Q: circuit suggestions for a contact sensing circuit.

[Jon Juhlin]

This is a little out of my normal field so I am seeking some outside input.

I am working on a machine that has tow large steel bodies that are clamped
together and share a common clamping interface surface. The components are
located in a region of the machine that is inaccessible for visual
inspection when running. The two components can sometimes begin to loosen
and when this happens a lot of damage can occur. Furthermore the parts
rotate and hence it is not possible to connect the sensing circuit directly
with the outside world, so I am assuming that I will need to build a
wireless interface to signal the outside world if the two parts are
beginning to come loose. I am attemping to detect separation between the two
surfaces at the clamping interface.

Can anyone suggest a circuit or a resource where I could research such a
circuit? The circuit will need to be battery powered and have a low enough
current draw that the batteries last a long time. It must detect very small
separation (.005"). The output signal must be able to communicate via
wireless communication over a small distance (5-20 feet).

Any suggestions welcome.

Jon Juhlin

 

[nospam]

"Jon Juhlin" <j_juhlin@efn.org> wrote:

This is a little out of my normal field so I am seeking some outside input.

I am working on a machine that has tow large steel bodies that are clamped
together and share a common clamping interface surface. The components are
located in a region of the machine that is inaccessible for visual
inspection when running. The two components can sometimes begin to loosen
and when this happens a lot of damage can occur. Furthermore the parts
rotate and hence it is not possible to connect the sensing circuit directly
with the outside world, so I am assuming that I will need to build a
wireless interface to signal the outside world if the two parts are
beginning to come loose. I am attemping to detect separation between the two
surfaces at the clamping interface.

Can anyone suggest a circuit or a resource where I could research such a
circuit? The circuit will need to be battery powered and have a low enough
current draw that the batteries last a long time. It must detect very small
separation (.005"). The output signal must be able to communicate via
wireless communication over a small distance (5-20 feet).

Any suggestions welcome.

Too vague to give any meaningful suggestions.

So this will probably turn into one of those long threads where everyone
offers a solution for what they think the problem might be.

 

[Jon Juhlin]

This sounds like one of those threads that may attract unnecessary sarcastic
replies to a reasonable question. But let me try to make the problem
statement more clear.

I have two pieces of metal, tightly clamped together and need to be able to
sense if they begin to separate. I need to sense the very small separations
on the order of .005". This situation is such that proximity sensors won't
work because of physical and other constraints and strain gage type sensing
of contact related strain would drain a battery powered system over a long
period of time.

I suspect that this problem has been solved before and I assumed that this
might be a reasonable forum to ask about it. I actually have an idea in mind
that would involve fashioning a switch in which and isolated region of two
contacting surfaces could act as a switch but this would be too difficult to
explain using only text.

If anyone knows of any types of contact sensing circuits I would welcome any
input and will determine if the suggestion is adaptable to my situation.

Jon Juhlin

"nospam" <nospam@nospam.invalid> wrote in message
news:gu26n0p434pr2a70539r7bpu1cc7kpigtv@4ax.com...

"Jon Juhlin" <j_juhlin@efn.org> wrote:

This is a little out of my normal field so I am seeking some outside
input.

I am working on a machine that has tow large steel bodies that are
clamped
together and share a common clamping interface surface. The components
are
located in a region of the machine that is inaccessible for visual
inspection when running. The two components can sometimes begin to loosen
and when this happens a lot of damage can occur. Furthermore the parts
rotate and hence it is not possible to connect the sensing circuit
directly
with the outside world, so I am assuming that I will need to build a
wireless interface to signal the outside world if the two parts are
beginning to come loose. I am attemping to detect separation between the
two
surfaces at the clamping interface.

Can anyone suggest a circuit or a resource where I could research such a
circuit? The circuit will need to be battery powered and have a low
enough
current draw that the batteries last a long time. It must detect very
small
separation (.005"). The output signal must be able to communicate via
wireless communication over a small distance (5-20 feet).

Any suggestions welcome.


Too vague to give any meaningful suggestions.

So this will probably turn into one of those long threads where everyone
offers a solution for what they think the problem might be.

 

[nospam]

"Jon Juhlin" <j_juhlin@efn.org> wrote:

This sounds like one of those threads that may attract unnecessary sarcastic
replies to a reasonable question. But let me try to make the problem
statement more clear.

Uuue touchy, let me be the first to come up with a solution to one of a
wide range of problems covered by your description.

I suggest you take a strip of white paper and clamp half of it between your
two pieces of metal. Look at the protruding half with an optical sensor as
it goes past due to the rotation of your two peices of metal.

When your two peices of metal separate the paper will fall out and you will
stop sensing it. The sensor is not rotating so you don't need a radio link
or battery supply.

 

[CWatters]

"Jon Juhlin" <j_juhlin@efn.org> wrote in message
news:10n5ua94hajfp50@corp.supernews.com...

I will need to build a
wireless interface to signal the outside world if the two parts are
beginning to come loose.

Wouldn't it be easier cure the problem and fix them together better rather
than try and detect failure?

Perhaps look into remote sensing strain gauges. This works as follows... You
tighten up the joint. Fix the guage across the gap and zero the output. When
the joint moves the load is transferred (in partl) to the guage which
reports this typicalyl as a change in resistance (but there are lots of
types).

More...
http://zone.ni.com/devzone/conceptd.nsf/webmain/C83E9B93DE714DB08625686600704DB1?OpenDocument

Radio for remote strain gauge/load cell outputs...
http://www.laboratorytalk.com/news/cls/cls114.html