Chapter 6 FUNCTIONING OF EQUIPMENT - TM-5-6350-262-14-10028

CHAPTER 6

FUNCTIONING OF EQUIPMENT

Section I. FUNCTIONAL OPERATION

The transmit transducer emits an ultrasonic signal

6-1. General

throughout the surveyed area. With no intrusion in the

area, the receive transducer picks up the 26.3 kHz

The Processor/transceiver ultrasonic motion signal

signal without change in frequency (Doppler). The

senses motion by a new adaptation of the commonly

received signal is mixed with the basic oscillator signal

used Doppler technique. The circuits employed respond

and when coincident, there is no detection and no alarm.

only to unidirectional motion. The equipment is able to

When an intruder enters the area and moves toward the

differentiate between actual intruder motion and

transducer, the frequency increases (closing Doppler)

conditions which may produce nuisance alarms in

and a movement away from the transducer causes the

conventional Doppler ultrasonic equipment.

frequency to decrease (receding Doppler). In either a

closing or receding Doppler, the received signal mixed

6-2. Simplified Functional Operation (fig. 6-1).

with the oscillator results in a difference signal output to

the detector. The detector actuates the alarm.

a. The processor/transceiver ultrasonic motion

signal contains a 26.3 kHz oscillator which drives the

transmit transducer and the signal mixer circuit.

Figure 6-1. Processor/transceiver ultrasonic motion signal - simplified block diagram.

b. In normal operation (no motion detected) the

lower frequency sides of the return signal. Alarms will

not be activated when the return signal spectra are

alarm relay is in an energized state and upon detecting

nearly balanced with respect to the transmitted signal.

a motion the alarm relay is de-energized. Therefore,

Alarms will be activated when the return signal spectra

loss of dc power to the processor, whether due to local

is unbalanced by a prescribed amount with respect to

power failure, cable damage, circuit fault, etc., results in

the carrier. Unbalanced returns occur when an intruder

the de-energizing of the alarm relay which signals an

moves either toward or away from the transceiver.

alarm. Spurious signals causing nuisance alarms have

been virtually eliminated by balancing the upper and

6-1