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Measuring the RPM of an Electric Fuel Pump

Measuring the RPM of an Electric Fuel Pump

Measuring the RPM of an Electric Fuel Pump

(OP)
I am doing some research on electric fuel pumps and I would like to determine the RPM. The motor is enclosed so none of the rotating parts are readily accessible. I have a test bench with a variable voltage DC power supply, back pressure control, and appropriate test fluid so the pumps are partially submerged and running under application conditions. I'd like to know what would be the best equipment (without breaking the bank). I'm thinking some kind of oscilloscope and transducer combination? If so, would I want a stand-alone or PC/USB based unit? Thanks.

RE: Measuring the RPM of an Electric Fuel Pump

I'm thinking maybe a linear Hall Effect chip could detect some of the rotating field leaking out of the motor shell.

But don't run out and buy anything until you snag an EE to help you; this stuff is clearly outside of your comfort zone.

Mike Halloran
Pembroke Pines, FL, USA

RE: Measuring the RPM of an Electric Fuel Pump

Call the mfg??

RE: Measuring the RPM of an Electric Fuel Pump

You will likely be able to find some sort of commutation noise, even from a brushless pump (the electronics still switches), so a decent scope should be able to see it. You will need to determine the relationship between the commutation noise and the speed initially.

RE: Measuring the RPM of an Electric Fuel Pump

What type of motor and how accurate do need the results?

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Measuring the RPM of an Electric Fuel Pump

You're using a variable DC power supply so is this a DC motor? Providing more detail than "a motor" does help.

Look for commutation switching on a DC motor. You might be able to see the pressure pulses from the impeller blades passing the discharge. Both will require knowledge of the pump construction.

RE: Measuring the RPM of an Electric Fuel Pump

(OP)
Basic DC motor with carbon brushes and copper or carbon commutator. It doesn't have to be super accurate.

RE: Measuring the RPM of an Electric Fuel Pump

"What would I need and how would I actually take the measurements? "

That's why you need an EE right there with you.


Maybe there's a market for a site that defines specific problem solving kits. This ain't it.
But let's do some marketing.
IF such a site existed, and would offer you an equipment list and detailed instructions, ... how much money would you pay to compensate the site for the effort of coming up with the documentation?

Mike Halloran
Pembroke Pines, FL, USA

RE: Measuring the RPM of an Electric Fuel Pump

I would use sound or vibration with spectrum analysis. Measure vibration with a small accelerometer, or measure sound pressure with a microphone. The microphone may be more accurate if the vane pass frequency is detected, since rpm = frequency/#vanes. You can use PC internal sound card or external USB sound module. There are several low/no cost spectrum analyzer programs for PC. You need to specify resolution and accuracy needed for the shaft speed measurement so that you can objectively evaluate different measurement methods and cost.

Walt

RE: Measuring the RPM of an Electric Fuel Pump

(OP)
I figured it out using a scope and a current clamp as a transducer. The pulses from the voltage output are pretty well defined and its accurate enough for what I needed.

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