Current measurement

In many applications it is vital to be able to register the current in a conductor, either to monitor, control or measure the consumption. Several different technologies are currently available, all having both advantages and disadvantages depending on the application in which they will be used.

Compotech offers current sensors in a wide range from 6 A up to 2500 A. We also have current transformers for both industrial applications and for energy meters designed for household use.

We are keen to be involved from the concept stage

A majority of all the products we supply are customised or specially developed for a specific application. With our extensive R&D facilities behind us, we are keen to be involved from the concept stage in order to adapt or develop the product and optimise it to meet your challenges.

Strömsensor CL med hallsensorer

Current sensor – open loop with Hall element

The primary conductor is enclosed by a core which has an air gap. A Hall element is located in the air gap. When the primary current drives the magnetic flux in the core, the Hall element is actuated so that a measurable voltage is created. The voltage signal must then be processed for reading. Measures both DC and AC up to 100 kHz.

Current sensor – closed loop with Hall element

Similar to the above but instead of measuring the output voltage from the Hall element, the voltage is allowed to control a compensation winding on the core which will balance the magnetic field to 0. The size of the compensation current is then proportional to the primary current. Closed loop technology provides greater precision than open loop.

Current sensor – closed loop with soft magnetic probe

The same principle as the Hall effect sensor but instead of a Hall element a probe (a small piece of amorphous material enclosed by a coil) is used, placed in the core’s air gap. The difference in the result is higher precision, lower temperature operation and a lower offset current.

Strömsensor OL hallsensor

Current transformer

The primary conductor is enclosed by a core which is wound with the wire from the secondary circuit. The secondary current is proportional to the primary current divided by the number of turns of the winding, e.g. 1/2000. Only measures AC. Some current transformers for energy meters are also tolerant of DC up to a specified level. This solution is characterised by high precision and good linearity.

Shunt resistor

A simple solution in which the current passes through a well-defined resistor in which a voltage is created which is directly proportional to the current. It measures both AC and DC with high precision but has disadvantages such as no insulation between the primary and secondary circuits and extreme sensitivity to external magnetic fields.

Fibre optics

An optical fibre that is open at one end and wound around the primary conductor. With the aid of the Faraday effect, you can measure the phase change in the light which is affected by a magnetic field. Can measure DC up to several hundred kA with great precision.

Rogowski coils

Rogowski coils are toroidal coils which have the advantage that they have an opening, enabling the coil to be hooked round a cable. This makes it easy to measure currents in long cables or in cables which cannot or should not be disconnected in order to fit the current sensor.

The primary conductor is enclosed by a coil which is either air-wound or is wound on a non-magnetic core. This can therefore have a flexible or rigid structure. The coil emits a voltage which is a function of the primary current and the common inductance of the primary conductor/coil. The integral of this voltage is proportional to the primary current. Measures AC. An advantage of the coil is that it cannot become saturated due to the lack of a core. A disadvantage is its sensitivity to external magnetic fields.

Jan Rollstedt

Project Manager

jan.rollstedt@compotech.se
+46 8 441 58 17