®
M o t i o n S e n s o r
PS- 210 3A
4
Equipment Mounting
Mount the Motion Sensor as illustrated on a vertical rod (a) or a
horizontal rod (b).
Integrated clips allow it to be attached to the end of a dynamics
track (c).
A threaded hole in the bottom of the unit (d) is provided for
attachment to the PS-2546 Magnetic Bracket (e), the ME-6743
Cart Adapter (f), and other 1/4-20 threaded mounting devices
such as a camera tripod.
To protect the Motion Sensor from being hit by an object, use a
device such as the SE-7256 Motion Sensor Guard (g) or
ME-9806 bracket with a rubber band (h). The Motion Sensor can
“see through” a wire screen or rubber band placed close to the
transducer.
Troubleshooting
If the Motion Sensor fails to perform satisfactorily, try these
steps:
•
Ensure that the target object is no closer than 15 cm.
•
Switch the range switch to the other setting.
•
Adjust the aim left, right, up, or down. In some cases the
Motion Sensor works best when it is aimed slightly to the
side or above the target in order to exclude interfering
objects.
•
Improve the target by adding a larger or harder surface to
reflect ultrasound. A small object can be a better reflector
than large object if it has a harder surface.
•
Remove interfering objects near the target object or sensor.
•
Increase or decrease the sample rate.
Theory of Operation
The Motion Sensor uses an electrostatic transducer as both a
speaker and a microphone. For each sample, the transducer trans-
mits a burst of 16 ultrasonic pluses with a frequency of about 49
kHz. This burst of pulses can be heard as a single click. The ultra-
sonic pulses reflect off an object and return to the sensor. The tar-
get indicator on the sensor flashes when the transducer detects an
echo.
Sound intensity decreases with distance; to compensate, the sen-
sor increases the gain of the receiver amplifier as it waits for the
echo. The increased gain allows the sensor to detect an object up
to 8 m away. The lower gain at the beginning of the cycle reduces
the circuit's sensitivity to echoes from false targets.
The sensor measures the time between the trigger rising edge and
the echo rising edge. It uses this time and the speed of sound to
calculate the distance to the object. To determine velocity, it uses
consecutive position measurements to calculate the rate of
change of position. Similarly, it determines acceleration using
consecutive velocity measurements.
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
