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Intellisense® - The New Standard In PLC Home Automation

This application note describes what Leviton's Intellisense® feature is...and why it is such a quantum leap in PLC technology.

Leviton's new Decora Home Control (DHC) X-10 Protocol receivers with Intellisense deliver the reliability you depend on in powerline carrier home automation products-Even in applications where electrical "noise" is present on the AC line. And Leviton's Intellisense circuitry assures excellent noise immunity without reducing command signal sensitivity so that top performance of the DHC system is assured.

With Leviton's new DHC receivers with Intellisense, you'll avoid time-wasting callbacks, boost customer satisfaction, and grow your entire Home Automation business.

The Problem
The Solution
Comparing Powerline Carrier Receiver Module Performance
Other New Features: Memory Dim and Soft ON/OFF

Noise on the line-A part of every electrical system

Powerline carrier home automation systems are easy to install because the home's existing AC wiring is used to carry command signals. However, in many homes, electrical interference can prevent receiver modules from operating properly. Electronic equipment found in virtually every household generates disruptive noise interference: TV's, VCR's, audio equipment, personal computers and peripherals, FAX machines, electronic lighting ballasts and many other electronic devices.

Figure 1 shows a typical powerline carrier command signal. Note that there are "empty" signal windows in the coded sequence.

How noise can disrupt powerline carrier systems

Powerline carrier systems transmit and receive command signals at the zero crossing of the AC power curve. That's because electrical noise is at a lower level here than at any other point in the cycle. The zero crossing point is the Signal Window where receiver modules listen for the special coded command sequence. If the receiver hears a steady stream of signals in every signal window, it interprets this as random noise and does not respond.

Figure 2 shows what can happen when there's noise on the powerline while a command signal is being transmitted. The noise fills in all the signal windows, disrupting the coded sequence. As a result, the receiver cannot hear the command signal and does not respond.

Amplifying the command signal may not solve noise problems

Problems from noise interference are more related to receiver sensitivity than to signal strength. The sensitivity of a receiver determines the minimum amount of signal it can recognize. In order to deliver reliable performance in a variety of applications, powerline carrier receivers must be sensitive to command signals that are lower than 1/10 of a volt (.100 volts). Boosting the command signal does not change a receiver's sensitivity. No matter how powerful the command signal is, the reciver will still be sensitive to noise that's only a fraction of a volt, and noise will still be capable of distrupting the system's operation.

Automatic Gain Control is needed, but not just any kind

Automatic Gain Control (AGC) is a special circuit that adjusts receiver sensitivity to help eliminate noise interference. While Automatic Gain Control can be very effective in reducing noise problems, some types of AGC circuits yield mixed results when it comes to overall system performance. Up until now, only a "non-gated" type of AGC was available in powerline carrier receivers. Non-gated AGC circuity is not synchronized with the signal window. Instead, non-gated AGC desensitizes a receiver to high noise levels that occur throughout the entire AC cycle. Powerline carrier receivers are only affected by noise within the signal window, which is the lowest level of noise in the entire AC cycle.

Therefore, non-gated AGC desensitizes the receiver to accommodate high noise levels that do not even effect receiver performance. That means the non-gated type of AGC currently available can desensitize the receiver from noise to such a degree that it also desensitizes it to command signals. There are installations where non-gated AGC circuity can create as many problems as noise does.

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A New Built-In Feature Provides Outstanding System Reliability

Leviton's DHC receivers feature Intellisense, the right type of Automatic Gain Control

Leviton DHC receivers use Intellisense, a special gated-type of AGC, to help eliminate noise problems. The Intellisense gated AGC circuit is ideal for powerline carrier systems because it only operates during the signal window when receivers listen for command signals. Noise levels in the signal window are never as high as they are during other portions of the AC power curve. Therefore, Leviton's Intellisense gated AGC will desensitize a receiver to noise signals with only a minimal reduction in command signal sensitivity. The result: Problems from noise interference are dramatically reduced without affecting overall system performance.

Leviton's new Intellisense is built into DHC wall-mounted switch and receptacle receiver modules. These modules are installed exactly the same way as they were before, and there's no change in their popular Decora styling, either.

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Comparing Powerline Carrier Receiver Module Performance

	No AGC - High sensitivity means receiver will pick up relatively low levels of noise as well as command signals. The Result: Noise may disrupt operation.
	Non-Gated AGC, Currently Available In Some Receivers: Sensitivity is reduced based on high noise levels that appear outside the signal window. This means sensitivity to command signals is also greatly reduced. The Result: Receivers may not respond to command signals.
	Leviton DHC receivers with intellisense gated AGC Intellisense Gated AGC only operates during signal window when the receiver listens for command signals. Sensitivity is reduced only enough to compensate for low-level noise inside the window. Command signal sensitivity is still high. The Result: Optimum performance.

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DHC Dimmer Switch Modules with Intellisense plus enhanced performance features

Leviton DHC Dimmer Switch Modules not only feature Intellisense for outstanding performance and reliability; they also provide new performance features for added comfort and convenience:

Preset-Switching Turns lights ON at last selected lighting level instead of full brightness. Eliminates the need to continually readjust for a desired dimmer setting every time the unit is switched On and Off.
Soft ON/Fade OFF Starts lighting with a gradual rise to the selected brightness level, and gently fades lights when they're switched off. Provides an eye-pleasing effect and helps extend bulb life.