materials and equipment
ELECTRICAL TESTING
The Davi non-contact electrical tester is sensitive to the electric fields surrounding a.c. conductors. It may be used to identify faulty earthing, in- correct poling of switches and plugs, broken conductors and blown fuses, or to trace the path of voltage-carrying cables.
A polypropylene case, measuring 5 in. long by 14in. wide by 14in. high houses the tester and its 9-v. PP4 battery, giving a total weight of 31⁄2 oz. One end of the case is angled, and a lamp with a 4.5-v., 0.27-w. L.E.S. bulb and a push button are mounted on top of the casing.
For testing, the Davi is held in the hand with the sloping end over the electric component. When the button is depressed, the lamp lights up in the presence of a.c. voltage, without phy-
Davi electrical tester
sical contact. Insulating material does not need to be removed, and the tester may be used with up to 250 v., opera- ting in temperatures from 0-50 deg. C.
The makers are Davi Marketting Ltd., 37 Great James Street, London, W.C.1.
ALARM SYSTEM
A portable alarm system, Portalarm, has been introduced for the protec- tion of enclosed locations from fire and theft. Offering protection over a radius of approximately 25ft., the unit weighs 281b. and may be operated on a mains supply or by its own recharge able batteries.
The Portalarm is an ultra-sonic de- vice utilising solid-state circuitry and is designed for the protection of fac tories, warehouses, offices and similar enclosed locations. A free-standing
unit in a stove-enamelled-steel housing which measures 13 by 13 by 5in., it is placed in the area to be protected and set in operation by a security key. Ap-
Portalarm
proximately 7sec. are allowed for the operator to leave the area, and after that time the ultra-sonic radiation will detect the movement of an intruder or hot air in the case of a fire.
Should either eventuality arise, a horn will sound for approximately 25 sec., stop for 4 sec. and then continue to sound intermittently as long as movement continues within the pro- tected area. Once movement stops, the horn ceases and the Portalarm auto- matically re-sets itself.
The makers are Alarm Equipment Supplies Ltd., Electro House, Third Cross Road, Twickenham, Middx, UK.
LIGHTWEIGHT CONCRETE
A French company, Societe Rhone- Poulenc, 22 Avenue Montaigne, Paris VIII, has developed a synthetic resin known as Rhodopor. A white powder, it is mixed with cement, filler and water to give a low density, cell con- crete with closed cells incorporating very finely divided air bubbles in the mixture. In this way the product acts first as a foaming agent, and second plays an active part in the mechanical properties of the concrete.
casting purposes. It simplifies the fabricating process and helps to solve a number of construction problems where weight is the enemy and heat in- sulation properties are required.
Depending on the aggregates used it is possible to obtain either extreme- ly light cell concretes better known as foam concrete, or merely lightened
concrete.
Foam concrete having a density of 0.5 to 1 inclusive is obtained by ad- mixture of fine aggregate. This has a great many applications for heat in- sulation purposes where high mech- anical properties are not essential.
Lightened concrete having a den- sity of 1.4 or 1.5 is obtained using an interesting formula based on sand of 0 to 6mm grain size. It has good heat proofing qualities. Its mechanical pro- perties permit its use in self-bearing structures or in bearing structures e.g. individual houses or buildings a few storeys high.
NYLON FLOORING
Marleytex, a resilient floor covering of 100 per cent. nylon, needled into a fibre base, is now being produced as tiles 50 cm (193⁄4 in.) square.
The tiles are resin impregnated and the coloured fibres are laid horizontal- ly to give maximum resistence to the
Marleytex flooring
penetration of stains and the flattening effects of heavy wear. They are stuck with adhesive.
There are eight colours in the Mar- leytex range, which is made by Marley, Sevenoaks, Kent, UK.
CIRCUIT BREAKER
An eight-way dual-tariff load cen- tre (Model QA8-T2) and a 24-way double pole load centre (QAP-224) has recently been added to the Square D range of miniature circuit-breaker
The material has potential for pre- equipment.
Far East BUILDER, March 1970
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