Plugs measure closed systems

separation and sent to the swarf house. The tank is designed to provide maximum cooling of the liquid. Large particles which settle out are removed bya sludge conveyor which takes them to the swarf house. A pump draws the coolant through a filter which removes fine entrained particles. At the end of the filtration process the coolant is passed through an oil collector and aerator. These remove tramp oils and inhibit bacterial growth. The company claims that its filter provides a cool, clean, continuous supply of coolant to the machine tools, which helps to improve efficiency and productivity by extending the lifetime of the cutting tools and minimising rejects.

Cera International Ltd, 'Cera' House, Mitcham Industrial Estate, Streatham Road, Mitcham, Surrey, UK

Microcircuit controls temperature Air-conditioning temperatures can be displayed and controlled bya universal digital t h e r m o m e t e r / c o n t r o l l e r microclrcuit available from General Instrument Microelectronics. The A Y - 3 - 1 2 7 0 circuit takes the inputs directly from a thermistor temperature sensor and drives our LED or LCD display panel, without the use of interface circuitry. There are two control outputs, one operating at set point plus hysteresis and the other at set point minus hysteresis. The hysteresis can be set to 0.2, 0.4, 0.8, 2.4 Or 8°C and the outputs can be used either for external alarm circuitry or for temperature control. An on-chip power failure detector gives warning if power

Universal digital thermometer/ temperature controller circuit

Volume 2 Number 3 May 1 9 7 9 ,

Ceramatic Filter which removes particulate matter from grinding coolant. Large particles are removed by the conveyor belt behind the open doors (top); clean coolant is extracted through the continuous filter (bottom right). The aerator at bottom left prevents bacterial growth when the system is not in use has been removed for longer than a specified time and also if the temperature varies outside normal levels. The warning is given by flashing the display on and off. There is a 0.05°C display hysteresis, designed to prevent jitter in the display and control output. Different thermistors can be used, making the microcircuit suitable for air conditioning, for freezer and boiler control, for automobile engine temperature measurement and heater control, and for other applications. It can be used at ambient temperatures from -25°C to 70°C.

General Instrument Microelectronics Ltd, Regency House, 1-4 Warwick Street, London W1 R 5WB, UK

Plugs measure closed systems Test plugs for the measurement of temperature and pressure in closed systems are now being marketed in Europe for SISCO Test Plugs, USA by Marine Ventures. The pressure gauge and temperature probe, supplied with the test kit, are inserted through a pressurized seal in the test plug. The manufacturers guarantee that when the probe needle is removed the test plug will reseal with no leakage. Brass is the standard material for the test plugs and adaptor bodies and type 316 stainless steel is available for corrosive service. This is also used as the probe material. The valve inserts

181

are either Neoprene, for use with natural gas and most petroleum products, or Nordel, for hot water service. With either material, there is a lower temperature limit of-18°C. The manufacturers claim the advantage of these probes is that they eliminate the uncertainty which may arise about the accuracy of permanently installed gauges. However, the pressure gauge can be kept permanently installed. Flow rate can be measured by mounting a test plug on each side of an orifice plate. The pressure drop between the two positions can then be found, and the flow rate calculated from this.

Marine Ventures Ltd, 8 Waterloo Place, London SW7Y 4BE, UK

Liquid nitrogen freezes yoghurt Speed of installation is one reason whya liquid nitrogen freezing tunnel was chosen for the manufacture of a suddenly I

Test plug built into line,with spare plug and pressure/temperatureprobes lying alongside popular new food, frozen yoghurt. The tunnel was manufactured by BOC and installed at Bridge Farm Dairies, Mildenhall. It is claimed that the tunnel freezes the yoghurt sufficiently fast to stop small crystals forming and to prevent shrinkage.

I

I

I

Bibliographie I

Fundamentals of Freeze-Drying J.D. Mellor A ca demlc Press (1978) xxvm + 3 8 6 p p $42.40

The searchforthe best meansof preserving biological materials has been continuing throughout the history of mankind. Only over the last two or three decades have freezing and drying been developed and used extensively

182

I

~n the lyophilization process for medical products, foodstuffs and other labile products. The need for a systematic and scientific approach was clearly acute; consequently, international courses have been run since 1958 to investigate fully the process and its wide range of applications. Fundamentals of Freeze-Drying reflects this current concern and sets out in a comprehensive fashion the background to the principles for

The Dairies have ordered another tunnel for a second factory, The are making the yoghurt in two textures, hardfrozen and soft-frozen, and in eight flavours.

BOC Limited, Hammersmith House, London W 6 9DX, UK use of both research and technical workers as well as students of food science, process and chemical engineering, physics and biology. The book is divided into three sections. The first deals with the classical theory of ice sublimation; the second with cyclicpressure operation, a freezedrying process newly developed by the author which gives up to 50% reduction in the long drying runs normally encountered; and the third with applications including the design of equipment and laboratory apparatus for foods, vaccines and microorganisms, histological specimens and other novel uses. M.A. Sepplngs

International Journal of Refrigeratior