Influence factors and countermeasures of thermocouple measuring error

Thermocouples are many causes of error, measuring precision, error reduction can prolong the service life of thermocouple. It puts forward higher requirements on technical personnel. Users should not only have the skills of operating instruments, but also to understand the chemical, physical and other professional knowledge. In temperature measurement, the technical personnel to ensure the accuracy of the thermocouple measurement, need to explore the influence factors and countermeasures of thermocouple measurement error. In temperature measurement, there are many reasons for the thermocouple have errors. Only to analyze the influence factors of temperature measurement, can be more targeted to take countermeasures to improve the measurement accuracy and measurement of thermocouple.

1, the analysis on the depth of insertion

it is very important to the choice of temperature measurement points. Thermocouple installation position is the location of the temperature measurement points, technical personnel's choice of temperature measuring point location carefully, because the location of the temperature measurement points should have representative, otherwise there would be no effect for its control.

if you need to be measured in the places to insert the thermocouple, heat will be produced along the direction of the sensor. If the environment temperature is reduced, can cause heat loss, resulting in the thermocouple temperature and the temperature object is different, so there will be a difference in temperature and the error of measurement.

insert depth can affect the heat transfer, thus cause measurement error. The material of insert depth and the protecting tube are closely related. Metal protection tube has good thermal conductivity, higher request on the depth of insertion. Ceramic material has good heat insulation performance, can be inserted into a shallow. Engineering measuring temperature, in a state and insertion depth are closely related. If measure high-speed airflow temperature, insert can be slightly lighter, through numerical experiments to determine the specific insertion depth.

2, analyze the thermal radiation

the measuring of temperature thermocouple electricity needs in inserted into the furnace. If higher temperature in the furnace, the object will produce thermal radiation so as to raise the temperature. If the transparent gas in furnace, and the furnace wall and electrothermal accidentally larger temperature difference, lead to the temperature measurement error. So, in order to reduce thermal radiation temperature, to ensure the furnace wall temperature and thermocouple temperature close to. In addition, the technical personnel to install thermocouple, scientific selection of thermocouple installation position, so that can reduce the temperature measurement error.

3, analyze the thermal impedance

if the temperature is higher, the use of state thermocouple under test is a gaseous medium. Protecting tube will melt on the surface of dust on it will increase the thermal impedance protection tube, if the melt is measured medium, in use with slag, thus make the use time of thermocouple increases, and form a relatively low temperature. Therefore, in order to reduce the error of measurement electric coupling, technicians of regular inspection and random sampling is required. For high temperature furnace smelting, not only the need of continuous temperature measuring thermocouple for installation, also need to install the thermocouple temperature measurement device, the measurement accuracy can be corrected.

4, analyze the response time

the contact method of temperature measurement is technical personnel commonly used method of temperature measurement. Its basic principle is the quantity of heat of temperature measuring element and the object being measured balance state, so need to continue for a period of time the process of temperature measurement, so that both could reach thermal equilibrium state. The duration of the affected by the temperature measuring element thermal response time. In addition, the conditions of measurement and sensor structure will decide on the thermal response time.

the static gas medium, need for half an hour will reach the equilibrium state. If the medium is liquid, the fastest also want to 5 minutes. If the temperature field is constantly changing, the response time of sensor has certain requirements, avoid common temperature sensor temperature change, lead to lag speed sensor. If you cannot reach thermal equilibrium, may produce error in the measurement process. It's requirements are put forward for the response speed of the sensor, need sensor speed is faster. Thermocouple to measure the diameter will affect the measured results. If the measuring end is smaller in diameter, the required response time is relatively less.

5, and analyze the thermocouple material inequality

when technicians test thermocouple, insert depth should be carried out in accordance with the standard requirement. If the thermocouple with the longer length, many accidentally silk's position is high. If you choose the quality of the thermocouple wire is uniform, can according to both epicuticular circuit to measure. Accidentally wire length will not affect the measured results. Thermocouple is not uniform, the quality of the temperature field belongs to the temperature gradient of temperature field, local produce thermoelectric emfs. Uneven material produced by the error is caused by a parasitic potential.

in metal verification rules, no regulations thermocouple inhomogeneous error problem. About the nonuniformity of thermocouple wire, thermocouple wire in the standard of the relevant requirements.

the place on put together is narrated, influenced by many factors, thermocouple measurement error is produced. The error based on the analysis of the influencing factors, to take effective countermeasures to improve the measurement precision of the electric coupling. This article mainly from & other; Insert depth, thermal radiation and thermal impedance, response time and uneven thermocouple material & throughout; Analyzing influence factors and countermeasures of thermocouple measurement error. Hope that through this paper study some help to the improvement of thermocouple measurements.