ECN Forum Forums General Topics of the Trade General Discussion Area Decorative Fountain Controls

use a bindicator. they're non contact, can't plug, bind, or get you in the water. it's like a probe but doesn't require capacitance of the liquid for sensing.
http://www.bindicator.com/pdffiles/LAG180180.pdf

We will check into the Bindicator. But, we only have 2 feet of water and we don't really want to mount anything above the max water level where it would be seen.

How would we mount this in our application?

Brian

As i recall, the bindicator needs about 5" of pipe in the water to toggle the switch. You could hide the sensor head in some decorative piece setting in the fountain.

One of the other guys in our company asked about induced voltages on the float sensor wire.

The float sensor wire (#12 THHN) shares a conduit with some of the fountain lights. (2 circuits). In the pit where the controls are located, the sensor wires share a conduit with lighting circuits as well as pump circuits for about 12 feet of conduit.

There is an induced voltage on the sensor wires. About 20 Volts on each wire with the sensor disconnected. He thinks that the induced voltage being present in the sensor conductors along with the control voltage of 24 volts may be the cause of the sticking contacts. I'm not so sure. Welded contacts, I believe, are a result of excessive current not excessive voltage.

We may, however, test his theory by installing a sheilded cable for the sensor.

We cannot, without major alterations to the fountain, install a seprate conduit for the sensor.

What do you guys think?

Brian

Induced voltage may trip a solid state relay, but I'd doubt it would melt dry contacts...as you said, that's from too much current. Hwhy don't you just run the fountain with the lights off and try it, or is this unacceptable to the client?

Try contacting these guys with your problem, they sell controls as well, might have a solution or advice for you! http://www.fountainpeople.com/site_2/index_home.htm

Mike

The SSRs I am familiar with (Crydom and ISO22) exhibit about 1000 ohms of resistance. I don't think you will induce enough current to "trip" it with incidental proximity to other conductors.

UPDATE

On Friday 10/6, as per my fellow workers recomendation, I installed sheilded cable to the float sensor, Grounded the control transformer secondary(24VAC) and rewired the controls so that the float switch is switching the grounded conductor to the time delay relays. The fountain has been working fine since. 11 consecutive days is a record.

So, why did I have to do that. And, what fixed it. Grounding the transformer? The sheilded cable? Or, switching the grounded conductor? Tell me what & why???

Brian

*** UPDATE ***

The switch started sticking again the day after my last post. It is sticking on average every three days.

OK Master66, I haven't been thrilled with the control scheme as described. Please use a Fluke or equiv. with min/max record on AC amps , then AC mA. to make and break the circuit in place of the reed switch. Also check it on fast min/max record if you have that setting. Then also please tell us the actual measured value of your 24VAC control voltage. Also, if you can secure things, leave your Fluke on ACV min/max record across the 24VAC and walk away from it for a while. Check for higher voltage excursions. We can use the data gathered to determine if a current limiting resistor might be appropriate to protect the reed yet still provide enough to the coils.
Joe

Are you sure the contacts are actually sticking, i.e. do they stay stuck even when not powered? Reed switches are operated magnetically. Even though you are in a still tube, level fluctuations could be "chattering" the switch and causing the iron strip inside to magnetize semi-permanently. The fact that they felt it necessary to debounce the circuit with a 5 minute timer makes me think that this was a problem they were trying to solve. The problem with that solution is that it only solves the control issue, the reed switches themselves may still be operating too frequently. Here is a web site that describes how reed switches work. I have found that as reliable as they are, they cannot be used for high speed high switching count operations because of that magnetic memory issue. http://www.osdc.co.jp/english/products/products.html

Or is it just that the timers are not de-energizing when they should? I have definitely had 24V circuits get enough energy induced on them to keep solid state circuits energized, even if it wasn't enough to energize them in the first place, essentially a seal-in of the circuit. A small resistor across the terminals of the time coil should take care of that.

The simple test would be to see if everything goes back to normal as soon as you take power off the circuit. If it is an induced voltage issue that is keeping the Idec TDRs from dropping out, they should drop out again as soon as power is removed. If the reed switches are sticking closed, they would stay that way until the residual magnetism dissipates.