Orbits and SCL Presentation

3

Orbits and Shaft Centerline

2014-01-29 ©SKF Slide 1 [Code]

Purpose of Orbits and Shaft Centerline • Bearing cap vibration information (acceleration/velocity) alone cannot truly indicate a machine shafts’s dynamic responses.

• Eddy current probes (ECP) measure the direct relative response of the shaft to the stationary bearing housing.

• Orbit displays are useful to study the shaft’s relative dynamic movements and clearly show rub, whirl etc. conditions as they happen.

• Shaft Centerline displays show the shaft’s average position with respect to bearing clearance.

Eddy current signals  An Eddy Current Probe (ECP) signal can be broken down into two parts:

• A DC signal which tracks the shaft’s average position. • An AC signal which tracks the shaft’s dynamic motion. The AC part of the signal forms the Orbit display The DC part of the signal forms the Shaft Centerline display.

Orbit and Shaft Centerline

What is an “orbit” ?

 An orbit is the combination of t w o  dynamic time domain signals, creating a graphic of the shaft’s movement around its center point. The two dynamic time domain signals must be acquired at the same time, with the same Fmax and the same number of data samples. Data acquisition systems that can be used to create orbits are: GX, DMx, IMx.

Constructing an Orbit  An orbit plot’s time domain signals are normally formed by ECP signals mounted under a 90 degree angle. Common sensor positions are: 0 and 90 degrees 45 and 135 degrees

   1    1    9    7    5    3    1

  e   m    i    T

Gap

1

3

Time

5

7

9

11

The Orbit Display Indication of  Sensor locations

Customer programmable Banded time cursor allows for precise selection reference of orbit curve anywhere within the time data.

Flash-Blank in indicates direction of orbit precession. (This is not necessarily the same as the direction of rotation

Filtered Orbits

Filtered Orbits with the press of a button cycles through 1x, 2x, 3x and raw. Filtered Orbits provide clarity in the synchronous modes of vibration

Shaft Centerline (SCL)

Speed plotted along the startup center line. Cursor indicates eccentricity value

Vector and Waveform compensation The vibration levels seen as slow-roll are typically caused by one or more of the following:

• Mechanical run out (e.g., scratches, non-homogenous materials) • Electrical run out (e.g., driver noise) • Shaft eccentricity This is not “real” vibration and should be removed from the actual vibration signal. This process is referred to as run out compensation. @ptitude Analyst supports vector as well as waveform compensation.

Orbit & SCL POINT setup Orbit setup allows arbitrary sensor angles. The actual angle is stored with the data so that when probe positions are changed, the data displays remain correct.

Vector & Waveform setup

Vector compensation is supported for the first three vectors 1x, 2x, 3x. Waveform compensation is also supported.

Triax POINT setup Requires triax sensor connected to GX (version 2.0 or higher)

DMx connectivity to @ptitude Analyst

@ptitude Analyst Client

@ptitude Monitor 

@ptitude Analyst Client

Dual channel GX support Multi-channel support for Microlog GX and DMx •

USB (Active Sync) only

•

ROUTE based

•

2-channel and 3-channel (Triax) measurements

•

 Applications…  – Force, Couple and Overhung Rotor Unbalance  – Eccentric Rotor  – Bent Shaft  –  Angular and Parallel Misalignment

Two channel data display

Triax data display

Triaxial support for Microlog GX v2.0

•Triax displays