115 Northeast Cutoff, Box 15036

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

ATS612LSB

DYNAMIC, SELF-CALIBRATING, PEAK-DETECTING,

DIFFERENTIAL HALL-EFFECT GEAR-TOOTH SENSOR

12

Recommended Evaluation Technique. The self-

calibrating feature of the ATS612LSB requires that a

special evaluation technique be used to measure its high-

accuracy performance capabilities. Installation inaccura-

cies are calibrated out at power on only; hence, it is

extremely important that the device be re-powered at each

air gap when gathering timing accuracy data.

Self-Calibrating Functions. The ATS612LSB is de-

signed to minimize performance variation caused by the

large air gap variations resulting from installation by self-

calibrating at power-on. This function should be tested

using the following procedure.

1.

Set the air gap to the desired value.

2.

Power down and then power on the device.

3.

Rotate the target at the desired speed.

4.

Wait for calibration to complete (64 output pulses to

occur).

5.

Monitor output for correct switching and measure

accuracy.

6.

Repeat the above for multiple air gaps within the

operating range of the device.

7.

This can be repeated over the entire operating tem-

perature range.

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 module. Wait for 64 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

module. Monitor the output for correct switching and

measure accuracy.

Gear Diameter and Pitch. Signal frequency is a direct

function of gear pitch and rotational speed (RPM). The

width of the magnetic signal in degrees and, hence, the

signal slope created by the tooth is directly proportional to

the circumference of the gear (

πDo). Smaller diameters

limit the low-speed operation due to the slower rate of

change of the magnetic signal per degree of gear rotation

(here the limitation is the droop of the capacitor versus the

signal change). Larger diameters limit high-speed opera-

tion due to the higher rate of change of magnetic signal

per degree of rotation (here the limitation is the maximum

charge rate of the capacitor versus the rate of signal

change). These devices are optimized for a 50mm gear

diameter (signal not limited by tooth width), 0.22

µF

capacitor, and speeds of 10 RPM to 8000 RPM. For very

large diameter gears (diameter >200 mm), the devices

must be configured with a lower value capacitor, but not

less than 0.1

µF. This allows for a range of 5:1 in gear

diameters.

Air Gap and Tooth Geometry. Operating specifications

target can be a gear or a specially cut shaft-mounted tone

wheel made of stamped ferrous metal. In general, the

following gear or target guidelines must be followed to

achieve greater than 2mm air gap from the face of unit:

Tooth width, T .............................. >2 mm

Gear material ............................... low-carbon steel

Gear face width (thickness), F ..... >3 mm

Deviation from these guidelines will result in a

reduction of air gap and a deterioration in timing accuracy.

APPLICATIONS INFORMATION