Cable locator/tracer design considerations - Page 1
Forum section: electronics / beginners

author: Xupicor
author_rank: Contributor
timestamp: January 25, 2022, 03:24:05 am
content: Sometimes at work I find myself in a situation where I need to make new plans of an existing, possibly very old, electrical installation. Sometimes I just need to find a cable that "should be there" but was left inside a plasterboard wall or that just was not documented and nobody knows where it actually is going.I, like anybody else in my situation, use a number of different approaches, and one of them that is very useful at times is a cable tracer. I can connect a signal source to one end of the wire, and use a wireless receiver/amplifier to locate it in an electrical cabinet or try to follow it inside a wall, a false ceiling, a floor, etc.This works pretty well on installations that are generally powered off, however it's not as easy when everything else is working and cables go some fair distances bundled up and tied together in cable trays and such. Oftentimes I can hear fire alarm system (pretty characteristic) or overwhelming 50 Hz buzz. Especially in big electrical cabinets where you can have a lot of cabling and a lot of breakers, it's not exactly easy to locate a cable until you basically put the receiver antenna almost directly on it. I've often had an issue of not being able to hear a traced cable at all in a bigger bundle, even though it was definitely there.So here come my questions. Would it be a feasible project for a beginner like me to design a cable tracer that could work a little bit better? I imagine I could use a 555 (or otherwise make an oscillator) to generate a changing tone, have an amplifier on the receiving side and "shift" the frequency to something audible. Details aside, the high level mode of operation "seems" not that complicated for a simple tracer.However, can I do something about the loud 50 Hz buzz and fire alarm digital signals swamping out my tracer signal? Ideally I'd like to have a couple of switchable modes:A: a low precision mode where I could trace a cable from a decent distance away (let's say 50cm?) to be able to tell whether it is or is not in a wall, a floor, etc, and roughly follow it (this is what my tracers aren't great at)B: a higher precision mode where I could tell which cable it is that I'm following (this is basically what my tracers do by default)C: a mode where 50 Hz buzz and other unwanted interfering signals are rejected or not an issue (this is what my tracers are not doing at all)I guess I could try to achieve A by simply scaling up the power of the signal, but that might possibly get me into some shady territory when it comes to law about RF transmitter power levels? (Don't really know a lot about that at all) But would there be a better/smarter way about doing it? Would using certain frequency ranges be beneficial over others?B I could implement by "just" copying existing designs. Not exactly trivial for me, but I'm fairly certain I could do it.Now, when it comes to C... I'm really struggling for an idea. Should I filter the incoming signal and just reject the bands that my transmitter doesn't touch anyway? A band-pass filter? Would that be enough to defeat the other signals? (But wouldn't other tracers already do that? I guess other signals can have strong harmonic responses all around the spectrum as well and thus still overwhelm the tracer even with a band-pass filter if that makes sense, but I'd have to build a proof of concept and try it out in real world conditions to say anything for certain)Should I try to use some fast digital signal and have the receiver interpret that? I can program STM32 so I guess I could play with something like that, but I wouldn't exactly know where to start when it comes to the signal part.I could go with that if it gave me a binary response in a certain radius around the traced cable, if it was a fast response thing. Nothing worse than tracing a cable using a slow response digital tracer... I've used a Fluke one, it was quite slow and thus made for a very frustrating experience versus an immediate response analog tracer.Other things that I would like to have is a simple continuity test and a mains power protection/test mode should the device be connected to a live circuit by accident. But these (or rather, integrating them in a single mode) might be a topic for the future.I'm open to ideas and suggestions. If I'm wrong in some of my assumptions above, please, do correct me. I'm just a newb, I mostly don't know what I'm talking about.

author: bob91343
author_rank: Super Contributor
timestamp: January 25, 2022, 04:14:17 am
content: I admire your enthusiasm for a project that will turn out to be much more complex than it currently appears.As you say, if it were easy, then current models would do it. I don't know your budget or time frame but as I see it, you would need to have a group of two or three engineers and technicians to devise, build, and test the various approaches. Of course you could start with commercially available receivers and generators so as to avoid to start building something that may not work.An analysis of signal levels, frequency range, filters, and receiver sensitivity should be made. Antennas are important, since coupling in and out as well as locating the signals makes a big difference.

author: Xupicor
author_rank: Contributor
timestamp: January 25, 2022, 04:44:26 am
content: Just to be clear, I'm not thinking about producing anything commercially (that RF transmitter power aside was just that), even a marginal improvement on what I have would be great, and the learning experience itself would probably be the most I expect to get out of it, even if the project doesn't go anywhere.I kind of expected an answer like that seeing how a Fluke device (that's probably fairly expensive) was not really up to scratch. I obviously can't compete with Fluke engineers, or any engineer at all.About a digital approach, I was thinking about sending digital packet (a series of pulses containing information) with varying power, maybe on various frequencies. Assuming that the receiver could make out and properly decode the information from more packets kinds when it's closer rather than further away, I could interpret that as a rough information on range.Anybody tried anything like that?