Switch closure needs to be monitored. On one side of the switch is
mains voltage (120vac); on the other, the load.

So have a relay on the hot side of the switch. When mains power is
present, the relay is closed. When absent, it is open.

Hi Dave,

One method might be to generate a small AC signal on an ISM frequency such as 13.56 Mhz and couple it through a small transformer to the two switch contacts. An HV capacitor can be used to prevent mains current through the transformer. Then monitor the current into that transformer. If the switch is closed there will be full current no matter what the power grid status. When it is open, the current will be a lot less. This can be pulsed if battery operated, to conserve battery power.

A small choke on one side of the switch prevents load or line conditions from shorting out your RF signal while the switch is open. Or course, you have to abide by EMC rules and obey electrical safety rules (isolation etc.). IOW, you really have to know what you are doing and be very familiar with safety and other legal regulations before doing any of this.

Also, make sure the pulses from the switch action don't fry anything.

Regards, Joerg

http://www.analogconsultants.com

On Fri, 7 Jan 2005 16:02:26 -0800, the renowned DaveC
wrote:

Switch closure needs to be monitored. On one side of the switch is mains
voltage (120vac); on the other, the load.

Simple enough to monitor the switch's status: when mains voltage appears on
the load side, it's closed.

But how to monitor this switch during a power failure? I'd like to be able to
report to an alarm sensor's input (simple current loop) when this switch
closes, whether mains power is applied to the switch, or power has failed.

When power fails, I could put a simple battery and coil of a l.v. relay
across the switch. But when mains voltage reappears, removing the battery
circuit in time becomes a bit risky.

How best to accomplish this task? Ideas?

Thanks,

Maybe something like this:
20K 20K
___ ___
+---|___|-------+--+----|___|-Vdd
| | |
| _/ | |
o------+--+ +----o/ o-+-------------- A
| | | | | |
V - | | | |
- ^ | | | +------ B
| | | | | |
+--+---------------+ .-. | |
120VAC | | | |
| | V -
Load '-' - ^
| | |
o------------------------------------+----+--+-------


If there is 120VAC on A, then the switch is closed

If there is not 120VAC on A, but (say) 300mVDC on B, then
the switch is open. You might have to shunt the load with a
resistor and perhaps reduce the mV comparison level if the load
doesn't look like a relatively low resistance.

It reduces the load voltage by one diode drop and the diodes on the
left have to be rated for the load current. The 20K on the left has to
be rated for any reasonable line voltage transients.



Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

DaveC wrote:

Switch closure needs to be monitored. On one side of the switch is mains
voltage (120vac); on the other, the load.

Simple enough to monitor the switch's status: when mains voltage appears on
the load side, it's closed.

But how to monitor this switch during a power failure? I'd like to be able to
report to an alarm sensor's input (simple current loop) when this switch
closes, whether mains power is applied to the switch, or power has failed.

When power fails, I could put a simple battery and coil of a l.v. relay
across the switch. But when mains voltage reappears, removing the battery
circuit in time becomes a bit risky.

How best to accomplish this task? Ideas?

The obvious answer is an extra pole on the switch - or even replacing it
with a change-over switch.

Other ways are easy enough - depending on the impedance of the source
and load.

You can couple a simple high freqency generator to one side of the
switch and sense the signal, or lack of it, on the other. You may need
the odd ferrite bead on the wire to stop the signal going through the
supply circuit and the load circuit - rather than only through the
switch contacts.

You can fire a pulse train into one wire (capacitively or inductively
coupled, for isolation purposes) and measure either the decay constant
or the harmonic content (much the same thing) - the impedance of the
load through the closed switch will be easy to detect. Again, you may
need a ferrite bead on the supply wire to increase the supplu source
impedance so as to not over-damp things. The advantage of that is you
only need access to one side of the switch.

Also only needing one side of the switch: You can couple an rf source to
the cable and monitor its standing wave as the switch is open or
closed. With the right rf source, you could just wrap a small coil of
wire round the cable with a rectifier and capacitor to produce a dc
signal. Find the peak voltage node of the standing wave with the switch
open by sliding the coil of wire up and down the cable. With the
switch closed, the peak voltage node will be somewhere else..

Or you could glue a bit of aluminium foil to the rocker of the switch
and position an LED (for greater range, use a laser diode) and
photodiode so that they "see" a reflection of each other with the switch
in one position but not in the other. With the added advantage that you
can make the alarm go off even before the switch is altered - the
approaching finger getting in the way would do it...You could put a sign
on it ..."do not even think of operating this switch"...

If you want more ideas, let me know...

--

Sue

"DaveC" wrote in message
al.net...
On Fri, 7 Jan 2005 17:09:10 -0800, Palindr~»me wrote
(in article ):

Or you could glue a bit of aluminium foil to the rocker of the switch
and position an LED (for greater range, use a laser diode) and
photodiode so that they "see" a reflection of each other with the switch
in one position but not in the other. With the added advantage that you
can make the alarm go off even before the switch is altered - the
approaching finger getting in the way would do it...You could put a sign
on it ..."do not even think of operating this switch"...

It's a float-operated microswitch in a well.
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.

DaveC

This is an invalid return address
Please reply in the news group



Perhaps isolating the float and use it to drive a relay with a couple of
sets of contacts from a backup battery ?
Depends on how important it is for ya I guess.

--
Regards ..... Rheilly Phoull

DaveC wrote:
Switch closure needs to be monitored. On one side of the switch is mains
voltage (120vac); on the other, the load.

Simple enough to monitor the switch's status: when mains voltage appears on
the load side, it's closed.

But how to monitor this switch during a power failure? I'd like to be able to
report to an alarm sensor's input (simple current loop) when this switch
closes, whether mains power is applied to the switch, or power has failed.

When power fails, I could put a simple battery and coil of a l.v. relay
across the switch. But when mains voltage reappears, removing the battery
circuit in time becomes a bit risky.

How best to accomplish this task? Ideas?

Thanks,

Turn the switch into a relay and a momentary contact switch to energize
it (with a feedback connection to keep it energized). Then you know
that if the power has failed, the relay is open. In other words,
instead of finding a way to answer the question, avoid having to ask it.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

DaveC wrote:
On Fri, 7 Jan 2005 17:09:10 -0800, Palindr˜»me wrote
(in article ):


Or you could glue a bit of aluminium foil to the rocker of the switch
and position an LED (for greater range, use a laser diode) and
photodiode so that they "see" a reflection of each other with the switch
in one position but not in the other. With the added advantage that you
can make the alarm go off even before the switch is altered - the
approaching finger getting in the way would do it...You could put a sign
on it ..."do not even think of operating this switch"...


It's a float-operated microswitch in a well.

In that case, use it for low voltage signaling with a battery backup.
I wouldn't put mains voltages down a well, anyway.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

On Fri, 7 Jan 2005 17:23:07 -0800, DaveC wrote:

On Fri, 7 Jan 2005 17:09:10 -0800, Palindr˜»me wrote
(in article ):

Or you could glue a bit of aluminium foil to the rocker of the switch
and position an LED (for greater range, use a laser diode) and
photodiode so that they "see" a reflection of each other with the switch
in one position but not in the other. With the added advantage that you
can make the alarm go off even before the switch is altered - the
approaching finger getting in the way would do it...You could put a sign
on it ..."do not even think of operating this switch"...

It's a float-operated microswitch in a well.

Single pole changeover? Thinks ....

DaveC wrote:

On Fri, 7 Jan 2005 17:09:10 -0800, Palindr˜»me wrote
(in article ):

Or you could glue a bit of aluminium foil to the rocker of the switch
and position an LED (for greater range, use a laser diode) and
photodiode so that they "see" a reflection of each other with the switch
in one position but not in the other. With the added advantage that you
can make the alarm go off even before the switch is altered - the
approaching finger getting in the way would do it...You could put a sign
on it ..."do not even think of operating this switch"...

It's a float-operated microswitch in a well.

Then it should have NO and NC contacts and you can wire up your relay and
battery to the contact pair which never have mains across them.

DaveC wrote:
On Fri, 7 Jan 2005 17:09:10 -0800, Palindr=C3=A2=CB=9C=C2=BBme wrote
(in article ):
=20
=20
Or you could glue a bit of aluminium foil to the rocker of the switch=
=20
and position an LED (for greater range, use a laser diode) and=20
photodiode so that they "see" a reflection of each other with the switc=
h=20
in one position but not in the other. With the added advantage that you=
=20
can make the alarm go off even before the switch is altered - the=20
approaching finger getting in the way would do it...You could put a sig=
n=20
on it ..."do not even think of operating this switch"...
=20
=20
It's a float-operated microswitch in a well.=20

LOL, well, you won't need the sign then - unless you work=20
for the Mafia.

As well as my original, rather more serious suggestion,=20
echoed by other posters, of using change-over contacts and=20
the very sensible suggestion of using the switch to control=20
a mains relay - which can have auxiliary contacts, if need=20
be, you might want to consider:

Stick another float-switch down the well and wire that to=20
you alarm circuitry.

Not only does that give electrical isolation, it also means=20
that you have a fail-safe - should the existing switch fail=20
or get jammed. This can be invaluable.

Presumably you are worried about too high well levels (it=20
happens here in the UK with some wells in cellars of old=20
houses - unless you start pumping, you end up with a full=20
cellar, which plays havoc with the port). In which case a=20
fail safe alarm that says the well isn't being pumped down=20
could be invaluable. You can set the alarm switch point a=20
little higher than the pump switch float, to save heart=20
attacks..

Or are worried about "pumping" an empty well (which also=20
happens in the UK) and thus wrecking the pump? Presumably=20
not, as not much pumping is going to happen anyway, with no=20
power.

On both cases an independent water level sensor can be a=20
very good idea.

I have a mercury tilt switch on my water system, which=20
directly switches the pump motor, taking water from a well=20
in the garden. It has a big float with a piece of cord=20
running over a pulley to operate the switch (thus keeping=20
the mercury-filled switch far away from the drinking water).
These mercury switches seem to go on and on for ever.=20
Your post has prompted me to go look and see how it is doing=20
- it hasn't been looked at in over 20 years, to my=20
knowledge..Thanks.

--=20

Sue

nospam writes:

DaveC wrote:

On Fri, 7 Jan 2005 17:09:10 -0800, Palindr➸»me wrote
(in article ):

Or you could glue a bit of aluminium foil to the rocker of the switch
and position an LED (for greater range, use a laser diode) and
photodiode so that they "see" a reflection of each other with the switch
in one position but not in the other. With the added advantage that you
can make the alarm go off even before the switch is altered - the
approaching finger getting in the way would do it...You could put a sign
on it ..."do not even think of operating this switch"...

It's a float-operated microswitch in a well.

Then it should have NO and NC contacts and you can wire up your relay and
battery to the contact pair which never have mains across them.

I bet it's down in the well and totally inaccessible.

There have been a few valid suggestions.

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header above is
ignored unless my full name is included in the subject line. Or, you can
contact me via the Feedback Form in the FAQs.

Switch closure needs to be monitored. On one side of the switch is mains
voltage (120vac); on the other, the load.

Simple enough to monitor the switch's status: when mains voltage appears on
the load side, it's closed.

But how to monitor this switch during a power failure? I'd like to be able to
report to an alarm sensor's input (simple current loop) when this switch
closes, whether mains power is applied to the switch, or power has failed.

Simple enough to do in practice- but the environment can make things
"sticky"- be sure your sensor input is isolated or else fuse it:

View in a fixed-width font such as Courier.




+-------------------------------+
| |
+----DPDT---+ +-----------------+ |
| | | | | |
|NC| | | | |
| o COM | | level sw | |
| \ o-----|--------o o------+ | |
LINE-+-------|--o | | \ | | |
| |NO | | ^ | | |
| | | | | | | |
| | | | --- | | |
| | +--------|--+ | | | | |
| | | | | | | | |
| |NC| | - - | | |
| | o COM | | | |
| | \ o-----|-----------------+ | |
| +-|--o | | |
| | |NO | | |
| | | | | |
| +-|-----------|-----------------+ | |
| | | | | |
| | ====== | | | |
+-------|---UUUUUU--|--+ | | |
+-----------+ | | | |
+----------------------+ | | |
| | | |
| +----+ | | |
NEUT-+------------+LOAD+-------------------+ | |
| +----+ | | |
| | | |
| | | |
| | | |
| lvl sw monitor relay | | |
| +--------+ | | |
| | ====== | | | |
+----------|-UUUUUU-|-----------------+ | |
| | | |
| / | | |
+--|--o o---|--------------------+-------
| | NO | |
| +--------+ | to sensor
| |
+----------------------------------+-----

Sam Goldwasser wrote:


I bet it's down in the well and totally inaccessible.

Nah- it's got to have "wahrs" coming back up to the surface.


There have been a few valid suggestions.

Give it time- some homebrew lamebrain has yet to insist that a gas
powered backup generator is the *ONLY* way to handle this.


--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header above is
ignored unless my full name is included in the subject line. Or, you can
contact me via the Feedback Form in the FAQs.

Your signature file is way too brief......more reading material, please.

CJT wrote:



In that case, use it for low voltage signaling with a battery backup.
I wouldn't put mains voltages down a well, anyway.


There are only a few hundred million submerged well pumps operating off
240VAC mains power, and they seem to be doing just fine.

Fred Bloggs writes:

Sam Goldwasser wrote:

I bet it's down in the well and totally inaccessible.

Nah- it's got to have "wahrs" coming back up to the surface.

Yes, but what I was trying to say is that all those suggestions saying
"replace the switch with such and such" might not be viable.

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header above is
ignored unless my full name is included in the subject line. Or, you can
contact me via the Feedback Form in the FAQs.
There have been a few valid suggestions.

Give it time- some homebrew lamebrain has yet to insist that a gas
powered backup generator is the *ONLY* way to handle this.

Fred Bloggs wrote:



Switch closure needs to be monitored. On one side of the switch is
mains voltage (120vac); on the other, the load.

Simple enough to monitor the switch's status: when mains voltage
appears on the load side, it's closed.

But how to monitor this switch during a power failure? I'd like to be
able to report to an alarm sensor's input (simple current loop) when
this switch closes, whether mains power is applied to the switch, or
power has failed.


Simple enough to do in practice- but the environment can make things
"sticky"- be sure your sensor input is isolated or else fuse it:

View in a fixed-width font such as Courier.




+-------------------------------+
| |
+----DPDT---+ +-----------------+ |
| | | | | |
|NC| | | | |
| o COM | | level sw | |
| \ o-----|--------o o------+ | |
LINE-+-------|--o | | \ | | |
| |NO | | ^ | | |
| | | | | | | |
| | | | --- | | |
| | +--------|--+ | | | | |
| | | | | | | | |
| |NC| | - - | | |
| | o COM | | | |
| | \ o-----|-----------------+ | |
| +-|--o | | |
| | |NO | | |
| | | | | |
| +-|-----------|-----------------+ | |
| | | | | |
| | ====== | | | |
+-------|---UUUUUU--|--+ | | |
+-----------+ | | | |
+----------------------+ | | |
| | | |
| +----+ | | |
NEUT-+------------+LOAD+-------------------+ | |
| +----+ | | |
| | | |
| | | |
| | | |
| lvl sw monitor relay | | |
| +--------+ | | |
| | ====== | | | |
+----------|-UUUUUU-|-----------------+ | |
| | | |
| / | | |
+--|--o o---|--------------------+-------
| | NO | |
| +--------+ | to sensor
| |
+----------------------------------+-----



You can do a better job of preserving the level sw contacts like so:
View in a fixed-width font such as Courier.

Sam Goldwasser wrote:
Fred Bloggs writes:


Sam Goldwasser wrote:


I bet it's down in the well and totally inaccessible.

Nah- it's got to have "wahrs" coming back up to the surface.


Yes, but what I was trying to say is that all those suggestions saying
"replace the switch with such and such" might not be viable.

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header above is
ignored unless my full name is included in the subject line. Or, you can
contact me via the Feedback Form in the FAQs.

There have been a few valid suggestions.

Give it time- some homebrew lamebrain has yet to insist that a gas
powered backup generator is the *ONLY* way to handle this.


Right- you don't won't to touch the switch.

Fred Bloggs wrote:


CJT wrote:



In that case, use it for low voltage signaling with a battery backup.
I wouldn't put mains voltages down a well, anyway.


There are only a few hundred million submerged well pumps operating off
240VAC mains power, and they seem to be doing just fine.

Touche. Let me alter that to say I wouldn't _unnecessarily_ put mains
voltages down a well.

;-)

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

"Sam Goldwasser" wrote in message
...

| Yes, but what I was trying to say is that all those suggestions saying
| "replace the switch with such and such" might not be viable.

Run an AF signal down the same cable and detect it - 20 KHz should be fine.
I've even seen 3 VDC used for similar purposes but you need honking big
chokes to isolate it.

N

On Fri, 07 Jan 2005 16:02:26 -0800, DaveC wrote:

Switch closure needs to be monitored. On one side of the switch is mains
voltage (120vac); on the other, the load.

Simple enough to monitor the switch's status: when mains voltage appears on
the load side, it's closed.

But how to monitor this switch during a power failure? I'd like to be able to
report to an alarm sensor's input (simple current loop) when this switch
closes, whether mains power is applied to the switch, or power has failed.

When power fails, I could put a simple battery and coil of a l.v. relay
across the switch. But when mains voltage reappears, removing the battery
circuit in time becomes a bit risky.

How best to accomplish this task? Ideas?

Do you have access to the switch leads, just raw, at the top of the well?

Then get a little battery-back-up supply - Maybe a hobby-sized lead-acid
on a float charge - and use the switch to control the coil of a 12V relay.
Use the relay contacts to control whatever you want, (like control the
pump, or not[0]) and it exactly follows the state of the switch, mains
power or no.

Good Luck!
Rich

[0] I can't help but wondering - What's the purpose of this thing? Some
kind of fail-safe?
Thanks. :-)

Kibo informs me that DaveC stated that:

Switch closure needs to be monitored. On one side of the switch is mains
voltage (120vac); on the other, the load.

Simple enough to monitor the switch's status: when mains voltage appears on
the load side, it's closed.

But how to monitor this switch during a power failure? I'd like to be able to
report to an alarm sensor's input (simple current loop) when this switch
closes, whether mains power is applied to the switch, or power has failed.

When power fails, I could put a simple battery and coil of a l.v. relay
across the switch. But when mains voltage reappears, removing the battery
circuit in time becomes a bit risky.

How best to accomplish this task? Ideas?

The least invasive (ie; safest) method would be to put a pickup coil
near the mains side of the cable, to detect 50/60Hz leakage when power
is available.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------

DaveC wrote:
Switch closure needs to be monitored. On one side of the switch is mains
voltage (120vac); on the other, the load.

Simple enough to monitor the switch's status: when mains voltage appears on
the load side, it's closed.

But how to monitor this switch during a power failure? I'd like to be able to
report to an alarm sensor's input (simple current loop) when this switch
closes, whether mains power is applied to the switch, or power has failed.

When power fails, I could put a simple battery and coil of a l.v. relay
across the switch. But when mains voltage reappears, removing the battery
circuit in time becomes a bit risky.

How best to accomplish this task? Ideas?

Thanks,
Use a double pole double throw switch, one site for the load and one
side for the position.

I was waiting to see who would come up with this simple and obvious
solution! Good job!

Roger wrote:

DaveC wrote:

Switch closure needs to be monitored. On one side of the switch is
mains voltage (120vac); on the other, the load.

Simple enough to monitor the switch's status: when mains voltage
appears on the load side, it's closed.

But how to monitor this switch during a power failure? I'd like to be
able to report to an alarm sensor's input (simple current loop) when
this switch closes, whether mains power is applied to the switch, or
power has failed.
When power fails, I could put a simple battery and coil of a l.v.
relay across the switch. But when mains voltage reappears, removing
the battery circuit in time becomes a bit risky.

How best to accomplish this task? Ideas?

Thanks,

Use a double pole double throw switch, one site for the load and one
side for the position.


--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"

The Lost Deep Thoughts By: Jack Handey
Before a mad scientist goes mad, there's probably a time
when he's only partially mad. And this is the time when he's
going to throw his best parties.

On Tue, 11 Jan 2005 00:10:51 -0500, **THE-RFI-EMI-GUY**
wrote:

I was waiting to see who would come up with this simple and obvious
solution! Good job!

Roger wrote:

Use a double pole double throw switch, one site for the load and one
side for the position.



???????? The O/P did post "It's a float-operated microswitch in a well." This
may not exactly lend itself to that.

**THE-RFI-EMI-GUY** writes:

I was waiting to see who would come up with this simple and obvious
solution! Good job!

Except that it doesn't solve the problem if he has to go down into the well
and replace the switch.

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header above is
ignored unless my full name is included in the subject line. Or, you can
contact me via the Feedback Form in the FAQs.

Roger wrote:

DaveC wrote:

Switch closure needs to be monitored. On one side of the switch is
mains voltage (120vac); on the other, the load.

Simple enough to monitor the switch's status: when mains voltage
appears on the load side, it's closed.

But how to monitor this switch during a power failure? I'd like to
be able to report to an alarm sensor's input (simple current loop)
when this switch closes, whether mains power is applied to the
switch, or power has failed.
When power fails, I could put a simple battery and coil of a
l.v. relay across the switch. But when mains voltage reappears,
removing the battery circuit in time becomes a bit risky.

How best to accomplish this task? Ideas?

Thanks,

Use a double pole double throw switch, one site for the load and one
side for the position.


--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"

The Lost Deep Thoughts By: Jack Handey
Before a mad scientist goes mad, there's probably a time
when he's only partially mad. And this is the time when he's
going to throw his best parties.

In article ,
budgie wrote:
On Tue, 11 Jan 2005 00:10:51 -0500, **THE-RFI-EMI-GUY**
wrote:

I was waiting to see who would come up with this simple and obvious
solution! Good job!

Roger wrote:

Use a double pole double throw switch, one site for the load and one
side for the position.



???????? The O/P did post "It's a float-operated microswitch in a well." This
may not exactly lend itself to that.

Ok, use a SPDT switch and assume that if one set of contacts is open, the
other must be closed.

--
--
forging knowledge

On Wed, 12 Jan 2005 02:46:04 +0000, Ken Smith wrote:

In article ,
budgie wrote:
On Tue, 11 Jan 2005 00:10:51 -0500, **THE-RFI-EMI-GUY**
wrote:

I was waiting to see who would come up with this simple and obvious
solution! Good job!

Roger wrote:

Use a double pole double throw switch, one site for the load and one
side for the position.



???????? The O/P did post "It's a float-operated microswitch in a well." This
may not exactly lend itself to that.

Ok, use a SPDT switch and assume that if one set of contacts is open, the
other must be closed.


It was also not specified that the switch was double-throw. The only
information given was one contact closure.

But then again, I've asked the OP about the switch itself, and what's
actually accessible, and haven't seen a response yet - maybe he's solved
it and hasn't bothered to come back and say so.

Thanks,
Rich

There are circuit breakers, of larger size, maybe 120 A and over, that can
sense their/open close condition, with auxilliary contacts.You may find a
residence-rated circuit breaker with this capability (also 40A, 63A-don't
know which size is standard in the USA).In HV gear this is a must;nothing
can be operated with 150 or 400 kV, except with the use of potential
transformers.Many LV breakers are supplied with a set of auxilliary
contacts.What is the circuit you want to control?

--
Tzortzakakis Dimitri?s
major in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr
? "DaveC" ?????? ??? ??????
al.net...
Switch closure needs to be monitored. On one side of the switch is mains
voltage (120vac); on the other, the load.

Simple enough to monitor the switch's status: when mains voltage appears
on
the load side, it's closed.

But how to monitor this switch during a power failure? I'd like to be able
to
report to an alarm sensor's input (simple current loop) when this switch
closes, whether mains power is applied to the switch, or power has failed.

When power fails, I could put a simple battery and coil of a l.v. relay
across the switch. But when mains voltage reappears, removing the battery
circuit in time becomes a bit risky.

How best to accomplish this task? Ideas?

Thanks,
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.

DaveC

This is an invalid return address
Please reply in the news group

(Ken Smith) writes:

In article ,
budgie wrote:
On Tue, 11 Jan 2005 00:10:51 -0500, **THE-RFI-EMI-GUY**
wrote:

I was waiting to see who would come up with this simple and obvious
solution! Good job!

Roger wrote:

Use a double pole double throw switch, one site for the load and one
side for the position.



???????? The O/P did post "It's a float-operated microswitch in a well." This
may not exactly lend itself to that.

Ok, use a SPDT switch and assume that if one set of contacts is open, the
other must be closed.

He'll hire you to climb down into the well!

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Important: Anything sent to the email address in the message header above is
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On Wed, 12 Jan 2005 09:08:43 -0800, DaveC wrote:

On Tue, 11 Jan 2005 22:19:53 -0800, Rich Grise wrote
(in article ):

It was also not specified that the switch was double-throw. The only
information given was one contact closure.

But then again, I've asked the OP about the switch itself, and what's
actually accessible, and haven't seen a response yet - maybe he's solved
it and hasn't bothered to come back and say so.

1 pair of wires coming up the well from the n.o. float switch. This is the
only sensor for level in the well (no other switches).

I've pretty much settled on the solution suggested by Fred Bloggs, earlier in
this thread which uses 2 relays:

One relay (d.p.) is set or released by mains voltage. When enabled, the float
switch (using mains voltage) controls a second relay (s.p.) which closes the
alarm contacts if/when the level rises in the well. When power has failed,
the primary relay, now de-energized, connects the float switch directly to
the alarm contacts (using battery voltage).

It seems the simplest solution.

Thanks for the update. I'm glad to hear you've got it solved. :-)

Cheers!
Rich

Usually these switches have two (at least) set of contacts.You can use one
for control, it is usually (here) one NO and one NC.A 4 core cable to the
switch will do.

--
Tzortzakakis Dimitri?s
major in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr
? "DaveC" ?????? ??? ??????
al.net...
On Fri, 7 Jan 2005 17:09:10 -0800, Palindr~»me wrote
(in article ):

Or you could glue a bit of aluminium foil to the rocker of the switch
and position an LED (for greater range, use a laser diode) and
photodiode so that they "see" a reflection of each other with the switch
in one position but not in the other. With the added advantage that you
can make the alarm go off even before the switch is altered - the
approaching finger getting in the way would do it...You could put a sign
on it ..."do not even think of operating this switch"...

It's a float-operated microswitch in a well.
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.

DaveC

This is an invalid return address
Please reply in the news group

Or 380 V ac in Europe.

--
Tzortzakakis Dimitri?s
major in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr
? "Fred Bloggs" ???a?e st? µ???µa
...


CJT wrote:



In that case, use it for low voltage signaling with a battery backup.
I wouldn't put mains voltages down a well, anyway.


There are only a few hundred million submerged well pumps operating off
240VAC mains power, and they seem to be doing just fine.

In college, we learnt about a float switch, japanese origination, with three
immersible contacts.One at the bottom;one in the middle of the well/tank and
one near the highest level.The way it works is obvious.

--
Tzortzakakis Dimitriïs
major in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr
Ï "Palindr?me" Ýãñáøå óôï ìÞíõìá
...
DaveC wrote:
On Fri, 7 Jan 2005 17:09:10 -0800, Palindra~»me wrote
(in article ):


Or you could glue a bit of aluminium foil to the rocker of the switch
and position an LED (for greater range, use a laser diode) and
photodiode so that they "see" a reflection of each other with the switch
in one position but not in the other. With the added advantage that you
can make the alarm go off even before the switch is altered - the
approaching finger getting in the way would do it...You could put a sign
on it ..."do not even think of operating this switch"...


It's a float-operated microswitch in a well.

LOL, well, you won't need the sign then - unless you work
for the Mafia.

As well as my original, rather more serious suggestion,
echoed by other posters, of using change-over contacts and
the very sensible suggestion of using the switch to control
a mains relay - which can have auxiliary contacts, if need
be, you might want to consider:

Stick another float-switch down the well and wire that to
you alarm circuitry.

Not only does that give electrical isolation, it also means
that you have a fail-safe - should the existing switch fail
or get jammed. This can be invaluable.

Presumably you are worried about too high well levels (it
happens here in the UK with some wells in cellars of old
houses - unless you start pumping, you end up with a full
cellar, which plays havoc with the port). In which case a
fail safe alarm that says the well isn't being pumped down
could be invaluable. You can set the alarm switch point a
little higher than the pump switch float, to save heart
attacks..

Or are worried about "pumping" an empty well (which also
happens in the UK) and thus wrecking the pump? Presumably
not, as not much pumping is going to happen anyway, with no
power.

On both cases an independent water level sensor can be a
very good idea.

I have a mercury tilt switch on my water system, which
directly switches the pump motor, taking water from a well
in the garden. It has a big float with a piece of cord
running over a pulley to operate the switch (thus keeping
the mercury-filled switch far away from the drinking water).
These mercury switches seem to go on and on for ever.
Your post has prompted me to go look and see how it is doing
- it hasn't been looked at in over 20 years, to my
knowledge..Thanks.

--

Sue

On Fri, 7 Jan 2005 16:02:26 -0800, DaveC wrote:

Switch closure needs to be monitored. On one side of the switch is mains
voltage (120vac); on the other, the load.

Simple enough to monitor the switch's status: when mains voltage appears on
the load side, it's closed.

But how to monitor this switch during a power failure? I'd like to be able to
report to an alarm sensor's input (simple current loop) when this switch
closes, whether mains power is applied to the switch, or power has failed.

When power fails, I could put a simple battery and coil of a l.v. relay
across the switch. But when mains voltage reappears, removing the battery
circuit in time becomes a bit risky.

How best to accomplish this task? Ideas?

---

10kHz IN--[1.6nF]--+
|
MAINS--------------+--------//------------O--- |
|
MAINS---------------+-------//-----[RL]---------O
|
10kHz OUT--[1.6nF]--+



If you can make sure that mains hot is, and stays mains hot, then:


10kHz IN--[1.6nF]--+
|
MAINS HOT----------+-------//------------O--- |
|
MAINS NEUT---------+-------//------[RL]--------O
|
10kHz OUT----------+


Even though 1.6nF looks like 1.6 megohms at 60Hz, at turn-on after a
mains failure the spike getting throught the cap and into the 10kHz
source might not be a good thing, so you might want to do something
like this:

10kHz IN-----+---[1.6nF]--+
| |
[CR1] |
|A |
|K |
[CR2] |
| |
MAINS HOT----|------------+-------//-----------O--- |
| |
MAINS NEUT---+------------+-------//------[RL]-------O
|
10kHz OUT-----------------+

Where CR1 and CR2 are Zener diodes with a voltage rating slightly
higher than the output voltage of the 10kHz source.

--
John Fields