PCIM 2012 Nuremberg, Germany: A new series of current transducers for motor drives and inverters will improve performance in thermal drift, response time, power supply, and noise, says developer LEM. The HO series of open-loop, ASIC based current transducers is based on Hall-effect current-sensing technology. They measure ac, dc, or pulsed currents with a nominal value of 8, 15, or 25 ARMS, with a response time of 2 to 6μs.
Both of these parameters, and several others, are user-programmable via a simple serial digital bit-sequence that’s generated by the system’s host microcontroller. Other user-programmable parameters include reference voltage, overcurrent 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-to-digital converter (ADC), which requires a reference voltage. The designer can program the HO-series transducer to output a reference of 0.5, 1.5, 1.65 or 2.5V on a dedicated pin. Alternatively, the transducers are able to be configured to make measurements relative to an external reference.
According to LEM, offset and gain drift figures are twice as good (over the temperature range -25 to +85°C) as previous-generation transducers of the same type. Typical accuracy equals 1% and 2.8%, at +25°C and +85°C, respectively, without offset, and with a high level of insulation between primary and measurement circuits.
One particularly innovative feature is programmable overcurrent detection, separate from the main current measurement. Using a single measurement range (for both detection and measuring functions), if the transducer must detect an overcurrent condition at (say) five times the nominal full-scale value, the measurement range must extend up to the overcurrent limit, reducing available accuracy within the nominal range. Separate overcurrent detection, with programmable threshold, ensures that maximum resolution is maintained up to the nominal full-scale value.