Feature request - rebreather solenoid signal

[doctormike]

Just a heads up I am not a rebreather diver but I am a design engineer and specialize in solenoids.

FINALLY!!!

The issue with a blinking light is that it would trigger when the solenoid is supplied voltage, however this isn't an indicator that the solenoid is actually moving. I have seen in life cycle testing that near the end of a solenoids useful life the plunger slows down and will fail to pull in even when supplied with the proper voltage. This is why audible confirmation is better than a voltage triggered light, if you hear the solenoid click that means it has pulled in fully. One way to do this is to monitor the current supplied to the solenoid and have a computer perform some mathematics on this waveform to determine when the solenoid has pulled in. The downfall is that this can not reliably be done in a small package without a large expense.

Right, that's what I was asking upthread - is there any way of monitoring the actual movement of the solenoid as opposed to just monitoring the triggering of the solenoid? So I guess the answer is "yes, but not technically feasible in a rebreather at this point."

the diver will have become accustomed to seeing the light and thinking everything is okay and I could see this causing an unfortunate accident. Not something that would be widespread but to me there is the possibility of failure there and why add the unnecessary risk when there are better ways of monitoring the functionality of the unit.

Once again, this is not in place of monitoring the PO2. The idea was an adaptation for people who can't hear the solenoid. So unless we are saying that the solenoid noise is not only unhelpful but it is misleading and should be blocked out so that people don't get accustomed to it and think that everything is OK, I don't see how this would be any different.

But thanks so much for your post, it's good to have the advice of an expert in the field...!

 

[rjack321]

Once again, this is not in place of monitoring the PO2. The idea was an adaptation for people who can't hear the solenoid. So unless we are saying that the solenoid noise is not only unhelpful but it is misleading and should be blocked out so that people don't get accustomed to it and think that everything is OK, I don't see how this would be any different..

Its different because a noise and the light are not saying the same thing:

Noise = yes the solenoid opened because the plunger movement made the noise, for sure O2 would go through the opening (if O2 is supplied and on)

Light = Voltage was delivered to the solenoid. The plunger may or may not have moved. Does not confirm the delivery of O2 to the loop even if the O2 is supplied and turned on

 

[broncobowsher]

Just a heads up I am not a rebreather diver but I am a design engineer and specialize in solenoids. The issue with a blinking light is that it would trigger when the solenoid is supplied voltage, however this isn't an indicator that the solenoid is actually moving. I have seen in life cycle testing that near the end of a solenoids useful life the plunger slows down and will fail to pull in even when supplied with the proper voltage. This is why audible confirmation is better than a voltage triggered light, if you hear the solenoid click that means it has pulled in fully. One way to do this is to monitor the current supplied to the solenoid and have a computer perform some mathematics on this waveform to determine when the solenoid has pulled in. The downfall is that this can not reliably be done in a small package without a large expense.

I like the idea of having an indicator light but the main problem with that is that after a few million cycles when the solenoid may start to have an issue it will not be an accurate indicator that everything is working properly and by that time the diver will have become accustomed to seeing the light and thinking everything is okay and I could see this causing an unfortunate accident. Not something that would be widespread but to me there is the possibility of failure there and why add the unnecessary risk when there are better ways of monitoring the functionality of the unit.

I see the indicator as a benefit in this case. "Look the light shows the solenoid is commanded to open, but I am not getting the spike in O2 that I would expect. It's not the controller is not commanding the solenoid, it is the solenoid is not responding. Looks like a diagnostic feature to me.

Anybody who is thinking/mentioning "the light is blinking, everything is fine" mentality of diving a rebreather needs to find a qualified instructor and start training over again. You were taught by an idiot.

The idea of the light is just a visual reference to a not always audible signal. Nobody is forcing you to look at the blinking light, but the option to see it would be nice for some.

 

[doctormike]

Its different because a noise and the light are not saying the same thing:

Noise = yes the solenoid opened because the plunger movement made the noise, for sure O2 would go through the opening (if O2 is supplied and on)

Light = Voltage was delivered to the solenoid. The plunger may or may not have moved. Does not confirm the delivery of O2 to the loop even if the O2 is supplied and turned on

No, that's the point. Right now there IS no "light" - the device doesn't exist. So I was trying to figure out how it would be implemented. One option (the simple but less useful one) would be just a visual indicator that the solenoid was getting a command to fire. The other option (more useful but less feasible from an engineering point of view, apparently) would be a visual signal that tells you when either the solenoid actually moves, or when it makes a certain sound.

The world is full of adaptations for people who have special needs. You can get your cell phone to flash instead of ring if you are deaf. And you can have your CCR HUD display modified if you are color blind.

It's not that you are going to see the blinking light and just assume all is good and that no more monitoring is necessary. it's more likely that if you are diving with the light going at a steady rhythm correlated to your O2 consumption, and it suddenly speeds up or stops, that could be an early warning with problems with the unit as discussed upthread. I'm not making up the idea about listening for the solenoid, all I'm saying is that for some of us, that's impossible.

 

[rjack321]

We're on page 3 and Shearwater hasn't said anything yet - I'm guessing if you want a solenoid light you'll need to make one yourself. Alternatively you could replace your JJ solenoid with a really loud one. Or modify the plunger so it "chimes".

 

[doctormike]

We're on page 3 and Shearwater hasn't said anything yet - I'm guessing if you want a solenoid light you'll need to make one yourself. Alternatively you could replace your JJ solenoid with a really loud one. Or modify the plunger so it "chimes".

Hah! I could also hire someone who isn't partially deaf to swim behind me and tap me on the shoulder every time it fires... Or maybe a service animal like a dolphin? They have good hearing...

 

[jgttrey]

In the realm of the purely theoretical....

What you really want is some audible or visual feedback that the solenoid is actually adding O2, not merely receiving voltage, so I agree with the above comments. In my case, my Meg handset tells me that voltage is being sent to the solenoid with an asterisk (which might be useful for diagnostic reasons, but is not something I monitor). Part of the reason I don't bother with it, in addition to the fact that it would require me to stare at the handset trying to catch it in the act, is that by itself it would not tell me if O2 was actually flowing, only that the solenoid was told to open. As noted, if I'm out of O2 or the solenoid is stuck closed, it wouldn't help me.

I do listen for the click and the sound of the gas injection. I can actually hear the O2 injection, not just the click. Sounds just like I added gas to my wing, but more muted. I understand that's what you are trying to duplicate. I find it useful and comforting and I can understand why you would want to replicate it.

In theory, I guess you could have a a rattle or something that is actuated by the gas flow out of the solenoid - sort of a playing card in the wheel spokes idea - that would give a sound that is easier to discern or even an actual vibration. You could attach the little noisemaker from a whoopie cushion if your dive buddies were understanding - if you could find one made from appropriate O2 compatible materials.....

Practically, I'm not sure how you would go about it. I will say that my Meg solenoid is threaded at the outlet and now has a delrin flow diverter that shoots the O2 towards the wall of the can at a 90 degree angle to how it would come out of the solenoid without it. This was a fix from ISC for the fact that without it, the solenoid would shoot right onto Cell #3 causing a transient cell disagreement. I honestly cannot recall what it sounded like before the diverter was installed, but it's quite audible to me now. I wouldn't be surprised if the diverter, which sprays out of 3 small holes (IIRC) is a bit louder than a naked solenoid as the O2 is being squirted at a higher velocity out of smaller holes. Maybe something along those lines would make it a bit louder for you (if the outlet of your solenoid is threaded).

Just spitballin here.

 

[rjack321]

Hah! I could also hire someone who isn't partially deaf to swim behind me and tap me on the shoulder every time it fires... Or maybe a service animal like a dolphin? They have good hearing...

I vote for dolphins.
Or maybe one of those deer whistles that supposedly go on the front bumper of your car. Although an O2 kazoo might be your thing.

But now I'm wondering how many shearwater controllers are actually out there that this might apply to?

 

[doctormike]

I vote for dolphins.
Or maybe one of those deer whistles that supposedly go on the front bumper of your car. Although an O2 kazoo might be your thing.

But now I'm wondering how many shearwater controllers are actually out there that this might apply to?

Lots, but I was only thinking of it being useful on the NERD. The whole idea of being in tune with your CCR by listening for the solenoid implies that you hear it throughout the whole dive. It would be useless if it was only seen when you checked your controller.

I wonder if another approach would be some sort of waterproof amplifier or sound feed, like a tiny electronic stethoscope that you would just stick on to the outside of the head and then run to your ear. Or even a little water filled tube - might be enough to transmit sound. Run the ear end into a custom earmold that was ventilated to avoid barotrauma..? That would also have the advantage of working on any CCR.

Gonna work on this with one of my audiology colleagues.

 

[rjack321]

Lots, but I was only thinking of it being useful on the NERD. The whole idea of being in tune with your CCR by listening for the solenoid implies that you hear it throughout the whole dive. It would be useless if it was only seen when you checked your controller.

I wonder if another approach would be some sort of waterproof amplifier or sound feed, like a tiny electronic stethoscope that you would just stick on to the outside of the head and then run to your ear. Or even a little water filled tube - might be enough to transmit sound. Run the ear end into a custom earmold that was ventilated to avoid barotrauma..? That would also have the advantage of working on any CCR.

Gonna work on this with one of my audiology colleagues.

The NERD is a solenoid controller now? I thought the NERD was just a monitor.

If you want the NERD to have a solenoid light you'd need it either hardwired and/or rewiring the head to adapt pins 5,6,7 to measure want/when your controller is sending to the solenoid.