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The gas chromatograph constant voltage circuit uses a regulated power supply to power the TCD bridge to ensure that the voltage across the bridges C and D is constant. Early gas chromatographs used this type of power supply. The constant voltage circuit uses a series voltage regulator circuit. Since the bridge current of the TCD is not allowed to exceed 400 mL, a three-terminal regulator that is relatively simple and convenient can be used as the constant voltage power supply. When the hot wire is selected, the regulator can be continuously adjusted.
When the gas chromatograph is adjusted with a potentiometer, the potentiometer is prone to poor contact, resulting in unstable output, which can directly manifest as baseline instability at the output of the TCD. Therefore, in actual use, the gas chromatograph often uses a digital potentiometer or a D/A converter as an adjustment terminal, which can realize a regulated output by the keyboard.