Current Clamps
Current Clamp Adaptors, or simply Current Clamps, convert measured current signals into a voltage signal suitable for multimeters, oscilloscopes, data recorders and other test instruments
Considerations when buying a clamp adaptor
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Do not compromise on safety
Make sure the clamp meter has the correct rating. Check that the design will allow you to use the meter easily while wearing Personal Protective Equipment (PPE). Checkout the convenience of the flexible current clamps utilizing the Rogowski Principle and exciting new wireless models.
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Make sure the clamp meter works where you do
Check the specifications for the amperage and voltage range you will be working. Also consider the ambient temperature range if you will be working in a hot environment. Is it rated only for indoor use only?
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Consider special features such as:
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Flexible current clamp adaptors based on the Rogowski Principle
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Current clamps that draw power from the conductor versus ones requiring batteries
How does a clamp adaptor work?
Fluke.com has a good explanation: The ability of clamp adaptors to measure large ac currents is based on simple transformer action. When you clamp the instrument’s “jaws” around a conductor carrying ac current, that current is coupled through the jaws, similar to the iron core of a power transformer, and into a secondary winding which is connected across the shunt of the meter’s input. A much smaller current is delivered to the meter’s input due to the ratio of the number of secondary windings vs. the number of primary windings wrapped around the core.
Usually, the primary is represented by the one conductor around which the jaws are clamped. If the secondary has 1000 windings, then the secondary current is 1/1000 the current flowing in the primary, or in this case the conductor being measured. Thus, 1 amp of current in the conductor being measured would produce 0.001 amps or 1 milliamp of current at the input of the meter. With this technique, much larger currents can be easily measured by increasing the number of turns in the secondary.
What is the Rogowski Principle used by Flexible Current Clamps?
The flexible and lightweight measuring heads utilizing the Rogowski Principle allow quick and easy installation in hard to reach areas. The Rogowski current clamp is a toroidal coil. The magnetic field produced by the conductor induces a voltage proportional to the rate of change or derivative of the current (oops some calculus). The voltage is then integrated in a circuit (more calculus) to produce a linear voltage suitable for multimeters, oscilloscopes, and recorders. See it in action: