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Re: Submersible limit switches? #66959 06/24/06 11:35 AM
Joined: Jul 2004
Posts: 9,571
G
gfretwell Online Content
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We use those float switches that just hang on the cord in our well aerators and they seem to last forever in some pretty nasty well water.


Greg Fretwell
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Re: Submersible limit switches? #66960 06/25/06 07:55 PM
Joined: Oct 2004
Posts: 132
M
mhulbert Offline
Member
Will a proximity sensor work instead? Many of them are at least IP67, I'm sure there are IP68 models out there, but I can't seem to find a specific one yet.

Also, what about an optical sensing unit, with a fiber optic strand run down to the sensing location? Might make maintenance easier.

Re: Submersible limit switches? #66961 06/25/06 08:35 PM
Joined: Sep 2001
Posts: 806
N
NJwirenut Offline OP
Member
Since we are building both the mechanism and the control system for it, a proximity switch is certainly an option. But they add the complications of providing DC power to the units and adding relays to convert the open collector outputs to NC relay contacts. Never having used prox switches underwater, how is their range and repeatability affected by sensing a target through water, rather than air?

For stuff like this, I'm a big fan of the KISS principle. And it doesn't get much simpler than a pair of switch contacts interrupting power to the motor starter coil.

Re: Submersible limit switches? #66962 06/25/06 08:54 PM
Joined: Jul 2001
Posts: 599
J
JBD Offline
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Many heavy duty industrial limit switches,like Square D Class 9007 Type C, are rated NEMA 6P submersible.

Re: Submersible limit switches? #66963 06/25/06 11:06 PM
Joined: Jul 2004
Posts: 783
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LarryC Offline
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"And it doesn't get much simpler than a pair of switch contacts interrupting power to the motor starter coil."

I really hope you mean interupting the signal to the hydraulic valve(s). Controlling a hydraulic system by turning the pump on and off isn't a reliable method of maintaining position or control. Use two adjustable stops on the threaded shaft. Set the prox switch to generate the stop signals at each end of desired travel, and use the shaft stops to hit hard stops to limit travel in case of end of travel switch failure.

Set the hydraulic relief valve to lift when the motor driven frame hits the hard stop.

LarryC

[This message has been edited by LarryC (edited 06-26-2006).]

Re: Submersible limit switches? #66964 06/26/06 06:14 AM
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Posts: 806
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NJwirenut Offline OP
Member
JBD:

If you read the actual specs for NEMA 6P classification, they specify TEMPORARY immersion in water of LIMITED DEPTH (1 meter, IIRC). My application involves continuous immersion at 6-7 feet.

Larry:

Actually, the plan is to cut power (using a pair of "ice cube" relays) to both the directional control (spool) valve AND the hydraulic pump starter.

Yes, the relief valve is going to be the backup safety device in case of a switch failure.


[This message has been edited by NJwirenut (edited 06-26-2006).]

Re: Submersible limit switches? #66965 06/26/06 10:09 AM
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Posts: 599
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JBD Offline
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The "P" stands for prolonged submersion versus the temporary rating of just plain NEMA/TYPE 6. I do not know the actual depth.

Re: Submersible limit switches? #66966 06/26/06 02:40 PM
Joined: Mar 2006
Posts: 30
F
FountainGuy Offline
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I like Tesla's idea best; photo optics is a good option, or use a pressure transmitter or pressure switch. Even though you're talking about 6P submersible enclosures, keeping electricity out of water is always a good idea. I'm all too familiar with reed switches. They fail too easily; moving parts. I try to design fountains as simple as possible. Whenever electronic water level controls are necessary, conductivity sensors are the simplest to maintain, modify and understand.

Re: Submersible limit switches? #66967 06/26/06 08:19 PM
Joined: Feb 2006
Posts: 25
F
feather Offline
Member
In the old days we would just solder a mercury switch to a couple of leads, seal with tar and mount them. o'course mercury is a bad word nowa days.

Re: Submersible limit switches? #66968 06/27/06 09:49 AM
Joined: Jun 2001
Posts: 161
M
Mike Wescoatt Offline
Member
What we did for our lifts underwater is used cable type position encoders. the encoders give us high resolution feedback on the position of the cable on a calibrated spool. The encoder sits above water and the only thing that is underwater is the stainless steel aircraft cable attached (by way of pulleys) to the lift. This gives us absolute (not realitive) feedback on position to 0.01" which we round off for error correction. We also used prox sensors mounted in the wall of a waterproof box mounted next to a magnet on a cylinder mount for "home" positioning. You could use a force home position if you need to.


Mike Wescoatt
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