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JohnN

AOI Pressure sensor triggered by temperature changes

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I've recently added an AOI pressure/moisture detector to my Ikelite housing and find that it is very sensitive to temperature changes.  Setting up in a warm room and then putting the camera outside or jumping into cold water (50 oF) will  trigger a loss-of-pressure alarm. 

Short of letting the housing acclimate, is there anything else that can be done?

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34 minutes ago, JohnN said:

I've recently added an AOI pressure/moisture detector to my Ikelite housing and find that it is very sensitive to temperature changes.  Setting up in a warm room and then putting the camera outside or jumping into cold water (50 oF) will  trigger a loss-of-pressure alarm. 

Short of letting the housing acclimate, is there anything else that can be done?

What procedure do you use?  Pump till first green  light and then stop?  Or give it 2-3 extra pumps?  Does the unit claim to include temperature compensation?

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3 hours ago, ChrisRoss said:

What procedure do you use?  Pump till first green  light and then stop?  Or give it 2-3 extra pumps?  Does the unit claim to include temperature compensation?

I pull it down by 5-6 psi. Less and it won't start the calibration sequence, more and it complains and won't start the calibration sequence. No temperature compensation mentioned in the specs

Is this a common behavior for these things?

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4 hours ago, JohnN said:

I pull it down by 5-6 psi. Less and it won't start the calibration sequence, more and it complains and won't start the calibration sequence. No temperature compensation mentioned in the specs

Is this a common behavior for these things?

No generally not, I have a Nauticam system and it works with no drama.   So you have a gauge on the pump setup then to read vacuum? 

Is this your unit?: https://shop.divingexpress.com/index.php?route=product/product&product_id=5714

I would suggest to do a test, pull the vacuum,  start the calibration sequence and once green stick the whole lot in the fridge  - Do you have a way to leave the gauge connected?  Or can you check the pressure again once it has cooled?  Try and see what pressure it alarms at.

The odd thing is that if the housing is cooling off - the pressure should be dropping as the gas inside gets colder.  which means the there is more vacuum - not less.  I calculate if you start with 5 psi vacuum which is 9.7 psia ( absolute pressure)  and you cool the gas by 10°C (18 F) the pressure will change to 9.4 psia which 5.3 psi of vacuum - 5.3 psi less than atmospheric pressure.  This should not cause it to alarm.  It should only alarm if the pressure goes up, indicating a leak.

I would suspect a passing valve until I could prove otherwise- either that or it's a faulty unit. 

 

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Thanks.  I've reached out to AOI (without a great deal of optimism) for their comments on what I'm seeing.

When the housing goes from warm to cold and the pressure warning light activates, I've checked the pressure on the housing and cannot see a difference between where I left it originally and the current pressure.

I'm suspecting that the pressure sensor is not temperature compensated and is giving me the faulty results

For the time being, what I have is much better than nothing (which is what I had before)

Thanks again for your input.

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6 hours ago, JohnN said:

Thanks.  I've reached out to AOI (without a great deal of optimism) for their comments on what I'm seeing.

When the housing goes from warm to cold and the pressure warning light activates, I've checked the pressure on the housing and cannot see a difference between where I left it originally and the current pressure.

I'm suspecting that the pressure sensor is not temperature compensated and is giving me the faulty results

For the time being, what I have is much better than nothing (which is what I had before)

Thanks again for your input.

But the point is - temperature compensated or not, when the housing gets colder the vacuum is stronger because gas contracts when it cools.  It should only alarm if it gets warmer and the gas expands meaning there is lower vacuum.

Yes it is better than nothing - what you can do is pump down in a place where the temperature is not going to drop dramatically and test it for several hours - if you have not lost vacuum in that time the housing is tight and all that can happen realistically is you press a button causing that button to leak in which case the leak alarm will go off well before the vacuum alarm responds.

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Do you have a moisture sensor on your system? Could it be that the temp change is causing condensation and setting off your moisture sensor? Just a shot in the dark.

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I'm not familiar with the AOI system, but have noticed that my Vivid vacuum system is sensitive to temperature changes. A friend who uses an Ikelite vacuum system has also noticed changes due to temperature. We've seen this when doing our vacuum stuff in air conditioned rooms and taking the pressurized housings out into higher temperatures.

It's not a real issue with my Vivid system if I do some extra pulls on the vacuum pump after getting a green light. The friend with the Ikelite vacuum system takes his pump along, makes an adjustment after he gets on the boat if necessary and checks the pressure gauge again before the housing enters the water.

Water temperatures (mid to high 80s) where we dive during the summer tend to be higher than those (low to high-70s) in air-conditioned rooms. Temperatures on a dive boat's camera table are frequently higher than those in air-conditioned rooms. I don't know where you are diving and what the temperature differences are between where you're setting your vacuum and the water temperature, but your issue might be a pretty simple one... maybe remove a little more air from your housing?

-Tinman

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2 hours ago, Dann-Oh said:

Do you have a moisture sensor on your system? Could it be that the temp change is causing condensation and setting off your moisture sensor? Just a shot in the dark.

I don't believe so, the moisture sensor starts a very annoying beeping in addition to the red LED flashing.

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8 hours ago, Tinman said:

Water temperatures (mid to high 80s) where we dive during the summer tend to be higher than those (low to high-70s) in air-conditioned rooms. Temperatures on a dive boat's camera table are frequently higher than those in air-conditioned rooms. I don't know where you are diving and what the temperature differences are between where you're setting your vacuum and the water temperature, but your issue might be a pretty simple one... maybe remove a little more air from your housing?

-Tinman

I regularly (pre lockdown) dived in Thailand.   Housing prep in aircon room, at 22°C(72F)  and then taking the camera out in 30-34°(86-93F) air temperatures and water temperatures in the range 29-31°C(84-88F).  On My Nauticam system I give it 2-3 pumps beyond solid green and I never had any indication of false alarms.

The description of the AOI system behaviour by the OP makes me suspect it is faulty.

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Like I said, I've no experience with AOI vacuum systems, so your suspicions about it being a faulty system may be correct. I do know that I have experienced housing pressure changes when moving from a 72° (F) air conditioned hotel room to a 90°+ (F) boat deck.

I did have an experience with a student once who's vacuum system would not cooperate with him. It would give him the green light and then change to red. We finally determined that the issue was a low battery on his vacuum system. Replacement of the battery was an easy fix. (LOL)

-Tinman

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