As a leader in the field of current sensors, LEM is committed to providing customers with innovative, high-quality solutions. LEM's core products are current and voltage sensors, which are widely used in various fields such as renewable energy, power supply, servo systems, welding, locomotives, and electric vehicles.
The rapid development of modern industry, especially the new energy sector, has placed increasingly higher demands on current and voltage sensors: miniaturization; accuracy; ultra-wide temperature range; and diverse and convenient installation methods, among others. LEM anticipated this trend and launched the HO series. The birth of this series of current sensors can be considered a new milestone in current sensors. It adopts a new generation of ASIC chips with built-in EEPROM, adding unprecedented programmable functionality. With its unique intelligence and flexibility, it more broadly covers market needs. Specifically, customers can select and change the internal settings of the sensor through programming to achieve the most suitable configuration for their application; even during use, the sensor can be programmed to adapt to local conditions and time, achieving the optimal sensor configuration.
The following introduces three practical programming functions of HO-NPPR:
HO-NPPR rated current
Traditional current sensors have fixed rated currents (except for some models that use a multi-turn method). This remains the case for almost all current sensor manufacturers; each model corresponds to a fixed rated current value, which customers cannot change. However, many customers have multi-specification product series. To ensure the technical performance of each specification, a suitable model is usually selected for each specification. But from a logistics and cost management perspective, minimizing part numbers is crucial for easier management and cost reduction. Sometimes, to balance technical performance, logistics, and cost, customers choose the same model of current sensor for several adjacent specifications. This can lead to the sensor not operating at its optimal accuracy (rated current value) on some models, resulting in decreased control accuracy or increased efficiency calculation errors.
The HO-NPPR series' programmable rated current function largely solves this problem. It breaks with previous models, allowing users to select different rated currents (8A, 15A, and 25A) through programming without any hardware changes. At the end of the sensor production line, LEM calibrates each sensor at these three rated currents and stores the corresponding parameters in EEPROM to ensure accuracy. In use, customers can select the closest rated current value based on their system's actual current through programming; clearly, what were originally three sensor specifications can now be replaced by a single HO-NPPR. Furthermore, since the HO primary side retains three independent sets of primary side conductors, three different combinations are possible: 1 turn, 2 turns, or 3 turns. This means that for each rated current, the rated current can be expanded to more specifications by changing the number of turns. For example, if the programmed rated current is 15A, the number of primary side turns can be changed through PCB routing, resulting in rated currents of 5A, 7.5A, and 15A. This means that by combining HO-NPPR programming with the multi-turn method, nine rated current specifications can be obtained, as detailed in the table below:
Clearly, this approach maximizes the fulfillment of customer needs by covering a wider range of specifications with the fewest possible part numbers. Conversely, regarding sensor production, the higher the demand for a particular model, the more beneficial it is for cost reduction. Furthermore, and very importantly, to compensate for the effects of temperature on the sensor's zero point and gain, the new ASIC incorporates high and low temperature testing. This allows for the acquisition of zero-point and gain drift values at different temperatures, and the corresponding correction values are then stored in the EEPROM. This enables compensation of the sensor output across the entire operating temperature range, significantly improving its electrical performance and bringing it close to that of a closed-loop sensor.
Reference voltage of HO-NPPR
The HO-NPPR reference voltage output can also be selected via programming, offering four options: 2.5V, 1.65V, 1.5V, and 0.5V. From the perspective of customer data processing systems, previously, AD or DSP chips were mostly powered by 5V, but now both 5V and 3.3V power supplies are available. To adapt to this trend, the HO-NPPR's power supply has expanded from a single 5V option to support both 3.3V and 5V. For a 3.3V powered system, a 1.65V reference voltage is clearly more suitable than 2.5V. This option eliminates the need for customers to convert between different reference voltages, simplifying the design, improving reliability, and reducing costs. For unidirectional current measurement, a 0.5V reference voltage can also be selected, thereby expanding the unidirectional measurement range. In practical applications, these four reference voltages basically meet the needs of the vast majority of customers. In addition, the HO-NPPR retains the original input voltage range of 0.5…2.65V, allowing customers to easily introduce their own reference voltage into the sensor to achieve a unified reference standard.
H0-NPPR's OCD function
Considering that current sampling may be used for protection in many systems, the HO-NPPR features an overcurrent monitoring OCD function, providing 16 overcurrent multiples from 0.7 to 5.8 times the rated value (Ipn). Customers can select this value through programming according to their needs. It is known that the measurement range of a typical small-range Hall open-loop sensor is up to 3 times the rated value, while this function directly expands the monitoring range to 5.8 times the rated value. Moreover, the OCD output directly provides a "1" or "0" switching signal, which can be directly used by subsequent circuits, saving customers' software and hardware resources to a certain extent. Furthermore, the overcurrent monitoring is located before the output filter, ensuring a fast response time of less than 2µs.
For OCD settings, please refer to the table below:
Our market research revealed that some applications do require adjustments to sensor settings to achieve more accurate measurements due to changes in environmental conditions. For example, in solar power plant applications, sunlight intensity varies significantly between morning, noon, and evening, resulting in substantial variations in solar panel power generation. If the current sensor is selected based on the current during periods of strongest sunlight, the current will fall far short of the rated value during periods of weakest sunlight, inevitably leading to decreased measurement accuracy and directly impacting the accuracy of system efficiency calculations. Programmable HO-NPPR sensors offer significant advantages, allowing for online programming to change the sensor's rated current setting based on time periods or sunlight intensity, thus achieving more precise measurements at various times.
Regarding LEM
LEM, a market leader in current sensors, provides customers with innovative technologies and high-quality current measurement solutions. Its core products are current and voltage sensors, widely used in driving and welding, renewable energy and power supplies, railways and rail transportation, high-precision applications, and traditional and new energy vehicles. LEM's strategy is to leverage the inherent strengths of its core business while developing new application areas and seeking growth opportunities in new markets. As a medium-sized global company, LEM has production centers in Beijing (China), Geneva (Switzerland), Machida (Japan), and Copenhagen (Denmark), with sales offices around the world providing comprehensive services to customers globally. The LEM Group was listed on the Swiss Stock Exchange in 1986 (stock code: LEHN). LEM Electronics (China) Co., Ltd., a wholly-owned subsidiary of LEM Electronics in China, has sales offices in various regions to provide seamless global services to Chinese customers.
