We need to build or buy economical submersible pressure transducers - Page 1
Forum section: electronics / general

author: viper
author_rank: Regular Contributor
timestamp: January 04, 2022, 10:15:40 pm
content: We are working on a small volume product where we need to monitor the pressure of water. The problem is the sensor, cable, etc, needs to go into the hole. This seems the change the price radically, by a factor of 100 for stuff that we can find. For this reason, we have considered trying to just source PCB transducers and we will build the housing system. That is assuming affordable sensors cannot be found.We need to read pressures to about 250psi at the very max, but typically only 100psi. I am curious if anyone knows where to shop for either the PCB unit, or complete sensor unit? Yes, places like Omega have them, but at prices that are beyond the entire budget for the sensor alone.As for accuracy, really about 1% is more than fine for this. Any added resolution is great, but right now we are focused on price, and reliability as driving factors.

author: SmallCog
author_rank: Frequent Contributor
timestamp: January 04, 2022, 10:40:31 pm
content: Druck make the sensor module used in their own units as well as their competitorshttps://in-situ.com/en/level-troll-500-data-loggerReading between the lines it sounds like you're making a similarly submersible (irrespective of function) product.Perhaps see if Druck will sell you the modules too?PM me if you want to see inside the InSitu unit I've got a dead one I cut open to see what was inside

author: viper
author_rank: Regular Contributor
timestamp: January 04, 2022, 11:23:57 pm
content: Thanks! You bet, i'd love to see the inner workings to get some ideas. However, we don't really need data logging inside the sensor as such. Design could go a different way though. Certainly don't need a titanium housing for our needs though. Appreciate the feedback. Seems very tough to find what we need.I thought about reaching out to Honeywell tomorrow as well as Delphi. Actually Delphi was quite receptive in years back on another project.

author: DC1MC
author_rank: Super Contributor
timestamp: January 05, 2022, 12:07:09 am
content: A price range will be nice, there are no heap submersible sensors at this range of pressures, but maybe the chinesium ones are good enough:https://www.robotshop.com/de/en/bar100-high-resolution-1000m-depth-pressure-sensor-r2.html

author: viper
author_rank: Regular Contributor
timestamp: January 05, 2022, 09:33:15 pm
content: Thread in water and oil pressure sensors in stainless housings can be bought for less than $10 at retail. FF to "submersible", and we are talking $1000.What I conclude from that is the electronics and/or transducer sections are probably similar, but you need a housing and such to seal everything. That is something we can handle, but would like to purchase the electronics/sensor. We intend to read the sensor data remotely via a long sealed cable.We have played with the retail sensors and though we can make them work, we are left to dismantle and hack sensors. It would be much easier to simply buy the sensor and PCB inside of one of these and construct our own sensor.Obviously all of this is assuming we cannot store buy a sensor to suit our needs. As for target price, we don't have a firm number on that but south of $100. We are also in the manufacturing biz so designing/building the housing is really not a concern, but I don't like remaking the wheel.I'd be open to just designing a custom PCB for the sensor unit but then we are taking on another task to build the sensor complete, calibrate it, etc. Rather buy if we can.

author: DC1MC
author_rank: Super Contributor
timestamp: January 05, 2022, 10:38:15 pm
content: The price difference between plugin and submersible sensors is HUGE, as one that I have worked on geophysics exploration equipment I can share with you our low cost solution for pressure measurement in the hole:We have used strain gauges (at that time called "tension marks") stamps like these (check KA series):https://www.zemiceurope.com/media/Documentation/Straingagescatalogue.pdfThey were glued on a case made of special material (here will be 95% of the cost) and connected to a simple VCO that was delivering a frequency proportional with the pressure, that was quite an ingenious circuit, but you don't have to care as there are many IC that are specialized for strain gauges:https://www.ti.com/tool/TIPD170The PCB are plenty and dirt cheap:https://www.elecrow.com/strain-gauge-module-p-735.htmlThe only issue here is designing the shape of the case that will elastically deform with high repeatability and seal it properly, at that time it was a wonder of manual calculating mechanical engineering and analogue VCO with curve compensation, but nowadays a cheap blue pill or RPi will do it. Sealing it along with electrical pass-trough will still be a huge problem.So here you have all the electronics you need (one can test this quickly for almost nothing in costs getting a number of sensors and using a tin can as sensor body. Let's see now your 200bar 90USD sealed case.Cheers,DC1MC

author: Marco
author_rank: Super Contributor
timestamp: January 05, 2022, 10:44:58 pm
content: Quote from: DC1MC on January 05, 2022, 10:38:15 pmWhat's wrong with potting?

author: DC1MC
author_rank: Super Contributor
timestamp: January 05, 2022, 10:53:18 pm
content: Quote from: Marco on January 05, 2022, 10:44:58 pmI don't know, I'm an electronics guy, I hate potting by default

author: IanB
author_rank: Super Contributor
timestamp: January 05, 2022, 10:57:46 pm
content: It might be interesting to think about the physics of this.A pressure transducer is going to measure the difference in pressure between the sensed pressure and a reference pressure, probably by deforming some kind of material and looking at its changing electrical properties.If the sensor is in the open, then the reference pressure is easy, it can be atmospheric pressure.If the sensor is submerged and down a hole, then what is the reference pressure? The sensor has to somehow be hermitically sealed, and presumably has to contain some kind of internal known pressure to compare against, which is stable over a long working life, and relatively insensitive to temperature and so on.This might illustrate the difference in cost of such sensors. I wouldn't say you could just pot an open environment sensor, because you might stop it working if you did that.

author: DC1MC
author_rank: Super Contributor
timestamp: January 05, 2022, 11:05:14 pm
content: Quote from: IanB on January 05, 2022, 10:57:46 pmWe've had an air bubble trapped there and on the whole "pole" that was inserted in the drill hole there was also a temperature sensor to compensate the change in the internal bubble, nowadays one can possibly use one of these cheap Bosch absolute pressure and temp sensors inside of the bubble. Sometime the case was cracking and the pressure was doing wonders to the little PCB that was there.

author: Gregg
author_rank: Super Contributor
timestamp: January 05, 2022, 11:32:16 pm
content: If you are going to have wires exiting the pressure vessel, why not use a thin tube with some sort of bladder or bellows on the end? It shouldn’t be too hard to attach an external pressure sensor, fill the system with a compatible liquid and have atmospheric pressure as the reference pressure.

author: DC1MC
author_rank: Super Contributor
timestamp: January 05, 2022, 11:36:30 pm
content: Quote from: Gregg on January 05, 2022, 11:32:16 pmThis may also work, but all in all it will put the price way over the target of 100USD.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: January 05, 2022, 11:39:03 pm
content: There are commercially available pressure and temp transducers used for fishing.Some of these are meant to goon the "cannonball" on an outrigger and are quite sturdy.Here is one:https://www.ebay.com/itm/353180164887?chn=ps&norover=1&mkevt=1&mkrid=711-213727-13078-0&mkcid=2&itemid=353180164887&targetid=4580702890871448&device=c&mktype=&googleloc=&poi=&campaignid=418640321&mkgroupid=1233652283797640&rlsatarget=pla-4580702890871448&abcId=9300602&merchantid=51291&msclkid=29e7f78baa4f1cfe8750965d8027da67

author: DC1MC
author_rank: Super Contributor
timestamp: January 05, 2022, 11:42:42 pm
content: Quote from: Wallace Gasiewicz on January 05, 2022, 11:39:03 pm"Range: 0 ~ 30 bar"A bit different from 0-200bar, don't you say?

author: viper
author_rank: Regular Contributor
timestamp: January 06, 2022, 12:01:49 am
content: I will comb back through the responses. Thanks guys! I just wanted to update that I 'did' find what I would consider to be about what we are looking for, but to be right honest, the complete Ahole at Amphenol done killed that one! If he was hired to lose business, he is good at it! Zero help, doesn't know the product, won't find out, no sh*ts to give....But if someone has seen something similar by another OEM, I'd like to take a look.But I do think that we might give these other off the shelf sensors another look at how to seal them. We did not want to mess with worthless plug terminations that we will have to pot anyway, but we might find another way. We torn down the sensors to solder them, but that is not practical for anything but R&D.

author: viper
author_rank: Regular Contributor
timestamp: January 06, 2022, 12:29:26 am
content: Quote from: IanB on January 05, 2022, 10:57:46 pmYou bring up a very good point sir! I am not yet sure, and will now find out, how these 'gauge' sensors are referenced. That could spoil a few things for us.

author: Marco
author_rank: Super Contributor
timestamp: January 06, 2022, 12:37:27 am
content: Quote from: IanB on January 05, 2022, 10:57:46 pmBuy an absolute pressure sensor and let the manufacturer worry about it? Then you can just pot the electronics?

author: IanB
author_rank: Super Contributor
timestamp: January 06, 2022, 02:00:29 am
content: Quote from: Marco on January 06, 2022, 12:37:27 amWell, sure. But I think the question was about why do pressure transducers suddenly get vastly more expensive when you give this requirement? If there is an inexpensive absolute pressure sensor that satisfies the environmental requirements, then that is presumably what the OP is looking for.

author: viper
author_rank: Regular Contributor
timestamp: January 06, 2022, 02:10:38 am
content: bam! I am on the trail! It seems there is competition in the type of sensor pictured above. Have now found an affordable one with pigtails, which is perfect for us. They are absolute sensing, and I now need to figure out how I can get them in for testing. The one vendor is showing end of the month delivery. Surely someone in the states has these..... I'd like to be a "buy American" fanboy, but we all know none of this is made here, just marked up to line pockets here.

author: SmallCog
author_rank: Frequent Contributor
timestamp: January 06, 2022, 02:32:28 am
content: Quote from: Gregg on January 05, 2022, 11:32:16 pmI’ve actually got an off cut of that sort of cable on my bench!Also has Kevlar in it for weight bearing

author: viper
author_rank: Regular Contributor
timestamp: January 06, 2022, 03:00:57 am
content: Smallcog, would that wire have any markings on it, if we need to do something like that? I've never seen that, but probably was not looking either.

author: SmallCog
author_rank: Frequent Contributor
timestamp: January 06, 2022, 03:54:07 am
content: InSitu make it for use with their sensors.Vega, Druck, and others supply similar vented cables with their sensors (most are potted to the sensor, insitu use connectors)Pretty sure insitu make their own cable in the US, not sure if the others are buying or making cable.For the curious about why you need an air tube:https://www.sensorsone.com/vented-cable/

author: Zoli
author_rank: Frequent Contributor
timestamp: January 06, 2022, 06:10:46 am
content: Quote from: viper on January 04, 2022, 10:15:40 pmQuote from: DC1MC on January 05, 2022, 11:42:42 pm30bar=435psiI think the range is enough.And as somebody who has experience with submersible sensors(of the expensive types), I would recommend to check the potting compound lifespan under water; some has a month lifespan fully cured.@viper: if you want to go with the build-yourself route, for the required accuracy range I would recomend MEMS transducers, potted in PVC tubing, voltage(0-5V) or current(4-20mA) output.