Telemetry is the monitoring and control of remote devices from a central location via wire-line or wireless links. Applications include utility meter reading, load management, environmental monitoring, vending machine management, and security alarm monitoring. Companies are deploying telemetry systems to reduce the cost of manually reading and checking remote devices.
For example, vending machines need not be visited daily to check for proper operation or out-of-stock conditions. Instead, this information can be reported via modem to a central control station so that a repair technician or supply person can be dispatched as appropriate. Such telemetry systems greatly reduce service costs. When telemetry applications use wireless technology, additional benefits accrue.
The use of wireless technology enables systems to be located virtually anywhere without depending on the telephone company for line installation. For instance, a kiosk equipped with a wireless modem can be located anywhere in a shopping mall without incurring line installation costs. Via wireless modems, data are collected from all the area kiosks at the end of the day for batch processing at a data center.
The kiosk also runs continuous diagnostics to ensure proper operation. If a malfunction occurs, problems are reported via the wireless link to a central control facility, which can diagnose and fix the problem remotely or dispatch a technician if necessary.
Security Application
A number of wireless security systems are available for commercial and residential use. Wireless technology provides installation flexibility, since sensors can be placed anywhere without proximity to phone jacks. Anumber of sensors are available to detect such things as temperature, frequency, or motion. The system can be programmed to automatically call monitoring station personnel, police, or designated friends and neighbors when an alert is triggered.
Such systems can be set to randomly turn lights on and off at designated times to give the appearance of occupancy. Depending on vendor, the system may even perform continuous diagnostics to report low battery power or tampering. In a typical implementation, the security system console monitors the sensors placed at various potential points of entry.
The console expects the sensor to send a confirmation signal at preset intervals, say, every 90 seconds. If the console does not get the signal, it knows that something is wrong. For example, a sensor attached to a corner of the window or other glass panel is specially tuned to vibrations caused by breaking glass. When it detects the glass breaking, the sensor opens its contact and sends a wireless signal to an audio alarm located on the premises, at a police station, or at a private security firm.
The use of wireless technology for security applications actually can improve service reliability. Asecurity service that does not require a dedicated phone line is not susceptible to intentional or accidental outages when phone lines are down or there is bad weather. Wireless links offer more immunity to such problems.
Traffic Monitoring
Another common application of wireless technology is its use in traffic monitoring. For example, throughout the traffic signal control industry there has been a serious effort to find a substitute for the underground hard-wired inductive loop that is in common use today to detect the presence of vehicles at stoplights. Although the vehicle detection loop is inherently simple, it has many disadvantages:
- Slot cutting for loop and lead-in wire is time-consuming and expensive.
- Traffic is disrupted during installation.
- Reliability depends on geographic conditions.
- Maintenance costs are high, especially in cold climates.
Awireless proximity detector can overcome these problems. Its signals activate traffic lights in the prescribed sequence. The proximity detector, usually mounted on a nearby pole, focuses the wireless signal very narrowly on the road to represent a standard loop. The microprocessor-based detector provides real-time information while screening out such environmental variations as temperature, humidity, and barometric pressure.
By tuning out environmental variations, the detectors provide consistent output. This increases the reliability of traffic control systems. Using a laptop computer with a Windows-compatible setup package, information can be exchanged with the detector via an infrared link. From the laptop, the pole-mounted detector can be set up remotely, calibrated, and put through various diagnostic routines to verify proper operation.
Role of Cellular Carriers
Cellular carriers are well positioned to offer wireless telemetry services. The cellular telephone system has a total of 832 channels, half of which are assigned to each of the two competing cellular carriers in each market. Each cellular carrier uses 21 of its 416 channels as control channels. Each control channel set consists of a Forward Control Channel (FOCC) and a Reverse Control Channel (RECC).
The FOCC is used to send general information from the cellular base station to the cellular telephone. The RECC is used to send information from the cellular telephone to the base station. The control channels are used to initiate a cellular telephone call. Once the call is initiated, the cellular system directs the cellular telephone to a voice channel.
After the cellular telephone has established service on a voice channel, it never goes back to a control channel. All information concerning handoff to other voice channels and termination of the telephone call is handled via communication over the voice channels. This leaves the control channels free to provide other services such as telemetry, which is achieved by connecting a gateway to a port at the local mobile switching center (MSC) or regional facility.
The gateway can process the telemetry messages according to the specific needs of the applications. For instance, if telemetry is used to convey a message from an alarm panel, the gateway will process the message on a real-time, immediate basis and pass the message to the central alarm monitoring service.
On the other hand, if a soft drink vending company uses telemetry to poll its machines at night for their stock status, the gateway will accumulate all the data from the individual vending machines and process them in batch mode so that the management reports can be ready for review the next morning. Individual applications can have different responses from the same telemetry radio.
While the vending machine uses batch processing for its stock status, it could have an alarm message conveyed to the vending company on an immediate basis, indicating a malfunction. Asimilar scenario is applicable for utility meter reading. Normal meter readings can be obtained on a batch basis during the night and delivered to the utility company the following morning.
However, realtime meter readings can be made any time during the day for customers who desire to close out or open service and require an immediate, current meter reading. Telemetry can even be used to turn on or turn off utility service remotely by the customer service representative.
Web-Enabled Telemetry
The next big market for telemetry systems is for those which distribute data through the Internet for access by a Web browser, which lowers the cost of implementing telemetry applications. Agrowing number of companies offer Webenabled telemetry solutions for such applications as ground station telemetry processing as well as remote and wide area monitoring.
With such systems, a host device acts as a network server that plugs into the local area network (LAN) with standard Category 5 cabling and RJ-45 connectors. The host device is connected to remote units over phone lines or wireless links to the Internet. Data are sent and received between the host and remote units in standard Transmission Control Protocol/Internet Protocol (TCP/IP) packets.
Client computers connected anywhere on the LAN or the Internet can use a standard Web browser to display the collected data with no requirement for additional software. In some cases, integrated Java applets provide real-time telemetry display. With accumulated data published as Web pages over an Ethernet LAN or over the Internet, it possible to monitor and control a process through a browser from anywhere in the world.
For example, using a remote unit attached to a heater with a wireless link to an access point, an engineer can monitor the temperature, change set points or alarm points, turn the heater on and off, or make other modifications from anywhere on the local network, or anywhere on the Internet, simply by using a Web browser. The remote unit also can send an e-mail message to the engineer alerting him or her to an alarm condition or updating the status of the remote device.
Leveraging the technology of the Internet even further, the engineer could receive a message from the remote unit on an Internet-capable pager or cell phone. Through the Web browser an administrator can set monitoring and measurement parameters from any computer on the network and configure and change all communication parameters of the remote units in the field. Access to configurations and data is protected through passwords. Selectable local disk archiving protects data for future reference should the primary storage disk fail.
Telemetry services, once implemented by large companies over private networks, are becoming more widely available for a variety of mainstream business and consumer applications. Wireless technology permits more flexibility in the implementation of telemetry systems and can save on line installation costs.
Telemetry systems are inherently more reliable when wireless links are used to convey status and control information, since they are less susceptible to outages due to tampering and severe weather. As data communications technology advances and companies continue to exploit the global ubiquity of the Internet, telemetry solutions will become more pervasive.
