PLCs and sensors on railway maintenance equipment

Larger vehicles manufactured by Harsco Track Technologies in Nottingham are now being fitted with a range of Siemens equipment including Simatic S7-200 PLCs

An innovative company which leads the market for versatile railway maintenance equipment designed to run on road or rails, is relying on Siemens to simplify control systems and deliver ruggedly efficient man-machine interfaces.

The larger vehicles manufactured by Harsco Track Technologies in Nottingham, which are widely used throughout the UK, are now being fitted with a range of Siemens equipment including Simatic S7-200 PLC's, AS-Interface, Simatic HMI TP27, BERO inductive sensors, and 3SB1 push buttons.

Meanwhile Land Rovers are now being equipped with the space-saving programmable LOGO universal logic module.

All the equipment is supplied by ERF in Ilkeston, Derbyshire, who have been instrumental in introducing Harsco Track Technologies to the various Siemens equipment and enabling them to deal directly with specialists within the Siemens Automation and Drives division.

Harsco Track Technologies specialises in the re-engineering of standard road vehicles to equip them for their new role with rail maintenance companies.

The company product range has been developed to cover all aspects of the Railway Infrastructure/Permanent Way/Overhead Line, Building and Signalling.

The fundamental need for these vehicles is ease of track access and the vehicles employ the Hy-Rail system developed by their parent company Fairmont Tamper.

Special guide wheels drop down to give the road vehicles a rail capability, while a 'Ride and Slide' system uses rams to lift the vehicle and move it across to mount or dismount from the tracks.

The vehicles range from Land Rover-based lightweight general purpose and crew vehicles to 17 tonne High Capacity Overhead Access Units and a new range of 26 tonne 6-wheel vehicles equipped with a variety of body units including tippers.

Another crucial feature of the Harsco Track Technologies vehicles is the remote control facility which enables all platform movements, remote traction, stabilisers and side-shift controls to be performed from a single hand held radio control unit.

From the work platform the traction control also allows an operator to implement "creep speed" in forward and reverse directions, and provides a full 1 tonne of tractive effort for towing trailers and tensioning of cables.

Each vehicle must also be equipped with the rail approved lights system, and must switch over completely from road lights and signals when it is placed on the network.

Reliability is an important consideration for Harsco Track Technologies and their customers, as breakdowns on track during maintenance windows in normal operation can have far reaching consequences.

Harsco Track Technologies previously used a conventional wiring system but it required a massively complicated series of cables and junction boxes to deliver the control required by the vehicles, as well as adding substantially to the installation and commissioning time.

The cabling also added substantially to the weight of the vehicle, reducing load capacity, and made maintenance and repair a complex business However, they discovered a radically better solution with Siemens AS-Interface which enables the networking of the field I/O through a single 2-core cable.

It links to Siemens comprehensive range of field devices and systems, and because it is an open system, non-Siemens items can also be linked for intelligent control via the Simatic S7-200 PLC and AS-Interface.

Another advantage is that the AS-Interface cannot be corrupted by other electrical sources.

Rob Reid, works manager at Harsco Track Technologies is delighted with the new system.

He explains: "The modular installation has saved us œ4-5,000 in labour costs for the re-engineering of the large vehicle because of the reduction in the wiring system.

Now the sensors, warning lights and other components can simply plug in and go.

The programming of the system to enable remote operation is the smart side of the work.

Rob has developed a programme using Siemens Micro/Win software, which makes the control system much more user friendly.

Moreover, there are sophisticated diagnostic functions available through the Siemens touch screen installed in the truck cab, to allow the operator to identify any faults, right down to the component part number which requires attention or replacement.

The on-board system can also be analysed using a lap top, or connected to a modem so that engineers in the field can link with Harsco Track Technologies in Nottingham using the inbuilt tele-service function of the Siemens Micro/Win software if they need assistance.

Rob adds: "There has been a fairly steep learning curve to adopt the AS-Interface but the support has been excellent from both Siemens and ERF and the results have certainly been worthwhile.

Before they were willing to move over to the Siemens system, Harsco Track Technologies carried out their own vibration testing of the system to simulate the punishing conditions the vehicles must endure.

Harsco Track Technologies built their own test rig in the factory to create double the vibration on the worst section of track they could find.

They installed the 16 bit interface and programming modules, then ran the rig for 14 days round the clock with the programme running and the Siemens system switching a full load constantly on and off every half second.

The Siemens equipment never faltered, and passed the gruelling test with flying colours.

In weight terms, Rob estimates that the overall tonnage of a large vehicle is reduced by hundredweights because of the massive saving in cabling, minimal junction boxes and smaller terminal box.

Harsco Track Technologies has been using Siemens BERO induction sensors and push buttons for some years and were impressed with their durability and performance.

The sensors are used to check that the hydraulic legs used for the Ride and Slide function remain fully retracted when not in use, and monitor the position of Harsco Track Technologies's uniquely versatile work platform on overhead access Foden trucks.

The push buttons control the emergency stop in the cab and in the latest models other controls are operated by a Siemens HMI TP27 touchscreen unit.

Harsco Track Technologies's introduction of the LOGO universal logic module to the workhorse Land Rover conversions replaces a former PCB and offers more flexibility in programming and cost reduction as well as freeing off space in the cab because of its compact design.

Rob Reid comments: "We are an innovative company and we pride ourselves on being at the forefront of technological developments while also delivering reliability.

The Totally Integrated Automation Solution offered by Siemens has fulfilled all our requirements and is quite literally changing the shape of our business.

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