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Model 501-B  Smoke Detector Tester


Calibrated Sensitivity Inspection

Of Installed Detectors


Meets Current NFPA 72                                                                          



For Calibrated                                                                                              Stable Smoke

Sensitivity Tests &

Functional Tests


For Ionization or                                                                                            Harmless to Detectors

Photoelectric Detectors                     

(Duct, wall or ceiling-mounted)                

even older larger size detectors                                                                    30 Seconds Per Test


Adjustable Range:                                                                                          Portable, Easy to Operate

0.3 to 4.0 %/ft                         


Digital Display


National Fire Alarm Code

The National Fire Protection Association recommends periodic inspection and testing of smoke detectors at their installed locations as stated by the National Fire Alarm Code (NFPA 72-E, 1996 edition).

The test includes a calibrated sensitivity test to assure that (1) each detector is within its listed sensitivity range, and (2) each detector would initiate an alarm when exposed to smoke of certain concentrations.

The Gemini 501-B Tester

The Gemini 501 Tester combines the above 2 objectives into a single and easy to perform test.  The tester generates an adjustable amount of aerosol smoke between 0.3 and 4.0 %/ft obscuration to challenge the detector under test.  During the test, the operator selects a smoke concentration level and directs the smoke through the hand-held wands and shroud to the detector at the ceiling.

If the concentration selected is below the sensitivity setting of the detector, the detector would not alarm.  However, if the concentration is equal to or greater than the setting, the detector should alarm within 30 seconds.

The minimum amount of smoke that triggers the alarm is the sensitivity setting of the detector.

Aerosol Smoke

The tester produces a consistent and stable smoke from a refined mineral oil.  The smoke particle sizes and size distribution resemble that of the smoke from the UL-268 Standard Smoke Box.  Because of its small particle sizes, low concentration, and short exposure time, the test smoke is not harmful to the detectors or the operator.  


In production, each instrument is individually calibrated with a Particle Mass Monitor and Standard Reference Detectors.  The instrument output is presented as mass concentration in mg/m3 and smoke obscuation in %/ft.

Inspection Service

The Gemini Tester was designed with the inspection personnel in mind.  It is a universal tester, suitable for all types and brands of detectors.  Furthermore, it lets you test the detectors in place, without having to remove them from the ceiling.

Depending on the type of facilities, an experienced operator should be able to test 150 to 200 detectors per day.


The only regular maintenance needed is to change the vacuum filter element after 200-300 tests.  A pint bottle of Rudol Liquid, a refined mineral oil, is sufficient for over 800 tests.  Standard reference smoke detectors may be used to check the need for recalibration of the tester.


For detailed specifications see:   Gemini 501B Brochure.pdf

For prices see: Gemini Price List