Non invasive sensor for hydraulic lines

Why not tap in a conventional gauge in line that could be read remotely ,like electric meters are currently being read ?

We could, but its not what we are trying to achieve. Imagine a piece of complex hydraulic equipment, thousands of hoses over hundreds of metres, the ultimate bag of spaghetti. Very hot, very noisy, extremely dirty and dangerous - underground coal mine. We want a piece of hand held kit, that just like an electrician with an inductive ammeter, can quickly and non invasively-test any hydraulic line for residual static pressure BEFORE he cracks it.

Its just not feasible to tap into every line. Electricians don't.

Mark

Interesting idea. Before an analysis of feasibility can be performed, the CR4 community will need a few parameters. Pipe rating, pipe material, pipe diameter, high and low pressures, accuracy required.

In your application, the pipes might be purposely rated so that they are under very little stress. If this is the case, it might be difficult to measure any significant physical change.

Installing strain gauges at specific points might be a compromise that you could live with.

+1

There are to much unknown parameters.

Maybe it is possible to understand internal processes through indirect parameter?

Vibration for example or Ultrasound Noise could be used. This is crude technique. It is need big experience and good statistical sampling.

Visit

www.bksv.com or www.bkvibro.com

A noninvasive continuous pressure meter that reproduces the pressure waveform, comprising an inflatable flexible cuff which incorporates an infrared transmitter and receiver and electronic circuitry connected to the transmitter and receiver and controlling a dynamic compressor. The dynamic compressor comprises a bellows which is compressed by a motor electrically activated by the electronics. The bellows is connected to the inflatable cuff by a flexible tube to which is also attached an electronic pressure transducer, in such a way that the hollow spaces of the bellows tubing, electronic pressure transducer, and cuff form one complete closed air-filled space. When the inflatable cuff is wound around the tube and the electronics are properly adjusted, the signal from the electronic pressure transducer will very nearly correspond to instantaneous pressure.

This is all based on the caveat that the line is under some level of stress - no stress then no measurement.

Just an idea that may or may not work in practice

Hi MLB,

we did this in an experimental approach with capacitive sensing.

Strain gages may be good too if bending stress is eliminated.

Inductive or optical methods will be possible too.

There are also existing pressure to frequency transducers.

So please specify your needs, then a deeper discussion will be needed.

Any of these methods need a section of the hydraulic line be made of a very high strength, very high quality elastic material to rely on expansion as a measurement of pressure. (No creep, no overload induced bias, low TC, no stress relaxation.)

It is not a straightforward approach but it is possible.

I have designed flexures for gyroscopic instruments, for accelerometers and tilt-sensors, for force sensing, to be used as scanner in an infrared imaging satellite and in nanometer resolution optical adjustment.

RHABE

(consultant in precision engineering and measurement)

All,

I believe that MLBennett's requirement is to take measurements on installed piping that is in operation and that taking it off line to install instruments or test sections is not an option.

Dear All,

Thanks for all your inputs, much appreciated. Snave, you're on the money. In an underground mining environment the hydraulic lines for the roof supports are like spaghetti (hundreds and hundreds of them on a long wall of several hundred metres). It is dirty, the place is full of noise, dark, etc etc etc. 2,000 psi plus. If you've never been down a longwall coal mine, take the opportunity if you get one - its a real eye opener.

We are seeking a way for a technician to simply test any standard high pressure flexible hydraulic hose (you are all familiar with them I'm sure) to tell if there is either static or dynamic pressure in the hydraulic line before attempting to do any work on the system. Its all about safety, speed, reducing needless breaching of hydraulic systems etc.

If fluid is moving we may be able to isolate its signature acoustically via a peizo sensor touching the hose and a bit of software. If its static pressure its much harder, especially in low(er) static pressure situations where pressure may not be high enough to strain the hose casing in any measurable way. Maybe a simple adhesive tape that changes colour when stretched, applied to every hose when manufactured or replaced?

It would have to work with all current existing flexible high pressure hydraulic systems. If it works it will have applications in earthmoving plant etc etc etc.

All in all, a very interesting technical challenge. But hey, that's why we do it.

Mark

Mark,

The piezo to listen to the pulses from the pump is definitely a possibility for detecting dynamic pressure. You would need to configure the sensor or controller to only record actual pulses and exclude conducted noise from adjacent hoses. As you would know this makes the listen through the screwdriver method less than reliable. The device that SKF use for their Shock Pulse Monitors for bearings could be worth an investigation, it detects shock pulses from bearing damage and contamination but ignores noise and vibration. For static pressure hose stiffness is a sign of pressure. This can be measured by force over length, like they do for mechanical stress graded timber. The source of error is unknown hose age / brand / stiffness, so much research would be required for accuracy.

Regarding Exia (IS) capability there is no need to exclude strain gauges, peizo or accelerometers. The most experienced manufacturers for Exia in Oz would be Ampcontrol and Bramko.

Dear MLB,

make an artificial finger to be pressed onto your hydraulic line, or two fingers to tweeze it. Put a vibratiing force on it. Measure radial deformation.

The force/deformation (to be sweeped in frequency) will give a direct measure of inside pressure plus radial stiffness at zero pressure.

Use phase sensitive demodulation to reject most noise from other sources than excited vibration.

If not enough signal at low pressure is existing, then elongate the "fingers" lengthwise so that a longer section of your hydaulic line is tweezed.

This will fulfil your requirements.

Make a first trial with your thumb on your car tires. I wish you a good success.

RHABE

If it is a flexible hose that you need to determine if it is pressurized or not. Would it not be possible to build a fixture that clamps onto the OD. The fixture would attempt to compress the hose on opposite sides a small percentage of the diameter using a predetermined amount of force. If it is pressurized, it won't squash much.

Just an idea. You can probably use a clamp on ultrasonic flow meter and have the flow readings converted into pressure reading by installing a PLC.

Yes,a clamp-on ultrasonic flow meters is a better Choice.

Abest Technology and Instruments

If you have searched Global Spec and not found devices which meet your needs, then in order for any of us to effectively help, you must supply all of the telemetry requirements, pipe specifications, operating conditions, temperatures, pressures, measurement ranges and a multitude of other data so one (or more) of our talented contributors can offer a source or design a potential solution to your problem.

Non- Intrusive - Like open up the pipe and if it keeps squirting in your face, then there's a little bit of pressure, if it blows off your face then it's a lot of pressure....