AC Current Sensors and Switches

Aim Dynamics is a well known AC current sensor supplier. We offer a wide variety of current sensors (also called current transformers, or simply CTs).

AC Amp Input -> 333mV Voltage Output Current Sensors: 
These AC current sensor devices output 333 mVac at the rated current you select, e.g. 2000A/333mV.  These are typically passive devices.

AC Amp Input -> AC 5 Amp Output Current Sensors: 
These “true” current transformers output up to 5 Amps AC at the rated current you select. These are all passive devices except for the 5A Rogowski coil kits, which require external power. This type of AC current sensor comes in various forms including solid an split core current transformer styles.

AC Amp Input -> AC 1 Amp Outpuvt Current Sensors: 
These current transformers output up to 1 Amp AC at the rated current you choose. These are all passive devices. This type of AC current sensor is offered in a couple styles including solid and split core current sensor styles.

AC Amp Input -> 4-20mA  Output Current Sensors: 
These current sensors output a 20 mA signal at the rated current and 4 mA at zero. The split-core current sensors are passive but the 4-20 mA Rogowski coil kits require either an external power source, or 9-36 Vdc power from the 4-20 mA loop, depending on the model.

AC Amp Input -> DC Voltage Output Current Sensors: 
These current transducers output a DC voltage on the secondary corresponding to the current detected on the primary. These exist as both split-core and Rogowski coil kit options.

AC Current Switch: 
These AC current switches turn on an electronic switch (connecting the secondary wires) at the threshold AC current (detected on the primary conductor). The thresholds range from 0.015A to 5A, depending on the model.  Some thresholds are configurable on the unit itself.

Input Rating
& Output Signal

There are two critical things to get right when ordering a current sensor:

1 – The input rating.
2 – The output type.

Input Rating
CTs have input ratings.  For example, the SCT-0750-100 has a 100A rating, and the manufacturer has specified that it will operate from 10% to 130% of the rated current with a specified accuracy.  IEC 61869-2 states the accuracy from 5% to 120%.  Therefore, the SCT-0750-100 would be suitable for a circuit where the current doesn’t drop below 10A often, and that doesn’t exceed 130A.

Output Type
CTs can output AC current, AC voltage, DC voltage, 4-20mA signals, and more.  Therefore, it is critical to understand what input your measuring device (e.g. meter) expects.  Getting this wrong can result in device failure, incorrect results, and more.

If you are unsure, contact your meter manufacturer to determine the input signal required.

Shape

Solid-Core vs. Split-Core

Solid-core current transformers offer a cost-effective and accurate solution for designing power meters dedicated to new equipment and buildings. They are not suitable, however, for the numerous applications involving power monitoring of existing machines and facilities, where it would be necessary to shut down power and disconnect cables before retrofitting the solid core sensors in all the places where they might be used. Installing power metering systems is generally not possible, prohibitively expensive or even dangerous if it requires a service interruption, even for a short while (e.g. stopping a production line, a telecom or datacenter power supply, some nuclear plant equipment, etc).

Split-core current transformers can simply snap over a conductor, without the need to screw or weld on complex brackets, making installation and maintenance simple. They can be installed in electrical control panels – thus avoiding complex wiring – to remotely monitor devices that sometimes operate in inaccessible or harsh environments. The beauty of the split core transformers is that they can be retrofitted into a live installation without disturbing it, which often make them the unique choice for engineers designing power meters.

But these advantages have a price, making the split core current transformers more expensive and less accurate than the solid core transformers. It is thus very important to understand the difference between the various technologies available, and make a choice according to specific application constraints.

Core Material

Does the core material used matter?

Ferrite vs. Nickel vs. Silicon Steel
Current sensors can be manufactured with many different types of core materials.  The most commonly used materials are:

Ferrite: 
The ferrite qualities are available at low cost, which puts the high performance split core current transformers on the market at very attractive price.  Ferrites are ceramic compounds of the transition metals with oxygen, which are ferrimagnetic but nonconductive. Ferrite ceramics are a class of ceramic compounds made from iron oxide, and one or multiple metallic elements. The magnetic cores made from ferrite ceramics are used in high-frequency applications. The ceramic materials are produced in different specifications to meet diverse electrical requirements. These ceramic materials serve as efficient insulators, and help decrease eddy currents.

​​​​​​​Nickel: 
Nickel still offers high accuracy rating with a lower cost but does not have the performance terms of Silicon Steel cores. This metal is glassy or non-crystalline, making it useful for high performance transformers due to low conductivity.

Silicon Steel: 
Silicon steel has high electrical resistivity and long-term performance stability.  Silicon steel offers high saturation flux density. A few years ago, characteristics of silicon steel was altered with chemical changes, and today, the new product is known as AISI type M6. The M6 steel has high permeability and low losses, and it is used in high-performance applications.