Radio Power Supply with a Difference
| Author | D. S. Clark |
| DOI | 10.1177/0032258X7905200313 |
| Published date | 01 July 1979 |
| Date | 01 July 1979 |
| Subject Matter | Article |
continuedfrom page 356
of
Volume
Ll
Number 4
...
D. S. CLARK
Inspector Kent County Constabulary
RADIO
POWER SUPPLY
WITH ADIFFERENCE
"There's a hole in my bucket .. ."
This power supply was built as a result of requests from Crime
Prevention Officers for a mains
adaptor
for the latest Marconi
V.H.F. radio alarm, as issued bythe Home Office.
It
seems that this
very compact high power alarm has been plagued with battery
problems. On closer inspection this is not surprising when you
consider its requirements of 21 volts at 4.5 amps., a considerable
burden for any battery.
As we are being constantly asked for more and more 'DeedBoxes'
(delayed entry exit device, as featured in the October-December 1978
issue of this Journal) I decided to construct asuitable power supply
with its own delays, plus a few other refinements built in, which
would be interchangeable with the 'Deed Box'.
To return to
our
theme of help for the Crime Prevention Officer,
who is often called on to set up burglar alarms at short notice using
the modern heat Imovement detector heads for space protection, one
of his biggest enemies in an unknown environment is the "built in"
false alarm. Bythis I mean the deep freezer which starts or stops with
ashudder, the central heating system which springs into life in the
early hours, even the pressure on a window caused by a sudden gust
of wind can be sufficient to trigger briefly the sensor. In a commercial
system these points are dealt with as they appear by moving the
sensor or reducing its range, over a considerable time period.
The Requirement
After consulting different Crime Prevention Officers, I came up
with the following specification:-
(a) More exit time
than
entry time, i.e. 20 seconds to get out after
switching on, but only 10 seconds to get in to the protected area
to switch the system off. Times to be extendible by a single
internal pre-set, fingertip adjustment. .Entry time always
automatically half of exit time.
(b) A system which ignores a single brief alarm from the sensor,
providing that the alarm signal does not last as long as the entry
time, i.e. that the sensor head re-settles within the 10 seconds.
(c) Completely automaticoperation, plug into the mains supply and
the exit time starts from switch-on.
288 July 1979
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