Temperature Measurement Using a Thermocouple

2 types of thermocouple are used in Fintech. Usually (not just Fintech) these 2 types are selected when a high temperature range of around 2012ºF (1000ºC) is required to be measured. Refer to the other site for information on the principle of thermocouples. The thermocouple used in Fintech products will be described from a practical perspective in this page.

K Thermocouple This is an inexpensive thermocouple and can be used to measure up to 2192ºF (1200ºC), but gets used up at high temperatures. The ones with a larger diameter can withstand high temperatures, in case of dia 1 we usually use up to a temperature of 1382ºF (750ºC). Therefore, if the K thermocouple which is embedded in the hot air heaters is used near its limit, the thermocouple may burn-out before the heating element. For such cases, we use the more expensive “R thermocouple”.

R thermocouple This thermocouple can measure up to 2912ºF (1600ºC), but will get consumed in the same way as K type and the temperature is limited to 2552ºF (1400ºC). However, this sufficient for temperature measurement of Fintech heaters. Material of the minus is pure platinum and plus is platinum alloy with 13% rhodium.

The thermocouple unit used in Fintech products has been removed and showed below.

In this way, temperature can be measured for example in case of K thermocouple just by connecting to the thermometer of the K thermocouple. There are many types of thermometers, perhaps the testers with thermometers shown below are the most convenient and inexpensive. For example, this can be purchased for 1,400 yen at Akizuki electronic commerce. (The terminal in the photo below is after installation)

If there is no thermometer, if the voltage generated in the millivolt meter is measured, temperature can be read from the number. However in this case, the value read from the thermoelectric power indicates the temperature difference between the measuring point and the millivolt meter terminal. Therefore, in this case temperature (usually room temperature) of the measuring instrument terminal needs to be added to the temperature read.

Temperature of the temperature measuring point = (temperature was calculated from the thermoelectric power) + (room temperature)

The above photograph shows a thermocouple used in Fintech products connected to the tester with thermometer. This can be used for temperature measurement.	Temperature measuring portion of the tip. Welding with argon arc. This portion has to be welded.
	Welds of the bigger diameter thermocouple wire and smaller diameter wire. This portion required proper reinforcement.

In the left photograph R thermocouple has been incorporated in the heater with platinum heating element. Therefore the size is dia 0.3.

The following are the graphs showing the thermoelectric power and temperature relationship of the K and R thermocouples. The temperature can be read in the graph conveniently. To determine more accurately, refer to the table below.

Characteristics Table of K thermocouple

Characteristics Table of K thermocouple