Back in December, I wrote an article on some tips for installing and selling wireless security systems. In the second diagram in that article, I had a siren device labeled as a “PLC” siren. During the last few months, some of you have sent inquiries asking, “What is a PLC siren?” In the words of famous radio man Paul Harvey, I thought this month would be a good time to look at “the rest of the [PLC] story.”
Defining PLC Devices
OK, so what is PLC? It is another one of those great acronyms and stands for power line carrier. These devices are designed to conveniently control other electronic equipment by sending and receiving a timed, pulsed signal over common 120VAC. A PLC siren is often a simple plug-in installation.
Understanding how to reliably interface these devices with alarm and home/building automation technology can make for a very versatile and profitable product and service. Most installers have either heard of or used a popular form of PLC technology known as X10. This technology has been used in the United States since 1978. If you worked with this technology early on, it was known for testing your patience and design skills.
Mastering the Technology
In recent years, manufacturers such as SmarthomeMFG, a division of Smarthome (www.smarthome.com), have addressed many of the technical issues that plagued X10 reliability in the past.
I had a conversation recently with Scott Kiodowski, director of distribution sales for SmarthomeMFG. He has a couple of decades of X10 experience and commented, “The three biggest problem areas that technical people have with X10 are phase coupling, signal attenuation and misapplications.” Kiodowski can be found traveling around the country conducting valuable product training sessions on X10 technology products.
Dealers should be aware that there are clear and distinctive quality classes of X10 technology. Customers have often had a bad experience with the basic DIY X10 units that can be bought at mass retail outlets. They are not as familiar with lines such as the X10 “Pro” lines, which can have features such as automatic gain control and extra filtering.
Gain Big Sales Opportunities
Everywhere consumers turn today, they are faced with the promise of integrated home and business automation. The introductory marketing phases of PLC technology have now passed and we are into the peak areas of applying this technology. This product lends itself well to both new and retrofit markets. The industry is expected to grow 25 percent in the next year. Technology-savvy customers like the aspect of a “smart” home, especially if they can get it at a reasonable price less than $1,000.
I have been surprised through the years by the number of times a security dealer will install a system and never go back to visit that customer with additional services and technology.
As a dealer, your marketing plan should include ways to sell that customer more. The retrofit PLC market is one of those markets. Try this next time: Sell an alarm panel that has PLC output technology – such as all lights on when an alarm sounds – and throw in one PLC device. The probability is very high that the customer will want additional home automation devices in the near future.
Surfing the Waves With PLC
In the X10 protocol, transmissions are synchronized with the zero-crossings on the AC power line. One bit of information can be transmitted per each zero crossing. A binary “1” is represented by a 1 millisecond-long burst of 120KHz, near the zero-crossing point of the AC. A binary “0” is represented by the lack of the 120KHz burst. Pulses are strategically placed to cover all three power phases (see Diagram A in May issue of SSI).
In a new technology called universal power line bus (UPB), the transmissions are synchronized with the zero-crossings on the AC power line (see Diagram B in May issue of SSI). Two bits of information can be transmitted each zero crossing. The binary values of “00,” “01,” “10” and “11” are represented by a large pulse, generated in one of four positions near the zero-crossing point of the AC. Within each pulse, there is a series of small pulses and the method of modulation is called pulse position modulation (PPM).
With UPB technology, a very simple circuit that discharges a small capacitor into the power line produces a strong, distinctive pulse. The pulse that is produced is very similar to a pulse produced by a lamp dimmer every half cycle that the lamp is turned on.
According to the UPB designer and manufacturer Powerline Control Systems (PCS) (www.pcslighting.com) of Northridge, Calif., the UPB pulse communication format is 100 times better than existing X10, thereby providing a reliability of 99.9 percent vs. 70 to 80 percent for X10. The manufacturer additionally states that there should not be any need for “fixing the system” with couplers, repeaters and filtering.
The punch of the UPB pulse appears to handle such things as line attenuation – due to its low frequency range of 4KHz to 40KHz vs. 120KHz for X10 – and a large signal level of 40V (see Diagram B in May issue of SSI), vs. less than 2V for other PLC technologies. This, in turn, should make the UPB technology good for commercial PLC applications, including utility communications.
Those currently using X10 technology will be glad to know that the physical communication methods employed by X10 and UPB are so different from each other that there is absolutely no problem with both systems communicating on the same power line simultaneously.
