Is it correct to use a accelerometers for creating the orbit plot or it is mandatory to use only proximity probe for creation of orbit plots.Waht is the general procedure adopted in the industry for creation of orbit plots.

For a true orbit you should use proximity probes, but i have had good results useing accelerometers.

Regards
Don

Basically, it's voltage in so the analyzer doen't know the source. Typically one looks at rotor dynamics from prox probes (X-Y) and a key phasor. Note the orientation of the X-Y probes and rotation of the machines as the X probe will or should be mounted in orientation with the direction of rotation. But, often machine design or the installer for this reason has placed each probe rolled 45 off TDC. So the X probe is on the side where the rotor climbs; so and if you use accels keep this in mind. There's no one to say you can't use accels.

So you get equally confused trying to interpret orbits using accel´s as with eddy probes? Sorry, couldn´t resist ;-). Olov

I resemble that remark! Why be normal?

I have, infrequently, collected casing orbits using accels to an O-scope. I've tried, also, to apply some of the commonly taught rotor orbit rules to these casing orbits for identifying imbalance, misalignment, etc. (Reference the Vibe Institute Level II chapter on "Orbital and Phase Analysis".) I assume that many of these orbit rules for fault analysis may be used for either rotor or casing orbits.

One of the differences between casing and rotor orbits, I suspect, would be for a rub analysis. A rotor rub commonly shows an external loop, indicating some period of reverse precession. This is due, I believe, to some "rebounding" occurring in the orbit at the moment of the rub. While the rotor rebounds in the direction of reverse precession, I suspect the motion of the casing would be in the opposite direction...in a forward precession as a result of this contact? I am asking...not stating this as fact. I am interested to know of others having experience using casing orbits, and possible differences with that of rotor orbits.

I have used casing orbits many times, but I would suggest that unless the bearing support is very, very flexible, say for a aeroderivative gas turbine, or a large electric motor, that the rules for shaft orbits do not apply to casing orbits.

I find casing orbits to be an excellent way to visualize the relative support stiffness in the X vs Y planes of a machine, but little else.