Metalworking Online prompts you that in the field of mechanical thermal processing, temperature testing and control techniques are critical to the quality of electromagnetic flowmeters. With the advancement of technology, the manufacturing level of domestic temperature measurement and control equipment has made significant progress, and some manufacturers have formed their own product features and advantages.
Temperature (T) is an important physical quantity. In modern industrial production processes, physical quantities such as temperature, pressure, flow, level and rotational speed must be strictly measured and controlled. The amount of temperature in each physical quantity is the largest, and it is estimated to account for more than 50% of the total amount, so temperature measurement is a major issue.
With the development of microelectronics and computer technology, instrumentation (secondary instrumentation) has been rapidly developed. For example, the precision of digital display instruments produced in China is one thousandth, the reliability is 60,000 hours, and the EMC indexes such as surge, radio frequency, static discharge and pulse group reach more than three levels, reaching the level of foreign equivalent products. In contrast, the development of sensors is relatively slow, and there are many problems that need to be studied and solved.
At present, the new temperature sensors mainly have the following types
(1) Fiber optic temperature sensor.
(2) Special temperature measurement thermal cable.
(3) Semiconductor integrated circuit temperature sensor.
(4) Quartz thermometer.
(5) Acoustic thermometer.
(6) Thermal noise thermometer.
(7) Nuclear four-stage resonance thermometer (NQR thermometer).
(8) Temperature and temperature sensing materials.
For the standard of the effective heating zone temperature measurement system of the heat treatment furnace, the components of the temperature measurement system can only be separately verified according to the current national standards. However, the error of the temperature measurement system for heat treatment using the discrete component method cannot meet most of the process requirements of the heat treatment industry. Therefore, if the thermocouple purchased by the factory is used without being verified, it will be highly dispersible, and the measured data is not reliable and cannot be used to guide production. In order to ensure product quality, an on-line online overall calibration temperature measurement system should be used.
One of the main reference standards for the determination of the effective heating zone of heat treatment furnaces in China is the high temperature measurement (AMS2750C) of the American Society of Automotive Engineers (SAE), which includes electromagnetic flowmeters, instruments, heat treatment equipment, system accuracy and temperature field. Uniformity test. Its characteristics are as follows:
(1) The sensor must be calibrated before use, and its magnitude can be traced back to the National Institute of Standards and Technology.
(2) The calibrated sensor must have a correction value or deviation and be corrected during use to obtain the actual temperature. For sensors for temperature field uniformity detection, the correction value should not exceed ±2 °C or 0.75% t. The sensor for system accuracy detection should not exceed ±1 °C or 0.4%t. The calibration period for inexpensive metal thermocouples for temperature field uniformity and system accuracy is 3 months, and the precious metal thermocouple calibration period is 6 months.
(3) Temperature field uniformity is a technical index that characterizes the temperature distribution state in the heat treatment furnace. It is related to the structure of the furnace body and the factors such as fire resistance and thermal insulation materials, and is also inseparable from the process parameters such as heating method. The requirement of this parameter only pays attention to the uniformity of the temperature field in the furnace. It is a relative concept and does not pursue the actual value of temperature.
(4) The accuracy or temperature measurement accuracy of the temperature measurement system is to characterize the deviation of the indication value of the temperature measurement system from the actual value or the true value. Therefore, the accuracy level of the sensor is required to be high, and it is combined with the thermocouple, the compensation wire and the instrument. The accuracy is related. Temperature control accuracy and temperature measurement accuracy are also different, which is to characterize the control of industrial furnace kiln temperature fluctuations.
For example, the temperature control accuracy of the vacuum heat treatment furnace is (900 ± 0.5) ° C, indicating that the furnace temperature can be controlled to fluctuate between 899.5 and 900.5 ° C. The United States has strict technical requirements for parts heat treatment furnaces and raw material heat treatment furnaces. Practice has proved that the electromagnetic flowmeter can only meet the requirements of the heat treatment industry for the process temperature if it has strict requirements on temperature measurement accuracy.
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