LEM LF Series Current Transducers: LF1005-S/SP36

Technical Dossier

Product Details And Specifications

LEM LF Series Current Transducers: Comprehensive Module Range and Technical Overview

The LEM LF Series is a family of closed-loop Hall-effect current transducers engineered for high-accuracy measurement of DC, AC, and pulsed currents in demanding industrial environments. Deployed across chemical processing plants, nuclear power stations, petroleum refineries, renewable energy installations, and heavy rail traction systems, the LF Series occupies a critical position in global industrial measurement infrastructure. Its combination of galvanic isolation, wide bandwidth, and compact PCB-mount or panel-mount form factors has made it a default specification in drive systems, UPS platforms, and power conversion equipment worldwide. Nominal measuring ranges span from 100 A to 3000 A, with variants supporting supply voltages of ±15 V and ±24 V. The series is manufactured by LEM International SA, headquartered in Geneva, Switzerland, and produced primarily at facilities in Switzerland and China.

The Evolution of LF Series Architecture

The LF Series was introduced by LEM as a successor to earlier open-loop Hall-effect transducers, addressing the accuracy limitations of open-loop designs in variable-frequency drive (VFD) and servo amplifier applications. Early LF variants used a single-turn primary conductor integrated into the transducer housing, establishing the form factor that persists across the product line today.

First-generation LF modules operated exclusively on ±15 V supplies and were optimized for analog output into low-impedance loads. As industrial power electronics migrated toward higher bus voltages and tighter current regulation requirements, LEM introduced the /SP36 sub-series, extending supply compatibility to ±24 V and widening the output voltage swing to improve resolution in digitized control loops.

The architecture relies on a compensation coil wound on a toroidal magnetic core. The Hall-effect element detects residual flux and drives a compensation current through the secondary winding, producing a current output proportional to the primary current. This closed-loop topology delivers linearity errors below 0.1% and bandwidth extending to 200 kHz, making the LF Series suitable for both fundamental-frequency measurement and harmonic analysis in power quality applications.

Compatibility considerations: LF Series transducers use a standardized 5-pin connector footprint across most variants, enabling direct substitution between nominal current ratings when the primary busbar geometry is unchanged. However, /SP36 variants require a ±24 V supply rail and are not interchangeable with standard ±15 V variants without supply modification. Engineers migrating from legacy LEM LA or LT Series transducers must verify connector pinout and output scaling before substitution.

LF Series Full Catalog & Functionalities (SKU List)

The following SKUs represent verified, commercially documented models within the LEM LF Series. Models are grouped by functional sub-category.

Standard Closed-Loop Current Transducers (±15 V Supply)

• LF 205-S: Closed-loop Hall-effect transducer, 200 A nominal, ±15 V supply, current output.
• LF 205-S/SP3: 200 A nominal, ±15 V, enhanced secondary turns ratio for extended output range.
• LF 305-S: 300 A nominal, ±15 V supply, PCB-mount, 5-pin connector, current output.
• LF 305-S/SP3: 300 A nominal, ±15 V, modified turns ratio, current output variant.
• LF 505-S: 500 A nominal, ±15 V supply, closed-loop, suitable for drive output measurement.
• LF 505-S/SP3: 500 A nominal, ±15 V, SP3 secondary configuration, current output.
• LF 1005-S: 1000 A nominal, ±15 V supply, closed-loop Hall-effect, high-current bus measurement.
• LF 1005-S/SP3: 1000 A nominal, ±15 V, SP3 turns ratio, current output, drive and UPS applications.

Extended Supply Voltage Variants (±24 V / SP36 Sub-Series)

• LF 1005-S/SP36: 1000 A nominal, ±24 V supply, closed-loop, extended output swing, current output — this listing.
• LF 205-S/SP36: 200 A nominal, ±24 V supply, SP36 configuration, current output.
• LF 305-S/SP36: 300 A nominal, ±24 V supply, SP36 secondary, current output.
• LF 505-S/SP36: 500 A nominal, ±24 V supply, SP36 configuration, current output.
• LF 1505-S/SP36: 1500 A nominal, ±24 V supply, SP36 variant, high-current industrial measurement.
• LF 2005-S/SP36: 2000 A nominal, ±24 V supply, SP36 configuration, large busbar applications.
• LF 3005-S/SP36: 3000 A nominal, ±24 V supply, SP36 variant, traction and substation-grade measurement.

Voltage Output Variants

• LF 1005-S/SP7: 1000 A nominal, ±15 V supply, voltage output configuration, 4 V full-scale.
• LF 505-S/SP7: 500 A nominal, ±15 V supply, voltage output, suitable for direct ADC interfacing.

Sourcing Hard-to-Find & Obsolete LF Series Parts

Several LF Series variants, particularly early SP3 sub-series models and low-volume nominal current ratings, have transitioned to limited-availability or end-of-life status as LEM has consolidated its catalog around the SP36 platform. Industrial facilities operating legacy drive systems, UPS installations, or power conversion equipment specified with these transducers face extended lead times or outright unavailability through standard distribution channels.

DriveKNMS maintains a dedicated inventory of both active and discontinued LF Series transducers sourced through verified industrial surplus channels, OEM overstock, and controlled decommissioning programs. Each unit is individually cataloged with traceability documentation covering origin, storage history, and inspection status. For facilities requiring long-term maintenance contracts covering LF Series transducers across multiple site locations, DriveKNMS provides scheduled availability agreements with defined lead-time commitments.

Customers operating in regulated industries — nuclear, petrochemical, rail traction — can request full documentation packages including date codes, batch records, and third-party inspection certificates to satisfy site qualification requirements.

Quality Control for the LF Series Range

LEM LF Series transducers incorporate precision magnetic cores and compensation windings that require functional verification beyond simple continuity checks. DriveKNMS applies a structured test protocol to all LF Series units prior to dispatch:

• Supply voltage verification: Units are powered at rated supply voltage (±15 V or ±24 V depending on variant) and quiescent output current is measured against LEM datasheet limits.
• Linearity test: Primary current is stepped from 0% to 100% of nominal rating in calibrated increments. Output current is logged at each step and compared against the specified conversion ratio (typically 1:2000 turns ratio).
• Offset and gain calibration check: Zero-primary-current output offset is measured and recorded. Units exceeding ±0.1% of full-scale offset are flagged for rejection.
• Bandwidth spot-check: A 10 kHz sinusoidal primary current signal is applied and output fidelity is verified to confirm compensation loop integrity.
• Insulation resistance test: Galvanic isolation between primary conductor aperture and secondary circuit is verified at 2.5 kV AC per LEM standard test conditions.
• Connector and housing inspection: 5-pin connector integrity, housing crack inspection, and label legibility are verified under magnification.

Test records are retained for each unit and are available to customers upon request.