Why Voltage Transducer Selection Matters

A voltage transducer measures the potential of a high-voltage circuit and feeds it to a low-voltage controller, so it must combine accuracy with isolation. Choosing the wrong voltage range, the wrong output type or the wrong isolation level costs either performance or safety. This guide presents a practical method for selecting a LEM voltage transducer across the LV, DVL and DVC families, from a 500 V PCB module to a 1000 V panel-mount part.

Step 1: Fix the Voltage Level

Start with the nominal voltage of the circuit you need to measure, whether that is a DC-link bus, a grid connection or a battery pack. Then add margin for overvoltage and transients, and choose a transducer whose measuring range covers the worst case with at least twenty percent headroom. A 400 V DC link that rectifies to about 680 V, for example, needs a range comfortably above 680 V. Selecting a range that is far too large reduces the effective resolution, so choose the smallest range that covers the worst case.

Working Voltage and Isolation

The isolation rating must match the system voltage class. Confirm the isolation test voltage and the creepage and clearance distances against the working voltage, and plan the primary-to-secondary spacing on the board or in the cabinet accordingly. Isolation is what makes the measurement safe and what protects the controller from the common-mode voltage of the power circuit.

Step 2: Choose the Family and Mounting

LEM offers two practical approaches. The LV closed-loop transducers, such as the LV 25-P, are current-input devices: an external resistor R1 converts the measured voltage into a nominal 10 mA primary current, so one part covers a wide voltage span on a compact PCB. The DVL and DVC ranges use insulation digital technology to measure medium and high voltages up to 1000 V and above with excellent accuracy; the DVL is panel-mount for rugged cabinets, and the DVC 1000-P is a compact PCB part with a single +5 V supply and a direct output. Choose PCB mounting for dense boards and panel mounting for higher voltage and current with stud connections.

Current or Voltage Output

A current output, such as the 25 mA of the LV 25-P or the 50 mA of the DVL series, is robust against noise and voltage drop over long wiring and is converted to a voltage by a measuring resistor at the controller. A direct voltage output, such as the DVC 1000-P, removes the external resistor and suits compact boards. Match the output to your signal chain and to the physical layout of your equipment.

Step 3: Size the Interface Components

For a current-input transducer, size the primary resistor R1 so the nominal voltage produces the nominal primary current, and size its power dissipation for that current and voltage. For a current-output transducer, size the measuring resistor so the maximum output current maps into your ADC range, respecting the maximum measuring resistance at your supply. These two resistors are part of the measurement accuracy, so treat them as precision components and keep their thermal drift low.

Step 4: Plan the Layout and Grounding

Keep the primary circuit away from the secondary and respect the isolation distances. Route the secondary signal away from switching nodes and use a short, screened connection to the ADC. Provide a clean, stable supply for the transducer and, where available, use the reference output to compensate for supply variation. A well-planned layout preserves the accuracy that the datasheet promises.

Getting Help

If you send your nominal voltage, worst-case transient, isolation requirement and preferred mounting to our FAE team, we will propose a shortlist with range, output, supply and stock status and support the design-in. BeiLuo holds mainstream LEM voltage transducers in regional stock and ships them with import declaration, certificate of origin and RoHS documents, so you can move from selection to production reliably.