User-programmable current transducers offers performance benefits

May 09, 2012 // By Paul Buckley
LEM has released the HO series of current transducers, setting a new standard of performance, programmability and ease-of-use for designers of the latest generation of motor drives and inverters.

The HO series of open-loop ASIC based current transducers deliver better performance in areas such as thermal drift, response time, power supply and noise driven by technology advances in power electronics applications.

LEM's HO series are open-loop devices, based on Hall-effect current sensing technology, that measure AC, DC or pulsed currents with a nominal value of 8, 15 or 25 ARMS, with a response time of 2 to 6 μsec. Both of these parameters, and several others, are user-programmable by a simple serial digital bit-sequence, generated by the system's host microcontroller. Other parameters that are user-programmable include reference voltage, over-current detection limits, fault reporting and low power mode.

The HO series delivers its output as a scaled analogue voltage; in most systems this will be converted to a digital value by an analogue/digital converter (ADC) which requires a reference voltage. The designer can program the LEM HO-series transducer to output a reference of 0.5, 1.5, 1.65 or 2.5 V on a dedicated pin. Alternatively, the HO-series can be configured to make measurements relative to an external reference.                        

For the HO models, LEM designed a completely new ASIC. The HO provides offset and gain drift figures twice as good (over the temperature range -25 to +85ºC) as previous-generation open-loop Hall-effect-ASIC based transducers. It achieves a typical accuracy of 1% and 2.8%, at +25°C and +85°, respectively, without offset, and with a high level of insulation between primary and measurement circuits.

An innovative feature of the HO series is programmable over-current detection, separate from the main current measurement. Using a single measurement range (for both detection and measuring functions), if the transducer must detect an over-current condition at (say) five times the nominal full-scale value, the measurement range must extend up to the over-current limit, reducing available accuracy within the nominal range. Separate over-current detection, with programmable threshold, ensures maximum resolution is maintained up to the