High-accuracy current measurement with low noise level & wide temperature range

May 22, 2017 //By Graham Prophet
High-accuracy current measurement with low noise level & wide temperature range
Swiss transducer maker LEM says it has “re-invented the fluxgate transducer” with its latest device, the IN 2000-S high accuracy current transducer for non-intrusive and isolated measurement of DC, AC and pulsed nominal current of 2000 A.

The fluxgate transducer measures current using a balanced-bridge, null-detection of induced current in a sensing loop around the primary conductor. The magnetic core of the device is driven into saturation in alternate directions by an applied square-wave magnetising current. This ensures that the measured current appears as a variation in the stable, saturated levels, yielding accuracy and providing immunity to external fields. The square waveform does imply that noise must be dealt with, and it is this that LEM has overcome in its latest design.

 

The outcome is a closed-loop Fluxgate transducer that measures DC, AC or pulsed current to 2000A; with a wide operating temperature range from -40 to +85ºC; and low offset over temperature range up to 10 ppm. It has linearity over temperature range up to 3 ppm; and maintains its ow noise level & high accuracy over a the temperature range.

 

LEM’s design performs maximum signal processing in the digital domain, and applyies a new approach to the fluxgate technology architecture for the ripple cancellation of the fluxgate drive frequency. These improvements have resulted in a compact transducer, that maintains its high accuracy over a wider temperature range, with reduced noise level vs the previous generation. Signal processing to be done in the digital domain means a complete immunity to temperature effects, interference and supply voltage variation after the ADC. In particular, offset and offset drift have been improved. The DSP has also been used to reduce the interference or ripple from the fluxgate driving signal at a fixed frequency. This led to higher frequency harmonics reduction.

The remaining interference has been eliminated by driving a ‘ripple compensation coil’ whose amplitude and phase are adjusted during the calibration of each transducer. After calibration, the remaining peak-to-peak ripple is less than 50 ppm.

 

A 200-turn test winding is provided so that the transducer function can be checked using a current of 1 Amp without


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