bought some allen bradley "800 type" control panel pushbutton switches.
they have seperate (screw-fastenable) rear contact blocks. I see one
type of contact block allen-bradley offers for these pushbuttons is
called a "logic reed", and wonder what it's purpose is? or how it's
supposed to function, or "what can logic reeds do for me?"

momentary offs and ons I understand, and normally offs and ons I
understand, but "what's the logic reed thing about"?

tried searching the net for this type info, unsuccessfully :-/

*thanks* guys

here's the (dirty, used) ones I bought
http://machines.netai.net/rotary_con...s/photo11.html

extreme closeup of switch rear contact block on mine "normally closed,
momentary open"
http://machines.netai.net/rotary_con...s/photo15.html

On Feb 6, 11:05*am, dave wrote:
bought some allen bradley "800 type" control panel pushbutton switches.
they have seperate (screw-fastenable) rear contact blocks. I see one
type of contact block allen-bradley offers for these pushbuttons is
called a "logic reed", and wonder what it's purpose is? or how it's
supposed to function, or "what can logic reeds do for me?"

momentary offs and ons I understand, and normally offs and ons I
understand, but "what's the logic reed thing about"?

tried searching the net for this type info, unsuccessfully :-/

*thanks* guys

here's the (dirty, used) ones I boughthttp://machines.netai.net/rotary_converter_parts/photos/photo11.html

extreme closeup of switch rear contact block on mine "normally closed,
momentary open"http://machines.netai.net/rotary_converter_parts/photos/photo15.html

Just a guess. You probably already know a reed switch is a sealed in
glass switch that is activated by a magnet. Either a permanent magnet
or by a solenoid coil wound around the reed.

In your case, the reed switch will be operated by a tiny permanent
magnet when the push button switch is operated. Your control circuitry
will assume when the reed switch closes, the main power push button is
also pressed. This keeps the control signals completely isolated from
the noisy power circuitry.

If you are not going to use any low power digital control circuitry,
then the reed switches can be ignored.

Paul

On Sat, 06 Feb 2010 14:05:17 -0500, dave
wrote:

bought some allen bradley "800 type" control panel pushbutton switches.
they have seperate (screw-fastenable) rear contact blocks. I see one
type of contact block allen-bradley offers for these pushbuttons is
called a "logic reed", and wonder what it's purpose is? or how it's
supposed to function, or "what can logic reeds do for me?"

momentary offs and ons I understand, and normally offs and ons I
understand, but "what's the logic reed thing about"?


For switching devices that draw very little current. Low current will
not reliably blow thru the oxide on the heavy contacts in the standard
blocks. The contacts in the logic level blocks are probably gold
plated and close with a wiping action. They could also be magnetic
reed switches, but I don't think they are.

--
Ned Simmons

On 2010-02-06, dave wrote:
bought some allen bradley "800 type" control panel pushbutton switches.
they have seperate (screw-fastenable) rear contact blocks. I see one
type of contact block allen-bradley offers for these pushbuttons is
called a "logic reed", and wonder what it's purpose is? or how it's
supposed to function, or "what can logic reeds do for me?"

Typically, they are designed purely as inputs to logic circuits.
Very low current and low voltage. They probably have some form of
debouncing circuit to keep form a bouncing contact giving a train of
pulses instead of a single one. If it has that, it will probably have
at least three terminals:

+5V
logic out
Ground

with possibly a forth one which would be an inverted logic out
(typically indicated by a bar over the name of the signal). This one
would go high when the other goes low and vice versa.

Given the name, it might simply be a mercury wetted reed switch
capsule actuated by a magnet moved by the button. In any case, it would
not be capable of handling much current, and I have experienced reed
switches latching on from the magnetic field created by the current
through them, so you need something else to interrupt the current.

But the mercury wetted reeds tend to not bounce at least, and
logic inputs are low enough current to avoid current latching of the
reed capsule.

momentary offs and ons I understand, and normally offs and ons I
understand, but "what's the logic reed thing about"?

For feeding logic circuits better than normal switches do, but
doing almost anything else more poorly. (Note that computer inputs cvan
count as logic circuits.)

Good Luck,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

dave wrote:

tried searching the net for this type info, unsuccessfully :-/

http://www.ab.com/en/epub/catalogs/1...1083/tab3.html


Down in body of link.

Logic Reed Contact Ratings

Minimum — DC: 5V, 1 mA
Maximum — DC: 30V, 0.06 A, AC: 150V, 0.15 A
Should only be used with resistive loads.




Wes

Wes wrote:
dave wrote:

tried searching the net for this type info, unsuccessfully :-/

http://www.ab.com/en/epub/catalogs/1...1083/tab3.html


Down in body of link.

Logic Reed Contact Ratings

Minimum — DC: 5V, 1 mA
Maximum — DC: 30V, 0.06 A, AC: 150V, 0.15 A
Should only be used with resistive loads.

Wes
Just what is your question? That is a standard logic level
switch rating.
...lew...

Lewis Hartswick wrote:

Wes wrote:
dave wrote:

tried searching the net for this type info, unsuccessfully :-/

http://www.ab.com/en/epub/catalogs/1...1083/tab3.html


Down in body of link.

Logic Reed Contact Ratings

Minimum — DC: 5V, 1 mA
Maximum — DC: 30V, 0.06 A, AC: 150V, 0.15 A
Should only be used with resistive loads.

Wes
Just what is your question? That is a standard logic level
switch rating.
...lew...

Lew, I was responding to Dave, the original poster. I totally agree on the logic level
only application. I've used these devices before.

Wes