Types of Current Clamps
The first decision you need to make is what type of current clamp to use.
The simplest current clamp is a current transformer. This current clamp does not contain active components and its function is based on the same principle as a power transformer. The current clamp (or transformer core) is placed around a conductor carrying alternating current, and the changing magnetic field established by the current passing through the conductor is coupled to the core of the current clamp.
In this special transformer application, the conductor acts as the primary winding. The secondary winding around the iron core of the current clamp will detect the current and transmit it to the current input socket of the digital multimeter, but the input current is much lower.
The current ratio of most current clamps is 1000:1. In other words, a current of 1A through the measured circuit conductor will generate a current of 1mA in the secondary winding of the current clamp. The current ratio of 1000:1 makes it very easy for a digital multimeter to obtain readings.
Although the range is set to mA level, when you read the reading displayed on the digital multimeter, you can think of the magnitude of the ampere current. For example, the 46.9mA reading on a digital multimeter is actually equivalent to the 46.9A current in the primary winding (in the secondary case, the measured conductor).
The transformer type current clamp is limited to measuring AC current. They are relatively sturdy and durable, and can measure non sinusoidal waveforms. Their prices are at the low end of the price range for current clamp products.
Active current clamps use active components that not only reduce the current, but also output a voltage signal proportional to the measured current. The active current clamp adopts a technology based on the Hall effect, which can measure both AC and DC currents. Active current clamp is suitable for measuring DC current or for use in conjunction with a digital multimeter without a current input socket.
Active current clamps require batteries to power their internal circuits and will not provide precise output of non sinusoidal signals unless specifically designed. Another function of some active current clamps is that they have selectable conversion ratios (such as 1000:1, 100:1, 10:1).
technical parameter
Each type of current clamp has its own set of technical parameters. The accuracy of measurement using a combination of a digital multimeter and a current clamp accessory is called a system technical parameter. It is calculated by combining the accuracy ratings of components within two ampere current ranges.
