Newsgroups: sci.electronics.misc
Subject: Inductive Amplifier / Speaker Probe

I would like to have some information on the following device:

Induction amplifier/tone generator, also known as a toner or cable
tracer, enables installers to identify a specific pair by generating a
tone on one end of the pair - with an inductive amplifier identifying
it at the opposite end. Most units are now a combination of tone
generator and continuity tester, commonly known as a wand and toner
set. 

Some examples of such commercial products can be found at 
http://www.sacelec.com/tone.htm

I have tried to find some information on those devices. 
It seems quite clear how those tone senders work: They 
are just simple signal generators that generally generate 
around 900/1000 Hz "warble" signal at few volts signal level 
(ypical signal level 0..7 dBm).

But the design of "inductive amplifier" is not that clear. 
The descriptions of those are not that clear, are those 
just high imoedance capacitive sensors (with propably some 
filtering for AC noise etc.) or are they rially some 
inductive sensors. I quess that mos of those are just 
some kind of capacitive sensors...

http://www.sacelec.com/tone.htm says
"Model 200FP
Progressive Electronics has been manufacturing inductive amplifiers
for over twenty-five years. The Model 200FP stands out as the "crown
jewel" of this product line. Any technician who has ever worked around
powered lines and equipment will instantly see the value of this
Filter Probe. Tone signals that were lost in a sea of hissing and
buzzing AC interference will become crystal clear.  With three types
of noise filtration, the Filter Probe virtually eliminates power
related noise from the tone-and-probe operation. By selectively
filtering out all 60Hz and 60Hz harmonics, the 200FP can be used with
any tone generator for faster, more accurate, cable and wire
identification.
probe tip resistance: 300 ohm, minimum
Gain 35 dB
Input impedance: 100 Mohm
"

Can anyone shed some more light on this and even give a circuit
diagram of such device (and construction hints).



-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/