How do I measure the current?

Why do you need to measure current? In this article, we will cover the reasons for measuring current, how to measure current and what to look for when measuring current.

We cannot see the current that is flowing with our own eyes. Therefore, specialized measuring instruments are needed to measure current and other parameters. But why do we need to measure current? And how should we measure it?

This article will detail the reasons why current measurements are needed, as well as the commonly used measuring instruments for measuring current and how they are used.

■ The need to measure current

The maintenance of electronic equipment is extremely important as it is extremely sophisticated and sensitive, so many of them need to be inspected regularly. Without measuring instruments, it is difficult to identify the location of faults during maintenance or in the event of a malfunction. Measuring current is therefore an important item in the maintenance of electronic equipment and in identifying the cause of malfunctions.

There are a variety of instruments available for measuring current. Three of the most commonly used are.

Digital multimeter

・Current probe (Observe the output voltage of the current probe with an oscilloscope.)

Clamp Meter

・Digital multimeters	・Current probes	・Clamp meters

Any measuring instrument can measure current. It is important to choose the right instrument for the purpose.

In this article, we will describe the methods of measuring current with various measuring instruments.

■ Measuring current with a digital multimeter

A digital multimeter is a measuring instrument that performs the basic functions of measuring current, voltage and resistance in an electrical circuit in a single instrument. Digital multimeters come in different types, ranging from large to card-type, and can be used in a variety of electrical measurement situations.

Many digital multimeters can be altered to change the measurement function by rotary switches, etc. The first thing to do before measuring is to set it to the current function.

Then plug the test lead into the black negative "COM" input and the red positive "A" input. Then, when connecting the circuit, connect the black test lead to the negative terminal of the power supply and the red test lead to the load terminal, and measure in series.

Note that the digital multimeter may be damaged if a voltage is applied while the test leads are plugged into the "A" terminal. Therefore, to avoid accidental or applied voltage, turn off the power to the measurement circuit before turning on the power, and make a series connection between the ports where the current is to be measured.

■ Methods of measuring current using a current probe

Current probes are tools that convert current to voltage in order to measure current waveforms on instruments such as oscilloscopes. They can be clipped directly onto the cable jacket to monitor the signal without destroying the cable. And since the measurement range covers from small to large currents, they are suitable for current measurement in a variety of scenarios.

Current probes are used in the following 4 ways and need to be selected according to the purpose.

Current Transducer (CT) Method

AC-specific current sensors. Relatively inexpensive, no power supply required, but can only measure AC, not DC.

Hall Element Method

Such current sensors can be used for both AC and DC. Although these sensors are also less expensive, they have disadvantages such as poor accuracy and unsuitability for long-term measurements due to offsets caused by temperature and aging.

Rogowski method

Converts and measures the voltage induced in an air-core coil by the AC magnetic field generated around the test current. This method is inexpensive and, since there is no magnetic core, there is no magnetic saturation, allowing the measurement of large currents and without the disadvantage of magnetic loss. However, since the method is susceptible to interference, it is not suitable for high-precision measurements. Another disadvantage is that it is in principle impossible to measure direct currents.

AC Zero Flux Current Sensor Method

This method improves the low frequency characteristics of the current transducer (CT) measurement method. It is suitable for power measurements and can measure a wide frequency band because of the small phase error. However, since it is also a type of current transducer (CT) measurement method, it cannot measure direct current.

AC/DC Zero Flux Current Sensor Method (Hall Element Detection Type)

By combining a current transducer with a Hall element, measurements from DC to AC can be realized.

AC/DC zero flux current sensor method (fluxgate type)

Measurement from DC to AC is possible by combining a current sensor with a fluxgate

The fluxgate sensor has a very small offset over a wide temperature range for accurate and stable measurements, making it ideal for use with high-precision power meters.

■ Measurement of current using a clamp meter

The current can be measured by simply clamping the wire to be measured into the clamp core of the clamp meter, so that the current value can be known without cutting off the circuit. The magnetic field generated when current flows is directly proportional to the size of the current, so this measuring instrument is based on the principle of "just measure the magnetic field".

When clamping a clamp meter to a wire, the magnetic fields cancel each other out if both wires are clamped together at the same time. The two wires should not be clamped together except when measuring leakage current.

If several turns of wire are wound around the core of a clamp meter in the same direction, the magnetic field increases proportionally, so there is also a technique where a large number of turns of wire are wound around the clamp meter to increase the magnetic field and thus the sensitivity.

■ Select the measuring instrument to be used according to the purpose of the measurement.

Measurement equipment for measuring current and other parameters are essential tools for maintaining sophisticated, sensitive electronic equipment and identifying malfunctions. For current measurements, digital multimeters, current probes, and clamp meters are commonly used. Please select the measuring instrument that best suits your needs based on the current you want to measure and the purpose of the measurement.