The method of annealing thermocouples

Before thermocouple calibration, annealing is required to eliminate external stress on the thermocouple and make its metallographic structure more regular. There are two methods of annealing, namely electrical annealing and furnace annealing. Let's take a detailed look above:

1. Electrical annealing

Electric annealing is the process of hanging a thermoelectric electrode on a bracket using borax scrubbing method, slowly adjusting the current to keep the electrode at a certain temperature for a certain amount of time, and then slowly reducing the input current to zero. The temperature and time for annealing various thermocouples are specified.

The advantages of electric annealing are simple equipment, convenient operation, even heating along the hot electrode, and easy loss of sufficient volatilization of nominal impurities. The problem is that the radial temperature of the thermoelectric electrode is affected by the surrounding atmosphere, and the nominal metal is prone to volatilization, causing a change in identity. However, it is still satisfactory for industrial thermocouples.

2. Furnace annealing

Annealing in the furnace is the process of threading a thermoelectric electrode through an insulating tube, placing it in the average temperature field of a common annealing furnace, holding it for a certain amount of time at a designated temperature, and then cooling it with the furnace. Its advantage is that the thermoelectric electrode is evenly heated radially, which can eliminate the stress caused by pipe penetration.

The problem is uneven heating along the longitudinal direction of the hot electrode. Both annealing methods have their own advantages and disadvantages. If adopted in sequence, excellent consequences can be achieved. Scale thermocouples (what is a scale thermocouple?) are annealed using two methods. Industrial low-cost metal thermocouples can be annealed in a calibration furnace. The annealing temperature and time of various thermocouples in the furnace are specified.