Open-loop Hall-effect transducers measure to 250A
These moulded components are configured either with primary conductors installed, for PCB mounting; or with apertures that accept a primary conductor (cable). Using LEM’s in-house-designed ASIC, they measure up to 250A DC, AC or pulsed, with over-current detection and fault reporting, over an operating temperature range from -40 to +105ºC,
By orienting a single snap-on moulding in different positions, the same unit can be panel-mounted in different orientations or can be locked to a busbar that is the primary conductor. HO series current transducers measure DC, AC, and pulsed signals using the latest generation of LEM’s Open-loop Hall-effect Application Specific Integrated Circuit (ASIC) which was introduced with the launch of the HO 8, 15, 25-NP and -NSM series and the HO 6, 10 and 25-P models.
The new series offer offset and gain drifts which are up to twice as accurate across the temperature range as the previous generation and have a faster response time of 2.5 to 3.5 µsec. Operating from a single supply voltage of 3.3V or 5V, the HO series can measure up to x 2.5 the primary nominal current and integrate an additional pin which provides over-current detection set at x 2.93 the nominal current I PN (peak value). This threshold detection is completely independent of the main measuring circuit, which maintains full resolution. They also provide fault reporting in the event of memory corruption.
High clearance and creepage distances of more than 8mm and a Comparative Tracking Index (CTI) of 600 mean that, despite small packages of 22.95 cm3 to 33.15 cm3, there is no compromise on the insulation level provided between the primary and measurement circuits.
These transducers deliver their output as a scaled analogue votlage, typically converted into a digital value by an ADC which requires a reference voltage provided by the HO. However, the HO series can also be configured to take measurements relative to an external reference voltage, enalbing use of the full measurement range with a shifted zero point.
LEM’s Stéphane Rollier comments that although transducer outputs are invariably digitised, and a digital output device is clearly on the horizon, in the markets that LEM serves there is no clear agreement as to what format of digital output will be preferred, and an external ADC continues to be the favoured solution for the present.