At the beginning of polysilicon production, the semiconductor silicon core is instantly broken down by high voltage in the reduction furnace, and the current through the silicon core makes the silicon core reach a process temperature of 1080°C. In the process of growing the silicon core from φ7mm to φ180mm, the process temperature needs constant. However, as the diameter of the silicon rod continues to increase, its corresponding impedance will continue to decrease, thereby reducing the heat resistance of the silicon rod. In order to keep the temperature of the silicon rod at 1080°C unchanged, the operating current can only be increased accordingly (the current is from 30A at the beginning to 2800A at the end). Large current changes within the dynamic range place high demands on production equipment and operators. In addition, the melting point of silicon rods is around 1420°C, so it is very important to accurately measure the temperature of polysilicon.

Difficulty in measuring:

1. The diameter of the silicon core is only φ7mm at the beginning of production, and the target size is too small.

2. When the monochromatic infrared pyrometer measures the temperature of the silicon rod, the equipment needs to be installed outside the reduction furnace and aim at the target in the furnace through the sealing window. The effect of window contamination on light transmittance results in errors in actual measurements.

3. Double-glazed windows have a great influence on the attenuation of infrared signals.

The advantages of using a two-color pyrometer:

1. Using the principle of two-color pyrometer, the actual temperature of the target is directly measured, which is not affected by the emissivity of the material, and does not need to compensate for the emissivity.

2. Aim directly at the target.

3. Not sensitive to slight window contamination.

4. It no longer relies on infrared energy and is not sensitive to signal attenuation.