|
|
|
|
|
|
|
|
| Home | Wireless
Communications
Communications between plants, wellsites and head offices is getting increasingly more affordable with new, reliable technologies available. Communications between facilities can be done using anything from landlines, cellular lines, to radios. These types of systems are often referred to as SCADA systems, short for Supervisory Control and Data Acquisition. Wireless communications are used for communications between wellheads, pipeline, plants and other locales. On a pipeline, monitored items can include compression, valves, cathodic protection, and other off-site station controls. Increasingly environmental monitoring is a part of SCADA applications. Choosing your best system depends on a number of factors. Factors affecting suitability for remote monitoring and the types of monitoring devices used are: number of sites, frequency of data requirements, the amount of data, location, terrain, and the local area classifications. Other criteria are wether you pay for your wireless communication on a per-use basis and wether you use existing infrastructure. Radio time can be rented but of course also carries with it continued costs. In addition, power requirements versus available power may play a role. Does your communications system require AC or DC; 1 Watt or 35 Watts? What are local Radio Frequency regulations? For example, radio frequencies restricted in Canada may not be in the U.S., or in South America and vice versa. The bands available here are VHF (140-170 ?Hz), and UHF (900 MHz). UHF is a lower frequency and tends to distort less. VHF tends to be used more in the satellite communications end. For radio, people have used a separate modem and radio combination and these work well together. Usually such units use up to 25 Watts of internal power, and offer a broad range of frequencies. The low frequencies these units work with tend to require a fairly high tower to prevent the radiowaves from hitting the ground. The price for low distortion is more path loss over distance. A typical licensed radio can cost around $ 1,700.00 to $ 4,000.00. After that your only cost usually is a annual license fee of $ 75.00/year /system. Add to that the cost of a master/repeater of between $ 2,000.00 to @ 4,000.00, some towers and things can be in place reasonably economically. What now of the marginal properties which ideally lend themselves to such automation equipment? At the above numbers, the economics, however reasonable, may not be there. The solution? Unlicensed Radio. Unlicensed radio tends to work within the 928-956 MHz range. Using "Spread Spectrum" technology with these unlicensed radios allows multiple users to work in the same spectrum in the same area. The radios automatically hop from one frequency to another at a set pattern. Thus, receivers and transmitters are set up to use the same pattern. The limit to these unlicensed radios is 1 Watt of power. Normally that may be considered limiting, but recent advances in spread spectrum technology have made them reliable and economical. The advantages are numerous: No license delays, built-in diagnostics, and smart systems with packaged radio frequencies. Data rates are in the 9600-Baud range allowing this system to be reliable for LAN applications. The price tends to be in the $ 1,500.00 to $ 2,500.00 range all-in, which allows many a SCADA system’s economics to pass the AFE (Approval For Expenditure) stage. These are well suited to installation in plant and well sites, but may lose some power through foliage. These systems work best in open areas, and work well with frequent use and a high number of sites. Cellular offers good coverage, especially if you can get dedicated cellular for data, which is sold at a lower rate. Cellular offers good performance, but may not be as well suited to a situation where there are many stations, each ringing up a phone bill automatically X times a day. Cellular units can be separate or integral, and feature no latency. Data rates are typically 9600 Baud. Cellular units are best left for situations of infrequent use, and relatively few sites. Another system, called CDPD, uses packet data over a network. Use of these systems is increasing in Alberta. These systems typically have about a 1-second network delay, faster than cellular, but are slower than radio would be. The delay here is that the system is required to connect to the SCADA host and a TCPIP or dialup convention is required to talk to the IP/Modbus Address. (ILLUSTRATE OR EXPLAIN THIS) CDPD is built on a once per kilobyte basis and costs accordingly. CDPD is good for small packs of less time-sensitive data. The final stage in wireless communications is the satellite. This system works well for remote locations where there is no land service, and no cellular service. There are a few satellite systems in use: OrbComm, VSAT, MSAT. OrbComm Equipment costs around $ 2,500.00 and is usually low power, but can be more dear. For example, a system that polls once a day can cost up to $ 180.00/month/station. VSAT costs between $ 2,400.00 to $ 6,400.00 per system. It uses a geostationary orbit satellite, and offers no latency as a great draw. This system is good for real time requirements, and is good for hubs or pipelines in remote areas. Keep in mind that power demand is higher. MSAT is much like OrbComm, and costs approximately $ 3,000.00 to 5,000.00 per site. Fees are usually $ 35.00/month plus $ 1.25/minute. MSAT can be expensive in continuous use applications. Other systems worth considering would be hybrids between the above, taking advantage of the geography where possible, and using technology where necessary. For the best system, call your wireless communications experts, and get wireless! |
|
Home |
Product Lines | Tech
Notes | Equipment
Catalog
|