Thermocouple verification items and verification methods

1. Appearance inspection 2. The point of indicating value verification is determined by the wire material and electrode diameter. For example, for a K-type thermocouple with an electrode diameter of 0.5mm/0.8mm/1.0mm, the verification point temperature is 400℃/600℃/800℃. (2) Verification steps 1. The point below 300°C is compared with the second-class standard mercury thermometer in the oil tank. 2. The point above 300°C is carried out in a tube furnace. 2.1 The standard 1, visual inspection 2, indicating value verification points are determined according to the wire material and electrode diameter. For example, for a K-type thermocouple with an electrode diameter of 0.5mm/0.8mm/1.0mm, the verification point temperature is 400℃/600℃/800℃. (2) Verification steps 1. The points below 300°C are compared with second-class standard mercury thermometers in the oil tank. The points above 300°C are carried out in a tube furnace. 2.1 Bundle the standard couple and the tested couple with fine nickel-chromium wire into a round bundle, the diameter of which is not greater than 20 mm, and evenly distribute the measuring end of the tested couple around the measuring end of the standard couple for a week, and be in the same vertical standard thermocouple On the cross-section (that is, on the same isothermal surface). The measuring end should be in the center of the furnace's highest temperature zone. The furnace mouths at both ends of the tube furnace are blocked with insulating refractory materials. In order to prevent the standard couple from being polluted and to ensure its stability, it needs to be protected by a quartz tube or porcelain tube. 2.2 Verification sequence, heating verification point by point from low temperature to high temperature, the deviation of the furnace temperature from the verification point temperature should not exceed ±5℃. 2.3 When the furnace temperature rises to the verification point, when the furnace temperature change is less than 0.2℃/min, starting from the standard couple, measure the thermoelectromotive force of each tested couple in turn. Sequential measurement: Standard—Inspected 1—Inspected 2—Inspected n------Inspected n—Inspected 2—Inspected 1—The standard reading should be rapid, and the measurement reading should not be less than 4 times , The temperature change of the tube furnace is not more than ±0.25℃ during measurement. (3) The verification method is divided into bipolar method (standard and tested couple models can be different), pole method with the same name and differential method (same model) according to the different connection methods of standard couple and tested couple. (4) Calculation method 1. The error of thermoelectromotive force below 300℃ Δetu003d be + Sbe•Δt check-e points: the arithmetic mean of the thermoelectromotive force measured by the tested couple; Sbe: the differential of the tested couple at the verification point Thermoelectromotive force; e points: the thermoelectromotive force value of the verification point checked on the graduation table of the inspected couple; Δt test u003d t test-t real Δt test: the difference between the verification point and the actual temperature. t test: temperature at the verification point; t actual: actual temperature (actual temperature u003d average value of reading + correction value) 2. Thermal electromotive force error above 300 ℃ Δe be u003d measured + (e standard-standard) S be / S standard-e Score: the arithmetic mean of the thermoelectromotive force measured by the tested couple; mark: the arithmetic mean of the thermoelectromotive force measured by the standard couple; e mark: the thermoelectromotive force value given on the certificate of the standard couple; e score: the graduation of the inspected couple The thermoelectromotive force value of the verification point checked on the table; S mark, S is: standard, the differential thermoelectromotive force of the inspected couple at the verification point. 4. Verification result processing and cycle 1. A verification certificate is issued for a thermocouple that is qualified; a verification result notification is issued for a thermocouple that is unqualified. 2. The verification period is generally half a year, and it can be determined according to the conditions of use under special circumstances.