ECN Forum Forums General Topics of the Trade General Discussion Area Submersible limit switches?

IP68 of IEC 639 states "that this rating is for immersion in water of depth of at least 20 metres, continuously".
Want to argue??.

A few questions Kenny.
What sort of load will the sensors be running?.
Could you do this with a PLC?.
All sensors I've worked with have a rating of IP 68, capacitive or inductive.

It's Bob, not Kenny...

Switches are in series with the coils of small relays, which in turn operate a dual coil solenoid hydraulic valve (to control the direction of oil flow), and a motor starter which runs the hydraulic pump (1.5 HP).

A PLC would seem to be extreme overkill to me for such a simple application. The control setup is simply a center-off SPDT switch which selects up or down motion, which pulls in one of 2 relays (through the associated limit switch) depending on desired direction. The selected relay then applies power to the appropriate solenoid, as well as the pump starter.

No argument at all about the meaning of IP68. That's exactly what I am looking for. But I haven't found any limit switches rated IP68, only IP67/NEMA 6P. If a proximity switch will work properly underwater (as opposed to simply surviving immersion), they might be an option. But they will require a DC power supply, and additional relays to interface them to the system. A pair of mechanical limit switches would be simpler, if I can get some that will tolerate life underwater.

[This message has been edited by NJwirenut (edited 06-27-2006).]

Bob, those float switches I am talking about live virtually forever underwater. I have one that came with my house that is at least 30 years old and they are cheap ($25-30)

I think I know the switches you mean, and they are great for float switches. Damn near indestructable. But i need something to sense the position of a mechanism very repeatably and with fair precision.

Not sure how I would do that with a float switch....

[This message has been edited by NJwirenut (edited 06-27-2006).]

Try a magnet and prox sensor mounted in a waterproof box with only the prox head sticking out. Most of the big names have harsh environment heads that will deal with heat, water, cold, chemicals...

Using a prox sensor means you could use 24VDC (preferred) or 24VAC in the pool for safety, then use that to pilot a relay to do whatever on the topside of the pool away from the water.

In 2003, Honeywell upgraded the entire 914CE limit switch line to fluorocarbon seals complying with IP68. See 914CE16-3, in stock at Allied:
http://www.alliedelec.com/catalog/pf.asp?FN=846.pdf

Thanks John! That looks like EXACTLY what I had in mind. I never thought of looking at an electronics catalog for these, but instead went to the electrical suppliers. Newark Electronics stocks those Honeywell units, as well, and we have a standing account with them.