouples are prone to damage and should be calibrated and replaced in a timely manner. 4) Thermal resistance error: At high temperatures, if there is a layer of coal ash or dust attached to the protection tube, thermal resistance increases, hindering heat conduction. In this case, the temperature indication is lower than the true value of the measured temperature. Therefore, the exterior of the thermocouple protection tube should be kept clean to reduce errors.

SUNDO sensor industry applications

Temperature sensors are one of the earliest developed and most widely used types of sensors. The market share of temperature sensors greatly exceeds that of other sensors. People began using temperature for measurement from the early 17 century. Supported by semiconductor technology, semiconductor thermocouple sensors, PN junction temperature sensors, and integrated temperature sensors were successively developed in this century. Two conductors of different materials, if connected together at a point and heated at this junction, will exhibit a potential difference at their unheated parts. The value of this potential difference is related to the temperature of the measurement point at the unheated part and the material of these two conductors. This phenomenon can occur over a wide temperature range. If this potential difference is measured precisely and the ambient temperature of the unheated part is measured, the temperature of the heated point can be accurately determined. Because it requires two conductors of different materials, it is called a "thermocouple". Thermocouples made of different materials are used in different temperature ranges, and their sensitivities vary. Thermocouple sensors have their own advantages and disadvantages; their sensitivity is relatively low, they are easily affected by environmental interference signals, and they are also susceptible to the temperature drift of preamplifiers, making them unsuitable for measuring minute temperature changes. Since the sensitivity of thermocouple temperature sensors is unrelated to the thickness of the material.

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