Double Shielded Coaxial Cable for a Vehicle Tachometer

[(*steve*)]

Connect a piece of wire rope shorter than the cable between the tacho and wherever the other end connects. That way, when you drop the tacho the cable doesn't take the load.

The cables are not made to take a load. even with king kong tightening them, the braid will stretch if pulled hard enough. That is probably enough to make the centre conductor disappear.

Do you have pictures showing how this tacho is mounted and used? I am having trouble thinking how dropping a tacho could be considered normal and how you don't consider yourself thankful that only a cable gets damaged.

 

[poor mystic]

Use a D4 video connector at each end. Twisted pairs are good for quite some bandwdth; consider them to replace the cable you're using now. Steve's idea about wire rope is good, too.


PS I mean good shielded audio twisted pairs not telephone jumper wire.

 

[dzlvs8]

Connect a piece of wire rope shorter than the cable between the tacho and wherever the other end connects. That way, when you drop the tacho the cable doesn't take the load.

LOL, we are all mechanical engineers and technicians here. That, of course is the solution I thought of. I came here to see if there were any solutions that were maybe less of a hack job. Like a real strain relief system I can buy. lol


I regards to NEEDING these low loss cables. I'm not entirely certain that some engineer down here just didnt just go out and buy the best cables he could find. It's very well possible that there wasn't a whole lot of electrical engineering expertise that went into the decision besides (just buy the best you can).

So the two clean solutions that I see as possible that people are recommending are possibly these.

1. Find a different amphenol triax connector that connects the wires internally different. THIS IS EXACTLY WHAT I HAVE BEEN TRYING TO FIND OUT ABOUT THE ENTIRE TIME! Does anyone know of a different amphenol tirax connector that is maybe soldered or connected differently internally. That sheilding frays and comes loose way too easily.

2. I am reading a 400rpm - 8000rpm signal (1 pulse per revolution) and the signal going to the tacho from the tach box is 5V. Is there any other cable that MAY satisfy my needs and give me a good quality signal?

 

[poor mystic]

Well since you seem unwilling to even consider the twisted pair solution I don't know what you think is wrong with it. Twisted pairs are a robust, high bandwidth bearer for signals up to hundreds of times the bandwidth of your signal. D connectors are robust, don't pull out, and are cheap and available. So go figure.

 

[dzlvs8]

I looked up D4 connectors and couldn't find much information on them. So are they two twisted wires and then also a sheilding around them? I will try some if so. Do you think they are good for low frequency signals though. I larger bandwidth doesn't help but I need them to be good for low frequency. They looked like you could get them with a nice strain relief built into them. I like the keyword cheap.

 

[poor mystic]

Hey it's OK,
These connectors will handle DC to megahertz. Both the connectors and the cable are cheap and robust. They are easy to solder up and are designed with f*wits in mind; they are polarised. You can connect twisted pairs to them - let every signal (data) wire be associated with an earth, which will be the other leg of the pair. You'll need to earth the shields on the metal case of the connector. (Earth only one end!)

What surprises me about the system you seem to be using is that I would expect the photodetector unit to provide a low impedance output that didn't require this coddling to get it to the instrumentation. A comparator at the detector would save trouble, in my mind.

 

[shrtrnd]

Your photo clearly shows a triax connector.
Co-ax is two conductor, the center wire and the shield
Tri-ax is three conductor, the center wire and TWO braided shield wires.
Why don't you check with your engineer, and see if you really need your low-loss triax
cable.
I just did a quick check on-line.
Newark 44F5331, is Pomona 3600, SOLDER connection for the braid. (Triax)
But like I said, they ain't cheap ($52 each).
Soldering the braid to the connector would give you a more sturdy connection, but con-
sidering the rough handling in your application, that may not help.
How's about using a cable clamp to act as your strain relief?
The wire comes out of your tac, give it a little loop, then bolt a cable clamp to the tac
housing to secure the looped end of the cable. Somebody knocks the tac off or whatever.
The cable is hanging on the dangling tac AT the cable clamp, instead of yanking the
wire out of the BNC connector.

 

[dzlvs8]

Your photo clearly shows a triax connector.
Co-ax is two conductor, the center wire and the shield.

Actually I read online that there is dual sheilded coax wire and it looks exactly like what i have. Maybe triax is just another name for it. I dunno

Why don't you check with your engineer, and see if you really need your low-loss triax
cable.

Like I said, our engineers in our area don't know the first thing about electrical stuff. We are a very very very very large company. The people who made the decisions about getting the equipment for this building probably dont even work in the same city as me. Hell, they amy even work in a different country. I cant just call up any ol electrical engnieer about this. Hence the reason I decided to come here. We dont have direct support for this "project" I am working on so I cant just pull in other departments help. Basically, everyone else here is too lazy to care how much time and money they waste on this stuff, and I just decided to look into other options.

How's about using a cable clamp to act as your strain relief?
The wire comes out of your tac, give it a little loop, then bolt a cable clamp to the tac
housing to secure the looped end of the cable. Somebody knocks the tac off or whatever.
The cable is hanging on the dangling tac AT the cable clamp, instead of yanking the
wire out of the BNC connector.

LOL Yeah, I assume there is something out there that is specifically made for cables to be able to do this. I actually was already in the process of taking some rubber hose and some zip ties and doing this exact thing. The problem with this is, ...well its kinda ghetto and the zip ties slip right off the end of the amphenol connector. The cylindrical barrel makes it hard (thats what she said). Instead I decided to try and tie it off to the equipment but then the cable becomes hard wired to the equipment. Thats wasn't really a good idea.



So basically what I am hearing is that the amphenol connector I am using is the only three conductor cable in the world that can handle low frequency and have low signal loss. ???????????????? D4??

This sure is frustrating.

 

[poor mystic]

No. Not so.
DC is so easy to move around the place that most manufacturers won't skite about the DC capabilities until they start handling big currents.
There's a bit of competition between ideas here in this thread but we are competent techs and our ideas probably all work.
There are heaps of good connectors... Canon make a really good series for a further example but ohh! the prices!
I can't tell you how to make your decision but I'd look for a clean, simple and cheap plan that provides a strongly locking connection. (You don't need anything special because the frequencies involved in your measurements are so low.)
Perhaps if I were you I'd take a couple of these ideas and put them to the test.
Please let us know how you get on!
Mark

 

[dzlvs8]

Mark mark mark mark mark. I have been asking for any different connector suggestions throughout this entire thread and the only suggestion I had was a D4 connector and then I was told that it was a type of two wire coax. i.e. not what I need.

I assumed there are many cable types that I can use but I dont have any specific experience with any 3 wire cables. I am looking for any recommendations on durable cables!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

For real man, thats all I need. A different workable cable. I've got one suggestion.

 

[poor mystic]

If you were on my team you'd be finding a few things out right about now... I'd fire you for that rude usage of my name alone. Just remember that I'm here helping you out of the goodness of my heart and is is fitting for you to either say "thank you" or b off and find somebody you can pay so that every word you utter costs you some money. That might keep your rude tongue in its place, since evidently you have no native courtesy.

 

[shrtrnd]

Put the strain on the cable, not the connector.
Newark 34C1955 thru 34C1954
Voltrex cushioned cable clamps.
Loop the cable from the connector, thru the cable clamp.
When the cable gets yanked, the cable clamp keeps the cable from being pulled out
of the connector.
Bolt the cable clamp to the tach.
You won't have to change the cable or the connector.
The costs you're talking about are indicative of triax, which is what your connector is.

 

[dzlvs8]

Put the strain on the cable, not the connector.
Newark 34C1955 thru 34C1954
Voltrex cushioned cable clamps.
Loop the cable from the connector, thru the cable clamp.
When the cable gets yanked, the cable clamp keeps the cable from being pulled out
of the connector.
Bolt the cable clamp to the tach.
You won't have to change the cable or the connector.
.

Awesome. Thanks. Thats sounds like the exact thing I'm trying to do if I cant get a different cable. In fact, it sounds like the professional version of my hacked up clamp method I made.

The costs you're talking about are indicative of triax, which is what your connector is.

Buuuuuut because of my low DC voltage and low Hz being utillized I was just told that earlier on here it didn't matter what type of cable I used as long as it was cable with a sheild and two wires. Therefore, I shouldn't need an expensive connector. Or I can at least get a different frickin connector.

 

[shrtrnd]

Hope the clamps solve your problem. If one way of looping the cable doesn't work, the
theory is sound, just try a couple different ways to make it work effectively.
I'm like you with your design engineer. I don't know why he specified what he did.
You've got a lot of ideas from a lot of other guys here to consider, if you want to try
a different cable and/or connector.
Whether you use something different or not, you just have to make sure the strain on
the cable to the connector is eliminated and you should be ok.

 

[dzlvs8]

ehhhh. I give up. I would have to drill into my photocell in order for those clamps to work. And in order to change the cable out I would have to unbolt it from each piece of equipment.

Im getting a different cable. Dont know why its so hard to find someone who has used a durable cable that is 2 pins with a sheild. Oh well.

I do appreciate the effort though, even though it took a week to get no resolution and I had to restate my needs and situation every few hours.

 

[(*steve*)]

even though it took a week to get no resolution and I had to restate my needs and situation every few hours.

You were given solution after solution after solution.

You want a different cable but when it's suggested you want to use the same cable.

You want a different plug, but when that's suggested you want the same plug.

You were told that it's best to simply not put strain on the cable, but you don't want to do that either.

You want strain relief, but when that's offered, it's not good enough.

I realise you want exactly the same (but cheaper) connectors with just the same (but cheaper) cable and have it work just the same (but be stronger). I think that's unrealistic.

I'm with Mark. You need to go out and pay for advice.