Microprocessor-Controlled Fire and Life Safety Protection

Microprocessor-Controlled Fire and Life Safety Protection

The incident commander is able to prompt the monitor to display needed information at the command post simply by activating buttons at the control module.

It was a truism with the conventional fire-protection system: the more functions you wanted, the more hardware and hard wiring you added.

No more!

Now, an advanced, microprocessorcontrolled fire-protection system can perform whatever the imagination of the engineer can devise. All functions programmed into memory are accomplished by smoke detectors, manual stations, and other initiating devices to perform fire detection and life safety—all on just two wires.

Furthermore, no matter how complex the functions of the system, the control module checks the status of the entire system—as many as 480 addressable devices—constantly and sequentially, 15 to 20 times each minute, immediately [ reporting any abnormal conditions it may find.

Each addressable detector on the system will respond to the system’s commands such as:

  • Report calibration.
  • Report identification.
  • Report sensitivity.
  • Flash your light emitting diode (LED).
  • Turn your relay on (or off).

All this within microseconds.

All detectors in the system are constantly monitored for calibration and proper voltage. Also, the functions of detector chambers are checked against reference voltage or sensitivity readings to ensure that each detector is functioning within its designed parameters.

In addition to smoke detectors, pull stations, photoelectric detectors, thermal detectors, etc., may be mixed in the system. By checking relays, the control module also guarantees that other devices on the system such as pull stations, stand-pipes, sprinklers, ventilation system controls, and Halon solenoids will function as they should.

The system is designed for simplicity, with no large amount of switches or highly complex devices. It communicates in plain English and offers the user the chance to use his own names for things, which can be phrased in up to 32 alphanumeric characters. For example, “3rd floor broom closet” rather than “Location XLiii-2.75XP.” Should any single detector on the system go into alarm, the control immediately identifies it by number and the user’s own identification.

The sensitivity of all detectors in the system, detectors of any group or any single detector, can be adjusted (increased or decreased in four steps within the limits set by Underwriters Laboratories 268 for smoke detectors) from the control panel. If desired, this can be done on a time control basis, such as lower sensitivity by day as people enter the building to work, maximum sensitivity at night for the earliest possible warning of trouble. The memory can be set to automatically adjust detectors for weekends, holidays, or vacation schedules.

The very accurate definition of the system in terms of printed circuit board memories ensures that the system will function precisely as designed, feature for feature, and device for device. This is a great advantage from the protection viewpoint because the system can’t be fooled, disabled, or its programming casually changed (with attendant high possibility of violating codes, unintentionally disarming or bypassing the system, etc.). The control module knows which and what type devices should be located where, and in case a change or bypass is attempted, the system will generate a “trouble” signal until its status is restored as intended.

“Mods” made via circuit board

The ability to expand or modify functions is inherent in the microprocessor-controlled system, but only with proper planning and forethought. The plant engineer tells the system manufacturer what new or changed functions are needed, and the manufacturer provides a new memory module that incorporates the additions or changes. In this way, the system is only disconnected for the few minutes it takes for a qualified technician to replace the memory board.

When the new memory is in and the battery reconnected, the first function of the control module is to run a status check. The first thing the module senses is that all the new devices are missing! It reports trouble at once, and continues to report trouble until all the devices described on the new memory board have been connected exactly as designed.

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Close-up of the data display within the control module. Directions for its manipulation for information are clear and simple.

Photo court osy of Pyrotronics

Continual check for functionality

A building protected by this new microprocessor system can be a fire chief’s or underwriter’s dream. To my knowledge, this is the only system in the industry that knows on a continuing basis if all detectors are functional. It signals bad detectors, bypassed detectors, or incorrectly located detectors.

In a conventional system, the only way to be sure every detector is working is by a physical check of every single device, which may happen every six months or once a year. Since a certain—admittedly small—percentage of detectors will go bad each year, portions of a building can be unprotected for months at a time. The actual number of outages can be quite serious on a large system. With the microprocessor system, each and every detector and relay is checked for functionality every three seconds, and problems are located by number, type, and location, so that corrections can be made immediately.

Another problem with a conventional system is that when a detector “fails safe” and alarms, the whole zone usually has to be disconnected until the repair is made. If a detector malfunctions in the microprocessor system, the system will continue its entire protective function except for the single detector, and will continue to report trouble on this detector until the replacement is made. There’s no way that trouble in one detector can impair the protective value of the whole system.

A microprocessor controlled system can perform literally thousands of functions with any degree of complexity and interrelation. For example, multiple levels of timing functions can be set up on a single circuit. Each device on the circuit is “seen” as its own unique zone, and can be given a unique function, timing sequence, order of priority and combination of outputs— all on just a single pair of wires!

Hardware-wise, this is not a complex system. It has just two input modules, two output modules, and the control module. Software-wise, however, the imagination’s the limit.

In the past, limitations were imposed by the amount of physical items that could be added to a system: hard wiring and hardware like diodes, timers, switches, and modules. Each additional function required more and more hardware and hard wire and more and more control cabinets. The microprocessor-based system needs only a small cabinet because its functions are defined by its printed circuit memory boards rather than by hardware.

System components

The system has five basic parts:

  • The control module includes power supplies, card racks, data displays, the memory, and the microprocessor itself, all in a compact cabinet.
  • The input module for the new technology accepts up to 480 addressable smoke detectors and other detection devices, each individually controllable and individually reporting as a zone.
  • The “backwards compatible” input module interfaces old technology with new, accepting up to 96 zones of conventional hardware (enough to handle the entire existing system of al• most any building).
  • The supervised output module or “signal circuit” communicates with public alarm circuits and should also be used to release Halon, carbon dioxide, steam, etc.
  • The high-power auxiliary mod-, ule, controllable by time or function, can be used to shut down large motors, fans, etc.

Within the control module, the memory bank will keep all records until it is manually erased. The system supervises its own line power supply and battery backup to best ensure continuance of memory and function.

An optional hard-copy printer offers instantaneous and continuous printout. The system can be addressed and functions can be controlled through the printer.

The new system can be used in conjunction with an existing system. The “backwards compatible” input module is specifically designed for retrofit to a conventional system, while the other input module is designed for use with the new technology. In this way, an existing system can be used with the new technology added in areas where the special functions of addressability, functionality, testing, remote adjustability, 100% annunciation, etc., are desired. The old system would continue to operate as it had, zone by zone, and could be gradually replaced as the need was perceived. This “backward compatibility” circuit can be used with any • of the traditional protective devices of any major manufacturer.

Precise timing

Time is a highly important commodity, and knowledge of timing can be essential to quick fire control, as all fire departments know. For example, even a small fire in a large building can cause many detectors to go off. Which detector sounded first? Where did the fire start? This is what the fire department wants to know when entering a smoke-filled building.

The microprocessor-control display panel will list each detector that goes off, in order, together with its location, date, and the exact time of alarm to the second, giving a complete record of the progress of the fire, and very valuable information for a quick strike at the seat of the fire.

The hard-copy printout of this information, which is usually available at the building’s fire command center, is ideal for insurance purposes. This detailed data, never before available except in controlled tests, can be invaluable for advancing the understanding of how fires can be prevented or de(continued on page 48) (continued from page 46) feated. The printout will also show actuation and timing of other parts of the system: which standpipes started flowing, exact time, etc.


The microprocessor-controlled system makes maintenance easier and cheaper than conventional systems. Laborious device-by-device checking of an entire zone is no longer necessary, as, on command, each device will report its operational status and all functions can be checked from the control panel.

Remote status checks and adjustability are always convenient, particularly when a large number of detectors are in relatively inaccessible locations.

Building maintenance people can perform these checks and make adjustments or replacements as needed.

The display panel even prompts what questions should be asked. For example, when key Number 1 is depressed on the control panel, the display responds by requesting, “Enter a command.”

If key Number 2 is now depressed, the panel reaffirms, “Check sensitivity?” If the user agrees by depressing the “enter” key, the display then prompts, “Enter device number.”

When that is entered, the display will show, “Sensitivity = –.-Volts,” and the data will remain on the screen for 30 seconds—but will actually be updated every three seconds as a status-check cycle is completed. All functional checks are performed in a similar pattern.

Remote status checks and adjustability are always convenient, but are a particular time and money-saving benefit where the building contains a large number of relatively inaccessible detectors—on the ceiling of an auditorium, or inside ventilation-system ductwork. At the push of a button, the maintenance engineer can assure himself that each device is fully functional, and can read the voltage and change the sensitivity as desired.

Costs and insurance benefits

A good fire protection system, even a conventional one, will never be “cheap,” but its cost is a small fraction of the value of the property—and lives—it protects. If the microproces-

Instead of a unit-by-unit check with notebook in hand, that information can be retrieved in minutes, neatly listed by device and voltage. sor system performs complex functions, its two-wire versatility can even be less costly than the wiring and hardware of a conventional system.

A further benefit of the microprocessor system is its compatibility with the requirements of insurance underwriters. Underwriters like a hard-copy listing of voltages to ensure that the system is operational, and some companies require such a listing every six months. Now, instead of a unit-by-unit check with notebook in hand, that information can be retrieved in minutes, neatly listed by device and voltage, day, date, and time. Even if the system has no printer, the values can easily be recorded from the display board, or the manufacturer will periodically loan the customer a printer for record-keeping purposes.

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