Measuring the RPM of an Electric Fuel Pump

[toddwmps]

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.

 

[MikeHalloran]

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

 

[MiketheEngineer]

Call the mfg??

 

[ScottyUK]

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.

 

[waross]

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

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

 

[LionelHutz]

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.

 

[toddwmps]

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

 

[toddwmps]

Found this write-up which I think describes what I'm looking for:

http://www.precisionmicrodrives.com...commutation-spikes-to-measure-motor-speed-rpm

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

 

[MikeHalloran]

"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

 

[Strong]

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

 

[toddwmps]

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.