Test & Measurement

Compact transducer with new improved accuracy

21st September 2016
Anna Flockett

Designed for insulated nominal voltage measurements in traction applications is the DVM series from LEM. This family of devices spans the range from 600-4200 VRMS and incorporates LEM’s proven and patented insulating technology. Despite achieving very high levels of isolation with a safety insulation voltage of 12kV, the DVM transducer is compact, measuring only 138x63.4x69mm.

It is fully compatible and out-performs the previous generation of transducers in terms of functions and performance with new improved levels of accuracy and temperature stability, thus greatly simplifying retrofits.

DVM is also suitable for base mounting, but with slightly different outline dimensions to take into consideration for primary and secondary connections locations for example. The DVM is 30% smaller in height, occupies 25% less volume and is 56% lighter. The reduction in size does not compromise the DVM’s high immunity against the external surrounding perturbations or against the high voltage variations. The new size is also an advantage when confronted with size constraints in modern railway propulsion converters.

LEM developed the DVM to be fully compliant with the International Railway Industry Standards (IRIS), providing engineers in the railway industry, who are working with both rolling stock and sub-stations, with a versatile new transducer that is equally applicable to measuring network voltages, or the main converter DC link on-board trains.

The feature set of the DVM voltage transducer also makes it an excellent fit for a broad range of medium to high voltage measurements in industrial markets.

DVM transducers measure voltages by a direct connection on their primary side, transfer the data across an internal isolation barrier and output a current from their secondary side; that is proportional to the measured voltage thanks to LEM’s patented insulating digital technology.

It delivers an improved typical accuracy, compared to existing products, of +/-0.5% at +25°C with a higher stability in temperature. The technology used provides very high levels of immunity to external magnetic fields and electromagnetic disturbances (unmatched level). Combined with a highly focused internal electronic design applied on the printed circuit as well as for mechanical design performance reached in common mode condition are exceptional: 0.5% of nominal voltage as error generated with a recovery time of less than 50µs against a voltage of 4,200V applied with a step of 6kV/us.

Its measurement frequency bandwidth (-3dB point) is 12kHz and the DVM consumes typically only 30mA when power supplied under +/-24VDC (power supply range from +/-13.5 to +/-26.4VDC). Two kinds of current output ranges are possible either +/-50mA, or the standard industrial current-loop range of 4-20 mA for unipolar current measurements and one voltage output at 10V for nominal voltage.

Other key features include a high level of partial discharge extinction voltage (5kVRMS at 10pC) ensuring product long life, and its compliance to a range of internationally-recognised safety standards in addition to its adherence to IRIS specifications. It also exhibits a fast response time. A range of connection configurations, on both the primary and secondary side, increases flexibility for the user.

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