A high-gain amplifier that amplifies weak magnetic flux by 1000 times

If the AC magnetic field is coupled with the pickup coil, it will induce voltage, and the DC magnetic field will also induce voltage due to the change of the magnetic field. Using this principle, it is possible to detect whether there is a magnetic object passing through the DC magnetic field. If the metal piece passing through is very small, the electromotive force generated is also small. At this time, the solution can be adopted to increase the number of coil turns or increase the amplifier amplification factor. In this circuit , a low-noise OP amplifier with strong amplification capability is used, which can amplify more than 1000 times.

How the Circuit Works

OP37 is a broadband ultra-low noise OP amplifier. When the signal source resistance is small, good noise characteristics can be obtained. We set the amplifier's amplification factor to 1000 times. In order to reduce the power supply interference, a CR decoupling circuit is added to the power supply line. In the low frequency band, if the resistance of the feedback resistance is not reduced , it will be restricted by noise. Here we select R1=100 ohms and R2=10 kilo ohms. Since the working level of the OP amplifier is very high, the influence of noise does not need to be considered. The low frequency characteristics are determined by C3, R3, C4, and R5, so the parameters of these components can be selected according to the signal frequency.