Microwave switch for 'Thrubeam' detection systems

Leading level measurement specialists Hycontrol are introducing their new versatile MicroSense microwave switch for multiple material detection applications in harsh conditions

'Thrubeam' technology has been used in industrial switching applications for a number of years, but in many installations product reliability and performance are questionable, especially in arduous industrial applications where extreme dust, vapours, side wall build up or high temperatures are present.

Now this new generation of microwave based instrument, which overcomes traditional Thrubeam shortfalls, is already finding a wide range of applications in areas where more traditional methods have failed, in industries ranging from food to quarrying and mining.

Each switch subsystem comprises of two components, a microwave transmitter, which generates a low power 24 GHz microwave beam, and a receiver unit, with a maximum operating range of 40 metres between the two antennae.

The two units are mounted facing each other and in the un-switched state the narrow beam from the transmitter is detected by the receiver.

If the path of the beam is then interrupted by a sufficiently reflective or absorbent material (within pre-programmed time and attenuation parameters) the internal relay is triggered, thereby activating the switch.

A time delay function can be set from 0.1 to 10 seconds to avoid spurious or unwanted beam interruptions.

The detection mode is selectable so that the relay is initiated either when the beam is broken or restored, similar to normally open or normally closed switching terminology.

The MicroSense switching capabilities are unaffected by dust, steam, smoke or heat, whilst build up of material on the antennae has little or no effect on the operation.

A critical part of the success of the innovative MicroSense is the fact that it uses the latest heterodyne microwave detection technology, which offers a number of operational advantages over competitive techniques.

Firstly it allows the system to operate with a minimum received power that is lower than the competitors units.

This increases the operating range and penetrability, without any need to increase the power of the transmitted microwave radiation.

Secondly, systems based on the older diode detection technology have to have multiple sensitivity set points for any given detection range and are therefore not easy to set up, requiring a complex three stage procedure to ensure satisfactory operation.

By comparison the MicroSense is calibrated in one easy step via the sensitivity dial.

The 15 LED indicator array at the back of the receiver unit displays the received power level from the transmitter and the set-point sensitivity, thereby allowing quick, simple and effective calibration.

Example Applications.

Microwaves will pass through a wide range of materials ranging from plastics to fire bricks, typically only being attenuated by metals and water.

The switches can be supplied with a range of different mounting accessories and, where necessary, they can be used in conjunction with microwave-transparent inserts to protect the antennae.

These are especially effective in applications involving elevated temperatures or corrosive material.

Switches can be supplied for ambient applications up to 180C, whilst for higher temperature applications up to 600C, wave guides can be used so that the units themselves are mounted sufficiently distant from the heat source.

This makes them suitable for applications in steel works, glass works and incineration plants.

Blocked chute or pipe detection.

Blocked chutes and pipes cause severe disruption to any manufacturing or processing industry.

In quarrying, product is constantly on the move along belts or down chutes.

Blockages can happen relatively quickly and are clearly detrimental in terms of production and also safety.

For such applications the switches are set up to ignore falling material and acceptable build-up of material on the walls, but detect any blockages.

In another example the switches can be used to detect unwanted build up in pipes of viscous products such as paste or slurry build-up.

Vehicle safety barriers.

With a range of 40 metres, the MicroSense is ideal for monitoring vehicle movements, for instance in applications involving the reversing of large vehicles at building sites and quarries or vehicle positioning in filling bays.

It is particularly useful in situations where drivers of large tipping vehicles forget to lower their tipping body after discharging their load.

The switch can also be used for height restriction warning for vehicles going under bridges, gantries or overhead cables.

At ports and terminals applications are as diverse as counting rail trucks or ensuring overhead crane safety.

Where applicable the receiver unit can be mounted on mobile equipment and the transmitter fixed at a selected location in order to provide a safety warning system.

Level Control.

The switch provides a cost effective and very reliable non-intrusive level control solution for liquids and solids, especially in simple high and low level alarm applications.

Where multiple sets are used in close proximity, the units are orientated so that there is no cross beam interference.

Several applications have been made on vessels such as separation cyclones that cannot use intrusive switches: therefore this non-intrusive technology provides the perfect solution.

Material Product differentiation.

Using the principle that microwaves will pass through low dielectric products, it is possible to use the Microsense to 'see' through one product and not through another.

Typical examples of this are to detect if a product is inside a carton, without seeing the carton when it is empty, or level detection in a glassfibre or plastic vessel, without the need to cut any process connections into the vessel: the switches can simply be mounted on the outside!.

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