PCE Instruments PCE-VM 25, Руководство пользователя

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3.5. Rolling Bearing Parameters K(t)
The rolling bearing parameter, also known as the diagnosis coefficient of Sturm K(t), is an approved parameter for the condition analysis of rolling bearings, as defined
in the VDI 3832 (and other guidelines). It is formed by the RMS and peak value of acceleration at a frequency range of 1 to 10 kHz. The 1 kHz high pass filter ensures
that the rolling bearing signal is not overlapped by the vibration of foreign mechanical parts, such as imbalances.
The K(t) value relates the currently measured RMS and peak values to the RMS and peak values at a starting point in time as follows:
within this:
a
rms
(0) RMS for the start point in time (reference point in time) a
pk
(0) maximum value (peak value) for start / reference point
a
rms
(t) current RMS
a
pk
(t) current maximum value (peak value)
The start or reference measurement is subsequent to first-time operation of the bearing. Ideally after the elapse of a certain running-in time. At this point in time the K(t)
value is 1. Following ongoing wear and tear of the machine i.e. running dam-age, the K(t) decreases. During operation the K(t) value may also increase at a low
rate. In this way the condition of the rolling bearing can be classified:
K(t) Rolling Bearing Condition
> 1 Improvement
1 .. 0.5 Good condition
0.5 .. 0.2 Damage progressive influences
0.2 .. 0.02 Advanced damage process
< 0.02 Damaged
Multiplication of the RMS and peak value indicates the acceleration over the course of time as well as changes caused by shock, local damage (pitting), a general
increase in mechanical vibration due to distributed damage
(worn race rings, corrosion, wear of rolling elements) or also insufficient lubrication.
The K(t) value only provides a statement about the condition of the bearing when the trends are viewed. One single measurement does not enable a diagnostic
statement to be made.
The K(t) value is strongly dependent on the rotational speed. It is therefore important to ensure that the rotational speed is the same, when viewing trends.
3.6. Rotational Speed
Alongside vibration the PCE-VM 25 measures the rotational speed by means of an inbuilt contactless optical sensor (Figure 34 on page 25). To enable this, the
instrument needs to be aligned with the rotating part, for which a laser pointer can be used to help with the positioning.
Notice: Please do not cover the sensor apertures on the back of the instrument with your fingers during measurement.
3.7. Temperature
The PCE-VM 25 has an inbuilt infrared thermometer for taking contactless temperature measurements (Figure 34).
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