[PSUBS-MAILIST] (no subject)

[Sean T. Stevenson via Personal_Submersibles]

If you can't measure something, you can't control it. No way around this problem but to use a higher quality pressure transducer, and data acquisition hardware with sufficient bit resolution to capture the available resolution of the instrument.  You can filter out noise, but that doesn't help with hysteresis, repeatability or absolute accuracy. I often use Honeywell STJE series pressure transducers in high accuracy applications, but they're pricy.

Sean


On August 28, 2015 6:52:27 AM MDT, Jon Wallace via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
>I like the autopilot feature for depth control, but one little nit that
>
>may mess things up from an observation perspective is the accuracy of 
>the pressure gauge.  It looks like I'm going to have an overall  +/- 6 
>feet accuracy based upon full scale accuracy on a 500 psi sensor.  So 
>relying on the microprocessor to maintain depth means a potential 6
>foot 
>vertical drift in either direction.  Operationally not an issue but if 
>your observing something and need to stay still to capture photo or 
>video you may still need to provide manual input if not perfectly
>buoyant.
>
>Jon
>
>
>On 8/28/2015 7:57 AM, Sean T. Stevenson via Personal_Submersibles
>wrote:
>>
>> I'd be inclined to link the two systems, such that you catch a trim 
>> with the VBT upon initial submersion, drive down with thrusters, and 
>> then at your operating depth, have a controller (PAC or PLC) maintain
>
>> that depth automatically using thrusters, but simultaneously 
>> auto-adjust the VBT level to bring the required thruster output back 
>> to zero.  That way they're never fighting the vessel's buoyancy and 
>> you maximize battery endurance.
>>
>> Sean
>>
>>
>
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