Just use laser sensor as a tachometer, Connect it with your vibrometer - it is possible in most of the equipment, I hope with your's also.

Thanks for your reply. Is there any such system available which just give me phase (with reference to tachometer only, not cross channel)? This system should be using only tachometer and one accelerometer.

What do you mean cross channel? A simple vibrometer with plenty of useful options I use is Commtest. Have possibility to measure accelerations and phase (via laser tachometer) and has in the software some dedicated options for balancing.

You did not say at what speed range you want to do the balancing. If it is over 1st critical speed and much below the 2nd, you may assume it to be a rigid rotor and use only a vibrometer (Laser or other type) with three point balancing method. With little calculations using vector diagrams it is possible to find the correction mass and its position for a single plane balancing.

Thanks for your replies. Actually I'm interesting in getting absolute phase at certain bearing. I've learnt on many places that balancing is done by using vibration magnitude and phase by using vector method or etc (Without using a dedicated balancing kit). Magnitude can be known by vibrometer but I want to know that how these phases can be measured?

Simple. Use the phase meter made by various companies like B&K (Bruel and Kjear of Denmark.)

Can you please tell me any model or phase meter name? I searched a lot on internet but couldn't find. At last I posted here. It'll be great help if you send me some specific model etc.

Please get into the B&K site and search. I am sure there would be one such device.

I used it long ago. That model is discontinued now. Else you may use any FFT Real time equipment and run it in Transfer function mode (Phase Mode) . You will find a point at a the operating frequency remains fixed on the screen which may be used in phase. Hope this helps.

Abid

There are several approaches:

1) use an optical tachometer as described above. This normally requires reflective tape be positioned somewhere on the rotor or shaft that can be observed by the tachometer, but some laser tachometers can recognise the variations in reflected light intensity from a shaft without reflective tape. B&K are one manufacturer, Monarch instruments (USA) and Compact Instruments (UK) may be cheaper. Feel free to contact me if you need help with the spec. Any tachometer with a 'TTL' output will be suitable. this is a positive going pulse of 1V output.

2) If you are balancing a rotating machine that has vibration protection instrumentation fitted there may already be a 'keyphasor' fitted. This is a proximity probe observing a hole notch or keyway in the shaft or rotor to provide a once-per-rev signal. This will provide an output on the machinery protection panel which is a negative going pulse, biased around the probe gap voltage which could be anywhere between -5 and -15V, but will probably be around -9V.

3) If you can see the base shaft at any point, use a stroboscope. Put a mark on the shaft (Or use some easily recognised feature) and mark the casing with the angles. Good strobes can be triggered by a vibration datacollector.

4) If you have a rigid rotor (running below 1st critical), as Ranjan said, you can use the four-run balancing method without phase (for a single plane), which you will find here. If you need to do a two-plane balance you will need seven runs without phase. What are you balancing???

BTW - a simple vibrometer may not give you the correct amplitude - you need the amplitude of the synchronous vibraiton (same frequency as running speed). Is your vibrometer filtered or does it give a power spectrum from which you can extract the running speed component.??? Furthermore, if you are using proximity probes, the synchronous probe signal may have an additional vector component due to the glitch - but you can easily measure this at low speed and do a vectorial subtraction.

Best regards & good luck

Andy

D'oh! forgot that link - try:

http://www.vtab.se/PHP-NBoard/html/images/materiali/Forum2/HTML/002710.html

and also, for a site which has a calculator:

http://www.vibronurse.com/NoPhaseBalance.html

Thanks you very much Andry. I've got a balancing kit now which have everything for balancing. Anyway, thanks you very much for your reply. And thanks you all who replied and helped.

If you are balancing in a single plane - i.e. a "short" rotor - there is a method than uses timed oscillation- it is described in a recent issue of Maintenance+Engineering magazine (UK). The only instrument you need is a stopwatch or your mobile phone. I have even used it on pump impellers, but learnt it on overhung fan-type coal mills back in ancient times (1964!).

Thanks you sir. I'll search on internet for this method. If you have any link or reference, please share.