Current sensors

Measurement sensors are current-transformation devices designed for instrumenting low-voltage electrical circuits. They send a secondary signal proportional to the primary current to DIRIS measurement units and COUNTIS energy meters. Three technologies coexist: TE closed sensors, TR split-core sensors and TF flexible Rogowski-coil sensors. Each type meets distinct installation constraints, depending on whether the circuit is accessible while de-energised or must remain live during fitting.

Types of measurement sensors and their operating principle

TE closed sensors for new or shut-down installations

TE closed sensors incorporate a rigid toroidal ferromagnetic core that encircles the primary conductor. This type of measurement sensor offers high accuracy and excellent secondary-signal stability. Our installation experience confirms that TE closed sensors are the standard choice for new panels or renovations with a full installation shutdown. The conductor must first be disconnected to allow it to pass through the core's opening.

TR split-core sensors for live interventions

TR split-core sensors allow the magnetic circuit to be mechanically opened without disconnecting the conductor. This feature eliminates the supply interruption needed with a standard closed sensor. Our commissioning tests show that TR split-core sensors significantly reduce intervention time on existing installations. The polyamide housing provides mechanical strength and isolation between the live parts and the secondary circuit.

TF flexible Rogowski-coil sensors

TF flexible sensors use a Rogowski coil, i.e. a winding with no ferromagnetic core on a flexible support. This technology allows positioning around busbars or large-section cables in confined spaces. In the field, we find that TF flexible sensors are particularly well suited to tertiary or industrial panels where space around the conductors is critical. The sensor's flexibility compensates for the absence of a rigid magnetic core.

Compatibility and current ranges of measurement sensors

Matching with DIRIS units and COUNTIS meters

Each measurement sensor is sized for a specific primary-current range, consistent with the inputs of DIRIS units and COUNTIS meters. Our standard practice favours systematically checking this match when choosing a sensor. A mismatch between the sensor's rating and the instrument's measurement range leads to a proportionality error or signal saturation.

IEC 61869 compatibility standard

Compatibility of measurement sensors with the requirements of the IEC 61869 standard guarantees the accuracy of ratio transformations and withstand under standardised test conditions. This standard defines accuracy classes, ratio-error limits and steady-state withstand requirements. Feedback from installers confirms that meeting this normative reference makes installation acceptance easier at design offices and during handover.

Typical applications and selection criteria for measurement sensors

Circuit instrumentation for energy supervision

Measurement sensors equip the outgoing circuits of tertiary panels, industrial production circuits and secondary distributions to be instrumented. They feed DIRIS units for consumption monitoring, power-quality analysis or imbalance detection. We observe growing use of these sensors as part of energy-management initiatives compliant with environmental regulations.

Choosing the sensor type according to the installation context

The choice between closed, split-core or flexible sensors rests on three decisive criteria: conductor accessibility, whether the circuit can be shut down, and the space available around the conductor. The TE closed sensor remains the preferred economical solution for new projects. The TR split-core sensor is needed when continuity of service is essential. The TF flexible sensor solves demanding geometric configurations where no other type can be fitted.

Frequently asked questions

What is the difference between a TE closed sensor and a TR split-core sensor?

The TE closed sensor requires the conductor to be disconnected for installation, whereas the TR split-core sensor opens mechanically to fit onto live circuits without interrupting service.

Does the Rogowski coil of a TF flexible sensor replace a conventional current transformer?

The TF flexible Rogowski-coil sensor delivers a voltage proportional to the derivative of the primary current, which is then integrated electronically; it is not a ferromagnetic-core current transformer, but a complementary solution for confined spaces.

How can the compatibility of a measurement sensor with a DIRIS unit be checked?

Compatibility is established by matching the sensor's primary-current range with the DIRIS unit's input characteristics, meeting the requirements of the IEC 61869 standard for the required accuracy classes.

Does the polyamide housing of measurement sensors withstand industrial environments?

The polyamide housing provides satisfactory mechanical strength and electrical insulation suited to electrical panel use, although the final protection rating choice depends on the exact positioning within the installation environment.