Searching \ for '[EE]: switch contacts' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/index.htm?key=switch+contacts
Search entire site for: 'switch contacts'.

Exact match. Not showing close matches.
PICList Thread
'[EE]: switch contacts'
2010\07\13@041525 by Jake Anderson

flavicon
face
I'm designing a tool length measurement device for a mill.
I've settled on the mechanical design which is a tripod arrangement, but
what I'm after is some contacts to actually make and break the connections.
I know such beasts exist but I'm having difficulty finding sources for them.

At the moment its looking like I'll have to settle with gold plated PCB
as the contact material.

I'm looking for gold at the moment because I want to run the contacts at
a very low current/voltage to minimise arcing.

2010\07\13@122019 by Adam Field

flavicon
face
> I'm designing a tool length measurement device for a mill.
> I've settled on the mechanical design which is a tripod arrangement, but
> what I'm after is some contacts to actually make and break the connections.
> I know such beasts exist but I'm having difficulty finding sources for them.
>
> At the moment its looking like I'll have to settle with gold plated PCB
> as the contact material.
>
> I'm looking for gold at the moment because I want to run the contacts at
> a very low current/voltage to minimise arcing.

Would pogo pins work for you? They are gold plated, spring loaded and
come in a variety of point styles. These are usually used for in
circuit programming and testing during manufacture.

www.idinet.com/_FileLibrary/PDF/pg42.pdf
mouser.com/ProductDetail/IDI/SX-0-ES-37-G/?qs=sGAEpiMZZMuSFBMFeRq2EWmzThOn%252bbiO

2010\07\13@124419 by Dwayne Reid

flavicon
face
At 02:15 AM 7/13/2010, Jake Anderson wrote:
>I'm designing a tool length measurement device for a mill.
>I've settled on the mechanical design which is a tripod arrangement, but
>what I'm after is some contacts to actually make and break the connections.
>I know such beasts exist but I'm having difficulty finding sources for them.
>
>At the moment its looking like I'll have to settle with gold plated PCB
>as the contact material.
>
>I'm looking for gold at the moment because I want to run the contacts at
>a very low current/voltage to minimise arcing.

Some more info would be useful.

Does the device move about or is it stationary when contact is being
made?  How much height do you have available for the connection?

If it is stationary, I'd consider using magnets to hold it in
place.  I've done projects where the magnets themselves were the
current-carrying contacts (worked very well) but if that doesn't work
for you, you might also consider using pogo pins - either contacting
a PCB or contacting another pogo pin.

The magnets I used for my projects were rare-earth magnets and
matching steel cup-holders from Lee Valley Tools.  Although Lee
Valley was one of the first people from whom I could purchase these
magnets, I see that there are lots of suppliers now.  But: the plated
steel cup holders still appear to be best obtained from Lee Valley -
I've seen some knock-offs from other suppliers and wasn't much impressed.

The nickel plating that completely covers the exterior of the magnet
carries current quite well.  I was passing perhaps 2A and measured a
few mV drop across the connection.  The magnet and cup-washer
combination was inserted into a flat-bottomed hole drilled into
plastic (forstner bit) such that the surface of the magnet was just
proud of the plastic.  The connection was made by soldering wires to
the bottom of the plated steel cup-washers.

dwayne

--
Dwayne Reid   <spam_OUTdwaynerTakeThisOuTspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax
http://www.trinity-electronics.com
Custom Electronics Design and Manufacturing

2010\07\13@140212 by RussellMc

face picon face
> I'm designing a tool length measurement device for a mill.
> I've settled on the mechanical design which is a tripod arrangement, but
> what I'm after is some contacts to actually make and break the connections.
> I know such beasts exist but I'm having difficulty finding sources for them.
>
> At the moment its looking like I'll have to settle with gold plated PCB
> as the contact material.
>
> I'm looking for gold at the moment because I want to run the contacts at
> a very low current/voltage to minimise arcing.

Be careful with wetting current needs with contacts with very low currents.
Something in hind brain suggests that even gold may not be optimum.
Whether contact is point/area or wiping contact will affect longer
term reliability.

Arcing is less important than energy in arc (intrinsically safe
black-hole beckons).

Normal lore is that anything under about 1 mA is unwise for wetting purposes.
Potential used also relevant - 10V often suggested as useful minimum
voltage for film breakdown but obviously very application dependant.

Use of a combined capacitive/conductive method (shades of SawStop) may
allow zero proximity / low conductivity operation.

Contact sets from other equipment may be useful - eg direct mechanical
operation of contacts from a relay specified for low contact current
operation

.
             Russell

2010\07\13@183518 by Jake Anderson

flavicon
face
On 14/07/10 02:20, Adam Field wrote:
>> I'm designing a tool length measurement device for a mill.
>> I've settled on the mechanical design which is a tripod arrangement, but
>> what I'm after is some contacts to actually make and break the connections.
>> I know such beasts exist but I'm having difficulty finding sources for them.
>>
>> At the moment its looking like I'll have to settle with gold plated PCB
>> as the contact material.
>>
>> I'm looking for gold at the moment because I want to run the contacts at
>> a very low current/voltage to minimise arcing.
>>      
> Would pogo pins work for you? They are gold plated, spring loaded and
> come in a variety of point styles. These are usually used for in
> circuit programming and testing during manufacture.
>
> www.idinet.com/_FileLibrary/PDF/pg42.pdf
> mouser.com/ProductDetail/IDI/SX-0-ES-37-G/?qs=sGAEpiMZZMuSFBMFeRq2EWmzThOn%252bbiO
>    
Unfortunately no I need to reliably and respectably detect movement on
the order of .001mm or better so spring loaded things wouldn't work
Basically the idea is to have 3 points of contact and then detect when
one of them opens.

Thanks for the links though I have been after some info on pogo pins for
programmers.

2010\07\13@184229 by Jake Anderson

flavicon
face
On 14/07/10 03:55, RussellMc wrote:
>> I'm designing a tool length measurement device for a mill.
>> I've settled on the mechanical design which is a tripod arrangement, but
>> what I'm after is some contacts to actually make and break the connections.
>> I know such beasts exist but I'm having difficulty finding sources for them.
>>
>> At the moment its looking like I'll have to settle with gold plated PCB
>> as the contact material.
>>
>> I'm looking for gold at the moment because I want to run the contacts at
>> a very low current/voltage to minimise arcing.
>>      
> Be careful with wetting current needs with contacts with very low currents.
> Something in hind brain suggests that even gold may not be optimum.
> Whether contact is point/area or wiping contact will affect longer
> term reliability.
>    
current plan is flat on flat, the wetting current was a concern hence
the desire for gold.
> Arcing is less important than energy in arc (intrinsically safe
> black-hole beckons).
>    
The problem is the arc will keep the switch "on" even though it has
opened and the goal is to detect the small movement to start.
Ideally we would like to detect it opening over .001mm or less.
> Normal lore is that anything under about 1 mA is unwise for wetting purposes.
> Potential used also relevant - 10V often suggested as useful minimum
> voltage for film breakdown but obviously very application dependant.
>
> Use of a combined capacitive/conductive method (shades of SawStop) may
> allow zero proximity / low conductivity operation.
>    
Probably not accurate enough is the problem (unless you have an idea for
an implementation?), The only non-contact method I've worked out is
laser interferometer, but that's "hard TM" ;->

> Contact sets from other equipment may be useful - eg direct mechanical
> operation of contacts from a relay specified for low contact current
> operation
>
> .
>                Russell
>    
I was hoping to be able to purchase the contacts off the shelf somewhere
rather than destroying existing equipment and hacking stuff up.

2010\07\13@190905 by RussellMc

face picon face
> Probably not accurate enough is the problem (unless you have an idea for an
> implementation?), The only non-contact method I've worked out is laser
> interferometer, but that's "hard TM" ;->

A probably workable alternative is to use hard contact and no contacts :-).

1.   eg a sprung loaded sliding end piece with an LVDT transducer.
Many refs to LVDT but eg

             http://www.sensotec.com/pdf/lvdt_selection.pdf

2. Here's someone with a "linear digital transducer" who claims
significant advantage over LVDT
That usually means "significantly dearer"

                          http://www.anter.com/TN105.htm

3. Back of brain suggests that systems using ball bearings can produce
utterly superb results. Various means suggest - capacitive as ball is
moved, optical, inductive (lvdt variant) , ...

4. Lever system where tool impacts lever near end point and then
provides mechanically magnified movement of other end of lever for
measuring.


             Russell

2010\07\13@203243 by Jonathan Hallameyer

picon face
>
>
> Unfortunately no I need to reliably and respectably detect movement on
> the order of .001mm or better so spring loaded things wouldn't work
> Basically the idea is to have 3 points of contact and then detect when
> one of them opens.
>
>

Ahh, well the "3 points of contact and detect when one opens" sets off bells
in my head, especially when related to machine tools.  Some CMM systems use
a similar method, where the touch head is connected to a Y shaped piece,
lightly spring loaded against the main housing of the probe head. The main
housing has a saddle for each pin of the Y shaped pin sticking out, (so
actually 2 contacts at each pin)  and it looks for one of the pins to lift
and go open.  (well they actually look for the resistance starting to
increase, but they do all sorts of other fancy stuff which I cant recall)
I could have sworn I saw this on a video on renishaw's website, but cant
find a reference for this again.   Is there a reason a standard tool setter
wont do for you?
-Jon Hallameyer

2010\07\13@204054 by Jonathan Hallameyer

picon face
On Tue, Jul 13, 2010 at 8:32 PM, Jonathan Hallameyer <.....jmhtauKILLspamspam@spam@gmail.com>wrote:

{Quote hidden}

And of course I find it minutes after posting.
http://www.renishaw.com/en/probing-glossary-and-terminology--12479

a few graphics explaining what I was saying more clearly.

--Jon Hallameyer

2010\07\13@215919 by ivp

face picon face

> the order of .001mm or better so spring loaded things wouldn't work

Would a hard drive voice coil mechanism be adaptable ? Or optical
interferometry ?

More... (looser matching)
- Last day of these posts
- In 2010 , 2011 only
- Today
- New search...