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G8MNY > TECH 20.06.05 20:38l 95 Lines 4522 Bytes #999 (0) @ WW
BID : 50580_GB7CIP
Read: GUEST OE7FMI
Subj: Coax Tester
Path: DB0FHN<DB0FOR<DB0SIF<DB0EA<DB0SM<PI8DAZ<DB0EEO<DB0GOS<ON0AR<ON0AR<
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Sent: 050620/0827Z @:GB7CIP.#32.GBR.EU #:50580 [Caterham] $:50580_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
From Brian G3YRH @GB7CAM.#12.GBR.EU Dec 02
Co-ax cable tester
==================
This tester detects steady short or intermittent open circuits. Momentary open
circuits or steady short circuits trigger a buzzer.
Schematic : Detection of intermittent discontinuities or steady shorts.
E
---------------O-------/\/\/\----O----<<---
| | R2 270 | (COAX UNDER TEST)
--------- | | -<<--- (SHORT FAR END)
| | | | |
------ < R1 ----- | | F
| BZ | > 680 --- 9 V | |
------ < ----- | |
| | --- | |
---------- | | |
C | | | |
O-------- | | |
| | | |
----- | | |
\ / | | |
\ / 2N1777 | | |
----- | | |
| \ | HIGH SIDE | |
| \___________|_________________|___|_________
O |nc |nc
\ B | | SEE NOTE 1
D \____________|_____________________|_________
O------O
A S1 LOW SIDE
NOTE 1: Alternative: Single wire under test or jumper to test internal
continuity of tester.
BZ = Buzzer
S1 = Switch
2N1777 = Silicon Controlled Rectifier
nc = No Connection
RESISTANCES ARE IN OHMS.
To test coaxial cable for intermittent discontinuities or steady shorts,
place cable at points E and F, then short far end of coax.
Details
A simple, portable, lightweight testing circuit sounds a long duration alarm
when it detects a steady short circuit or a momentary open circuit in a coaxial
cable or other two conductor transmission line. The tester is sensitive to
discontinuities that last 10uS or longer. Previously, there was no simple,
portable instrument to detect momentary shorts or discontinuities. Such
conventional instruments as ohmmeters and lamp or buzzer type continuity
checkers give visible or audible indications of steady open or closed circuits
only.
To detect an intermittent open circuit in a coaxial cable, the far end of the
cable is shorted by a jumper, and the tester is connected as shown in the upper
portion of the figure, with the switch in position B. If the cable is in good
condition, the high side terminal remains ungrounded, the silicon controlled
rectifier remains off, and the buzzer does not sound. If an opening occurs in
the center conductor or shield of the coaxial cable, the current from the high
side terminal to the low side terminal that would be otherwise shunted by the
cable flows into and triggers the silicon controlled rectifier and thereby
turns on the buzzer. Even if the coaxial cable starts to conducts again, the
buzzer remains on until the silicon controlled rectifier is reset by turning
the switch to position A. An intermittent discontinuity in a single wire (or an
internal discontinuity in the tester) can be detected in this manner if no
coaxial cable is connected and the wire or jumper is connected as shown in
dashed lines. (See Note 1).
To detect a steady short circuit, the jumper ( At note 1) is removed. If the
buzzer does not sound, there is a steady short circuit between the inner and
outer conductors. If the buzzer does sound, then the cable is either good or
open.
The tester is used extensively for detecting intermittent open shorts in
accelerometer and extensometer cables. The tester can also be used as an
ordinary buzzer type continuity checker to detect steady or open circuits.
For this purpose, the switch is set a position A and the probe leads are
connected as shown by dashed lines in the lower portion of the figure (points
C and D). In this case the silicon controlled rectifier is not part of the
circuit, and the buzzer remains on only so long as the circuit under test
provides a conducting path.
This work was done by Bobby L. Anderson of Rockwell International Corp. for
Marshall Space Flight Center. No further documentation is available.
NASA Tech Briefs January 1990.
rgds Brian g3yrh@gb7cam
Why don't U send an ineresting bul?
73 de John G8MNY @ GB7CIP
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