4-20 mA Output Current Transformer

Aim Dynamics offers a range of products for applications that require current transducers and voltage transducers with a 4 to 20 mA output. Many power meters, building automation systems and other devices require a 4-20 mA signal to preform their designated tasks. Unlike other standard output signal types, the 4-20 mA signal sends a 4 mA signal when the source is not providing current, or voltage. This helps to ensure that the sensor is working even when the source is completely off. Aim Dynamics offers sensors for AC current, DC current and DC voltage that output the 4-20 mA signal. We also have a unit that takes a 333 mV signal (a common standard output) and converts it to a 4-20 mA signal for situations that require it. One thing to keep in mind when using 4-20 mA products, is that they will always require external power since they produce a minimum of 4 mA at all times.

AC Amp Input ->4-20mA Output:   

This line of current transformer with 4-20mA output produce a 20 mA signal at the rated current and 4 mA at zero. These sensors are available in split-core, or Rogowski coil styles. All of these units require external power.

AC Volt Input -> 4-20mA Output:  

These small-sized 4-20mA voltage transducer devices convert the 333mV output of a CT into a 4-20mA signal.

DC Amp Input -> 4-20mA Output:   

This line of DC current transducer measures DC current and outputs a corresponding  4-20mA signal.  These devices provide a 20 mA signal at the rated DC current, and a 4 mA when there is no signal. These DC current transducers require external power.

DC Volt Input -> 4-20mA  Output:
 

These current transducers convert a DC Voltage, up to 1000 Vdc, to a corresponding 4-20 mA signal.

Input/Output Types

AC vs. DC Current

Alternating current (AC) input offers three types of output choices; analog output – which duplicates the wave shape of the sensed current; bipolar output which duplicates the wave shape of the sensed current and unipolar output which is proportional to the average or RMS value of the sensed current.
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Direct current (DC) input, offers two types of output choices; unipolar output which duplicates the wave shape of the sensed current and digital output which switches when the sensed current exceeds a certain threshold.

Once you understand what type of input will work best for your application, then you will need to evaluate our output requirements.  Aim Dynamics carries current transformers in every possible output selection including transformers that feature AC and DC outputs.

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.