An ammeter is an instrument used to measure the current in AC and DC circuits. In the circuit diagram, the symbol of the ammeter is "Circle A". The standard unit of current value is "A" or "A". When the measured current in the circuit exceeds the range of the instrument, an external shunt or voltage divider can be used, but it should be noted that its accuracy level should match the accuracy level of the instrument. In addition, it should be noted that the operating environment of the instrument should meet requirements and be kept away from external magnetic fields.