LEM's HO series of open-loop devices, based on Hall-effect current sensing technology, measures AC, DC, or pulse currents with a nominal value of 8, 15, or 25 ARMS, with a response time of 2 to 6 µs. These parameters, among others, are user-programmable via a simple serial bit sequence generated by the system's host microcontroller. Other user-programmable parameters include reference voltage, overcurrent detection limits, fault reporting, and low-power mode.
The series provides an analog voltage output signal; in most systems, this will be converted to a digital value by an A/D converter that requires a reference voltage. The designer can program the LEM HO series transducer to supply a reference of 0.5, 1.5, 1.65, or 2.5V via a dedicated pin. Alternatively, the HO series can be configured to perform measurements relative to an external reference.
For the HO models, LEM designed a completely new application-specific integrated circuit (ASIC). The HO series offers offset and gain drift values twice as good (within the temperature range of -25 to +85°C) as previous generation ASIC-based and open-loop Hall-effect transducers. It achieves typical accuracy values of 1% and 2.8% at +25°C and +85°C, respectively, with zero offset and a high level of isolation between the primary and measurement circuits.
An innovative feature of the HO series is programmable overcurrent detection, separate from the main current measurement. With a single measurement range (for both detection and measurement), if the transducer needs to detect an overcurrent, for example, at five times the full-scale nominal value, the measurement range must be extended to the overcurrent limit, thus reducing the accuracy available within the nominal range. Separate overcurrent detection, with a programmable threshold, ensures that maximum resolution is maintained up to the full-scale nominal value.
The LEM HO series transducers operate with a single-pole supply voltage of 3.3 or 5V. They are supplied in a small (12 mm wide x 23 mm long x 12 mm high) and lightweight (5 g) package for PCB mounting, incorporating three separate primary leads to allow for multi-range measurement configurations (for nominal value measurements starting at 2.67 ARMS when programmed to 8 ARMS for the nominal range). The HO series transducers will be available for push-in or surface mount (SMD) versions. Their construction offers long creep distances and clearances (8 mm) and a comparative tracking index (CTI) of 600 for excellent isolation.
The high degree of programmability and flexibility of the HO series allows designers to use a single part number in a wide variety of circuit configurations, thus simplifying designs and reducing component inventory. In addition to contributing to the efficiency of variable speed drives, the LEM HO model is also ideal for numerous applications, such as inverters and junction boxes for solar energy, uninterruptible power supplies and switched-mode power supplies, air conditioning, household appliances, static converters for DC motor drives, and robotics.
The transducer is CE marked, complies with EN 50178, and is suitable for industrial applications with a wide operating range of +115°C. LEM provides sample microcontroller code for configuring the serial bit current and programming the parameters of the HO series. LEM offers a five-year warranty on all its transducers.
