Perdix AI has pressure reading

[hilljo88]

my Perdix AI has suddenly started reporting Nitrox tank pressure at 10% below mechanical gauge. Batteries are new, and I checked voltage. Ideas?

 

[Landau]

If you haven't already, try a different mechanical gauge to determine if issue is with the gauge or Perdix.

 

[scubadiver888]

Just did a quick check on one of my tanks. Perdix = 2978 PSI, analog backup gauge = ~3000 PSI, analog tank checker = ~3050 PSI. Part of the difference could be my eyesight on the analog gauges. But being off by 10% (300 PSI on an AL80) is a lot.

If you don't have a third source to use, bring a tank to your dive shop with your regulators and Perdix AI. Check all three at the same time at the dive shop. I'm sure they have a tank checker you can use.

 

[RayfromTX]

In the absence of corroboration, I would sooner trust the Perdix transmitter over the mechanical gauge. My experience is limited but my 4 transmitters are far more consistent than my 4 mechanical gauges, especially at the top and bottom ends of their ranges. I have yet to have one seem sticky either.

 

[MargaritaMike]

I would trust the transmitter over the SPG, but that's just the way I am. The technology has moved on. I use to dive with a SPG and AI, but the extra hose is unnecessary on a REC dive. Tech diving would be a different perspective. IMO the analog SPG is less accurate because of the scale of the device (display 3000 psi in 1½ in. or less), but 10% is significant.

Good luck.

 

[hilljo88]

So issue seemed to be temporary and hasnt reappeared on subsequent dives. I checked pressure readings on several different mechanical guages and. on that afternoon, there was a difference between the AI transmitter and the mechanical guages. But next day and thereafter, the transmitter seemed accuate. Maybe a grain of sand or salt crystal in first stage.
Thanks to all for your comments and suggestions. By the way, Shearwater customer service responded promptly with similar thoughts. Much appreciated.

 

[Alastor]

uhm, and if the mechanical had a salt crystal developing in the gears and it slowly respond to pressure dropping ?
It is slow and until the force is not enough the mechanical seem "sticking" ... if you suddenly drop the pressure you could not notice it, but during the dive pressure drops slowly ....
I noted a similar behaviour in a SPG until after a dive, after disconnecting the regulators from the tank, I noted the SPG indicating 60 bar (!) ,,,
I replaced it but, just for post-mortem sake I opened the SPG and discovered salt build-up on the hand shaft (a rack and pinion connected to the bourdon tube).
Once removed the salt the SPG worked flawlessy, but because I was not able to seal again it, I threw it somewhere....

 

[bryanf145]

my Perdix AI has suddenly started reporting Nitrox tank pressure at 10% below mechanical gauge. Batteries are new, and I checked voltage. Ideas?

My AI is reading on average close to 300 psi difference. Being that a mechanical gauge will give my tank pressure at 3500 and my AI gives it around 3250 to a little more. I don't know which one to go by.

 

[RayfromTX]

Have you breathed a tank down at the end of a dive after surfacing to see which one is accurate as to the low end of the scale? I would care more about the low pressure readings than the high pressure readings. I have found the AI to be more consistent than my mechanical gauge.