<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div></div><div>Thanks Cliff,</div><div>I just noticed the second half of your email below the product picture :(</div><div>I like that O2 sensor you linked to & have noted the 10-15mv specs so I</div><div>can write code & do the electronics for it, but buy them when I have finished</div><div>the rest of the sub. If I bought them first they may expire before I finish.</div><div>I am wanting to do similar to you except use 3 X O2 sensors. I am going to</div><div>compare the readings & go with the average of the nearest 2, as in a rebreather </div><div>system.</div><div>One reason is it is a 1 person sub & I want to be able to send inexperienced</div><div>people down in it who may panic if alarms went off for a sudden sensor</div><div>failure & also may not recognise what was going on. I also want to signal which </div><div>sensor is going out of range & monitor it.</div><div>Alan</div><div><br></div><div><br></div><div><br>On 20/08/2019, at 1:59 AM, Cliff Redus via Personal_Submersibles <<a href="mailto:personal_submersibles@psubs.org">personal_submersibles@psubs.org</a>> wrote:<br><br></div><blockquote type="cite"><div><!--[if gte mso 9]><xml><o:OfficeDocumentSettings><o:AllowPNG/><o:PixelsPerInch>96</o:PixelsPerInch></o:OfficeDocumentSettings></xml><![endif]--><div class="ydpd9d22049yahoo-style-wrap" style=""><div style="font-family: times new roman, new york, times, serif; font-size: 16px;"></div>
<div dir="ltr" data-setdir="false" style="">Alan, I am with Jon on the span for the O2 sensor. Granted under NOP a 0-25% span for O2 percent is fine but 0-100% span is handy to detect if you have HP O2 bleed into the cabin. On one dive weekend a few years ago, when I got ready to dive the next day I powered up the boat and a high O2 alarm sounded in the boat. After checking I found that I had left the HP O2 blocking valve on my O2 tank open over night with the hatch secured. With my system it is possible to have a very low flow bleed into the cabin. The cabin atmosphere had risen to 27% O2. I got out my handy leaf blower and aired out the cabin and proceeded to dive.</div><div dir="ltr" data-setdir="false" style=""><br></div><div dir="ltr" data-setdir="false" style="">I use the <span><a href="https://www.maxtec.com/product/sensing/fio2/max-250/" rel="nofollow" target="_blank" class="enhancr_card_6422436473">Max-250 | Maxtec</a></span><div><br></div><div id="ydpe1395bfeenhancr_card_6422436473" class="ydpe1395bfeyahoo-link-enhancr-card ydpe1395bfeymail-preserve-class ydpe1395bfeymail-preserve-style" style="max-width:400px;font-family:Helvetica Neue, Segoe UI, Helvetica, Arial, sans-serif" data-url="https://www.maxtec.com/product/sensing/fio2/max-250/" data-type="YENHANCER" data-size="MEDIUM" contenteditable="false"><a href="https://www.maxtec.com/product/sensing/fio2/max-250/" style="text-decoration:none !important;color:#000 !important" class="ydpe1395bfeyahoo-enhancr-cardlink" rel="nofollow" target="_blank"><table border="0" class="ydpe1395bfecard-wrapper ydpe1395bfeyahoo-ignore-table" cellpadding="0" cellspacing="0" style="max-width:400px"><tbody><tr><td width="400"><table border="0" class="ydpe1395bfecard ydpe1395bfeyahoo-ignore-table" cellpadding="0" cellspacing="0" width="100%" style="max-width:400px;border-width:1px;border-style:solid;border-color:rgb(224, 228, 233);border-radius:2px"><tbody><tr><td class="ydpe1395bfecard-primary-image-cell" background="https://s.yimg.com/lo/api/res/1.2/N1du_J39U0YXDfNAdTHK2g--~A/Zmk9ZmlsbDt3PTQwMDtoPTIwMDthcHBpZD1pZXh0cmFjdA--/https://cdn.maxtec.com/www/R125P01-002-max-250-lightbox.jpg.cf.jpg" bgcolor="#000000" valign="top" height="175" style="background-color: rgb(0, 0, 0); background-size: cover; position: relative; border-radius: 2px 2px 0px 0px; min-height: 175px;"><!--[if gte mso 9]><v:rect fill="true" stroke="false" style="width:396px;height:175px;position:absolute;top:0;left:0;"><v:fill type="frame" color="#000000" src="https://s.yimg.com/lo/api/res/1.2/N1du_J39U0YXDfNAdTHK2g--~A/Zmk9ZmlsbDt3PTQwMDtoPTIwMDthcHBpZD1pZXh0cmFjdA--/https://cdn.maxtec.com/www/R125P01-002-max-250-lightbox.jpg.cf.jpg"/></v:rect><![endif]--><table border="0" class="ydpe1395bfecard-overlay-container-table ydpe1395bfeyahoo-ignore-table" cellpadding="0" cellspacing="0" style="width:100%"><tbody><tr><td class="ydpe1395bfecard-overlay-cell" background="https://s.yimg.com/cv/ae/nq/storm/assets/enhancrV21/1/enhancr_gradient-400x175.png" bgcolor="transparent" valign="top" style="background-color: transparent; border-radius: 2px 2px 0px 0px; min-height: 175px;"><!--[if gte mso 9]><v:rect fill="true" stroke="false" style="width:396px;height:175px;position:absolute;top:-18px;left:0;"><v:fill type="pattern" color="#000000" src="https://s.yimg.com/cv/ae/nq/storm/assets/enhancrV21/1/enhancr_gradient-400x175.png"/><v:textbox inset="0,0,20px,0"><![endif]--><table border="0" class="ydpe1395bfeyahoo-ignore-table" height="175" style="width: 100%; min-height: 175px;"><tbody><tr><td class="ydpe1395bfecard-richInfo2" style="text-align:left;padding:15px 0 0 15px;vertical-align:top"></td><td class="ydpe1395bfecard-actions" style="text-align:right;padding:15px 15px 0 0;vertical-align:top"><div class="ydpe1395bfecard-share-container"></div></td></tr></tbody></table><!--[if gte mso 9]></v:textbox></v:rect><![endif]--></td></tr></tbody></table></td></tr><tr><td><table border="0" align="center" class="ydpe1395bfecard-info ydpe1395bfeyahoo-ignore-table" cellpadding="0" cellspacing="0" style="background:#fff;position:relative;z-index:2;width:100%;max-width:400px;border-radius:0 0 2px 2px;border-top:1px solid rgb(224, 228, 233)"><tbody><tr><td style="background-color:#ffffff;padding:16px 0 16px 12px;vertical-align:top;border-radius:0 0 0 2px"></td><td style="vertical-align:middle;padding:12px 24px 16px 12px;width:99%;font-family:Helvetica Neue, Segoe UI, Helvetica, Arial, sans-serif;border-radius:0 0 2px 0"><h2 class="ydpe1395bfecard-title" style="font-size: 14px; line-height: 19px; margin: 0px 0px 6px; font-family: Helvetica Neue, Segoe UI, Helvetica, Arial, sans-serif; color: rgb(38, 40, 42);">Max-250 | Maxtec</h2><p class="ydpe1395bfecard-description" style="font-size: 12px; line-height: 16px; margin: 0px; color: rgb(151, 155, 167);">Replacement oxygen sensor for Maxtec OM-25, Fluke VT Mobile,</p></td></tr></tbody></table></td></tr></tbody></table></td></tr></tbody></table></a></div><div><br></div><div dir="ltr" data-setdir="false">with a custom PCB that converts this 10-15mV signal into a 0-5V signal I use for analog input on my PLC. I find you have to replace this element every 3-4 years. It comes factory calibrated. For field calibration, I added some ladder logic to PLC that lets me add a bias error correction to sensor by comparing what the sensor is measuring to the air it is measuring in the cabin when the hatch is open. I find this works quite well. Normal air has 20.95% O2, if I look at my life support display on my boat and find it much off from this, I hit the calibration button and difference between what it is reading and 20.95% is stored as a bias error correction calibration constant.</div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false">The accuracy of Max-250 sensor is +/- 1% full scale so the benefit of going to a O2 sensor with a 0-25% span even with with a +/- 2% would be a more accurate measurement because of the span. Having said that, I have had no issues with 0-100%, <span><span style="color: rgb(0, 0, 0); font-family: times new roman, new york, times, serif; font-size: 16px;">+/-1% full scale sensor.</span></span></div><div dir="ltr" data-setdir="false"><span><span style="color: rgb(0, 0, 0); font-family: times new roman, new york, times, serif; font-size: 16px;"><br></span></span></div><div dir="ltr" data-setdir="false"><span>The nice part about having the output from the O2 sensor go through the PLC is that I can have the PLC sound an alarm and lock out diving the boat if the O2 measurement is high or low.</span></div><div dir="ltr" data-setdir="false"><span><span style="color: rgb(0, 0, 0); font-family: times new roman, new york, times, serif; font-size: 16px;"><br></span></span></div><div dir="ltr" data-setdir="false">For my boat I sound a high O2 alert if O2 is > 23% and a low O2 alert if the O2 is <18%. These alarm levels have worked pretty well.</div><div dir="ltr" data-setdir="false"><span><span style="color: rgb(0, 0, 0); font-family: times new roman, new york, times, serif; font-size: 16px;"><br></span></span></div><div dir="ltr" data-setdir="false"><span><span style="color: rgb(0, 0, 0); font-family: times new roman, new york, times, serif; font-size: 16px;">Cliff</span></span></div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false"><br></div></div><div style="font-family: times new roman, new york, times, serif; font-size: 16px;"><br></div>
</div><div id="ydp7f7b92bfyahoo_quoted_7194629844" class="ydp7f7b92bfyahoo_quoted">
<div style="font-family:'Helvetica Neue', Helvetica, Arial, sans-serif;font-size:13px;color:#26282a;">
<div>
On Monday, August 19, 2019, 08:15:04 AM CDT, Jon Wallace via Personal_Submersibles <<a href="mailto:personal_submersibles@psubs.org">personal_submersibles@psubs.org</a>> wrote:
</div>
<div><br></div>
<div><br></div>
<div><div id="ydp7f7b92bfyiv1727708494"><div><div class="ydp7f7b92bfyiv1727708494ydpf71027dcyahoo-style-wrap" style="font-family:times new roman, new york, times, serif;font-size:16px;"><div></div>
<div dir="ltr">Hi Alan,</div><div dir="ltr"><br clear="none"></div><div dir="ltr">I still think the major advantages of the optical sensor is the digital output and it's expected life of 5 years. But I have a hard time getting past the 25% scale because there's a lot of "head room" between 25-100% and you just don't know where you are in that range. My concern is not from a biological perspective since short term high levels of O2 are not an issue at 1-ATM, but from an environment one...high levels of 02 start representing a real fire danger.</div><div dir="ltr"><br clear="none"></div><div dir="ltr">Calibration in free air is easiest and why handheld (mobile) sensors are convenient. I'm not sure I would trust just opening the hatch to get fresh air in the vessel, unless you forced fresh air inside with a fan or something. Getting into an open air environment would be best.</div><div dir="ltr"><br clear="none"></div><div dir="ltr">Jon</div><div dir="ltr"><br clear="none"></div><div><br clear="none"></div>
</div><div class="ydp7f7b92bfyiv1727708494ydp7e23d944yahoo_quoted" id="ydp7f7b92bfyiv1727708494ydp7e23d944yahoo_quoted_6386327282">
<div style="font-family:'Helvetica Neue', Helvetica, Arial, sans-serif;font-size:13px;color:#26282a;">
<div class="ydp7f7b92bfyiv1727708494yqt5816499019" id="ydp7f7b92bfyiv1727708494yqtfd50400"><div>
On Monday, August 19, 2019, 05:58:02 AM EDT, Alan via Personal_Submersibles <<a href="mailto:personal_submersibles@psubs.org">personal_submersibles@psubs.org</a>> wrote:
</div>
<div><br clear="none"></div>
<div><br clear="none"></div>
<div><div id="ydp7f7b92bfyiv1727708494ydp7e23d944yiv9274357921"><div><div></div><div>Jon,</div><div>am having second thoughts about the optical O2 sensor.</div><div>I was given data that said calibration was needed after a while because of a drift</div><div>caused by temperature fluctuations.</div><div>Although calibration would only need to be done every year or two, I would </div><div>need to write a program for that. And I would need to write a program for</div><div>calibration of galvanic O2 sensors if I went with them. So although the optical</div><div>sensors are factory calibrated, this is not going to be that much of an advantage</div><div>to me. They would also be more difficult to source than the standard sensor.</div><div>The optical sensors only have the 0-25% O2 range but I can't imagine going over</div><div>25%. The optical sensor has better accuracy, as all the information I have seen </div><div>on the galvanic sensors say they have an accuracy of +/- 2% on full scale.</div><div>I wonder what procedures Psubbers take with regards to checking calibration</div><div>of their O2 sensors. I am thinking a best practice would be to leave the hatch</div><div>open before a dive & check that the O2 reading corresponds to the standard</div><div>level of O2 in air.</div><div>Cheers Alan</div><div><br clear="none"></div><div><br clear="none"></div><div><br clear="none"></div></div></div></div>
</div></div><div class="ydp7f7b92bfyiv1727708494yqt5816499019" id="ydp7f7b92bfyiv1727708494yqtfd04620">
</div></div></div></div><div class="ydp7f7b92bfyqt5816499019" id="ydp7f7b92bfyqtfd03842">_______________________________________________<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>
</div>
</div></div></blockquote><blockquote type="cite"><div><span>_______________________________________________</span><br><span>Personal_Submersibles mailing list</span><br><span><a href="mailto:Personal_Submersibles@psubs.org">Personal_Submersibles@psubs.org</a></span><br><span><a href="http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles">http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles</a></span><br></div></blockquote></body></html>