Special thermocouple temperature probe for rapid hydrogen measurement of aluminum melt

1、 The necessity of using a dedicated thermocouple to measure temperature for hydrogen meters in aluminum liquid

In the process of measuring hydrogen, due to the significant increase with temperature, it is necessary to measure the gas content in the melt at the same time as measuring the temperature in the melt. Due to the requirement of simultaneous temperature measurement for hydrogen, the instrument should have temperature measurement function. Considering that the temperature of aluminum alloy solution is around 700 ℃, ELH-IV aluminum melt rapid hydrogen measuring instrument dedicated thermocouple (dedicated temperature probe) is used for temperature measurement, and it should have cold end automatic compensation function. The instrument should be able to display temperature values. When using this type of hydrogen analyzer to measure hydrogen, an external thermocouple is used to measure the temperature. The measured temperature and the combined number are input into a small programmable calculator to obtain the hydrogen content reading.

IISpecial thermocouple temperature probe for rapid hydrogen measurement of aluminum meltTechnical Specifications

1. Temperature range for aluminum liquid testing: 650-800 ℃

2. Measurement error ≤ ± 0.5%

3、 Principle of ELH-IV rapid hydrogen analyzer for aluminum melt

In the pipeline of the ELH-IV aluminum melt rapid hydrogen analyzer, it circulates without loss along a closed circuit. When bubbles of inert gas pass through the melt, hydrogen in the metal diffuses into the bubbles. When the bubbles and hydrogen in the melt reach equilibrium, the cycle stops and a thermal conductivity detector is used to measure the circulating gas. Hydrogen meters produced based on the same principle are used in many countries. It can directly detect and record hydrogen content online, long-term, and continuously. The measurement of hydrogen partial pressure in aluminum melt adopts thermal conductivity measurement method. The thermal conductivity cell, alumina ceramic probe, ELH-IV aluminum melt rapid hydrogen measuring instrument special thermocouple (special temperature probe), aluminum liquid, and pipeline form a circulating gas path. The electric pump promotes the closed circulation of inert gas in the circulating gas path, allowing hydrogen in the aluminum melt to diffuse into the circulating inert gas, changing the thermal conductivity of the gas and causing the heating resistance in the thermal conductivity cell to change, thereby causing the measurement bridge where the thermal resistance is located to output an unbalanced potential. The unbalanced potential is amplified and converted by an amplifier composed of a chopper stabilized zero integrated operational amplifier 7650 for A/D conversion into a digital signal.

4、 Temperature measurement of hydrogen analyzer

Due to the fact that the temperature of aluminum alloy melt is around 700 ℃, the upper limit of temperature is not high, and the temperature measurement range is usually between 650 ℃ and 750 ℃, which is relatively narrow, it is better to use ELH-IV aluminum melt rapid hydrogen analyzer dedicated thermocouple (dedicated temperature probe) for temperature measurement. In order to convert the thermoelectric potential signal for ease of A/D converter conversion, and considering the compensation of thermocouple cold junction potential, an amplifier consisting of a chopper stabilized zero integrated operational amplifier 7650 is used to complete cold junction compensation and signal conversion amplification. Cold junction compensation utilizes the temperature characteristics (-3mv/℃) of the PN junction between the electrodes of a transistor.

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