Existing time grating is based on the principle of variable coupling coefficient transformer that adopt the method of winding coil around the detecting probe to extract signal of magnetic coupling coefficient variation between detecting probe and gear. But experiment shows that the extracted electrical signal extracted by this method is relative weak

meanwhile

the detection distance is extremely small. To solve the above problems

a new method of signal extraction based on tunnel magneto resistance（ TMR） is presented. TMR is a kind of magnetoresistance effect

which has a very high sensitivity for weak magnetic field

variation good effect are achieved by this method in experiment and detection distance as well as signal amplitude are improved.