Communications: electrical – Selective – Having indication or alarm
Patent
1980-10-31
1982-11-09
Swann, III, Glen R.
Communications: electrical
Selective
Having indication or alarm
340568, G08B 1326, G08G 101
Patent
active
043587496
ABSTRACT:
In a vehicle detector installation employing an inductive sensing loop that is a frequency determining element of an oscillator, the oscillator is provided with a voltage controlled capacitor as another frequency determining element and is made the voltage controlled oscillator (VCO) of a phase locked loop whereby the VCO is locked to a reference frequency. The presence of a vehicle in the vicinity of the loop causes the capacitor voltage to vary to maintain lock. The varying voltage is applied to an auxiliary VCO whose frequency is accordingly varied and may be analyzed for vehicle detection purposes. The oscillator containing the sensing loop is thereby prevented from influencing nearby installations by the FM sidebands that would be produced in the absence of the frequency locking. A group of such installations may use a common reference frequency source with each installation operating at its own locked frequency by virtue of means providing a programmable frequency division ratio from the source. Microcomputer control of the operation of the installations is disclosed using the clock source of the microcomputer as the reference frequency source. Each installation is provided with a counter for sampling its auxiliary oscillator frequency and the microcomputer is connected over a bus system to poll the counters, all vehicle detection analysis being performed by the microcomputer.
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Redland Automation Limited
Swann III Glen R.
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