Alt-BEAM Archive
Message #09519
To: beam@sgiblab.sgi.com
From: "Travis D." beam_bot@yahoo.com
Date: Mon, 24 Jan 2000 19:28:02 -0800 (PST)
Subject: [alt-beam] Re: Incredible gear motors
Just out of curiousity, what is the torque of these
motors?
>
> Order micro motors at 800-453-4652, part number
> 5119. $11 including
> shipping (in the US).
>
> Scott
>
>
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9520 Mon, 24 Jan 2000 22:54:11 -0500 [alt-beam] Re: Beam And IR light beam@sgiblab.sgi.com Richard Weait At 06:25 PM 1/24/00 -0600, Brad wrote:
[snip]
> Now for the real question-What is a relay, how does it work, and how
>do you read the schematic symbol. I ask this because the only ir
>transmitter receiver pair of schematics i have uses a relay. I suspect
>it is like an electronic pushbutton switch, but that is a guess. any
>help is welcomed
Hi Brad,
A relay is a device that has mechanical, electrical and
magnetic properties. It is like a switch in some ways.
Let's start with the schematic symbol:
1______
_)|| |> /<|
_)|| | / |
2______)|| | / |
| | |
3 4 5
Figure 1 Single pole relay
Okay. Terminals one and two are the ends of a "coil." Three,
four and five are the "contacts." In the schematic, contact four
is bent, and looks like it is touching contact five. Contact four
is called the "common" contact; in a real relay it can move so
that it will touch either contact five or contact three. A spring
will hold the common contact against the "normally closed" contact,
number five; four and five are a normally closed switch.
When the correct voltage is connected to the coil (and enough
current is available) the coil becomes magnetic and overcomes the
spring that is holding the common contact. This causes number
four to leave contact five and connect to the "normally open"
number three contact. When the voltage is disconnected the common
contact returns to it's normal position.
The schematic shows a single pole relay; multi-pole relays can
be shown by duplicating the contact section.
1______
_)|| |> /<| |> /<|
_)|| | / | | / |
2______)|| | / | | / |
| | | | | |
3 4 5 6 7 8
Figure 2 Double pole relay
Sometimes the contacts are shown far away from the coil in a
diagram, or with no coil at all. Sometimes the contacts look
like this:
| |
----| |----
| |
normally open
| |/
----|/|----
/| |
normally closed
Each industry may have special terms for relay parts or functions.
I've heard normally open contacts called "'making' contacts" and
normally closed called "'breaking' contacts" You can also see
references to "Form A", "Form B" and "Form C" contacts.
Relays can be used to switch one type of power in the contacts
with another type in the coil. For instance, an elevator-lift
motor of many horsepower can be switched by relay contacts that
have a 24Vdc coil.
Relays can be used to implement logic, latches, lockouts and
many other 'L'-words :-)
Relays can be found in many sizes from 'teeny-tiny' to 'Wow!
That's huge!' and in many input and output configurations.
Example input (coils) low voltage DC, low voltage AC, line voltage,
low current. . . Example output (contacts) single pole, double
pole, many pole, multi-Amp current rated, multi horsepower.
Special features: latching relays, wetted contacts, time-delay,
indicator light. . . etc.
Cheers,
Richard.
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