Underwater Speed Measurment

I think the unit is full coverd and you can`t put in any cables inside the casing.

I think the motor will sound when it is working, is there any way to put in a microphone and listen to it? The sound frequency can bee translated to speed. Maybee you must have a DSP for processing the signal.

Anders

Hydraulic fluid differential pressure between the feeding port and the return line of the motor is easily translated into speed. All you have to do is calibrate the no-load /full load conditions. Usually you can obtain this info from the motor manufacturer. The pressure gauge is calibrated directly into RPM.

Wangito.

You don't give any details on the motor, but if it is a positive displacement motor (or nearly so) which is likely, you can measure RPMs by measuring the flow in units per minute going through it, at either the supply or discharge end and dividing by the displacement of the motor per revolution (in the same units of course). The motor's displacement is part of its specifications.

Measuring the pressure drop (differential) across the motor is an indirect and far less accurate way of obtaining the speed, and can be error prone if changes in load take place, depending in part on the type of motor. This (the pressure drop) method can yield good results, but you have to calibrate it which apparently isn't possible in your case.

Regarding my post #3 (above):

The additional advantage of measuring the flow is that provided you can get the motor specs (displacement), everything can be done above the water, since the flow going through the motor is obviously the same at all points in that circuit, and you only have to break the circuit at one point to install the flow measuring device.

hello sir

u can measurethe rpm of ur under water motor by keeping strain gauges as the amount of strain is proportional to the pressure and accordingly the rpm

Hello hesham,

do you want to measure the underwater speed of a motor-driven unit (in meters/sec) or the rotations per minute of the motor ??

The rpm values can possibly be determined very simple (depends on motor type) by measuring the ripple of the motor current which indicates a frequency term.

The underwater speed of a unit can be measured by ultrasonic sensors (calibration depending on salt-water or not).

regards uweka

uweka:

Try re-reading the question!

Regards,

Greg