Clampless current sensor


Current sensors are used in various applications to measure currents ranging from micro currents to large currents. Micro current measurement includes evaluating power and control circuits and measuring the power consumption of FPGAs and other low-voltage devices. Large current measurement includes measuring the power consumption of plant facilities during operation and maintenance, the power efficiency of motors, and power in wind power and photovoltaic applications.

Existing types of current sensors include the current transformer (CT), Rogowski sensor, and magnetic balance type current sensor that uses a magnetic core and sensor. These sensors clamp the conducting cable and detect the magnetic field around the cable.


Electric motor

Central computer processor CPU concept

Solar panel


Yokogawa has developed a sensor that can measure current simply by attaching it to a conducting cable, eliminating the need for clamping. This new sensor uses a magnetic sensor in the current sensor head to measure the magnetic field induced when a current flows through the cable. By using Yokogawa’s original algorithm, the sensor derives current values and thus measures current without clamping the cable.


Clampless current sensor


Vision for the future

The clampless current sensor offers the following advantages for customers.

Measurement in narrow spaces

Since the current sensor does not use a magnetic core, it is compact and lightweight and can be easily installed in various places such as inside switchboards and the motor compartment of electric vehicles where parts are tightly packed. To measure large current, conventional sensors need a large magnetic core and thus take up much space. Coreless sensors are highly advantageous for measuring large currents.


Power supply, control panel fragment

Modern plug-in hybrid vehicle transmission


Measuring DC

The Rogowski sensor is widely used for measuring current in narrow spaces. A Rogowski sensor coil detects a magnetic field by encircling the electric cable, but it can only measure AC in principle. Yokogawa’s current sensor uses a magnetic sensor to detect the magnetic field around the cable, and so can measure both AC and DC.