ATS632LSC
HALL-EFFECT
GEAR-TOOTH SENSOR
SUBASSEMBLY
APPLICATIONS INFORMATION — Continued
Measurement of the effect of changing air gap after power
on:
1. Set the air gap to the desired value (nominal, for
example). Rotate the target at the desired speed.
Apply power to the subassembly. Wait for 16 output
pulses to occur. Monitor output for correct switching
and measure accuracy.
2. Change the air gap by
±
0.25 mm. Do not re-power
subassembly. Wait for 64 output pulses to occur.
Monitor the output for correct switching and measure
accuracy.
Device Switch Points.
The device switch points are
referenced to the peak-to-peak values of the gain-ad-
justed signal. The comparator thresholds have been
chosen to provide timing accuracy, as well as limited
immunity from mis-detection caused by short valley
conditions or by gear run-out.
Gear Design Criteria.*
The system was designed to
work correctly with minimum valley depths of 5 mm and
minimum valley widths of 13 mm. As the valley depth
decreases, the valley field rises above the open-circuit
value of the magnetic circuit when the sensor is at mini-
mum air gap. The same is true when the valley width
decreases. In both cases, the metal mass from the valley
bottom or side walls provides an interference at minimum
air gap and will provide a signal that may be interpreted
as a tooth upon power on. It is important to note that this
anomaly will normally only affect the power-on state of the
device and the self-calibration circuitry will null this
baseline shift when the device is in running mode.
* In application, the terms “gear” and “target” are often
interchanged. However, “gear” is preferred when motion
is transferred.
Signal-Timing Accuracy.
Timing accuracy is improved
with larger gear diameters. The magnetic field profile has
a defined spread that narrows in degrees as the target
diameter increases. The slope of this magnetic profile
also changes with air gap. For highest accuracy, targets
greater than 100 mm diameter should be used.
Operation with Fine-Pitch Gears.
The self-calibration
routines allow the detection of fine-pitch gears once the
target is rotating. The major issue in these applications is
the impact of gear run-out on the baseline of the magnetic
field. Excessive run-out may result in tooth edges not
being detected.
Signal Duty Cycle.
For regular tooth geometries, precise
duty cycle is maintained over the operating air gap and
temperature range due to the good symmetry of the
magnetic switch points of the device.
Output.
The output of the subassembly is a short-circuit-
protected open-collector stage capable of sinking 20 mA.
An external pull-up (resistor) to a supply voltage of not
more than 24 V must be supplied either at the sensor
module or at the controller.
Output Polarity.
The switching of the output is independent
of the direction of gear rotation.
Power Supply Protection.
These devices require
minimal protection circuitry during operation from a low-
voltage line. The internal voltage regulator provides
immunity to power supply variations between 6 V and
24 V. EMI/RFI protection is provided as part of the
internal regulator. In extremely noisy environments,
additional (external) components may be required.
Additional applications Information on gear-tooth and
other Hall-effect sensors is provided in the
Allegro Inte-
grated and Discrete Semiconductors Data Book
or
Application Note 27701.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
ALLEGRO [ ALLEGRO MICROSYSTEMS ]
