When the heat is on…

12 September 2008

Martin Wheatley, managing director of Contrinex UK, discusses applications for high temperature sensors.

High temperature sensors from Contrinex
High temperature sensors from Contrinex

Many manufacturing processes such as furnaces, steel plants, casting machines, engine control, foundries, heat treatment plants, plastic moulding machines, food processing and cooking and baking lines run at temperatures well above 70°C at which most conventional feedback sensors begin to malfunction and fail. All production line failures are expensive but are especially so in high temperature processes because of protracted cool-down and start-up times.

If you can’t stand the heat...
H.F.W. Plastics of Gateshead, claims to have cut costs with Contrinex HT sensors. The company works in PVC, polypropylene and paper-over-board to make a range of stationery products.

H.F.W. Plastics approached Contrinex distributor, W. Mearns, because of repeated failure of M18 sensors used on moulding machines. It takes up to an hour for a plastic moulding machine to cool sufficiently for it to be serviced and the same time to get back to its working temperature, making line failure very costly. Two years ago W. Mearns replaced the failing M18 devices with Contrinex DW-HD-603-M18-312 sensors that are rated at 180ºC and since then say there have been no sensor failures.

At the extreme end of the temperature range, Contrinex HT sensors, rated at 230ºC, are used in a steel manufacture and rolling mill in Yorkshire, where billets of steel emit huge amounts of heat.

In addition, Contrinex sensors are on trial in a brick kiln in Northern Ireland where heat-soak was literally killing the inductive control sensors mounted on a handling system. Initial trials have been successful and a full up-date programme is now being planned.

Temperature assessment
It is extremely important when designing high temperature sensors to estimate the absolute maximum temperature experienced by the sensor.

A plastic carton and packaging tray manufacturer in the Republic of Ireland used sensors to control a hot part of the process line that had an ambient temperature of 120ºC. These sensors kept breaking down and it was established that higher-than-anticipated fluctuations in temperature were causing failures. The sensors were replaced by Contrinex HT sensors, rated to 180ºC.

Hair raising applications in the food industry
Heat is a major problem on food processing lines where line failure invariably means expensive loss of in-process product.

Contrinex distributor, Industrial Controls, based in East Anglia has recently installed two systems in the food industry. The first is in a plant producing pasta food products where sensors where required to work inside an oven of a rotating heating drum to count and monitor gear teeth to control drum speed.

The second application was in an abattoir. Before a pig carcass can be processed all the body hair has to be burnt off and this is achieved by passing the carcass on a bar through a furnace containing flame torches. Contrinex HT sensors are used to detect the bars and trigger the burn process and, although not in contact with the direct flame, the whole area gets extremely hot.

All Contrinex high temperature sensors include built-in short circuit, reverse connection and voltage overload protection and are available as ‘normally open’ configuration for all sizes and temperature options in NPN and PNP and operate over a wide supply voltage from 10V to 30VDC and can switch a current of 150mA.

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