FEATURE SENSING TECHNOLOGY
HALL-EFFECT SENSORS MEET the demands of medical market
equivalent to 2.5µs (0.06° /360° /4000 RPM x 60s). Therefore, the estimated response time is half the transition increase or about 1.25µs total. Comparison testing for reliability and response time showed that the non- chopper stabilised part has a repeatable output with a response time that is between 10µs to 20µs faster than chopper-stabilised products, including high-sensitivity samples. Testing indicates that chopper
New quad Hall-effect technology from Honeywell delivers the next generation of BLDC motor sensors without chopper stabilisation
EM designers using brushless DC (BLDC) motors in different sectors such as robotics, portable medical equipment and HVAC want quieter and more efficient motor performance plus high sensitivity and stability across a range of temperatures. Honeywell Sensing and Control has
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developed new technology that delivers a sensor with faster response time, greater accuracy and minimal electrical noise without the need for additional filtering and the commensurate costs. At the heart of the new technology is a quad Hall element and proprietary programming without the need for chopper stabilisation resulting in a highly sensitive and stable sensor. Initially designers may be cautious of using a sensor that does not have chopper stabilisation, but not only does the new technology overcome chopper stabilisation drawbacks, it also brings additional performance advantages of faster response time, repeatability, improved jitter performance and no additional electric noise generation over a range of temperatures. To prove the efficacy of its new
technology Honeywell evaluated its product’s performance by testing it against a number of ‘traditional’ stabilised products – including those with higher sensitivity.
16 FEBRUARY 2015 | ELECTRONICS
TEST SET-UP The test itself comprised a circular target with 48 magnetic pole pairs used to trigger the product samples. The samples were placed in the magnetic field as close to each other as possible and centered in the Y-axis. The tests were performed at a 0.020 inch air gap. All results were measured against a Top Dead Centre (TDC) trigger that has a very fast response time. To calculate the response time, the target was revolved at various frequencies, clockwise and counter-clockwise, with a 0.020-inch sense gap. The target’s angle of rotation was measured at the point where the sensor output switched. When the target is sufficiently slow, the response time is much faster than the moving magnetic field of the target so the expected latency between the 0 gauss level angle and the angle of the field detection depends on the test set-up and product sensitivity. When the target is faster, the angle recorded is a combination of the magnetic field latency and the response time of the sensor. Results show that the angle of the
transition remains fairly stable at the lower frequencies of 500RPM to 2000RPM. At 4000RPM, the angle shifts due to the response time of the sensor, increasing about 0.06° over the entire angle of the transition. At 4000RPM, 0.06°C is
Figure 1 & 2:
Honeywell Hall-Effect sensor IC
stabilisation may cause repeatability due to variances in actuation. Higher frequency of the chopper stabilisation may resolve this issue, but even if the chopper-stabilised parts exhibit high sensitivity, they still show a slower response time. Sensitivity level is based on the placement of the sensor relative to the magnet, the air gap and magnet strength. As the magnet rotates past the sensor, a highly repeatable sensor changes state at the same angular position each time the magnet passes by, providing a consistent response time that will maintain all of the angular measurements very close to the same value. A delayed response to the target will have a negative effect on the efficiency of the motor commutation. Any error in the switching point of the Hall- effect sensor will reduce the torque of the motor, which results in lower motor efficiency. In addition, testing for sensitivity to air gap shows that the non-chopper- stabilised part maintained a better response time as the air gap increased. A faster response time to a change in the
magnetic field delivers greater efficiency in commutating a BLDC. If a sensor switches at a different magnetic field level than what is required due to slow response or delay, this could result in accuracy errors. This latest new quad Hall technology offers a more functional, cost effective solution available for OEM designers using brushless DC (BLDC) motors in different sectors such as robotics, portable medical equipment and HVAC who want a quieter and more efficient motor performance plus high sensitivity and stability across a range of temperatures.
Honeywell Sensing and Control
www.sensing.honeywell.com 01698 481 481
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