Best sensors for measuring fuel flow rate in vehicles

@beacon_dave 

Thanks, your inputs are valuable. Accuracy +-1% is what I'm aiming.  To start with, I agree, I'm using low cost flow rate sensor but how true it is that the overall Turbine flow rate sensors have accuracy of more than +-5% as claimed by many above. If so, how come devices like this or this are commercially viable? All i'm trying to do is make the product cheaper & for end users which makes it a buyable product rather than fitting it in the trigger nozzle. 

What is the purpose of venturi tube. Is it to measure flow or just to maintain a steady rate?If it is just to maintain the steady rate, then e.g. 'A device like a fuel tank cap which measures and displys the readings of fuel volume pumped'. The fuel getting flown from the nozzle with the venturi tube to this device is already flowing at a steady rate, so why we would need it?  

I didn't understand the point why it needs to be hidden from the scammer? The fuel pumps have the liability to give what is paid & all this device is going to do is to give an assurance that there is no short-changed. 

@Gough, Accuracy +-1% is what I'm aiming.  To start with, I agree, I'm using low cost flow rate sensor but how true it is that the overall Turbine flow rate sensors have accuracy of more than +-10% as claimed by many above. If so, how come devices like this or this are commercially viable? All i'm trying to do is make the product cheaper & for end users which makes it a buyable product rather than fitting it in the trigger nozzle. 

The original water flow meter you linked to appeared to have an accuracy of +/-3% and as previously suggested that will likely be under ideal conditions e.g. at a certain installed angle and at a certain flow rate. That will be still be viable for many applications.

I think that petrol pumps tend to use a piston type flow meter rather than a turbine arrangement and they will also likely be well matched to the flow rate of the pump passing the liquid through them. They are likely to be serviced and calibrated at regular intervals as well.

Hence why I was wondering about the accuracy necessary to make it viable over say the existing fuel gauge. At what point do you challenge the reading on the pump.

If you doubt the advice given about accuracy, then perhaps do some experiments with some of the cheaper flow meters and see what accuracy you can achieve under different conditions. Perhaps also get a piston flow meter from an old decommissioned petrol pump and try that for comparison.

The venturi tube controls the trigger mechanism in the petrol pump nozzle. It shuts off the pump when the tank is full or if you get blow-back.or if the tank's venting is faulty. It's a simple principle but the design is quite intricate. If your design attempts to couple a petrol pump nozzle directly into the input of a flow meter, you may find it affects the functioning of the venturi tube and shuts off the pump in the process. Some tubes vent to the outside of the nozzle through a small hole, others are contained inside of the nozzle itself so any design needs to accommodate the different types. 

A scammer wants to make money so if they see such a device fitted then they may not want to serve you and wave you on so as they can scam the next person. Others may think it simply looks like a suspicious device and refuse to serve you. Depends on the type of petrol station it is though - attendant at the pump, self-serve but pay the attendant in the exit booth, or self-serve, pay with card at the pump. If it is hidden from view, then you avoid these sorts of scenarios.

I've already told you. I've used these sensors in various versions - brass, plastic, clear plastic ... they're all not very accurate especially in case of varying flow rates or flow rates that include rates below the minimum that the sensor is capable of. I used them in a number of applications including dispensing water for developing countries - we couldn't get it to accurately fill a 600mL bottle even with a consistent flow rate - even if you do calibrate it once and get it right, it doesn't take too long for it to drift away from the calibrated value due to changes in temperature, or movement of the sensor, or wear, or biofilms in the water, etc. Similarly, I have wanted for better, cheaper sensors for a long time ... but to no avail.

Devices like that aren't really viable ... I don't see any reputable company ever selling them. I don't see anyone who cares ever using them either. The fact they need to be calibrated first and only have 0.5% repeatability (i.e. discounting accuracy, the relative error is 0.5%) is pretty shocking to me.

You need to think carefully about the basics of metrology - as a rule, you can't use a clock of the same sort to check if a clock is accurate. You need something with more accuracy - usually 10x to 100x more accuracy to verify. Otherwise, all you're doing is measuring with very little certainty as the errors can go both ways for both devices in a nearly equal manner.

Why are you asking questions of people over and over when you could buy 20 of them and test them out yourself with your own code and a calibrated pumping system to see what the errors are like yourself? Do some of your own science - don't expect people to have all the answers you seek!

- Gough

But since you asked - this is probably the closest thing to what you're looking for that I can find on the open market with a remote display:

https://www.digiten.shop/products/digiten-lcd-flow-control-meter-g1-2-fuel-oil-gasoline-diesel-milk-gear-flow-counter

Claims a 0.5% accuracy just like your Chinese stuff because it's likely built around the same thing.

I have some of the 2%-rated Digiten stuff that is the same as the YF-201C /YF-S201 and similar Chinese flow sensors ... I measured the accuracy in a university lab to about 10-12% under a fixed flow rate, which is why i wouldn't trust the claimed accuracy regardless. That being said, you might get lucky ...

Otherwise, you'll just have to build your own as I previously explained.

- Gough

Have you got any conceptual sketches of what the new fuel cap might look like ?

Fuel caps tend to vary between cars and not only that but the recess/access flap they are fitted into/behind tends to vary as well. Hence why pump nozzles tend to be the design that they are, to reach into awkward places.

Coupling onto the car's fuel tank filler pipe with a good seal might get you a more compact device but then it might not be so universal.

If the idea is to be able to pass the pump nozzle through the fuel cap and into the existing filler pipe, then that means that the flow sensor will somehow have to end up inside the car's filler pipe. Perhaps spring-loaded so the end of the nozzle pushes it out of the cap into the filler pipe and then retracts it back into the cap after removing the pump nozzle. Otherwise the new cap requires its own filler pipe  

If you want to keep it universal, then you are probably going to have to cut the end off a standard pump nozzle, cut the end of the filler pipe off a standard petrol tank and then insert the flow meter between the two sections. The nozzle end fits into the petrol tank filler pipe and the pump nozzle fits into the filler pipe end, with the flow meter and display in some sort of housing the middle.

A capacitive sensor could do the work fuel-level-sensors

The best method for measuring fuel is a capacitive system. This is the same system that is used on aircraft. You need a minimum of two cap sensors, one is in the bottom of the tank and is used for calibration, or weight (you have to know the specific gravity of the fuel). the other sensors are mounted vertically. This sensor is easy to make basically two tubes inside each other and they have holes in them to let fuel flow between and through them. The two tubes are the capacitor, which is measured by a bridge.  here is one blog about a car sensor. The sensor at the bottom of the tank measures fuel temperature, and the dielectric constant, which is performed by a cadensicon.  I found this patent. The rule of thumb is that big planes measure fuel by weight and sport aircraft, and your car measure fuel by gallons. 

The following is from the Federal Register. Caveat: This system has been used on military aircraft for decades, without incident, To be fair the only planes that had incidents were on Boeing 777 and 737. so the moral of the story uses low-voltage and currents in your system.  -CAH

DEPARTMENT OF TRANSPORTATION Federal Aviation Administration 14 CFR Part 39 [Docket No. 2002–NM–119–AD; Amendment 39–13392; AD 2003–25–09] RIN 2120–AA64 Airworthiness Directives; Airbus Model A300 B4–600 Series Airplanes, Model A300 B4–600R Series Airplanes, Model A300 C4–605R Variant F Airplanes, and Model A300 F4–605R Airplanes AGENCY: Federal Aviation Administration, DOT. ACTION: Final rule. SUMMARY: This amendment adopts a new airworthiness directive (AD), applicable to certain Airbus Model A300 B4–600 series airplanes, Model A300 B4–600R series airplanes, Model A300 C4–605R Variant F airplanes, and Model A300 F4–605R airplanes. This AD requires modification of certain components of the 115 Volts Alternating Current (VAC) supply wiring and of the fuel gauging system. This action is necessary to prevent short circuits between 115 VAC wiring and certain fuel system electrical wire runs with subsequent overheating of the cadensicon sensor thermistor or fuel level sensor, which could be great enough to ignite fuel vapors in the fuel tank and cause an explosion. This action is intended to address the identified unsafe condition. DATES: Effective January 27, 2004. The incorporation by reference of certain publications listed in the regulations is approved by the Director of the Federal Register as of January 27, 2004. ADDRESSES: The service information referenced in this AD may be obtained from Airbus Industrie, 1 Rond Point Maurice Bellonte, 31707 Blagnac Cedex, France. This information may be examined at the Federal Aviation Administration (FAA), Transport Airplane Directorate, Rules Docket, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC. FOR FURTHER INFORMATION CONTACT: Dan Rodina, Aerospace Engineer, International Branch, ANM–116, FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington 98055–4056; telephone (425) 227–2125; fax (425) 227–1149. SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an airworthiness directive (AD) that is applicable to certain Airbus Model A300 B4–600 series airplanes, Model A300 B4–600R series airplanes, Model A300 C4–605R Variant F airplanes, and Model A300 F4–605R airplanes, was published in the Federal Register on September 8, 2003 (68 FR 52862). That action proposed to require modification of certain components of the 115 Volts Alternating Current (VAC) supply wiring and of the fuel gauging system. Comments Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received. The commenter supports the proposed AD. Conclusion After careful review of the available data, including the comment noted above, the FAA has determined that air safety and the public interest require the adoption of the rule as proposed. Cost Impact The FAA estimates that 70 airplanes of U.S. registry will be affected by this AD, that it will take approximately 29 work hours per airplane to accomplish the proposed actions, and that the average labor rate is $65 per work hour. Required parts will cost approximately $8,938 per airplane. Based on these figures, the cost impact of this AD on U.S. operators is estimated to be $757,610, or $10,823 per airplane. The cost impact figure discussed above is based on assumptions that no operator has yet accomplished any of the requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted. The cost impact figures discussed in AD rulemaking actions represent only the time necessary to perform the specific actions actually required by the AD. These figures typically do not include incidental costs, such as the time required to gain access and close up, planning time, or time necessitated by other administrative actions. Regulatory Impact The regulations adopted herein will not have a substantial direct effect on the States, on the relationship between the national government and the States, or on the distribution of power and responsibilities among the various levels of government. Therefore, it is determined that this final rule does not have federalism implications under Executive Order 13132. For the reasons discussed above, I certify that this action (1) is not a ‘‘significant regulatory action’’ under Executive Order 12866; (2) is not a ‘‘significant rule’’ under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and (3) will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act. A final evaluation has been prepared for this action and it is contained in the Rules Docket. A copy of it may be obtained from the Rules Docket at the location provided under the caption ADDRESSES. List of Subjects in 14 CFR Part 39 ■ 1. The authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. 106(g), 40113, 44701. § 39.13 [Amended] ■ 2. Section 39.13 is amended by adding the following new airworthiness directive: 2003–25–09 Airbus: Amendment 39–13392. Docket 2002–NM–119–AD. Applicability: Model A300 B4–600 series airplanes, Model A300 B4–600R series airplanes, Model A300 C4–605R Variant F airplanes, and Model A300 F4–605R airplanes; as listed in Airbus Service Bulletin A300–28–6066, dated November 8, 2000; or Airbus Service Bulletin A300–28–6070, Revision 01, dated March 22, 2002; certificated in any category. Compliance: Required as indicated, unless accomplished previously. To prevent short circuits between 115 Volts Alternating Current (VAC) wiring and certain fuel system electrical wire runs with subsequent overheating of the cadensicon sensor thermistor or fuel level sensor, which could be great enough to ignite fuel vapors in the fuel tank and cause an explosion, accomplish the following: Modification (a)Within 4,000 flight hours after the effective date of this AD, modify elements of the electrical wiring to separate the cadensicon wiring from the 115 VAC wiring, in accordance with Airbus Service Bulletin A300–28–6066, dated November 8, 2000. (b)Within 4,000 flight hours after the effective date of this AD, modify elements of the electrical wiring to separate the 115 VAC supply wiring of the fuel gauging system, in accordance with Airbus Service Bulletin A300–28–6070, Revision 01, dated March 22, 2002. Alternative Methods of Compliance (c) In accordance with 14 CFR 39.19, the Manager, International Branch, ANM–116, FAA, Transport Airplane Directorate, is authorized to approve alternative methods of compliance for this AD. Incorporation by Reference (d) The actions shall be done in accordance with Airbus Service Bulletin A300–28–6066, dated November 8, 2000; and Airbus Service Bulletin A300–28–6070, Revision 01, dated March 22, 2002. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from Airbus Industrie, 1 Rond Point Maurice Bellonte, 31707 Blagnac Cedex, France. Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC. Note 1: The subject of this AD is addressed in French airworthiness directives 2002– 172(B) and 2002–171(B), both dated April 3, 2002.

BTW with the above solution you know the volume of your tank at a standard temperature. So the math is not that big of a deal. also, this will give you a fuel rate over time. and in airplanes, you have multiple sensors in a tank as you don't want your meter to change in a climb, or in a bank that is turning, where fluid will move due to both side forces and or centripetal forces, and acceleration.