LEM Voltage Transducers

LEM voltage transducers use a combination of primary resistors and Hall effect current measurement. The measured voltage is applied across an integrated high-value resistor (primary resistor), creating a small current proportional to the voltage. This current flows through a Hall effect current transducer which provides isolated measurement. The Hall sensor output is processed to provide a voltage or current output proportional to the input voltage. This architecture provides inherent galvanic isolation between the high-voltage input and low-voltage output circuits. The primary resistor value determines the input impedance and power dissipation, with higher values offering lower power loss but potentially limiting bandwidth.

For standard DC bus monitoring, LV series with integrated primary resistors are simplest. For very high voltages or custom requirements, consider adding external series resistors to share power dissipation and extend voltage range.

Instantaneous voltage transducers provide an output that follows the input voltage waveform in real-time, preserving amplitude and phase information. They are used for waveform analysis, synchronization, and control applications where the instantaneous voltage value matters. RMS (Root Mean Square) voltage transducers calculate the true RMS value of the input voltage over a defined time window, providing a DC output proportional to the AC voltage magnitude regardless of waveform shape. RMS sensors are used for power monitoring, metering, and protection applications where the effective voltage value is important. LEM offers both types - instantaneous models like LV series and RMS models like DVL series for different application needs.

Choose instantaneous output (LV series) for control applications, waveform analysis, or when phase information is needed. Choose RMS output (DVL series) for metering, power monitoring, or when measuring distorted AC waveforms where true effective value matters.

Primary resistor power dissipation is calculated using P = V²/R, where V is the measured voltage and R is the primary resistance. For example, an LV 25-P measuring 500V with 12kΩ primary resistance dissipates P = 500²/12000 = 20.8W. This is significant and must be considered for thermal management. To reduce dissipation: 1) Select models with higher primary resistance

2) Use external series resistors to share power

3) Ensure adequate ventilation or heatsinking

4) Consider that higher resistance may reduce bandwidth. LEM datasheets specify primary resistance values and maximum continuous voltage ratings. For high-voltage continuous operation, consult our FAE team for thermal design guidance.

Calculate power dissipation at your maximum operating voltage. If exceeding 10W continuously, consider using external series resistors mounted on heatsinks to share the thermal load, or select a model with higher primary resistance.

Yes, LEM voltage transducers can measure both DC and AC voltages. The Hall effect principle responds to the current through the primary resistor, which is proportional to voltage regardless of DC or AC. For DC voltage measurement, the sensor provides a stable output proportional to the DC level. For AC voltage measurement, instantaneous output models accurately track the AC waveform, while RMS models provide a DC output proportional to the RMS value. The bandwidth specification indicates the maximum AC frequency that can be accurately measured. Most LEM voltage transducers have bandwidths from DC to several kHz, with some models extending to 100kHz or higher for high-frequency applications.

All LEM voltage transducers measure DC. For AC applications, choose based on output type needed - LV series for instantaneous waveform tracking, DVL series for RMS measurement of AC or distorted waveforms.

LEM voltage transducers carry multiple safety certifications including: IEC 61010-1 for measurement, control, and laboratory equipment

UL 508 for industrial control equipment

EN 50178 for power electronic equipment

and UL 1577 for optocoupler isolation (applicable to isolation specifications). These certifications ensure the sensors meet rigorous safety standards for dielectric withstand, creepage distances, and clearance requirements. The isolation voltage ratings (2.5kV to 12kV depending on model) are verified through 100% production testing. For specific certification requirements in your application or region, consult the product datasheet or contact our technical support team.

For general industrial applications in Europe, IEC 61010-1 certification is typically sufficient. For North American markets, UL 508 certification may be required. For medical applications, additional IEC 60601-1 certification may be necessary.

For voltages exceeding the transducer's internal primary resistor rating, external resistors can be added in series: 1) Calculate required total resistance: R_total = V_max / I_primary (typically 10-50mA)

2) Subtract internal resistance to determine external resistor value

3) Select resistors with adequate voltage rating and power dissipation capability

4) Use multiple series resistors if single resistor voltage rating is insufficient

5) Ensure proper creepage and clearance for high-voltage connections

6) Consider temperature coefficient for accuracy requirements. The external resistors share voltage and power dissipation with the internal resistor. Always include safety margins and consult relevant safety standards for high-voltage design.

For continuous operation above rated voltage, use external resistors to share power dissipation. Mount external resistors on heatsinks if total dissipation exceeds 5W. Use high-voltage resistors with adequate voltage rating (typically 500V-1000V per resistor).