Hangjing Company Launches a Three-Channel True Redundant Design RVDT Sensor

I. Design Background

1.1 The Necessity of Redundant Design and High-Reliability Redundant Architecture

In strategic domains critical to national economic development and people’s livelihood, the stable operation of equipment is not only a core technical performance indicator but also a linchpin for fortifying the safety defense. Whether in the construction of critical national infrastructure or in mission systems operating under extreme conditions, high reliability is an essential requirement—serving as the fundamental foundation for ensuring mission success, safeguarding the safety threshold, and achieving cost-effectiveness across the entire lifecycle.

Reliability refers to a product’s ability to perform its intended functions under specified conditions and within a specified time frame. In conventional design, system reliability can be enhanced through the selection of high-quality components, simplification of the structural design, and rigorous testing and validation. However, when confronted with extremely demanding mission requirements and highly complex operating environments, redundant design emerges as a more efficient and direct solution.

The core of redundant design is to equip critical system components with backup units, such that when the primary channel or component fails, the backup unit can automatically and instantaneously take over, ensuring uninterrupted system operation and undiminished performance. This approach offers multiple advantages, including high fault tolerance, a high success rate, long operational life, and low operational risk.

A dual-redundancy architecture operates in a dual-channel parallel mode, such that a single-channel failure allows the remaining healthy channel to maintain normal system operation. In contrast, a triple-redundancy architecture offers even higher reliability: in the event of a single-channel failure, the processors can employ a “majority-vote” logic to ensure stable system operation. Consequently, for systems with stringent safety and reliability requirements, triple redundancy represents a more efficient and dependable design choice.

Figure 1 Error Detection in Dual-Redundancy Architecture

Figure 2 Error Detection in a Triple-Redundant Architecture

1.2 High-Reliability RVDT Sensor

Sensors are the “sensory nerves” of the modern technological ecosystem, serving as the core bridge that connects the physical world with digital systems. They perform the critical functions of information perception and data acquisition, making them the fundamental cornerstone for the implementation of automation and intelligent technologies. From automatic screen rotation in smartphones and precise operations by industrial robots to smart home control, scientific management in smart cities, precision diagnostics in medical devices, and comprehensive control in new-energy vehicles, all rely on sensors to provide accurate data support.

According to their measurement principles, sensors can be classified into various types, including photoelectric, capacitive, piezoelectric, inductive, and Hall-effect sensors.

The RVDT is a rotary variable differential transformer—a type of electromechanical sensor—that operates on the principle of electromagnetic induction as a non-contact inductive transducer. It is used for measuring angular displacement and features high precision, high reliability, long service life, and high resolution, making it indispensable in industrial automation, aerospace, the automotive industry, and other fields.

Figure 3 Peripheral Circuitry Required for Operation of Electromechanical Sensors

Inductive sensors operate based on the electromagnetic coupling between coils; movement of the ferromagnetic core alters the coupling strength, thereby inducing changes in the output signal, with the amplitude of the output signal exhibiting a linear relationship with the core’s displacement. Inductive angular and linear displacement sensors enable non-contact transduction of physical signals into electrical signals, offering advantages such as long service life and high precision, and thus hold broad application prospects.

However, such sensors require external excitation and demodulation units, resulting in a large number of peripheral components and a complex structure. When employed for redundancy design, they not only occupy substantial space and pose significant design challenges but also make it difficult to control overall system costs. Moreover, their electromechanical architecture and the principle of magnetic mutual inductance coupling render them highly susceptible to interference from strong external electromagnetic environments, which can introduce errors into the solution results.

1.3 Strategic Layout in the Aerospace Crystal Technology Sector

In response to the aforementioned application challenges, Hangjing Company has continuously deepened its expertise in sensing and signal conditioning, establishing a comprehensive technology and product portfolio: starting with the high-temperature-resistant fluxgate sensor HJ11867, the company has successfully achieved complete domestic substitution for imported AD598 and AD698 components, and has launched and mass-delivered the HJG598 and HJG698 LVDT/RVDT excitation-demodulation modules. Building on this foundation, the company has expanded into the measurement of weak magnetic signals with the HJMAG803–HJMAG805 series, as well as a high-performance Hall-effect magnetic-sensing product line, thereby constructing a full-chain, highly reliable sensor solution that covers fluxgate sensors, excitation-demodulation, weak-magnetic-field detection, and Hall sensing.

Figure 4: Schematic diagram of a triple-redundant Hall-effect RVDT sensor (requires only power supply)

Figure 5: Overview of the Quartz Crystal Sensor Field

At this stage, the company is proudly launching the HJR402 RVDT angular displacement sensor, which is based on the differential Hall magnetic induction principle. This sensor generates sine and cosine signals by sensing the internal magnet, then performs high-precision sampling and angle calculation to output a voltage signal that exhibits an ideal linear relationship with the angular position. It features high-accuracy output across the full measurement range, excellent anti-interference capability, and the ability to achieve linear conversion of angular displacement signals into electrical signals.

The product features convenient lead connections that require no external components, and it adopts a true triple-redundant architecture in which three independent channels acquire signals and perform mutual verification. This design perfectly meets the high-reliability requirements of safety-critical systems, making it a high-quality, comprehensive sensor solution in the industry today.

II. Introduction to the HJR402 Sensor

2.1 Sensor Physical Structure

Figure 6: Electrical Principle and Structural Diagram of the HJR402 Triple-Redundant Hall Sensor

The HJR402 sensor’s electrical architecture consists of a permanent magnet and a three-channel Hall-element signal processor. All internal circuit components are made from non-magnetic materials, which effectively enhances measurement accuracy; the housing is constructed from aluminum alloy and features a hermetically sealed design. A photograph of the physical device is shown below:

The aluminum alloy housing assembly includes a pivot bearing, a scale dial, mounting holes, and lead wires. The device is easy to install and simple to use, requiring no external components. The sensor package dimensions are shown in the following figure.

The lead wires shall comply with the ARF-250-1/1×0.2mm² aviation flexible cable standard, with a wire length of 450 ± 20 mm (customization supported). The specific functions of the lead terminals are as follows:

Table 1: Lead Terminal Functions

2.2 Sensor Electrical Parameters

Table 2: Electrical Characteristic Parameters

Unless otherwise specified, VCC = +5 V, TA = +25°C.

Note: *Design Assurance

2.3 Description of Typical Characteristics

1. This sensor device employs a triple-redundant design, in which the operating and output states of the three sensor channels are independent of one another and do not interfere with each other. Failure of any single channel will not affect the normal output of the other two channels, making this a true redundant sensor architecture.

2. This sensor allows flexible configuration of the output voltage range and angular measurement span according to the user’s specific requirements. In the low-linearity-error mode with a tolerance of ±1%, the maximum angular span can be set to 90°; within a 60° measurement span, the device exhibits superior linearity, with errors maintained within 0.5%. When the shaft rotation angle exceeds the calibrated range, the device output will remain in a stable high- or low-level state.

3. This product is equipped with a permanent magnet whose magnetic field strength is no less than 3,000 Gs; it features a high intrinsic operating magnetic field and strong resistance to external electromagnetic interference. Test results demonstrate that, under complex and intense electromagnetic environments, the maximum deviation of its output voltage can be controlled within 1.5%, representing approximately a threefold improvement in anti-interference performance compared with conventional electromechanical RVDT sensors.

4. This product is easy to use and requires no external auxiliary components. It features high output accuracy, strong reliability, excellent consistency among multiple output channels, and outstanding immunity to electromagnetic interference and noise, enabling precise conversion of angular displacement into corresponding electrical signals.

5. Since the output signals VO1, VO2, and VO3 are proportional to the supply voltage VCC, it is recommended to power these outputs using separate reference supplies VCC1, VCC2, and VCC3, respectively. Direct powering from a 5 V digital supply is strictly prohibited.

III. Summary

By analyzing the operating principle of the HJR402 sensor and comparing it with the structure and operating principles of conventional electromechanical sensors, the following comparative table is presented.

Table 3: Comparison Between the HJR402 Sensor and General Electromechanical Sensors

As shown in the table above, the HJR402 triple-redundant sensor significantly outperforms conventional electromechanical sensors in overall performance and can fully replace traditional electromechanical RVDT sensors in high-end applications requiring high precision, high reliability, and operation in complex electromagnetic environments.