Vilka är orsakerna till dålig kontakt mellan den heta änden av termoelementet och objektet som mäts?

De främsta orsakerna till den dåliga kontakten mellan den heta änden av termoelementet och objektet som mäts är installationsmetod, yttillstånd, mekaniska faktorer och miljöfaktorer . Följande är en detaljerad introduktion:
Installationsmetodproblem
Insufficient insertion depth: If the thermocouple is not inserted deep enough into the object being measured, the hot end cannot be fully immersed in the measured medium, which will result in a small contact area and insufficient heat transfer. For example, when measuring the temperature of the fluid in the pipeline, if the thermocouple is inserted too shallowly, it can only contact the fluid near the inner wall of the pipeline, and cannot accurately Mät vätsketemperaturen i mitten av rörledningen .
Improper installation position: The thermocouple is installed at the edge or corner of the object being measured. These positions may not represent the overall temperature of the object being measured and are easily affected by the external environment. For example, in a heating furnace, if the thermocouple is installed near the furnace door, the temperature near the furnace door is low due to the fast heat dissipation.
Inappropriate installation angle: The angle between the thermocouple and the surface of the object being measured is unreasonable, which will reduce the contact area between the hot end and the object being measured and affect the heat transfer efficiency. For example, when measuring the temperature of a flat object, if the inclination angle between the thermocouple and the surface of the object is too large, only part of the hot end will be in contact with the object, which will cause Mätfel .
Ytvillkor för objektet som mäts
Ojämn yta: Om det finns ojämnhet, burrs eller oxidskala på ytan på föremålet som mäts, kan den heta änden av termoelementet inte passa tätt med ytan på objektet, och det kommer att finnas luftgap .} den dåliga termiska konduktiviteten för en hinder värmeöverföring och leda till otillbörlig mätvärden {{}}} för att mäta en mätning av en mätning av en metallgjutning, en metallhall. Gjutningen kommer att orsaka ett luftskikt mellan den heta änden av termoelementet och gjutningen, som påverkar temperaturmätningsnoggrannheten .
There are dirt or impurities on the surface: Dirt or impurities such as oil, dust, and scale on the surface of the object being measured will form an insulating layer between the hot end of the thermocouple and the object, reducing the efficiency of heat transfer. For example, when measuring the temperature of the outer wall of the heat exchanger pipe, if there is thick scale on the surface of the pipe, the heat transfer between the hot end of the Termoelement och röret kommer att hindras, vilket resulterar i en låg uppmätt temperatur .
Mekaniska faktorer
Unsecured fixation: After the thermocouple is installed, it is not reliably fixed. Under the action of vibration, impact or thermal expansion of the object to be measured, the contact between the hot end and the object to be measured will become loose or displaced. For example, if the thermocouple is installed on a rotating device or a vibrating machine, if it is not fixed tightly, the hot end of the Termoelementet kommer gradvis att avvika från sin ursprungliga position när utrustningen körs, vilket resulterar i dålig kontakt .
Thermal stress effect: In a high temperature environment, the thermal expansion coefficients of the thermocouple and the object to be measured are different, which will produce thermal stress. If the thermal stress is too large, it may cause a slight displacement or deformation between the hot end of the thermocouple and the object to be measured, affecting the contact effect. For example, in a ceramic kiln, the difference in Termisk expansion mellan keramiska produkter och termoelement kan leda till att den heta slutet på termoelementet har dålig kontakt med keramiska produkter efter långvarig användning .
Självproblem
Deformation of the protective sleeve: The protective sleeve of the thermocouple is deformed by external force during transportation, installation or use, resulting in the hot end being unable to have good contact with the object to be measured. For example, after the protective sleeve is squeezed or collided, it may be bent or dented, causing the hot end to deviate from the correct measurement position .
Varmskador: Den heta änden av termoelementet kan skadas på grund av långvarig exponering för hög temperatur eller kemisk korrosion, mekaniskt slitage, etc. ., såsom den heta ändens lödfogar faller av, elektroden brytning, etc. ., resulterar i dålig kontakt med objektet som mäts . till exempel, i en högkammare, den elektriska miljö Termoelementets varm ände är lätt korroderat, vilket ökar kontaktmotståndet och påverkar mätnoggrannheten .
Miljöfaktorer
High temperature oxidation: In a high temperature environment, the surface of the object being measured and the hot end of the thermocouple are prone to oxidation reactions to form an oxide layer. The oxide layer has poor thermal conductivity, which will hinder heat transfer and cause poor contact. For example, in a heat treatment furnace, metal workpieces and the hot end of the thermocouple will oxidize at high Temperaturer, som påverkar noggrannheten för temperaturmätning .
Chemical corrosion: If there are corrosive gases, liquids, etc. in the object being measured or the surrounding environment, it will corrode the hot end of the thermocouple, destroy the contact surface between the hot end and the object being measured, and increase the contact resistance. For example, in an electroplating bath, the acidic electrolyte can corrode the thermocouple hot junction, causing increased Mätfel .