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I installed the thermometer to measure the temperature of the exothermic part.
 Thermometer
I used the type which has the range of the measurement of 300°C from -50°C as the thermometer.
The temperature sensor is doing the figure of stick with the 3-mm diameter. The sensor is installed in the about 10-mm position from the tip. The length is 120 mm.
The body of the thermometer displays the measurement temperature with the LCD(Liquid Crystal Display). There is a switch of the display in the back of the body and it can switch the display of °C and °F. The size has the 52-mm width, the 28-mm height, the 14-mm depth.
As the power supply, the button cell(LR-44 or AG13) is used and it works for about 1 year. I changed the power supply part for the AC power supply.
Change of the power supply part
The thermometer itself is small and the reorganization is difficult. I attached the pole of the outside power supply instead of the button cell.
 Button cell adapter
I made the pole with the size which is the same as the button cell. The body is wooden. I shaved the wooden board with the knife and made it the size which is the same as the button cell. I used the copper foil tape as the pole. The circumference is the positive pole and the bottom is the negative pole. I connected the wire with each pole and let out it from the hole at the side of the cell box. The exactly good hole was open. So, I could use the body of the thermometer without changing it.
Transformer
I used the small transformer to make the line voltage with AC100 V. The electric current flows through the thermometer hardly. In the result which I measured, it is about 150 µA. Because it is, the output current is OK with the tens-of-mA transformer. As for the transformer which I used this time, the secondary side nominal voltage is 3 V and 6 V and the permissible current is 150 mA. It was to 4.3 V be when measuring the voltage of the 3-V terminal in case of the no-load.
Stabilised power supply
I made the output voltage be stable using the light-emitting diode (LED). When the LED lights up, the forward voltage becomes about 1.5-2 V. This time, I am making the stable voltage of 1.5 V using the characteristic of this LED. This way can use the electric current of the output when small.
Installation of the temperature sensor
The sensor of the thermometer is doing the figure of stick. The sensor part is installed in the about 1-cm place from the tip.
I made the contact part with the exothermic part and the part of the support using the aluminum board with the 0.5-mm thickness.
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