<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto">Alan, not true, I have two altimeters. Lol. Plus ear drums. Jon is a computer wizz- he is one of the few that can make electronics work in a Psub because it’s his thing. We work with what we know. Jon will be able to tell you if a mosquito passed wind in his K600 by the pressure change<div><br><div>Hank<br><br><div dir="ltr">Sent from my iPhone</div><div dir="ltr"><br><blockquote type="cite">On Jul 22, 2020, at 3:30 PM, Alan via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<br><br></blockquote></div><blockquote type="cite"><div dir="ltr"><meta http-equiv="content-type" content="text/html; charset=utf-8"><div></div><div>Hi Jon,</div><div>Just a dig at Alec & Hank.</div><div>I am enjoying delving in to the technology side of subs.</div><div>I have taken up building a hex copter as a hobby as I thought it would be compatible technology wise with my sub build. You may already be familiar with their flight</div><div>controllers but here is a brief summary.</div><div>The flight controllers have a number of gyroscopes, magnetometers, accelerometers,</div><div>& barometers in them. I believe the barometers are accurate to 10cm (4").</div><div>The flight controller I'm using ( Pixhawke 2.4.8) cost $50, but there are others in the $ hundreds.</div><div>The Arducopter firmware for the Pixhawk is open source & free, as is the highly configurable "Mission Planner" software. Mission Planner displays altitude, attitude,</div><div>the level of the craft etc, with autonomous mission planning, but this relies mainly </div><div>on GPS.</div><div>There is "Ardusub" as part of the suite. The development of this is mainly through</div><div>blue robotics, so aimed at ROVs & AUVs but may be able to be piggy backed in future</div><div>as an instrument display for submarines. The Pixhawke has various ports for</div><div>additional sensor inputs.</div><div>You could set up a Pixhawke flight controller to fly your sub using a RC transmitter</div><div>or a hard wired device that puts out a pwm signal, as long as your speed controller</div><div>had a PWM input. This would give you external control of your sub as well as internal,</div><div>also auto GPS hold if you wanted to leave your sub in the water while you parked</div><div>your truck. BTW the taranis transmitters are highly configurable through "open Tx"</div><div>firmware & software.</div><div>Cheers Alan</div><div><br></div><div><br></div><div><br>On 23/07/2020, at 8:48 AM, Jon Wallace via Personal_Submersibles <<a href="mailto:personal_submersibles@psubs.org">personal_submersibles@psubs.org</a>> wrote:<br><br></div><blockquote type="cite"><div><div class="ydpdba404ddyahoo-style-wrap" style="font-family:times new roman, new york, times, serif;font-size:16px;"><div></div>
<div dir="ltr" data-setdir="false">Alan,</div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false">Noted. But a few points...</div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false">1. I enjoy the challenge, and it's cool.</div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false">2. I've been programming computers for 35+ years. I refuse to ever, ever, ever, ever, ever, ever, ever, NEVER, let a machine best me. I've dealt with some stubborn silicon in my time and have always ended up pinning it to the floor and beating it. This is no time to give up. :)</div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false">3. I'm invested enough both in time and money that it wouldn't make sense to give it up now. Besides, my ego won't let me.</div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false">Jon</div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false"><br></div><div><br></div>
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On Wednesday, July 22, 2020, 04:32:03 PM EDT, Alan via Personal_Submersibles <<a href="mailto:personal_submersibles@psubs.org">personal_submersibles@psubs.org</a>> wrote:
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<div><div id="ydp7a4637feyiv2640226427"><div><div></div><div>Jon,</div><div>forget the calibration & decimal points, Alec & Hank just use their ear drums</div><div>for cabin pressure!</div><div>Popping means negative pressure, painful means positive pressure & burst</div><div>means something badly wrong!</div><div>Alan</div><div class="ydp7a4637feyiv2640226427yqt6517689911" id="ydp7a4637feyiv2640226427yqt21875"><div><br clear="none">On 23/07/2020, at 7:46 AM, Sean T. Stevenson via Personal_Submersibles <<a shape="rect" href="mailto:personal_submersibles@psubs.org" rel="nofollow" target="_blank">personal_submersibles@psubs.org</a>> wrote:<br clear="none"><br clear="none"></div><blockquote type="cite"><div>0.5% full scale on a 500 psia transducer is 2.5 psi, which corresponds to a little over 5.75 ffw. I respectfully suggest that this may not be a sufficiently accurate transducer for the application, depending on whether that error is predominately scale error, or offset. <br clear="none"><br clear="none">Also, check the error plots on the ADC datasheet. Total error will be cumulative: transducer error plus (or multiplied by) ADC error. Unless I'm reading the datasheet incorrectly, it also looks like full scale is +/- 6.144 V (bipolar) on that ADC. Step resolution in that case is [(6.144 - (-)6.144)/(2^15 -1)].<br clear="none"><br clear="none">Sean<br clear="none"><br clear="none"><br clear="none">Sent from ProtonMail mobile<br clear="none"><br clear="none"><br clear="none"><br clear="none">-------- Original Message --------<br clear="none">On Jul. 22, 2020, 13:04, Jon Wallace via Personal_Submersibles < <a shape="rect" href="mailto:personal_submersibles@psubs.org" rel="nofollow" target="_blank">personal_submersibles@psubs.org</a>> wrote:<blockquote class="ydp7a4637feyiv2640226427protonmail_quote"><br clear="none"><div class="ydp7a4637feyiv2640226427ydpea6d3badyahoo-style-wrap" style="font-family:times new roman, new york, times, serif;font-size:16px;"><div></div>
<div dir="ltr">Sean,</div><div dir="ltr"><br clear="none"></div><div dir="ltr">Might be a false alarm. As I was writing a detailed report for you I realized the discrepancy is looking like only 1.97 psi which is within the specs of the .5% full scale accuracy.</div><div dir="ltr"><br clear="none"></div><div dir="ltr">The transducer is 500 psia, 1-5v analog output with 0 psi at 1v. Three wires (power, ground, output), length of 3 feet. Data sheet accuracy is published as .5% full scale.</div><div dir="ltr"><br clear="none"></div><div dir="ltr">The ADC is ADS1115 (sourced through Adafruit) and configured for a range of 0-6.144v.</div><div dir="ltr"><br clear="none"></div><div dir="ltr"><span><span style="color:rgb(0, 0, 0);font-family:times new roman, new york, times, serif;font-size:16px;">6.144/32768 = .0001875 v per step over the full range of the ADC. Mathematically that puts 1v around step 5333 and 5v around step 26666. This then provides a range of 21,333 steps for the PSI range, or .</span><span style="color:rgb(0, 0, 0);font-family:times new roman, new york, times, serif;font-size:16px;">0234378662166596 psi per step assuming linear consistency.</span></span><br clear="none"></div><div dir="ltr"><span><span style="color:rgb(0, 0, 0);font-family:times new roman, new york, times, serif;font-size:16px;"><br clear="none"></span></span></div><div dir="ltr"><span><span style="color:rgb(0, 0, 0);font-family:times new roman, new york, times, serif;font-size:16px;">I'm simply testing atmospheric pressure, obviously at the low end of the transducers scale. Confirmed pressure of 14.7 via multiple weather sources. </span></span>14.7 psi should produce an ADC output of around 5960 calculated as 14.7 / .0234378662166596 = 627 steps, and then added to the base 5333 representing 0 psi. In reality I am seeing the ADC produce 5878 which is 82 steps or 1.947 psi less than expected. So this is an almost 4.5 foot depth discrepancy that will be more noticeable at shallower depths than deeper ones. I thought it was a lot more than that which had me frustrated, but after reviewing the numbers for the 498th time it looks like the transducer is reporting within spec. If you feel like doing the math I'd appreciate confirmation.</div><div dir="ltr"><br clear="none"></div><div dir="ltr">Through empirical testing I have been able to adjust software to "calibrate" the water depth transducer to 14.7 psi. It matches almost exactly to two decimal places my analog 0-60 psi Honeywell cabin pressure device. I've also tested my software calibration with an air tank pressurized up to 50psi and have found that to be nearly perfect as well, at least within two decimal places which exceeds my requirements. So the software calibration may give me the accuracy I need, I'm just not sure it will translate accurately all the way up to 500 psi. I'll have to build a smaller, simpler, display unit and find someone with a pressure tank that can take the transducer up to it's limits.</div><div dir="ltr"><br clear="none"></div><div dir="ltr">Jon</div><div dir="ltr"> </div><div><br clear="none"></div>
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On Wednesday, July 22, 2020, 12:57:32 PM EDT, Sean T. Stevenson via Personal_Submersibles <<a shape="rect" href="mailto:personal_submersibles@psubs.org" rel="nofollow" target="_blank">personal_submersibles@psubs.org</a>> wrote:
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<div><div id="ydp7a4637feyiv2640226427ydp77730bd3yiv8883491919"><div><div>Jon - What are the specs on your SSI transducer? Are you using voltage, current or unamplified? 15 bits on 500 psia should give you 0.01526 psi resolution, provided the input range of your signal conditioner matches the output range of the transducer. Check that. There could be a range mismatch, and possibly a unipolar / bipolar mismatch which would double the achievable step size (e.g. if that 15 bits corresponds to -10 V to 10 V, but the transducer signal is unipolar etc.).<br clear="none"></div><div><br clear="none"></div><div>You will likely see some temperature drift if the transducer is not temperature compensated within the range of service conditions, and I would also check for grounding of the transducer body, and shielding of the signal cable if it is not 4-20 mA.<br clear="none"></div><div><br clear="none"></div><div>If it is a current transducer, is it loop-powered or independently powered? If it is amplifed (voltage or current signal), check the stability of your power supply. If it's a bridge, that's even more critical. On the signal processing side, check how you are obtaining the reading. Acquisition frequency of the ADC vs display update frequency, etc. It could be that a lowpass filter on the measurement will make it behave better.<br clear="none"></div><div><br clear="none"></div><div>Sean<br clear="none"></div><div><br clear="none"></div><div class="ydp7a4637feyiv2640226427ydp77730bd3yiv8883491919protonmail_signature_block ydp7a4637feyiv2640226427ydp77730bd3yiv8883491919protonmail_signature_block-empty"><div class="ydp7a4637feyiv2640226427ydp77730bd3yiv8883491919protonmail_signature_block-user ydp7a4637feyiv2640226427ydp77730bd3yiv8883491919protonmail_signature_block-empty"><br clear="none"></div><div class="ydp7a4637feyiv2640226427ydp77730bd3yiv8883491919protonmail_signature_block-proton ydp7a4637feyiv2640226427ydp77730bd3yiv8883491919protonmail_signature_block-empty"><br clear="none"></div></div><div><br clear="none"></div><div>‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐<br clear="none"></div><div class="ydp7a4637feyiv2640226427ydp77730bd3yiv8883491919yqt0847155879" id="ydp7a4637feyiv2640226427ydp77730bd3yiv8883491919yqt32545"><div> On Wednesday, July 22, 2020 7:11 AM, Jon Wallace via Personal_Submersibles <<a shape="rect" href="mailto:personal_submersibles@psubs.org" rel="nofollow" target="_blank">personal_submersibles@psubs.org</a>> wrote:<br clear="none"></div><div> <br clear="none"></div><blockquote class="ydp7a4637feyiv2640226427ydp77730bd3yiv8883491919protonmail_quote" type="cite"><div style="font-family:times new roman, new york, times, serif;font-size:16px;"><div dir="ltr">Sean,<br clear="none"></div><div dir="ltr"><br clear="none"></div><div dir="ltr">I think you've talked about sourcing pressure transducers in the past, do you have any recommendations for ones that you have found reliable? I'm getting quite frustrated trying to interface the SSI Technologies P51 series with a 16-bit ADC (using 15 bits) and unable to get results that are anywhere close to my calculated/expected results even considering worst case accuracy limits. I don't mind paying more for a sensor that is going to perform close to it's datasheet specs. Specifically, looking for 500 psia with .5% or better accuracy. I'd prefer .25% or better accuracy but can live with .5%.<br clear="none"></div><div dir="ltr"><br clear="none"></div><div dir="ltr">Jon<br clear="none"></div></div></blockquote></div><div><br clear="none"></div></div></div><div class="ydp7a4637feyiv2640226427ydp77730bd3yqt0847155879" id="ydp7a4637feyiv2640226427ydp77730bd3yqt10357">_______________________________________________<br clear="none">Personal_Submersibles mailing list<br clear="none"><a shape="rect" href="mailto:Personal_Submersibles@psubs.org" rel="nofollow" target="_blank">Personal_Submersibles@psubs.org</a><br clear="none"><a shape="rect" href="http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles" rel="nofollow" target="_blank">http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles</a><br clear="none"></div></div>
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