ATS632LSC

HALL-EFFECT

GEAR-TOOTH SENSOR

SUBASSEMBLY

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

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.

APPLICATIONS INFORMATION — Continued

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.