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Sonic
Transmission Duration Control Byte
This
parameter determines the duration of the transmitted signal. Some
transmitters require as much as 2 milliseconds of signaling before
reaching full output strength. Keep in mind that crystals continue to
vibrate after the excitation has seized. The value of the byte determines
the number of waves transmitted. For a 40Khz system, the period of each
wave is 25 microseconds, hence for 2millisecond duration.
Signal
Duration Byte =
Total Duration / Period = 2 milliseconds / 25 microseconds = 80
Sensitivity
Byte
Internal
sensitivity can be selected by the content of the Sensitivity Byte. If the
value of the byte is 03 hex (low sensitivity) the internal level is set at
about 330mV. When this level is exceeded the clock is stopped and the
counter value saved, if the returning signal qualifies. If the value of
the Sensitivity Byte 00 (high sensitivity) the level is about 106mV,
(Note: noise level of the device is about 10mV rms). The user can also
desensitize the receiver, by application of a voltage divider on the
sensor.
Auto
Tracking
Auto
Tracking feature allows the device to focus on a particular distance, or
piece of the timeline. Data from last acquisition cycle determines where
the first signal is located, on the timeline. During the next acquisition
cycle, the device will not start to listen for a return signal until just
before the signal is expected. The user can determine how long before the
signal is expected the receiver is enabled. The Auto Track value is 16
bits, consisting of a high significant byte (HSB) and a low significant
byte (LSB). If the LSB is 02 hex and HSB is 0A hex, or 0A02 hex, this is
equal to the decimal value 2562. For a timer ticking every 2 lS, this
means the receiver starts to listen for first signal 5.124mS prior to
signal expected. It is important to understand that the object being
tracked, must move slowly enough so as to stay within the Auto Tracking
window over the acquisition aperture. Otherwise the device will loose
track, and during recovery or relocking procedure it can display a few erroneous
readings. |
A
voltage divider circuit can be formed using a resistor and a capacitor,
see illustration to the right. The capacitor should always shunt the HE660
Sonic input or receiver
line (Yellow). The
value of the resistor should be from 2 to 5Kohm, and the value of the
capacitor from 1 to 10nF. For example if you wish to reduce the HE660
sensitivity, the following relationship helps. In case of dual elements a
receiver and a transmitter the receiver should be divided.