How hit in the implementation of an infrastructure wireless?

The first challenge to the that confronts an agent of projects interested in implanting a network wireless, is the one to argue properly his decision, in front of the alternative, always existent, to use wired up conventional. They exist different questions of character so much technician like economic that they can bend the scales in one or another sense.

Once the decision is firm and the wireless option is the chosen, results indispensable a precise evaluation and detailed of the zone on which has planted execute said installation.

To the hour to pose the need to develop a wireless infrastructure, one of the main questions to which will confront the manager of the project, will be the comparative study of the system wireless in front of the conventional installation by means of wired up physicist. The costs of installation are the first factor that will appear in the preliminary discussions, although they exist other related directly with requirements and factors exclusively technical, such as the criticidad of the signal to transmit, the time of update of the measure or the typology of information transmitted.

- Costs of installation. In this point fits to review that the instruments of field with option wireless have, usually, of upper costs to his homologous with wired up direct. In a lot of cases, and of erroneous way, tends to realise a mere comparative between the prices of the equipment, considering, only, a factor of correction that allows to compensate the own costs of the wire to use. A more detailed study, allows to take out to the light split to value, that can compensate this initial inequality, doing that the difference reduce considerably. The costs associated to infrastructure for the wired up (trays, boxes of interconnection, etc.), as well as for the own setting (andamiaje, permissions of work for dangerous zones, etc.); they can represent in a lot of cases a percentage of the final budget, upper to the of the own equipment. It results necessary a study detailed, no only of the cost of the equipment, but also of the materials and additional services required for both typologies.

- Criticidad Of the signal. Given the relatively little experience that accumulate the systems of wireless communication in determinate industrial states, generates one some reticencia the possibility to implement routine of control in system wireless. The fear or uncertainty in front of a possible failure in the system of communication, causes that in a lot of cases the managers to give green light to the execution of these projects, opt for focusing the system to signals of character indicativo and no executive. This decision is used to take with the aim to preserve the bows of control of possible failures no wished or injerencias external. However, on the one hand, many of the current systems of wireless communication, have of levels of encryptions that ensure a safe communication. On the other hand, they exist able topologies to manage the signal transmitted by different channels simultaneously, fact that ensures a sufficient redundancy in the transmission.

- Costs of implantation of new technologies of communication. Although in the still big actuality part of the installations bet by the solutions that include analog signals 4-20 mA, is not less true that the possibility to have of protocols of communication series (Modbus, Fieldbus Foundation, Profibus, etc.) have allowed an evolution to equipment Smart. The concept Smart deepens in the possibilities to increase significantly the capacities of configuration and connectivity of the instruments of field. However, this big fan of possibilities that surface with the new generations of transmitters, remain, in a lot of cases, without execution given the costs of installation. This is because of the impossibility, in the majority of cases, to be able to take advantage of the existent infrastructures, since these have been designed and dimensionadas for analog equipments. The technology wireless gives answer to the requisición of a fast and economic system to implant intelligent transmitters in plants where already exist equipment communicated on an analog network.

- Costs of supervision and maintenance. The loop 4-20 mA can see affected by different problematic such as:

• Accumulation of water or humidity in conductive
• Problems of humidity in prensaestopas and intermediate boxes
• Corrosion on creameras by environingingmental effects
• Insufficient electrical supply for all the bows
• wrong Identification of cables and/or creameras
• Errors in the conexionado electrical
• Problems of conexionado to earth to all the long of the wired up

In front of a problematic generated by a wrong indication, the possible sources of error are cuantitativamente upper for the case of the installation wired up with regard to his alternative wireless. Independently of the size of the site, the points to supervise from the own transmitter until the DCS, in systems of physical communication, will require some means of personnel, equipment and time; likely upper to the that the same problematic would generate with a system wireless. This second is not exento of requests, but so much the elements involved in the communication, as well as the proofs required will be noticeably lower.

Once have decided tackle an installation wireless, results recommended to evaluate properly the zone on which said infrastructure will have to work. Although it is not indispensable said study, this type of installations demand to his agents a high reliability that can not remain to expensar of problematic that arise during his execution. A study of coverages of radiofrecuencia will allow to the user have of a valuable information on different appearances of his future installation such as: area covered by the network, quality of signal or capacity of the same. This procedure can pose like a simple test, or can form part of a complete study of coverage wireless that include, among others points:

- Analysis of the spectrum radioeléctrico of the zone

- Evaluation of the different type of available antennas for the optimisation of the results

- physical Verification of the location of the points of access

- Comparative with other existent networks

- Possible location of equipment to integrate in the network

- Comprobación that the equipment chosen fulfil with the requirements specified by the customer.

In some cases, studies of back coverage to the implantation of the structure wireless, have showed deficiencies that have repercutido in a lower service of the expected. This problematic even being important in any project, is it more, if it fits, in those industrial installations where a part, or the whole of the equipment, have to be situated in zones with risk of explosion (Atex). It results evident that the equipment, as well as the interventions in this type of installations, comport upper costs to the usual. An error or a little developed execution, can mean an upper quantity of initial equipment, or in case to discover errors in the dimensionado back to the commissioner, second interventions with the consequent problems to level of production, hygiene, etc.

In addition to a suitable study of coverage, exist a series of questions that the user has to fill properly previous to the execution of the installation

An application focused exclusively to the treatment of instrumentation of field, requires characteristics very different of which would demand, for example, an infrastructure for the monitoring of a system of video-surveillance. It is evident that the bandwidth required by a camera of video, is considerably upper to the that some transmitters of pressesure, for example, would demand to the infrastructure wireless. The bandwidth, the speed of transmission, quality of the service, represent, among others, criteria in a lot of cases will be critical for a reliable execution.

A network mesh uses typically frequencies of 2,4 or 5 GHz. 2,4 GHz is also used for IEEE802.11b/g, IEEE802.15.4 and communication ISA100. Other forms of communication wireless use frequencies in ranks of 700 to 900 MHz. In function of the application and the frequency of work to use, the previous requests will be different. Typically, what greater is the frequency, less effective is and more mitigation suffers in front of possible obstacles.

Obviously, what lower is the area to cover, simpler is the structure to design, except cases of high density of structures and pipes that prevent the entrance of light. Although the equipment of RF can be applied in industrial installations more or less disordered, thanks to reflections, creating multiple ways or rebounding in objects; the fact of not having a direct vision can repercutir in a low reliability of the system. In these cases, can propose alternatively an increase in the quantity of antennas and locations, with the end keep the minimum requests specified for the installation.

The current or future coexistence with other infrastructures wireless in an industrial installation, is an important factor to the hour to decide the scope of the study of implantation to realise. It results evident that if the forecast to half and long term does not include another wireless infrastructure more than the posed in the project, can not being necessary a study of coverage detailed of all the zones involved. If by the contrary poses with hygiene the existence of other networks and therefore a high density of information, will be highly recommended to execute a study radioeléctrico and of coverage very detailed.

This point depends to a large extent of the information that has posed transmit. A network of transmitters of field, require a ‘simple ‘' connectivity to the DCS that can solve by means of standard protocols of field (Modbus for example). If by the contrary pose us an installation by means of gas detectors with connectivity wireless, that allow the positioning of personnel in plant, at the same time that generate maps of hygiene; the interface required will be of an upper capacity. In this second case, also would go in applications with systems of video-surveillance to centralise signals of the enclosed circuit of television.

Valuing the different points posed previously, the managers of the new infrastructure wireless, have to have of sufficient scoreboards to decide if the project requires of a study detailed of implantation; or on the other hand, some simple proofs of coverage allow to ensure a suitable operation of the future installation.