Sensor and automatic calibration method applied thereto

An automatic calibration method for correcting sensing distance of a sensor, comprising the following steps:

• (A1) setting a default trigger value, the default trigger value comprising environment factor noise;
• (A2) sampling a signal and accumulating a signal value to perform signal judgment from a plurality of positions;
• (A3) determining whether a trigger condition is met or not for every signal value from the plurality of position;
• (A4) if yes, recording an accumulated signal value meeting the trigger condition, and if not, going back to step (A2);
• and
• (A5) analyzing and updating the default trigger value by obtaining an average value and filtering out relatively far deviated distance signal values away from the average value for the plurality of positions, wherein the step (A5) further comprises the following steps:
• (A5-1) obtaining the average value of the signal recording sensing values meeting the trigger condition;
• (A5-2) deleting several data farthest away from the average value and obtaining a corresponding new average value from the remaining data repeatedly and continuously until a preset number data of different positions are left for calibrating an updated average value, wherein the remaining data for calculating the corresponding new average value and deleting several data farthest away from the corresponding new average value is gradually reduced in this process;
• and
• (A5-3) obtaining the updated average value of the preset number data of different positions for updating the default trigger value.