How do I start selecting a LEM current sensor?

Fix the nominal current from your rated load, size the measuring range for the worst-case overload, then choose closed-loop or open-loop by accuracy budget. Finally pick the supply, the mounting and the output type for your board. Those decisions narrow the catalog quickly.

Closed-loop or open-loop Hall: which do I need?

Choose closed-loop for high accuracy, low drift and fast response, as in field-oriented motor control. Choose open-loop for smaller size, lower cost and lower power, as in solar inverters and general power supplies where moderate accuracy is enough. Decide by accuracy budget first.

Can BeiLuo help finalize my sensor choice?

Yes. Send your nominal current, overload profile, supply, mounting and accuracy target and we will propose a shortlist with range, output and stock status, then support design-in. Getting the sensor right saves project time.

What selection mistakes should I avoid?

The usual mistakes are choosing too small a measuring range, ignoring the supply-dependent range and placing the sensor where external fields disturb it. Each adds risk without benefit. Validate the choice on the bench before committing the BOM.

How do I choose between LV, DVL and DVC voltage transducers?

Use the LV25-P for a compact, low-voltage PCB measurement, choosing the range with an external resistor R1. Use the panel-mount DVL range for medium and high voltages up to 1000 V in rugged cabinets, and the DVC 1000-P for compact 1000 V measurement on a board. Voltage level and mounting drive the first decision.

How do I size the primary resistor for the LV 25-P?

Choose R1 so the nominal voltage produces a primary current of about 10 mA, for example 25 kohm for 250 V, and size its power for that current and voltage. Accuracy is best at the nominal current. Our FAE team can size R1 for your voltage.

What output and supply should I plan for?

A current output is robust over long cabinet wiring and needs a measuring resistor at the controller, while a direct voltage output simplifies a compact board. Match the supply, single +5 V or bipolar ±15 V, to your existing control rails. The table shows output and supply per model.

Why is isolation so important for voltage measurement?

Isolation separates the high-voltage primary from the low-voltage secondary, protecting the controller and the operator from common-mode voltage and allowing the measurement to float. Every LEM voltage transducer provides this galvanic isolation. Confirm the isolation rating against your voltage class.

Why does the primary conductor layout affect accuracy?

The conductor geometry is part of the factory calibration, so the field the sensor measures depends on how the current is routed through the aperture. Keep the conductor centered, symmetric and of the recommended width and thickness. A poor layout adds gain and offset error that no calibration can remove.

How do I keep noise out of the current signal?

Keep the secondary output away from switching nodes and the transformer, use a short screened connection to the ADC, and filter at the ADC input if needed. Place the measuring resistor close to the ADC and keep its ground return clean. Layout is the first lever on signal noise.

How do external magnetic fields disturb the measurement?

A Hall transducer measures a magnetic field, so a strong external field can add an error. Place the sensor away from transformers, inductors and high-current traces, and where possible use a sensor with good stray-field immunity and a symmetric layout. Our FAE team can review the placement.

What about thermal design around the sensor?

The primary conductor carries the full current and self-heats, so keep the copper adequate and the sensor clear of the hottest components. Respect the maximum primary conductor temperature in the datasheet. Verify the temperature under worst-case load.

My current reading has a constant offset. Where do I start?

First confirm the offset with zero primary current and the sensor in its final position, because a nearby magnetic field or an asymmetric conductor can add an offset. Then check the supply and the measuring resistor, since a supply or resistor error appears as an offset. Measure the offset cold and hot to separate a real fault from thermal drift.

Why does my reading drift with temperature?

Some drift is inherent and specified in the datasheet, but excessive drift often comes from an oversized measuring resistor, a supply that moves with temperature, or self-heating from an undersized primary conductor. Check each in turn. An open-loop sensor drifts more than a closed-loop part by design.

My current signal is noisy. What should I check?

Check the routing of the secondary signal, the proximity of switching nodes and the ground return. Move the measuring resistor close to the ADC, screen the connection and add a filter sized for the control bandwidth. Noise is usually a layout problem. Our integration notes cover the layout rules.

How do I diagnose an isolation fault?

An isolation fault usually points to a layout or assembly issue rather than the transducer itself. Check the creepage between primary and secondary, look for solder bridges or contamination across the barrier, and confirm the board meets the required spacing. A hipot test locates the failure. Never operate a high-voltage measurement with suspect isolation.

What is the standout feature of the LEM closed-loop current transducer?

The closed-loop principle holds the magnetic core at zero flux, which gives high accuracy, excellent linearity and very low offset drift over temperature. That combination is what makes it the default choice for field-oriented motor control and precision measurement. The main design care point is the primary conductor layout.

How does closed-loop compare with open-loop in practice?

In practice, closed-loop parts cost more and need a slightly larger supply, but they hold accuracy and drift far better, especially across temperature and when the current crosses zero. Open-loop parts win on size, cost and power where moderate accuracy is enough. Match the technology to the accuracy budget.

Does the single-supply LTS range match the bipolar LA range?

The single-supply LTS range brings closed-loop accuracy to boards that only provide a logic rail, and it holds its accuracy over a wide temperature range. For higher current or a bipolar analog design, the LA range is the natural choice. Our FAE team can compare them at your operating point.

Can I get samples to evaluate?

Yes. We provide samples of the LEM current transducers for your own accuracy and thermal testing, with documentation included and FAE support during bring-up. Request a sample and we will confirm stock and lead time.

Technical Support | LEM Expertise | BeiLuo

Guides, application notes, troubleshooting and reviews from BeiLuo's FAE team covering LEM current transducers and voltage transducers for power design.

Guides 2 Application Notes 1 Troubleshooting 1 Reviews 1

How to Select a LEM Current Sensor

2026-07-26 - Guides - By Chen Wei Ming

Compare LEM closed-loop and open-loop Hall current transducers by nominal current, measuring range, supply and mounting to choose the right sensor for your design.

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How to Select a LEM Voltage Transducer

2026-07-21 - Guides - By Zhao Yun Fei

A practical method for selecting LEM voltage transducers by nominal voltage, primary resistor, isolation and output type for your measurement task safely.

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LEM Current Sensor Integration and Layout Notes

2026-07-16 - Application Notes - By Sun Jie Lin

Layout, shielding and thermal guidance for integrating LEM current transducers into power stages with accurate, low-noise current feedback for drives.

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Troubleshooting LEM Current and Voltage Transducers

2026-07-09 - Troubleshooting - By Sun Jie Lin

A systematic method for diagnosing offset, drift, noise and isolation problems in LEM current and voltage transducers inside power electronics systems.

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LEM Closed-Loop Current Transducers: A Practical Review

2026-06-30 - Reviews - By Chen Wei Ming

A hands-on review of LEM closed-loop Hall current transducers for drives, solar and battery systems, covering accuracy, drift, response and layout practice.

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Meet Our FAE Team

Chen Wei Ming

Senior FAE Engineer, Current Sensing

Current SensorsClosed-Loop HallMotor Drives

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Sun Jie Lin

FAE Engineer, Integration and Layout

PCB LayoutEMCIsolation

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Zhao Yun Fei

FAE Engineer, Voltage and Isolation

Voltage TransducersIsolationSolar and Storage

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