LEM’s HO series of current transducers provides performance, programmability and ease of use for designers of the latest generation of motor drives and inverters. Driven by technology advances in power electronics applications, the open-loop, ASIC-based devices deliver better performance in areas such as thermal drift, response time, power supply and noise.
The transducers are based on Hall-effect current sensing technology and measure AC, DC or pulsed currents with a nominal value of 8, 15 or 25 ARMS, and a response time of 2 to 6 s. Both of these parameters are user-programmable using 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 analog voltage. In most systems this is converted to a digital value by an analog/digital converter (ADC) which requires a reference voltage. The designer can program the transducer to output a reference of 0,5 V, 1,5 V, 1,65 V 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 application-specific integrated circuit (ASIC). This provides offset and gain drift figures twice as good as previous generation open-loop Hall-effect ASIC based transducers over the temperature range of -25°C to 85°C. It achieves a typical accuracy of 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.
An innovative feature of the HO series is the programmable over-current detection, which is separate from the main current measurement. For example, if the transducer must detect an over-current condition at five times the nominal full-scale value using a single measurement range for both detection and measuring functions, then 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 nominal full-scale value.
The transducer operates from a single supply voltage at 3,3 V or 5 V. It occupies a PCB-mountable, small, lightweight 5 g package which is 12 mm wide x 23 mm long x 12 mm high. It incorporates three separate primary conductors to allow for multi-range measurement configurations, enabling nominal measurement as low as 2,67 ARMS when programmed at 8 ARMS for the nominal range.
Versions of the HO-series transducers are available for both through-hole and surface-mount assembly. The construction provides long creepage and clearance distances of 8 mm and a comparative tracking index (CTI) of 600 for excellent insulation.
As well as contributing to the efficiency of variable speed drives, LEM’s HO model is ideal for a range of applications, including solar power inverters, solar combiner boxes, uninterruptible and switch-mode power supplies, air conditioning, home appliances, static converters for DC motor drives and robotics.
The transducer is CE marked, conforms to the EN 50178 standard and is recognised for industrial applications with a wide operating temperature range of -40 to 115°C. LEM supplies example microcontroller code to configure the serial bit stream and program the parameters. A five-year warranty is offered for each transducer.
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