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High-Performance Power ICs and Hall-Effect Sensors
Hall Sensor High-Voltage Testing
By Nick Tsacoumangos, Sr. Applications Engineer
Hall sensors are frequently called upon to perform in very adverse
environments. It is well known that they are robust to various contaminates
and mechanical shock, but their resistance to high- voltage impulses
and spikes is generally not well understood. Such high-voltage impulses
can be found in automobile ignition systems, as well as proximal (close)
to self-defense high-voltage
A series of simple tests were conducted with an A3141 Hall sensor, in order to evaluate the robustness of the device when exposed to high-voltage electrical fields. The test generator output voltage used was approximately 50,000 volts, as judged by the arc distance and standard arc-over length calibrations. Of prime concern was whether the Hall sensor demonstrated high-voltage susceptibility by exhibiting either FALSE ON or FALSE OFF events. The sensor was configured in a standard circuit, as shown in figure 2.
Test Conditions
- Device: A3142EUA
- Supply voltage: +5 V
- R pull-up: 1 kilo-ohms
- Arc Source: 50 kV high-voltage self-defense arc unit, with approx. 20 Hz pulse rep rate.
Test Procedure
The hand-held high-voltage source was brought into close proximity with the Hall sensor circuitry, while carefully avoiding arcing to the wiring. An oscilloscope was put into a slow "roll" mode, and false trigger events were observed. The tests were performed with the Hall sensor in two different states; turned OFF, and turned ON by a nearby magnet. The magnet was positioned within various (uncalibrated) distances from the branded face of the sensor. Tests were also conducted at the "threshold distance", where the sensor just begins to be magnetically biased ON.
Results
The Hall sensor exhibited both FALSE ON and FALSE OFF trigger events, but only if the magnet was positioned at the edge of trip sensitivity for the Hall sensor. If the magnet was placed directly against the Hall sensor branded face, no false trigger events of any kind could be induced. This is important information for the user who plans to subject their Hall sensor to high-voltage impulse fields.
Electrical or magnetic; conducted or radiated?
The question now arose as to whether the offending field was an electrical or a magnetic one, and what mechanism was really behind the sensor coupling. The arc generator contains a large (0.75" x 1.5") induction coil, with a laminated iron core. A core of this type has a significant magnetic fringe field around it. Therefore, additional tests were needed to determine if a magnetic field was responsible for the Hall sensor false-trigger events.
The first step was to shield the power and signal cables with coaxial shielding, grounded at one end. This technique typically provides the highest level of stray electrical field rejection. An oscilloscope probe was then soldered into place, and a Faraday cage was built with aluminum foil, and the entire assembly was connected to the power cable ground potential. This is shown in figure 3.
With the Hall sensor totally enclosed within the Faraday cage, no false triggers were observed. This test implied that electrical fields were the primary coupling mechanism, because you will recall that magnetic fields can pass freely through a Faraday cage. With the Hall sensor body exposed, false trigger events were again observed.
The above test also showed that the offending field was radiated in nature, since any conducted events were excluded by the shielding. Further testing was needed to conclusively determine the coupling mechanism. Thus, multiple types of shielding material were introduced between the arc generator and the Hall sensor. The shielding materials used ranged from a special EMI-resistant coating to a steel plate. By exclusion, it was clearly established the offending field was electrical in nature, and not magnetic.
Conclusions/Recommendations
High-voltage electric fields can be very aggressive and disruptive to nearby circuitry. However, it appears that Hall sensors can be reliably used in the presence of high-voltage impulses if standard shielding techniques are employed. A high-voltage field can induce both FALSE OFF and FALSE ON trigger events if the triggering magnet is positioned at the edge of the sensor's trip point sensitivity. FALSE OFF events are easier to control with shielding than FALSE ON events. The A3141 Hall sensor has been shown to be resistant to false triggering from proximal high-voltage fields (50 kV) if the magnetic element triggering the sensor is of sufficient strength, and is in intimate contact with the Hall device. These tests were qualitative in nature, and are not meant to be applicable to all Hall sensors and applications. Users are encouraged to individually evaluate their specific designs with an experienced applications engineer.