LEM CASR 50-NP Closed-Loop Fluxgate Current Sensor

CASR 50-NP Product Overview

The CASR 50-NP is a fluxgate closed-loop current sensor from LEM (LEM Group). It accurately measures DC, AC, and pulsed currents and is widely used in industrial automation, power electronics, and renewable energy. The sensor provides full galvanic isolation between the primary (high-power) circuit and secondary (electronic) circuit for safe and reliable system operation.

With a rated current of 50 A and a measurement range up to ±150 A, it supports bidirectional current sensing (e.g., motor forward/reverse, battery charge/discharge) without needing external switching circuits. It operates from a single +5 V supply, delivers a ratiometric voltage output, and is designed for PCB through-hole mounting – ideal for compact, modular system designs.

CASR 50-NP Five Key Advantages

① 0.3 µs Ultra-Fast Response – Capture Microsecond Transients

The 300 ns response time lets you handle motor inrush currents, fault current surges, and high-frequency switching noise effectively, enabling faster system protection.

② 300 kHz Bandwidth – Faithfully “Hear” Every Switching Event

With high-frequency response covering the typical 10 kHz to 200 kHz switching range, the sensor reproduces PWM waveforms, high-frequency ripple, and switching transients without distortion.

③ ±0.8% Accuracy over Full Temperature Range

Accuracy ±0.8% (typical) and linearity ±1% meet strict industrial control requirements. For example, in a PV inverter at 85 °C, the total error for DC injection measurement is only 0.36%, well below the 0.5% limit.

④ Very Low Temperature Drift – Reliable in Harsh Outdoor Environments

Low offset and gain drift, combined with a wide operating temperature range of –40 °C to +85 °C, ensure stable performance from arctic cold to desert heat – ideal for outdoor PV inverters.

⑤ PCB Mounting + 1000 V Isolation – Safety and Compactness Combined

The through-hole module fits dense PCB layouts. A 1000 Vrms isolation voltage protects low-voltage circuits, and the sensor meets UL 94-V0 flammability rating and international standards such as UL 508.

CASR 50NP Key Technical Specifications

CASR 50-NP Typical Applications

Industrial Automation

Servo drives & variable frequency drives (VFDs) – Real-time motor current monitoring for precise speed/torque control.

Robot joint drives – Monitor motor currents to prevent overload and improve positioning accuracy.

DC drive static converters – Accurate DC current measurement and control.

Renewable Energy & Power Electronics

PV / wind inverters – Detect DC input and AC output currents for grid-tie efficiency and safety; wide temperature range suits outdoor use.

Solar inverters – Meet <0.5% DC injection requirements for grid connection.

UPS – Monitor battery charge/discharge and output load currents for intelligent fault protection.

Switch-mode power supplies (SMPS) – Precise input/output current sensing for higher efficiency.

Welding power supplies – Ensure stable weld current over a wide dynamic range.

Battery Management Systems

Battery-powered equipment, electric forklifts, EV charging management – Bidirectional measurement covers both charging and discharging paths, giving accurate battery state information.

Why Choose the CASR 50-NP?

In demanding applications such as motor drives, PV inverters, and switch-mode power supplies, the current sensor is both the system’s “eye” and a key safety guard. The CASR 50-NP combines the proven advantages of LEM’s fluxgate closed-loop technology in a compact package:

Closed-loop architecture – Eliminates core saturation distortion and hysteresis errors, providing high linearity and true bidirectional precision.

Very low temperature drift – Stable and reliable under industrial and extreme outdoor temperatures, ensuring DC measurement accuracy.

High dv/dt immunity – Maintains a clean output in noisy switching environments without false tripping.

LTSR-compatible footprint & reduced height – Drop-in replacement for older series without PCB redesign.

Full certifications – Meets EN 50178, UL 508, IEC 61010-1, UL 94V-0 – ready for global export.

Family scalability – Also available in 6 A, 15 A, and 25 A ratings (CASR 6/15/25-NP) with the same pinout, offering flexible BOM options.