1. The card reader sends the carrier signal through the antenna, and the carrier frequency is 125KHZ.

2. After the ID card enters the work area of the card reader, the resonant circuit composed of inductance and capacitance in the card receives the carrier signal sent by the card reader, and the RF interface module of the chip in the card generates power supply voltage, reset signal and system clock according to the signal, so that the chip is "activated".

3. The chip reading control module modulates the data in the memory onto the carrier wave after phase modulation coding, and sends it back to the card reader through the antenna in the card.

4. The card reader demodulates and decodes the received card echo signal and sends it to the background computer.

Possible reasons:

1. The second card has a problem. Try changing it to a regular card.

2. The line contact of the card reader is poor. Check whether the line connection is stable.

3. The aging of the sensor chip of the card reader will also happen. Consider replacing the card reader.

4. Other reasons.

Solution:

1, restart the computer.

2. Replace the card reader.

3. Replace the charger computer.