Current transducer vs. current transformer – similarities and differences

In power engineering and measurement automation, the question often arises: what is the difference between a current transducer and a current transformer and when should each of these devices be used? Although both serve a measuring function, their operation and purpose differ slightly.

A current transformer is an electromagnetic component that converts a high primary current into a proportional secondary current of lower value. This makes it possible to measure high currents using meters with smaller measurement ranges, e.g. 5 A or 10 A.

A current transducer, on the other hand, is a measuring device that not only reduces the current value but also converts it into a standardized electrical signal – analog (e.g. 0…20 mA, 4…20 mA, 0…10 V) or digital (e.g. Modbus).

Current and measurement in practice

Electric current in a circuit can reach hundreds of amperes. Measuring such large values cannot be safely performed with an ordinary ammeter. Current transformers come to the rescue, using primary and secondary windings and a ferromagnetic core to reduce the primary current to a rated value, e.g. 5 A.

Current transducers, on the other hand, allow not only measurement but also monitoring and transmission of current values to controllers, energy management systems, or measuring devices located away from the controlled circuit.

Principle of operation of a current transformer

The principle of operation of a current transformer is based on the phenomenon of electromagnetic induction. The current flowing in the primary winding generates a magnetic field in the core, which induces current in the secondary winding. The value of the secondary current depends on the transformer ratio, i.e. the ratio of the number of turns in the secondary winding to the primary winding.

Thanks to this, a primary current of e.g. 200 A can be converted into a secondary current of 5 A, which can be safely measured with a meter or fed into an electricity meter.

Current transducer – operation and role

A current transducer works somewhat differently. Its task is not only to reduce the value of the current but also to convert it into an electrical signal suitable for further processing. This can be:

• a current signal 4…20 mA or 0…20 mA,
• a voltage signal 0…10 V,
• a digital signal transmitted via a communication protocol.

Current transducers are therefore more versatile – they can be directly connected to controllers, measuring devices, or SCADA systems.

Differences between transducers and transformers

In practice, there are clear differences between transducers and transformers:

1. A current transformer reduces the current to a rated value, usually 5 A or 1 A, and is mainly used to supply ammeters, electricity meters, and power protection devices.

2. A current transducer converts the measured current into a standardized output signal, making it easy to use in monitoring and control systems.

3. A current transformer operates solely based on magnetic induction, while a transducer may use electronic circuits and additional signal processing.

4. A transducer provides galvanic isolation and higher resistance to interference, which is crucial in industrial applications.

Transducers and transformers in AC and DC current measurement

Current transformers are mainly used for measuring alternating currents (AC). In the case of direct current (DC), their application is limited because the operating principle of a transformer is based on changes in magnetic flux.

Current transducers, on the other hand, can be designed for both AC and DC currents. Thanks to this, they are used in photovoltaic systems, battery systems, or in measuring current in electronic devices.

Accuracy class and measurement parameters

Each current transformer and current transducer is characterized by a specific accuracy class, which indicates how precisely it reproduces the measured current values. For transformers, the accuracy class depends on the secondary load and the transformation ratio.

For transducers, important parameters include:

• primary current measurement range (e.g. 0…20 A),
• type of output signal,
• galvanic isolation,
• resistance to electromagnetic interference.

Applications of current transformers

Current transformers are mainly used in power engineering and high-voltage installations. Their main tasks are:

• enabling the measurement of high currents using meters with smaller measurement ranges,
• supplying electricity meters,
• working with protection and safety devices,
• monitoring the load of power lines.

Thanks to measuring transformers, it is possible to measure current at a considerable distance from the controlled circuit.

Applications of current transducers

Current transducers are mainly used in:

• industrial automation,
• energy consumption monitoring systems,
• DC and AC power supply systems,
• PLC controllers and SCADA systems,
• device overload protection.

They are indispensable where the measurement of secondary current alone is not enough, but a signal for further processing is also required.

Application example – 5 A and 20 A

In many applications, the standard is a 5 A current transformer, i.e. one that reduces a primary current of e.g. 200 A to a secondary current of 5 A. Such standardized current can be fed into an ammeter or electricity meter.

A current transducer, on the other hand, can measure values up to 20 A and convert them into an output signal of 4…20 mA or 0…10 V, which then goes to the controller. This makes it possible to precisely monitor the technological process and quickly respond to load changes.

Summary – transducers and transformers together

Current transformers and current transducers do not compete with each other but rather complement their applications. A current transformer allows the measurement of high currents with meters of smaller ranges, while a current transducer provides a standardized electrical signal for further analysis and control.

The choice between these devices depends on specific requirements – whether only measurement is needed, or also an output signal compatible with automation systems and controllers.

We invite you to explore our offer and choose the right measuring solution. Contact us to find the best transducer or transformer for your needs.