SCADA, Telematics & GPS Technologies

An Awarepoint white paper describes critical factors required to maximize your RFID system’s return on investment.

Real-time location systems (RTLSs) are an increasingly important strategic capability for a variety of business applications. RTLSs allow organizations to efficiently identify and track the location of supplies, personnel, equipment, and other items in real-time, as a cost-effective operational management tool.

With the success early adopters have had with RTLSs, the question is not whether to implement, but which technology is best suited for the many applications that can benefit from location awareness. An Awarepoint white paper, “Considering a Real-time Location System? First Consider the 5 Critical Success Factors,” can help maximize your return on investment and ensure long-term success of your RTLS investment.

“The implementation of RTLS technology should pay for itself as a result of shrinking the incidence of misplaced equipment, decreased rental costs, and increased utilization of equipment,” stated Jason Howe, CEO of Awarepoint Corp.

The five critical factors outlined in the white paper to obtain maximum benefit include:

• Enterprise-wide coverage—because assets and people move throughout your entire enterprise, to achieve maximum benefit, your RTLS deployment must cover every square inch of your enterprise.
• Location accuracy—to affect the highest impact for your strategic initiatives, room-level accuracy is a clear critical success factor.
• Installation and maintenance—a minimally invasive solution that does not compromise your existing IT network, does not interrupt daily business operations, and can be installed in days or weeks, is vital. Maintenance impact for hospital staff should be considered as well. It shouldn’t take a team of IT professionals to keep the system running.
• Interoperability—your RTLSs should be supported by standards-based technology and should offer an open application programming interface so that it’s capable of providing location and status data to both your end-users and to third-party applications.
• Low risk—you should partner with a vendor vested in your success. Look for a flexible business model that doesn’t require a large capital purchase or long-term contractual commitment, and allows you to easily expand assets as needed.

Added Howe, “In hospitals particularly, RTLSs can play an important role in automation of common tasks—improving operational efficiency, increasing patient flow, and enhancing patient safety. Knowing the location, status, and movement of equipment and people can be used to improve hospital business processes and asset utilization, reduce capital expense and rental costs, and improve staff productivity.”

The full white paper “Considering a Real-time Location System? First Consider the 5 Critical Success Factors” can be downloaded free off the company’s Web site.

[nmarquardt] has put up an interesting instructable that covers building RFID tags. Most of them are constructed using adhesive copper tape on cardstock. The first version just has a cap and a low power LED to prove that the antenna is receiving power. The next iteration uses tilt switches so the tag is only active in certain orientations. The conclusion shows several different variations: different antenna lengths, conductive paint, light activated and more.

The AVR-Based House Monitoring System is designed around the ATmega8515 microcontroller. The system offers hard-wired and wireless control along with a 1-Wire temperature network. A web-based, user-friendly interface enhances the project. [source]

AVR-Based House Monitoring System - [Download Project] [View Abstract]

Augmentation

Augmentation methods of improving accuracy rely on external information being integrated into the calculation process. There are many such systems in place and they are generally named or described based on how the GPS sensor receives the information. Some systems transmit additional information about sources of error (such as clock drift, ephemeris, or ionospheric delay), others provide direct measurements of how much the signal was off in the past, while a third group provide additional navigational or vehicle information to be integrated in the calculation process.

Examples of augmentation systems include the Wide Area Augmentation System, Differential GPS, Inertial Navigation Systems and Assisted GPS.

Precise monitoring

The accuracy of a calculation can also be improved through precise monitoring and measuring of the existing GPS signals in additional or alternate ways.

After SA, which has been turned off, the largest error in GPS is usually the unpredictable delay through the ionosphere. The spacecraft broadcast ionospheric model parameters, but errors remain. This is one reason the GPS spacecraft transmit on at least two frequencies, L1 and L2. Ionospheric delay is a well-defined function of frequency and the total electron content (TEC) along the path, so measuring the arrival time difference between the frequencies determines TEC and thus the precise ionospheric delay at each frequency.

Receivers with decryption keys can decode the P(Y)-code transmitted on both L1 and L2. However, these keys are reserved for the military and “authorized” agencies and are not available to the public. Without keys, it is still possible to use a codeless technique to compare the P(Y) codes on L1 and L2 to gain much of the same error information. However, this technique is slow, so it is currently limited to specialized surveying equipment. In the future, additional civilian codes are expected to be transmitted on the L2 and L5 frequencies (see GPS modernization, below). Then all users will be able to perform dual-frequency measurements and directly compute ionospheric delay errors.

A second form of precise monitoring is called Carrier-Phase Enhancement (CPGPS). The error, which this corrects, arises because the pulse transition of the PRN is not instantaneous, and thus the correlation (satellite-receiver sequence matching) operation is imperfect. The CPGPS approach utilizes the L1 carrier wave, which has a period 1000 times smaller than that of the C/A bit period, to act as an additional clock signal and resolve the uncertainty. The phase difference error in the normal GPS amounts to between 2 and 3 meters (6 to 10 ft) of ambiguity. CPGPS working to within 1% of perfect transition reduces this error to 3 centimeters (1 inch) of ambiguity. By eliminating this source of error, CPGPS coupled with DGPS normally realizes between 20 and 30 centimeters (8 to 12 inches) of absolute accuracy.

Relative Kinematic Positioning (RKP) is another approach for a precise GPS-based positioning system. In this approach, determination of range signal can be resolved to a precision of less than 10 centimeters (4 in). This is done by resolving the number of cycles in which the signal is transmitted and received by the receiver. This can be accomplished by using a combination of differential GPS (DGPS) correction data, transmitting GPS signal phase information and ambiguity resolution techniques via statistical tests—possibly with processing in real-time (real-time kinematic positioning, RTK).

GPS time and date

While most clocks are synchronized to Coordinated Universal Time (UTC), the atomic clocks on the satellites are set to GPS time. The difference is that GPS time is not corrected to match the rotation of the Earth, so it does not contain leap seconds or other corrections which are periodically added to UTC. GPS time was set to match Coordinated Universal Time (UTC) in 1980, but has since diverged. The lack of corrections means that GPS time remains at a constant offset (19 seconds) with International Atomic Time (TAI). Periodic corrections are performed on the on-board clocks to correct relativistic effects and keep them synchronized with ground clocks.

The GPS navigation message includes the difference between GPS time and UTC, which as of 2006 is 14 seconds due to the leap second added to UTC December 31st of 2005. Receivers subtract this offset from GPS time to calculate UTC and specific timezone values. New GPS units may not show the correct UTC time until after receiving the UTC offset message. The GPS-UTC offset field can accommodate 255 leap seconds (eight bits) which, at the current rate of change of the Earth’s rotation, is sufficient to last until the year 2330.

As opposed to the year, month, and day format of the Gregorian calendar, the GPS date is expressed as a week number and a day-of-week number. The week number is transmitted as a ten-bit field in the C/A and P(Y) navigation messages, and so it becomes zero again every 1,024 weeks (19.6 years). GPS week zero started at 00:00:00 UTC (00:00:19 TAI) on January 6, 1980 and the week number became zero again for the first time at 23:59:47 UTC on August 21, 1999 (00:00:19 TAI on August 22, 1999). To determine the current Gregorian date, a GPS receiver must be provided with the approximate date (to within 3,584 days) to correctly translate the GPS date signal. To address this concern the modernized GPS navigation messages use a 13-bit field, which only repeats every 8,192 weeks (157 years), and will not return to zero until near the year 2137.

GPS modernization

Having reached the program’s requirements for Full Operational Capability (FOC) on July 17, 1995, the GPS completed its original design goals. However, additional advances in technology and new demands on the existing system led to the effort to modernize the GPS. Announcements from the U.S. Vice President and the White House in 1998 initiated these changes, and in 2000 the U.S. Congress authorized the effort, referring to it as GPS III.

The project aims to improve the accuracy and availability for all users and involves new ground stations, new satellites, and four additional navigation signals. New civilian signals are called L2C, L5 and L1C; the new military code is called M-Code. Initial Operational Capability (IOC) of the L2C code is expected in 2008. A goal of 2013 has been established for the entire program, with incentives offered to the contractors if they can complete it by 2011.

Our database which is storing every minute telemetry data is now getting bigger and need to be relocated to another newly mounted drive. So, I need to relocate the old data to a new disk. Actually, I don’t need to do this if my drive is a dynamic drive.

As we already know, PostgresSQL for Windows installs the PGDATA directory by default into “C:\Program Files\PostgreSQL\8.3\data”. This mini-HOWTO explains how to change the default PGDATA directory to another location. Note that 8.3 is the version number of my current PostgreSQL installation. It could be varied based on your installed version. (more…)