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Sensing the Way Ahead

Published: 10th Jan 2010

ARTICLE CONTINUES BELOW

Only rarely in business do we witness a ‘quantum leap forward’ in the application of new technologies (think Dyson, i-Pod, Wii), but when we do it invariably alters the landscape of a particular industry, and of the way in which we attain a desired outcome.

Developments in technologies relating to personal gas detection, combined with a greater understanding of standard data communications platforms have recently coalesced, and are now beginning to have a significant impact on the methodology and delivery of fixed gas detection systems in industry. We are seeing the kind of fundamental shift described above, and along with it, very significant benefits to purchasers of these systems - not least amongst them being that Health and Safety Officers and Engineers without specialist gas sensing system backgrounds can now install, maintain and service their own bespoke sensing systems without the need for specialist back-up.

The miniaturisation of gas sensing devices and of data processing technology; advances in data display technology; and developments in the audible and visual capabilities of alarm technology, along with rapid improvements in battery capabilities, all of which were developed in order to bring down the size and improve the performance of hand-held units, have now allowed this conceptual shift to take place. And it is a shift not simply in how fixed gas detection systems are created, but also in how they are installed, commissioned, serviced, calibrated, and integrated with plant-wide systems and even monitoring requirements on a global scale.

Until recently a typical fixed gas detection system would be integrated by a gas sensing consultant or, in the case of larger companies, by a dedicated individual or department within the company who would have associated repairs capability, calibration and servicing equipment or would out-source all of this to a specialist support company. Often a full team of electronics and software experts would be required to deliver and support the systems, particularly where datacomms or multiple systems were involved. The creation of a system would often require the integration of sensors, controllers, alarms, standby batteries, cabling and accessories from separate suppliers, and would need specialists to install and commission them. Invariably, this process would continue with on-going technical support throughout the life of the installation.

All of this is now changing. A new range of integrated, single-supplier, multiple-use systems is being brought to market based on a universal technology architecture that is designed specifically to allow Occupational and Environmental Health and Safety (OEHS) professionals to install gas sensing systems of any complexity in their Article | Gas Detection workplace without the need for specialist back-up.

The benefits are considerable and wide-ranging - reduced cabling, installation and commissioning costs, reduced maintenance costs and downtime, a smaller number of failure risk-points, improved integration of plant-wide monitoring collateral, reduced size, weight and storage requirements, easy and fast calibration without the need to power-down, and a fully scalable and flexible technology base for responding to and integrating future requirements. Finally the ability to communicate directly with standard protocols means that any number of systems can be integrated, on a single data cable and controlled and monitored from a central location, and all of this utilising only standard plant maintenance skills. It’s gas sensing made simple - giving enormous benefits on a single system, but when applied across an entire plant or even throughout a global organisation the cost-savings and safety improvements can have a huge impact on a company’s bottom-line.

Plug-and-play - with a difference

The concept of ‘plug-and-play’ sensor heads, which can be easily inserted and removed as and when required, allowing the user to determine the types of gas monitored, is not a new one - it’s been around and in use in personal and portable units for around 20 years. However with the advances in processing capability, the new generation of interchangeable sensing elements now incorporates all of the information processing capability and data intelligence of the entire unit - information that was previously stored on large circuit boards within the main architecture of the sensor.

“the new generation of interchangeable sensing elements now incorporates all of the information processing capability and data intelligence of the entire unit”

The small physical size of modern electronic components means that each sensor head can contain its own microcontroller, data storage and signal conditioning circuits. These operate independently of the main unit electronics and continuously monitor their respective gas level. Background operations also check for sensor and operational faults within the head. Different versions of the sensor head cover most of the common toxic and flammable gases and can be calibrated either to standard or user-specific ranges. In addition to this other types of sensor head with the same architecture can be used for temperature measurement, processing of 4 to 20mA and 0.4V to 2V signals and so on.

The main unit of these new integrated systems interrogates each sensor head on a regular basis and displays the reported gas levels on an LCD screen. This unit is also fitted with a sounder and warning beacon. In normal operation, the sounder and beacon provide a ‘confidence’ signal every 15 seconds. Under alarm conditions, they operate at a much faster rate. It can transmit the data retrieved from each sensor head over an RS485 data link to a remote computer. The main unit is also fitted with relays that can be configured to operate at specific trip points or to operate as the result of a combination of events rather than being tied to one specific sensor.

"the main unit interrogates each sensor head and displays the reported gas levels on an LCD screen"

This means that the gas identity, measuring range, real-time data-logging, service history, predicted life-span of the element, calibration history, set points, calculation of time-weighted averages, failure modes and over/under range settings stays with the sensing head throughout its life cycle. This gives a number of advantages to the user – calibration and routine maintenance can be done by simple periodic i-module change-out without the need for local application of test-gases or cleaning and replacement of filters. The whole maintenance routine can become part of a fixed system bringing consistency and familiarity to all aspects of the sensing collateral with the consequent improvements in safety levels. Changes to the gas measured, calibration points and indeed any other parameters can be achieved through the same module change-out procedure, without the need to re-programme the sensor or change any other aspects of the system.

"relays are fitted that than can be configured to operate at specific trip points or as the result of a combination of events"

It also means that the same module can be used and applied across the whole range of a company’s gas sensing equipment – personal, portable and fixed, giving a consistent logistical approach to sensors on the plant, simplifying plant-wide maintenance, service and calibration requirements, and allowing end-users to stock replacements that can be applied to all units within their gas detection armoury, as and when required.

Datacomms development

The increased processing capabilities of the new technology allows the sensors to communicate directly with the Modbus protocol, whereas previously conventional analogue signals would have had to go through data conversion modules in order to communicate with datacomms systems. Once again the potential benefits within large plants or on multiple sites are huge.

Modbus is a serial communications protocol originally designed for use with PLCs (Programmable Logic Controllers) but it has now been universally accepted by industry as the default communications protocol. This is partially due to the open source nature of the protocol, but also due to its simplicity and flexibility. Modbus allows for communications between multiple devices from different manufacturers using the same network. A typical network will have a single master unit and up to a maximum of 32 rRemote tTerminal uUnits (RTUs). The Sentro 8 from Trolex is an example of one of these new integrated devices that can be configured as an RTU. Typically the master unit will be a PC running a SCADA (Supervisory Control And Data Acquisition) software package. The Sentro 8 uses a standard RS485 physical layer for the serial communications. It is used in the half duplex multi drop mode.

The benefits of this are that it only requires a single twisted pair cable and it resists electromagnetic interference from power line and motors etc. The Sentro 8 is capable of communicating over distances in excess of 1km on standard cable. If greater communication distances, or branches are required, then this can be achieved by using inline signal repeaters. It is also possible to link the local RS485/Modbus network onto larger Ethernet networks. This can be achieved by using a RS485/Modbus to Ethernet/TCP/IP convertor. This then opens up the possibility of monitoring the Sentro 8 from anywhere in the world via the internet.

Typically up to 32 of the new integrated units can now be linked together on a single RS485 comms link, utilising a single data-cable and without the need to rationalise the signals. Once installed it is possible to interrogate the sensors, download the data from them and change the calibration and other settings from a central PC – and because of the new integrated, interchangeable sensing heads, all of this information stays with the module. It also means that when the sensing head is changed-out, the sensor doesn’t have to be re-programmed to communicate because the basic comms programme is stored within the sensing module.

Gas sensing made simple

These advances in capability have not led to a subsequent increase in complexity. On the contrary, the power of the internal technology is exploited in order to best serve the user; despite the fact that all this advanced processing technology is being utilised, the end result of this new concept in systems is pure simplicity. No complex functionality, simple 2-button programming, clip-in clip-out heads, standard set-points incorporated in the unit, fully rationalised output signals and easy access to the interior.  Furthermore, the intrinsic intelligence embedded in the powerful data processing technology enables much higher levels of self monitoring of the sensor integrity with clear and concise menu driven, user calibration instructions and detailed diagnostic data.

…Indeed, all types of sensing made simple

The universality of the technology platform means that sensing systems enter a new dimension, that of complete flexibility of sensing capability. This means that any other type of system that an end-user wants to create – involving alternative alarm outputs, plant condition monitoring (utilising flow, level, pressure, vibration, temperature or proximity sensors etc) can be incorporated into the same system architecture. Whether it’s a tunnel monitoring system, a ventilation fan monitoring system, a dust and gas monitoring system, a conveyor monitoring system, pump condition monitoring system or a continuous level monitoring system in a tank farm – the system architecture remains the same.

Indeed it’s possible for the same unit to achieve all of the above systems with a simple change out of sensing heads and remote units, and a small amount of re-programming. The new concepts are an excellent example of conformity to the WEE directives on sustainable product development which states that products should be designed so that they can be adapted for use for another purpose in the future.

Size Matters

The smaller space envelope demanded by the new integrated systems means that is easier to design housings suitable for applications in hazardous areas, and to exploit more sophisticated hazardous area protection techniques. The small size of the units improves durability and makes it easier to achieve improved levels of ingress protection.  This inherent robustness is extremely important in harsh industrial and mining environments.

Circuit miniaturisation also has the benefit of dramatically reducing overall power consumption and this fact also simplifies the design of circuits for use in hazardous areas.  Whereas once a sensing system would have been needed to be housed in a large and heavy explosion proof housing, it is now possible to successfully design highly efficient devices to intrinsically safe standards (ia) and at the same time, giving a higher level of Ex protection.

An incidental result of this is the added safety factor.  The more that a sensing system is engineered as a integrated whole, the more secure will be the functional compatibility of the system, together with the absolute assurance of safety integrity.  It eliminates the risk of invalid equipment combinations that can occur in a ‘piece-meal cobbled-up’ system.

Increased technical capabilities of this new breed of small independent sensors clearly have far reaching benefits for industry and it will be interesting to see how staffing and procedures change in the future for health and safety officers all over the world.

Author Details:

Mark Rowland

Technical Director, Trolex Limited

Trolex are recognised as world leaders in the design and manufacture of sensors and systems for tunnelling, mining and hazardous industry. We have been at the forefront of safety monitoring and machine condition monitoring for 50 years.

A co-ordinated product design strategy makes for a closely integrated range of sensors and control modules, with unparalleled choice of user options and functional compatibility. We are able to offer the total package including gas detection, temperature sensors, flow sensors, pressure sensors, vibration sensors, level sensors, proximity sensors and integrated control systems.

mark.rowland@trolex.com,

+44 (0)161 4831435

website www.trolex.com

Published: 10th Jan 2010 in Health and Safety International

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