Measurement-computing Medallion Rotate rev.2.3 Manual de usuario descargar pdf (Pagina 23)

October 2000 Medallion Rotate Manual

APPLICATIONS

Processing the tachometer signal results in an RPM curve describing the

instantaneous machine speed. Medallion Rotate uses a spline-fit process to

create a smoothed speed curve from the tachometer signal. The speed curve is

a high-resolution view of the machine speed.

You can use this smooth speed curve to diagnose problems related to the

speed or speed change of a machine. This provides an independent verification

of the machine speed, since some process control indicators suffer from “flat

spots” in their response to speed changes.

Other applications include the following:

• Examining the effects

of changing load or

other process dynamic

on the speed.

• Determining the effect

of power fluctuations

(brownouts) on the

speed.

• Speed profiling on a

multi-drive machine to

determine if there slip at any of the drive units (over- or under- speed).

• Threading analysis on a sheet mill.

• Evaluating the actual machine speed against the ideal constant speed.

• Verification of the speed change between two points to determine the

elongation of the material, such as in a rolling mill.

• Examination of the speed curve to diagnose speed oscillation due to a

loose coupling, hunting motor, or other cause.

INPUT SIGNAL REQUIREMENTS

The input signal to the tachometer analysis is a tachometer or other

machine speed signal. As with all analysis techniques, the better the input

signal, the clearer the results—so a good, clean tachometer signal is essential.

For a pulsed tachometer signal (non-contact probe, encoder, …) the

sampling rate must be at least 2.5 times the maximum frequency of interest to

avoid aliasing effects. A good rule of thumb is to use 5–10 time oversampling of

the tachometer pulse frequency (not the machine speed) to get good, clean

tachometer pulses. For example, if a tachometer produces one pulse per

revolution on a 600 RPM machine, sample the tachometer data at a rate of 50–

100 samples/second (Hz).

For a DC voltage tachometer signal, you must know the machine speed

when the signal is at 0 volts. For some sensors, the DC speed signal falls to 0

volts before the machine is at a standstill.

600 RPM x

1 minute

60 seconds

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