The clamp-on ammeter is referred to as the clamp-on meter. Its working part is mainly composed of an electromagnetic current meter and through the heart of the current transformer. Through the heart of the current transformer core made of active openings, and into the clamp, so the name of the clamp-on current meter. It is a portable instrument that can directly measure the AC current of the circuit without disconnecting the circuit, which is very convenient to use in electrical maintenance, and is quite widely used.Clamp meter is a current transformer and ammeter in one instrument, is an important branch of the digital multimeter, its working principle and current transformer current measurement is the same. Clamp meter is a combination of current transformer and ammeter. The core of the current transformer can be opened when the wrench is pinched; the wire through which the current is measured can be passed through the open gap of the core without cutting it off, and the core is closed when the wrench is released. Through the core of the measured circuit wire becomes the primary coil of the current transformer, which passes through the current will be induced in the secondary coil current. So that the secondary coil connected to the ammeter will have instructions ----- to measure the current of the line under test.Clamp meter is initially used to measure the AC current, but now the multimeter has the function it also has, can measure AC and DC voltage, current, capacitance capacity, diode, transistor, resistance, temperature, frequency, etc. Product Model:MT87Function ------ Range -------- AccuracyDC voltage600V 1.0%AC voltage450V 1.2%AC current20-400A 2.0%Resistance200K 1.0%Special Features3 1/2 LCD display, maximum reading 1999Low battery power indication functionOverload protectionData hold more convenient readingBuzzer on/off and diode test functionProduct FeaturesBattery: 2 No. 7 batteries (AAA) (not with battery included)Jaw diameter: 21.3mmBody color: yellow Body weight: about 200g Body size: 150 60 28mm Standard accessories: test meter pen, manual, warranty card