Portable detector tests rate-of-rise temperature devices. Incandescent light bulb is calibrated to produce rate of temperature rise necessary to activate properly functioning alarm

Clawson, G. T.

English

NASA Technical Reports Server

March 1973	 B73-10128 
• 
NASA TECH BRIEF 
Goddard Space Flight Center
	
_4V 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Detector For Inspection of Fire Alarms 
l6lnches(4Ocm) 
12 Inches (30 cm)
Electronic 
Control 
43/4 Inches	 Heat Source 
(12 cm)
	 (Incandescent 
Bulb) 
S
The problem: 
Everyone expects added safety in buildings equipped 
with fire alarms. But rarely does one consider that fire 
alarms as any other system are subject to failures. 
Although such failures are considerably reduced by 
periodic inspection, fire alarms that use rate-of-rise 
temperature devices are difficult to test. 
The solution: 
A simple, portable detector has been developed for 
inspection of rate-of-rise temperature devices. 
How it's done: 
A rate-of-rise temperature device operates by detect-
ing changes in air pressure. The device consists of two 
enclosed chambers which are separated by a flexible 
diaphragm. Built into one chamber is a calibrated leak 
which is set to the desired alarm sensitivity. When the 
temperature of the surrounding air rises at a slow rate, 
air in the lower chamber begins to expand pushing the 
diaphragm into the upper chamber. At this point the 
calibrated leak begins to release part of the expanded 
air so that the diaphragm does not advance sufficiently
Temperature 
Control Knob 
On-Off 
Switch 
into the upper chamber. However, when the rise rate is 
rapid, the leak cannot compensate for the rapid air 
expansion. Thus the diaphragm expands into the upper 
chamber to the point where it activates a switch to 
sound the alarm. 
The detector developed for testing these devices is a 
metal cylinder (see figure), 4-3/4 inches (12 cm) in 
diameter and 16 inches (40 cm) long, fitted with a 
pistol grip which contains an on-off switch. Inside, the 
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This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights.
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cylinder is divided into two compartments. The first 
one, used for heating an enclosed air mass, is 12 inches 
(30 cm) long and open in the front. It contains a 100-W 
incandescent bulb as the source of heat. The second 
compartment encloses a solid state circuit which is 
used to control the bulb temperature. An additional 
box (not shown), 2 by 2 by 4 inches (5 by 5 by 10 cm), 
is mounted in the vicinity of the bulb. It contains a 
photocell, a battery, a switch, and a meter to check the 
bulb for proper output intensity which may vary with 
line voltage. 
The first step in inspection of the fire alarm device 
requires calibration of the bulb to produce a certain 
temperature. It is estimated that a 44-W input to the 
bulb will heat 0.123 ft 3
 (0.004 m 3) of air at a rate of 
15° F/mm (8.5° C/mm). Calibration is done by turning 
on the bulb and taking a reading on the meter while the 
open end of the cylinder is covered by a suitable 
material. The meter reading corresponds to a bulb 
temperature, and if it is incorrect, the bulb temperature 
control is adjusted. With the calibration complete, the 
open end of the detector cylinder is placed over the 
alarm device. If a rate of 15° F/mm (8.5° C/mm) is 
selected, a properly functioning alarm device will be 
activated in approximately 40 seconds.
Notes: 
1. The detector must be cooled for approximately 5 
minutes between tests to make sure that each test 
is started at ambient temperature. 
2. Requests for further information may be directed to: 
Technology Utilization Officer 
Goddard Space Flight Center 
Code 207.1 
Greenbelt, Maryland 20771 
Reference: TSP73-10128 
Patent status: 
This invention is owned by NASA, and a patent 
application has been filed. Inquiries concerning non-
exclusive or exclusive license for its commercial develop-
ment should be addressed to: 
Patent Counsel 
Goddard Space Flight Center 
Code 204 
Greenbelt, Maryland 20771 
Source: George T. Clawson 
Goddard Space Flight Center 
(GSC-1 1600)
0 
B73-10128	 Category 06


Detector for inspection of fire alarms

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