Feature request - rebreather solenoid signal

[doctormike]

From what I have read, listening to the solenoid fire is one way of being more in tune with the functioning of an eCCR, specifically as a way of knowing the rate that the controller is attempting to add O2. It's a check on other systems, it's reassurance, and it does give you information that just observing a stable PPO2 does not. I'm not saying that you HAVE to have that information, but I'm also pretty sure that I have heard of it's value from other sources. For example, on the Meg website failure tree, the "closed solenoid failure pathway" starts with not hearing the O2 flowing in the solenoid. And this information could alert you to issues before there is a drift in your loop PO2.

For example, if the solenoid is firing faster or constantly and the PO2 is stable, one possibility is that you are metabolizing more O2. Another possibility is that your cells (or the controlling cells) have become current limited, and the eCCR is trying to catch up to a setpoint that it won't reach. On the other hand, if the solenoid stops firing for any length of time with a stable PO2, something is obviously wrong since you continue to metabolize O2. That might mean a frozen board which will not add O2 even as the actual loop PPO2 drops.

Or if the solenoid is firing and the loop PO2 is dropping, that suggests that you might be out of O2 or that there is an O2 feed problem.

I'm just saying that since it seems to be a helpful thing to hear the rhythm of the solenoid, I don't see why I can't have that information just because I have a high frequency hearing loss.... Certainly, it would be something on the HUD, and something that could be turned off for people who don't want it.

So the next question would be if this would simply tell you when the controller fires the solenoid (an easy software fix), or when the solenoid actually opens (which might require some sort of feedback from the head (does DiveCAN provide this? I don't know).

In any case, I just thought that I would discuss it here so that people could point out things that I haven't thought of. And I do appreciate everyone's input!

 

[blatter]

Just some thoughts about visual indicator: On my Meg (2.7/eCCR) a little asterix appears on the handset when the solenoid fires. There are also changing symbols that indicate the electronics are working. While a visual indicator may be helpful, I can't help thinking that there is risk that indicators may be working while the solenoid isn't due to solenoid failure or a disconnected O2 hose. Even if there was a feedback system, a failing indicator might still be misleading.

I can actually hear the solenoid firing and gas flowing on my unit even with a thick hood. It does provide a bit of feedback but I would never rely on that to confirm things were working. For me, checking cell O2 readings are OK, in agreement and changing according to depth and gas inputs seems to me to be a better way to confirm the unit is working OK. It is also quicker than waiting to hear solenoid firing. I guess what I am thinking is that the visual indicator is nice to have but I would not miss it too much even if I could not hear the solenoid.

 

[doctormike]

I can actually hear the solenoid firing and gas flowing on my unit even with a thick hood. It does provide a bit of feedback but I would never rely on that to confirm things were working. For me, checking cell O2 readings are OK, in agreement and changing according to depth and gas inputs seems to me to be a better way to confirm the unit is working OK.

In case it wasn't clear, I was in no way implying that an audible confirmation of the solenoid firing would take the place of standard PO2 monitoring. That's one of the main reasons I have a NERD.

 

[blatter]

No - sorry - didn't think you were saying that - but was trying to make the point that for me even though I have visual indicator for solenoid operation on my ccr and even check it is working on predive check, I don't find that feature very useful. Apart from possible failure of the failure indicator it just seems to me to take too much time to watch for the thing to indicate solenoid is firing as opposed to just monitoring the cells for normal/expected readings which you do and which I think should be done by all ccr divers.

 

[doctormike]

it just seems to me to take too much time to watch for the thing to indicate solenoid is firing as opposed to just monitoring the cells for normal/expected readings which you do and which I think should be done by all ccr divers.

Right, I understand, but again you seem to be implying that this is an either/or thing. I really wasn't saying that. It's helpful to be closely in tune with your machine by using all of your senses. This is why being aware of your own internal sensations is part of training - not as a replacement to PO2 monitoring but as a supplement. If you feel "funny", go to bailout no matter what the PO2 sensors say - it's not only CO2 that can make you feel "off".

I guess it's sort of like saying that a race car driver would notice any odd engine noise as an indication that something has changed. Listening for that doesn't mean that you are not watching the track through the windshield. Similarly, if you hear the steady click of the solenoid during a dive and it suddenly speeds up or stops, that's a sign that something is changing, so maybe try to figure out what that is.

 

[broncobowsher]

I've thought about this as well. I would like to see an indicator as well. I don't always hear the solenoid fire (thick hood and such mentioned above). But I would like to keep track of how often it is firing. If I see it is firing a lot more often than normal, something is up. Is the orifice clogged? Do I have an IP issue on the O2 side? Workload spiked? A little green dot in the corner that comes on during the solenoid signal and fades out over 5 seconds or something like that. Maybe green on fire and white for the afterfire for a few seconds. That way you don't have to catch the display the exact moment it fires but you can look and see that it just fired.

 

[doctormike]

Is the orifice clogged?

I hadn't thought of that, since I don't have CMF on my rebreather, but that's another good point about when being more in tune with the functioning of the unit could help pick up problems early...

 

[rjack321]

My .02

If your PO2 isn't dropping, you're somehow getting oxygen. A little blinky would just tell you when it was firing, your PO2 rising would tell you that you're really getting oxygen.

I'm not sure why one would need the extra blinky.

agree with you 100%

Part of the issue with blinky feature requests is that the brain really does have a finite capacity to process indicators/alarms/lights etc. Adding one most likely means your attention to something else has to give.

 

[doctormike]

The point is that it’s an accommodation for people who don’t have the option of audibly monitoring the solenoid. So if you can hear it and don’t want a light, then just turn it off. But for those of us who would like to be able to use data that’s available to people with normal hearing, it would be a nice option. Just like the HUD option for color blind people... it’s availability doesn’t mean that people with normal sight have to use it...

 

[Southside]

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.