HELP Finding a low pressure sensor - Page 1
Forum section: electronics / beginners

author: CristianAnd
author_rank: Newbie
timestamp: April 24, 2020, 04:34:32 am
content: Hi, I have a motorcycle that doesn't have a fuel gauge, and I decided to make one by using a pressure sensor connected to the fuel hose. Although this idea it's already in the market, I want to make it myself because I want to use my own skills. See this product made by a company so you know how the system works:https://www.lskelectronics.com/fuelgaugepro1I can do the electronic parts and programming for my project, but I encountered a problem finding the right sensor.I used a regular non-electrical pressure gauge (similar to those tire pressure gauges) to measure a simulated load in a container filled with water. See the link I posted above to know how the gauge is connected. My gas tank can take up to 4.5 gallons = 17 litres of gasoline. So I used a similar amount of water. The gauge needle barely moved and showed a reading of less than 1psi. Knowing that, I started searching on the internet for a gauge that could measure that much pressure. I decided to get a sensor that could measure from 0 to 2 psi or even 3psi. However, the sensors I found were extremely expensive for my budget. Some of them were over 200 US dlls. I found some cheap ones, however, they are surface mounted without any kind of housing and most importantly they don't seem to handle gasoline, which I am really concerned about. Let alone the heat given off by the engine.That's the reason I came here looking for help to know if someone knows a sensor or know where I can get one with the following specs:1- Be able to measure low pressure: from 0 to 3psi2 - Not be damage by gasoline3.- Can handle heat (up 125 Farenheit or 50 Celsius or more if possible)4.- Be cheap. I looking for something around $50 US dlls or lessAgain I just need help finding this critical component for my project. It doesn't matter whether the sensor is analog or digital. I can handle all of that and build the appropriate circuitThanks for your help!

author: StuartA
author_rank: Regular Contributor
timestamp: April 24, 2020, 07:46:48 pm
content: In the UK, the first people I would contact would behttps://www.fluidcontrols.co.uk/, but your budget of $50 may well be an issue. The route I usually take with stuff like this is to ask who/where else would use such a thing, but I cannot think of anything.3psi would support a column of mercury ~6 inches high; use a column of mercury in something like a 1/4 inch Teflon-PFA tube as a capacitive sensorStu

author: StuartA
author_rank: Regular Contributor
timestamp: April 25, 2020, 07:19:39 am
content: This is a "visualisation" I put together with stuff in my garage. The heart of it is a small plastic bottle (1" dia, 2" high) with screw-on lid.Through the lid goes a connection to a syringe - this is a way of pressuring it. Out of the bottom is a 1/8 inch exit pipe - mercury will be pushed up that tube (the welding rod is only there to stop the pipe curling up). What I have not shown is that you'll need a wire to connect into the mercury and you'll need to put something like aluminium adhesive tape on the 1/8 inch to act as a capacity sensor. So, your electronics will need to measure C from say 5pF to 20pF and that will indicate hydrostatic pressure.Best not tell anyone you're thinking about mercury, it spooks people out of all proportion!

author: max_torque
author_rank: Super Contributor
timestamp: April 25, 2020, 09:37:09 pm
content: I can see a ot of problems with this approach, especially as a motor bike "pulls g" straight down it's CofG.........I'm not sure where you got 3 psi from either?3 psi is roughly 1/5th of an atmosphere, a pressure that can support a coloumn of water 33 feet high (10 Meters) , so 3 psi is eqivalent to about 6.5 feet (2 m) of water. Gasoline has a specific density of around 75% of that of water, so 3psi would support a column of gasoline nearly 9 feet tall. That is a VERY deep fuel tank on a motorbike.. Hell, it's a deep fuel tank on a ship!!!My suggestion would be to use an off-the-self capacitive "dip tube type" probe

author: SmallCog
author_rank: Frequent Contributor
timestamp: April 26, 2020, 07:35:36 am
content: I believe some white goods like dishwashers use millibar range pressure sensors for water level measuring. A new one would fit your budget if you could identify its range and interface from a service manual but you can probably get one (along with the rest of the machine) for free second hand.Not sure it’s the best way to tackle a fuel gauge on a bike but I’m all for making / trying random things

author: StuartA
author_rank: Regular Contributor
timestamp: April 26, 2020, 12:20:00 pm
content: Quote from: SmallCog on April 26, 2020, 07:35:36 amThat's an interesting idea, but I think they only operate a switch to open/close a solenoid valve, so they don't actually gauge anything. Also, not sure how well it will fair against long term exposure to fuel vapour? Assuming that the bike has an "open" tank rather than foam-filled, the propellant is going to slosh around like crazy, so whatever sensor it uses will need to cope with that - one way or another. I'm a car guy and never owned a bike - no doubt this problem has been addressed many times before?

author: DTJ
author_rank: Super Contributor
timestamp: April 26, 2020, 12:56:14 pm
content: The 3PSI seems off a bit.Say the tank is vented (it's not subject to pressure or vacuum dues to emission control fittings);Fuel may be 6 inches deep = 6 inches water pressure x 0.7 (fuel density) = 4 inches pressure = 0.15 PSI = 1kPaIf you want to pursue this path I'd see what I could repurpose from another motorcycle fuel system.Buying a pressure sensor with a suitable stainless diaphragm and then frigging around with signal conditioning is going to be a PITA.