Printed-circuit process produces ordnance-initiated start/stop switches. Method is faster and less costly than fabriction by hand, and produces switches of uniform quality

Grimes, W. E.

Wise, J. P.

English

NASA Technical Reports Server

October 1975	 B75-10255 
NASA TECH BRIEF 
John F Kennedy Space Center 
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. 
Start/Stop Switches for Testing Detonation Velocity of Explosives 
.
The problem: 
Ordnance-initiated start/stop switches are used in 
measuring detonation velocities of various explosives. 
The switches are manufactured by hand. This process 
is costly and time consuming, ,
 and the product is not 
always uniform in quality. 
The solution: 
The switches can be manufactured using a 
printed-circuit process. The process is faster, and the 
product is less costly and more uniform in quality. 
How it's done: 
A newly developed switch is shown in Figure 1. It 
includes two pairs of conductor strips marked 
"primary start" and "secondary start." The two pairs 
are used for improved reliability. Both are activated 
by the explosive, and if one fails, the other still turns 
on to connect the circuit. A stop switch is constructed 
similarly.
The conductor strips are mounted on a flexible 
printed-circuit (PC) board. Each pair is made from a 
0.125-in. (3.2-mm) conductor forming a double direct 
overlay. The strips within each pair are separated by 
an airgap of approximately 0.005 in. (0. 127 mm). The 
strips are connected to the electronic equipment with 
a four-conductor ribbon wire. The other dimensions 
are shown in the figure. These can be made smaller 
using 0.0625-in. (1.59-mm) PC conductors. 
For a test the switches are connected to the 
electronic equipment as shown in Figure 2. They are 
set a measured distance apart, and a train of explosive 
material is placed over them as shown. 
The test is initiated by detonating the explosive 
train with the firing cable. As the explosive burns over 
the start switch, the switch closes, activating the pulse 
generator to trigger the electronic counter. A short 
time later, the explosive burns over the stop switch, 
triggering the pulse generator to stop the count. 
Explosive 
Train 
f.e____2.25 in. (5.72 cm) - _____________ 
2.00 in. (5.08 cm) —
Conductor 
0.625 in. 0.375in. (0.953 cm) ) 
Strips 
I. 
Primary Start  
0.588 cm)	
L_	 To 
-- 
--t I-
Electronic
 (it
— I Secondary Start
 
ILL 
L_ 
PC Board
Figure 1. Typical Switch Configuration
(continued overleaf) 
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.
https://ntrs.nasa.gov/search.jsp?R=19750000255 2020-03-19T20:15:25+00:00Z
------J. 
Start Switch	 -- -	
=	
Stop Switch 
Figure 2. System for Determining Detonation Velocity of Explosives 
	
Detonation velocity of the explosive is computed by 	 Patent status: 
	
dividing the distance between the switches by the	 NASA has decided not to apply for a patent. 
recorded burn time. 
	
Special Bakelite switch holders have also been	 Source: John P. Wise and Walter E. Grimes 
	
constructed. These are shaped to hold the switches 	 (KSC- 10793)
during the testing of confined detonation charges. 
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
Kennedy Space Center 
Code AA-PAT 
Kennedy Space Center, Florida 32899 
Reference: TSP75-10255 
Firing 
Cable
S 
Categories: 01 (Electronics - Components 
and Circuitry) 
04 (Materials) 
02 (Electronics Systems) 
B75-10255
	 06 (Mechanics)


Start/stop switches for testing detonation velocity of explosives

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