PCE Instruments PCE-VM 25 User manual

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User Manual
VIBRATION TESTER
PCE-VM 25
EN Version 1.0
© PCE Instruments

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PCE Instruments contact information
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Contents
English 4
1. Purpose...................................................................................................................... 4
2. Function......................................................................................................................4
2.1. The Vibration Sensor....................................................................................................4
2.2. The Measuring Instrument............................................................................................. 4
3. Measuring Ranges......................................................................................................... 5
3.1. Measurable Vibration Quantities...................................................................................... 5
3.2. Vibration Acceleration................................................................................................... 5
.3. Vibration Velocity.......................................................................................................... 6
3.4. Vibration Displacement................................................................................................. 7
3.5. Rolling Bearing Parameters K(t).......................................................................................9
3.6. Rotational Speed.........................................................................................................9
3.7. Temperature.............................................................................................................. 9
4. The Batteries...............................................................................................................10
4.1. Inserting the Batteries..................................................................................................10
4.2. Switching On and Off.................................................................................................. 10
4.3. Battery Display and Battery Type.................................................................................... 11
4.4. Shut-off Timer........................................................................................................... 11
5. Preparation of Measuring Points....................................................................................... 12
5.1. General Information on Measurement Point Choice..............................................................12
5.2. ISO 10816-1 Recommendations..................................................................................... 12
5.3. VMID Measurement Point............................................................................................. 13
5.3.1. How the VMID Measurement Point Functions.................................................................. 13
5.3.2. Mounting the VMID Measurement Point......................................................................... 13
6. Measurement.............................................................................................................. 13
6.1. Measurement Value Display.......................................................................................... 13
6.2. Selecting the Display Quantity....................................................................................... 14
6.3. Measurement Point Detection........................................................................................ 14
6.3.1. Reading the VMID Data with the PCE-VM 25................................................................... 14
6.3.2. Entering the Measurement Point Text............................................................................ 15
6.3.3. Editing and Deleting Measurement Point Data..................................................................16
6.4. Saving Measurands.................................................................................................... 16
6.6. Viewing Saved Measurement Values............................................................................... 17
6.7. Deleting Saved Measurement Data................................................................................. 18
6.8. K(t) Measurement...................................................................................................... 18
6.9. Frequency Analysis.................................................................................................... 20
6.9.1. Settings................................................................................................................ 20
6.9.2. FFT Memory.......................................................................................................... 22
6.10. Rotation Speed Measurement...................................................................................... 22
6.11. Temperature Measurement......................................................................................... 24
7. Measurement Evaluation with Standard Values..................................................................... 25
8. Setting the Date and Time...............................................................................................27
9. Calibration.................................................................................................................. 27
10. Sensor Check............................................................................................................ 29
11. Headphone Output...................................................................................................... 29
12. Reset Key.................................................................................................................30
13. Connection to a PC..................................................................................................... 30
14. Firmware Update........................................................................................................ 30
1 Spezifikationen....................................................................................................... 32
Limited Warranty............................................................................................................. 33
Declaration of conformity................................................................................................... 34

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1. Purpose
The PCE-VM 25 has been developed, particularly, for the measurement and monitoring of vibrations on rotating machines. The purpose of such measurements is to
monitor the condition of the machine in order to avoid unscheduled shut-down. Furthermore vibration measurement is carried out prior to the distribution of new
machinery and subsequently to repair with a view to quality control and the issuing of product guarantees.
The basis for successful machine condition monitoring is the measurement of the vibration severity over a longer period of time. Measurements are taken at regular
intervals of time and recorded.
The PCE-VM 25 measures and records vibration acceleration, vibration velocity or vibration displacement. The
PCE-VM 25 specification complies with the ISO 2954 regulations for machines that measure vibration velocity and is therefore suitable for measuring, among other
things, machine vibrations in accordance with ISO 10816.
In addition to vibration quantities the PCE-VM 25 also measures the temperature and the rotation speed with contactless sensors.
An external piezoelectric accelerometer is used as the sensor, and is provided together with the instrument.
The PCE-VM 25 is fitted with an electronic measurement point detector (VMID) which enables it to take routine measurements of a large number of measurement
points very effectively. A software package for transferring the measurement data to a PC is also available from PCE.
In the common hierarchy of condition monitoring the PCE-VM 25 is equivalent to ‚Level 1‘. This represents the long term monitoring of parameters with low technical
and personnel requirements.
For fault detection (‚Level 2‘), as a further step, spectral diagnostic measurements are taken, which require a large degree of expertise and sophisticated measurement
technology.
In the development of the PCE-VM 25 value was placed on simple operation and maintenance requirements, which enable trained personnel to operate the instrument
without the need of being specially qualified.
2. Function
2.1. The Vibration Sensor
The PCE-VM 25 operates with a piezo ceramic shear accelerometer. Piezoelectric vibration transducers are characterized by high precision and resolution with great robustness.
The accelerometer of the PCE-VM 25 has an integrated electronic circuit for impedance conversion in accordance with the IEPE standard. At the base of the sensor a magnet has
been integrated for mounting to the measurement point. In the center of the magnet there is a contact point from which the identification number can be read. The measurement
point ID is saved in the available
VMID measurement points.
The coupling surface is protected by a metal cap which attaches to the sensors magnetic base.
2.2. The Measuring Instrument
Figure 2: Block Diagram
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The Figure shows the block diagram. The PCE-VM 25 supplies the IEPE Sensor with 2 mA constant current. At the sensor output, a vibration acceleration proportional
AC voltage arises, which is amplified in the instrument to produce an optimum level. The gain switch-over takes place automatically. The subsequent analogue/digital
converter
is a Sigma-Delta converter with 24 bit resolution.
Further signal processing, such as filtering, integration (for calculating velocity and displacement from acceleration) as well as the RMS and peak value rectification is
carried out in the micro controller. The micro controller also controls the graphic display, the infrared thermometer, the rotation speed sensor, the USB communication
and storing of measurements.
3. Measuring Ranges
3.1. Measurable Vibration Quantities
The PCE-VM 25 can display the vibration quantities acceleration, velocity and displacement. Velocity and displacement are generated by single or double integration of
the sensor acceleration signal.
Furthermore, various frequency ranges can be selected.
The display rate adjusts itself according to the selected quantity in order to ensure that the RMS does not fluctuate even at lower frequencies. The following table shows
the display rates.
Measurand
Frequency Range
Display Rate
Sample Rate
Vibration acceleration
0,2 Hz – 10 kHz
5.6 s
23.438 kHz
Vibration acceleration
3
Hz – 1 kHz
1.4 s
2.930 kHz
Vibration acceleration
1 kHz – 10 kHz
1.4 s
23.438 kHz
Vibration velocity
2
Hz – 1 kHz
1.4 s
2.930 kHz
Vibration velocity
10 Hz – 1 kHz
1.4 s
11.719 kHz
Vibration displacement
5
Hz – 200 Hz
2.8 s
2.930 kHz
3.2. Vibration Acceleration
The PCE-VM 25 has the following frequency ranges for vibration acceleration:
• 0.2 Hz to 10 kHz: full frequency bandwidth of the accelerometer
• 3 Hz to 1 kHz: lower frequency acceleration
• 1 kHz to 10 kHz: high frequency vibration only
In this way specific signal components can be measured whilst others are attenuated. For example, when taking measurements on machines, at a frequency of 1 kHz
to 10 kHz predominantly the running noise of rolling bearings can be monitored, whilst vibrational unbalances are attenuated.
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Figure 3: Frequency response curves for acceleration
.3. Vibration Velocity
Measuring vibration velocity is a common procedure for assessing the running smoothness of rotating machines. Vibration velocity, commonly known as
vibration severity, represents the energy expenditure of occurring vibrations. Vibrations are caused by rotational unbalances, for example as a result of loose
screws, bent parts, worn or slack bearings or dirt residues on the fan blades. Often several factors have a mutually reinforcing effect. Besides rotating machines,
the measurement procedure is also suitable for reciprocating machines.
The specifications of vibration velocity measuring instruments are described in ISO 2954. In the ISO 2954 a band filter for the vibration velocity of 10 to 1000 Hz
is defined.The displayed value of the vibration severity is the true
RMS.
Besides the frequency range of 10 to 1000 Hz, the PCE-VM 25 has a further frequency range for vibration severity measurements from 2 to 1000 Hz. This is
suitable for measurements on slow running machines with a nominal speed of less than 120 min-1 and on reciprocating engines according to ISO 10816-6.
The corresponding PCE-VM 25 frequency response graph can be viewed here:
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Figure 4: Frequency response curves for velocity
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Vibration velocity is formed through integration of the acceleration measured by the sensor.The following formula applies to sinusoidal signals:
Figure 5: Amplitude range for velocity (RMS)
It is evident that in the case of constant acceleration (a) the value of velocity (v) drops at higher frequencies (f). As a consequence the measuring range limits of the velocity
measurements are frequency dependent. (Figure 5).The maximum velocity measurable with the PCE-VM 25 is around 1000 mm/s (RMS). It yields a frequency independent
modulation range of up to 40 Hz. At higher frequencies (RMS) the measuring range limits for acceleration of around
240 m/s² take effect. In the attenuation range of the low pass filter the modulation is further restricted.
3.4. Vibration Displacement
The vibration quantity most easily observed is displacement, also known as the deflection of the vibration. It is formed by double integration of the acceleration. In
comparison to velocity, the practically usable frequency range is even more restricted. On the one hand it requires a high pass filter in order to attenuate low frequency
noise signals, which would otherwise appear amplified in the measurement values because of the double integration. On the other hand, frequencies in the range of
less than one hundred Hertz are so strongly dampened that an evaluable display value is no longer recognizable.
Due to these restrictions, displacement measurements should only be applied where acceleration or velocity is not capable of delivering the desired assessment. The
PCE-VM 25 measures the vibration displacement from 5 to 200 Hz. The frequency response diagram is shown in Figure 6. The curve ends at 200 Hz because even in
the case of a fully modulated sensor only single digit measurement values still occur.
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Figure 6: Frequency response curves for displacement
The following formula applies to sinusoidal signals which have been formed through double integration:
In the case of constant acceleration (a) it is visible that the displacement value (d) decreases quadratically with increasing frequency (f). As a consequence the
measuring range limits of displacement measurements are strongly frequency dependent. The next Figure 7 shows the measurement range limits depending on
frequency.
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lis
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Figure 7: Frequency response curves for displacement (RMS)
The maximum displacement of the PCE-VM 25 that can be measured is around 60 mm (RMS). It yields a frequency independent modulation range of up to 10
Hz. At higher frequencies the measuring range limits for acceleration of around 240 m/s² take effect.
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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:
arms(0) RMS for the start point in time (reference point in time) apk(0) maximum value (peak value) for start / reference point
arms(t) current RMS
apk(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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4. The Batteries
4.1. Inserting the Batteries
The PCE-VM 25 is supplied by three alkaline standard cell type AAA (LR03) batteries. NiMH batteries (HR03) may also be used. The minimum energy requirement of
the PCE-VM 25 enables maximum utilization of the batteries. Attention: Please switch the instrument off before changing the batteries. When switched off, the contents
of the memory are stored for a few minutes, without need of the batteries, and the internal clock continues to run. If the batteries are removed when the instrument is
switched on or if they remain in the instrument until the batteries have been completely discharged, the date and time will need to be reset. Further settings as well as
the saved measurands, are stored without need of the batteries
To insert the batteries, remove the two screws from the back cover of the device and open the battery compartment (Figure 8). When inserting the batteries, please
ensure that their polarity is correct, (see the engraved markings inside the compartment).
Figure 8: Battery Compartment
Important:
• Always use three batteries of the same type and same date of manufacture.
• Remove old batteries from the instrument, and take out the batteries if the instrument will not be used for a long period of time. Otherwise
leaking battery acid
may cause severe damage to the instrument.
Please use your local collection point to dispose of batteries.
Batteries do not belong to the household waste.
4.2. Switching On and Off
The instrument is switched on by a short press of the ON-OFF button. A start screen will be shown on the display for 3 seconds. (Figure 9).
Figure 9: Start screen
This displays the hardware version number (the 3 digits before the point) and the software version number (the 3 digits after the point) followed by the serial number
corresponding to the type label. The month and year of the last calibration are displayed (cf. Section 9) along with the memory capacity.
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By pressing the ON-OFF button again the PCE-VM 25 switches itself off. In addition, the instrument has an automatic shut-off timer for saving the battery power (cf.
Chapter 4.4).
4.3. Battery Display and Battery Type
In the upper left corner of the PCE-VM 25 display there is a battery level indicator (10). When the green battery symbol is full, the battery is fully charged.
Figure 10: Battery indicator upper left / Figure 11: Select battery type
While non-rechargeable batteries have a cell voltage of 1.5 V, NiMH rechargeable batteries deliver only 1.2 V per cell. The PCE-VM 25 battery indicator can be adjusted to both
voltages. To adjust the voltage, open the main menu by pressing F3 and scroll through the menu options by repeatedly pressing the ▼ button until you reach ‚Instrument
Settings‘, then press OK.
Within the sub-menu select “Battery type” (Figure 11) by following the same instructions as before and then by pressing▼ select between “Alkaline” (nonrechargeable,
1.5 V) or “NiMH accu” (rechargeable, 1.2 V). Confirm your choice by pressing OK and exit the menu by pressing F3 repeatedly.
If the power supply drops below 3.3 V when using alkaline batteries or below 3 V with rechargeable batteries, the battery indicator becomes red. Further measurements
can be taken until the power supply reaches 2.8 V in keeping with the instrument specifications. At this point the battery level indicator is completely empty and the
instrument switches itself off automatically.
If the PCE-VM 25 is connected to a USB port, it will be supplied by the USB voltage in order to spare the batteries. In this case, “external” is displayed on the screen
instead of the battery level indicator.
4.4. Shut-off Timer
The PCE-VM 25 has a shut-off timer to help prolong the battery operating life. To set the shut-off timer, open the main menu by pressing F3. Scroll down into the sub-menu
‚Instrument Settings‘ by pressing▼and OK, and within this sub-menu select the menu option “Shut off Timer”. Press keys ▼▲ to select the timer duration from the options
1, 5, 15 and 60 minutes or to deactivate the timer select (‚none‘). The switch off timer starts to run after the last press of a button. If any button is pressed then the timer
restarts and counts down again according to the duration selected.
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5. Preparation of Measuring Points
5.1. General Information on Measurement Point Choice
When monitoring machines it is important to take measurements under the same operating conditions, at the same measurement point. Choosing the suitable
measurement point is therefore decisive. Where possible, qualified staff experienced in machine monitoring should be called upon.
It is generally advisable to record machine vibrations near to their source. This helps to reduce distortion of the measuring signal to a minimum when it is being carried
through transmission parts. Suitable measurement points include rigid machine components such as bearing housings or gearboxes.
Light or mechanically flexible machine components such as cladding and casing are unsuitable for the measurement of vibrations.
5.2. ISO 10816-1 Recommendations
The standard ISO 10816-1 recommends bearing housings or their immediate surroundings as preferred measuring location points for the measurement of machine vibrations
(Figures 13, 14, 15 and 16). For the purpose of monitoring a machine it is normally sufficient to take measurements in only one direction, either vertically or horizontally.
On machines with horizontal shafts and rigid foundations the largest vibration amplitudes occur horizontally. With flexible foundations, strong vertical components also
arise.
For the purpose of acceptance tests, measurement values are to be taken from all bearing point locations at the center of the bearing and in all three directions (vertical,
horizontal and axial).
The following illustrations give a few examples of suitable measurement point locations.
The Standard ISO 13373-1 also gives recommendations for measurement points on various machine type.
Y
Y
X
X
Z
Z
Figure 13: Measuring points on verticalbearings
Figure 14: Measuring points on flange bearings
Z
X4
Y4
Figure 15: Measuring points on electric motors
Figure 16: Measuring points on machines with vertical
rotors
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5.3. VMID Measurement Point
5.3.1. How the VMID Measurement Point Functions
The PCE-VM 25 is equipped with an electronic measuring point detector. Metra offers a type VMID measurement point, which is made of magnetic stainless steel and
has aninbuilt memory with an individual serial number.
The serial number stored inside the measurement point is a unique 16-digit hexadecimal number, e.g. “000000FBC52B”.
Figure 17: VMID Measuring point
Each measurand can be easily and reliably allocated to a specific measuring point. To read the serial number, contact is made through the sensor‘s magnetic base.
The maximum permissible operating temperature for the VMID is 80 °C.
5.3.2. Mounting the VMID Measurement Point
A VMID measurement point is mounted onto the machine using two component epoxy adhesive. For an accurate vibration transmission, Metra recommends the
following adhesive:
• LOCTITE Hysol 3430 without filler for even surfaces
• LOCTITE Hysol 3450 with filler for uneven surfaces
Before applying the adhesive ensure that all residues of grease have been thoroughly removed from both contact surfaces. The two component adhesive can be
applied directly onto the chosen surface. The adhesive takes 5 minutes to harden and after 15 minutes the first measurement can be taken.
6. Measurement
6.1. Measurement Value Display
In the top margin of the screen (Figure 18) the battery power is displayed. Next to this the date and time are also indicated.
Figure 18: Measurement display
Below the measurand (v: 10 Hz-1 kHz RMS) the currently measured value. The display “No Point ID” indicates that
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a measurement point number has not been identified.
Note: The decimal point may appear in one of two positions, dependent on the measurand. This is due to the automatic gain switch-over. In this way smaller
measurands with high resolutions are sure to be detected
6.2. Selecting the Display Quantity
With keys ◄► you can select from among the six available operation modes:
• Vibration velocity 10 Hz – 1 kHz
• Vibration velocity 2 Hz – 1kHz
• Vibration acceleration 0.2 Hz – 10 kHz
• Vibration acceleration 3 Hz – 1 kHz
• Vibration acceleration 1 kHz – 10 kHz
• Vibration displacement 5 Hz – 200 Hz
• K(t) value for rolling bearing monitoring
• Rotational speed and temperature
By pressing F2 you can switch between RMS and peak value for the acceleration velocity and displacement. The RMS is the so-called “true” root mean
square value.
The peak value, also known as crest or maximum value, is the highest vibration value since the last displayed value. The crest factor, is the relation between
crest value and RMS. It is used to describe the curve form. For a sinusoidal signal it amounts to √2 = 1,41. The more impulsive the signal, the higher the crest
factor.
Note: When saving measurement values (chapter 6.4) the RMS and peak value are always saved both irrespective of the currently selected setting.
If the sensor locates a VMID measuring point which is already saved in the PCE-VM 25 memory, in order to prevent unintentional switch-over, a warning signal
will be displayed when the measurand changes (Figure 19). By pressing OK the measuring range can still be changed. The warning signal will not appear again
until the next
measuring point is detected.
Figure 19: Warning at mode change
6.3. Measurement Point Detection
6.3.1. Reading the VMID Data with the PCE-VM 25
The VMID measurement points are designed, so that the magnetic sensor base centers itself. To avoid mechanical shock do not let the sensor snap onto the
measurement point, instead, roll it slowly over the edge. To improve the vibration transmission the measuring point can be lightly lubricated.
As soon as the Sensor base comes into contact with the measurement point, the PCE-VM 25 displays the measurement point number (Point ID) (Figure 20).
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Figure 20: Newly recognized VMID
6.3.2. Entering the Measurement Point Text
If a measurement point has not yet been assigned a text, press the▼ key to reach the text edit menu (Figures 20 and 21). A space of two rows consisting of 10
characters each is assigned for each measurement point text. The text is entered using keys ▼▲. By pressing keys ◄► you can change the character position. Both
capital letters (A to Z) and numbers (0 to 9) are available. To move down to the next row press F1. By pressing F1 again and using keys▼▲ the operation mode can be
selected.
Figure 21: Entering ID text
By pressing OK the entries will be saved and the menu exited.
Press F3 to exit the menu without saving the changes.
Note: More conveniently, the measurement point texts can also be entered using the available computer software.
Figure 22: ID text display
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Once you have assigned the VMID serial number a text, the PCE-VM 25 will display the text continually, as soon as the sensor makes contact with the measuring point
(Figure22).
Aside from this, the PCE-VM 25 reverts automatically to the saved operation mode. In this way it is ensured that measurements are always taken with the correct
settings.
Note: Changing the measuring point data also effects the display of saved measurands (cf. Chapters 6.5 and 6.6). The current saved text of the respective VMID serial
number is always displayed in the measurement data. Changing the operating mode of a measuring point only affects measurands saved subsequently and does not
have any effect on the measurands that have already been saved in the memory.
The measurement point data is saved in the instrument. If several instruments are used at the same measurement point location, the measurement point data will need
to be saved within each instrument. The available PC software enables the convenient management of measurement points.
6.3.3. Editing and Deleting Measurement Point Data
Open the main menu by pressing F3 and select the sub-menu “Point ID memory” by using keys ▼▲.
Within the menu option “Edit Point ID”, as previously explained in section 6.3.2, the measurement point texts and the operating mode allocated to the measuring point
can be changed. In the sub menu “Edit Point ID” press or hold down▼▲, until the text you wish to edit is displayed and then press OK to edit.
Within the menu option “Erase Point ID”, measurement point data records, each consisting of a VMID serial number, text and operational mode, can be deleted one by
one. In the subsequent menu “Erase Point ID”, press or hold down ▼▲, until the record you wish to delete is shown, then press OK and confirm the warning by
pressing OK again(Figure 23).
Figure 23: Deleting an ID record
In the same way, the entire measurement point data can be deleted as a whole by selecting “Erase all Point IDs” in the “ID Menu”. The PCE-VM 25 memory can store
data for a maximum of 1600 measurement points.
Note: Deleting measurement point data effects the display of saved measurements. (chapter 6.6). Instead of the measurement point serial number and the
measurement point text being shown, “none” is displayed. The measurement point data records can always be newly generated, as described in 6.3.2.
6.4. Saving Measurands
Pressing the ▼ key saves the currently displayed measurand. Independently of whether RMS, peak or crest factor display has been selected, the PCE-VM 25 always saves the
RMS and peak value. Furthermore the respective measurement point number (if known), the chosen display mode and the date and time are also saved.
Note: If the sensor locates a measurement point which has not yet been assigned a text or operational mode (cf.
Chapter 6.3.3), use the ▼ key to enter the text.
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6.5. Graphical Trend Display
The purpose of measuring vibration according to ISO 10816 and ISO 13373 is as follows; To make assessments concerning the operating condition of a machine based
on changes in its vibration behavior. To achieve this it is imperative, that measurements are taken at regular time intervals, from the same points and under the same
conditions.
To deliver the service staff on site a report about the periodic changes in vibration severity and consequently the previous history of the measurement point concerned,
the PCE-VM 25 provides a graphical trend display. The prerequisite for retrieving graphical trends is placing the sensor on the relevant VMID. The trend display is
obtained by pressing the F1 key (Figure 24).
The trend display only takes values from the data memory into account which belong to the VMID operation mode currently active. If the VMID operation mode is
changed (cf. Chapter 6.3.3), the previously saved data with a different operation mode will not be shown in the trend display.
Figure 24: Trend display
The vertical axis indicates the RMS of the vibration quantity and the horizontal axis indicates time. The K(t) values are represented by the vertical axis K(t). Both are
scaled to their respective maximum value. The time axis shows the interval between the first and last saved measurement. Below the diagram there is a red marker.
This can be moved horizontally to read the magnitude, using the◄► keys. The marker only skips forward to time points which already have a measurand. At each data
point the date and time of the measurement as well as the measured RMS or K(t) value are displayed. Above the diagram the text assigned to the measurement point is
displayed. In order to be able to display trends, the points are joined together by a line.
Press F3 to exit the trend display.
If only one or zero measurands for a selected measurement point can be located in the memory, the error message “Too few data for trending” will appear instead of
the trend graphic.
Note: The available PC software enables you to view the trends more conveniently, even without it being connected to the measuring point .
6.6. Viewing Saved Measurement Values
In addition to the graphical trend readings for current measurement points, saved measurement data can be viewed in text format. Open the main menu by pressing F3, then select
the sub-menu option “Meas. data Memory”. From within the submenu select “View meas. data memory”. The measurement data can be viewed in order of the VMID serial number
or the date it was saved. Select your preferred menu option using keys ▼▲ and press OK to confirm. The first data record will now be displayed. At the top, a consecutive number
and the number of the data record within the memory will also be shown. Below these, the measuring point serial number and its assigned text are also displayed. The RMS and
peak value are displayed underneath the date, time, display mode and filter type.
(Figure 25).
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Figure 25: Display of saved measurements
Press ▼▲ to scroll to the next measurand. The currently displayed measurands can be deleted by pressing F1.
Press F3 to exit the menu. The PCE-VM 25 memory can hold 16000 measurement values.
6.7. Deleting Saved Measurement Data
In the menu option “Measurement data” / “Erase meas. data Memory” you can delete the entire measurement data. After pressing OK a warning message will appear
showing the total number of records.
6.8. K(t) Measurement
The basics of rolling bearing parameters K(t) can be found in section 3.5
First, use keys ◄► to select the operation mode “Roll. bearing” (Figure 26).
Figure 26: PCE-VM 25 in K(t) mode without VMID
K(t) measurements are only intended for use in conjunction with a VMID measurement point. The start / reference values RMS and peak of values which have been measured on
the new rolling bearings are required for calculating K(t). These start values are saved in the PCE-VM 25 together with the measuring point ID. Place the sensor on a VMID
measuring point of the relevant bearing. If the VMID measurement point ID has not yet been saved in the
PCE-VM 25 (Figure 27), then first of all enter the ID name by pressing the ▼ key (cf. Section 6.3.2).
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Figure 27: K(t) mode with newly detected VMID
If the VMID point ID has been saved but not the K(t) start values, then this is the next step. By pressing the ▼ key the currently measured RMS RMS(t) and peak value
Peak(t) are saved as K(t) the start value RMS(0) and Peak(0) (Figure 28).
Figure 28: Saving K(t) start values
When the sensor is newly placed on the VMID measuring point, the instrument automatically switches to the K(t) display. It then reads the start values from the memory
and calculates the K(t) value from the currently measured RMS(t) and Peak(t) values (Figure 29).
Press the ▼ key to save the K(t) values. Press F1 to view the graphic trend display. (cf. Section 7.5)
Note: If the instrument displays OVERLOAD, it is not necessarily the result of a too high acceleration value. It can also be due to a base value of zero, which causes a
division through zero.
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Figure 29: K(t)-display
To view or delete the saved K(t) start values open the menu “K(t) base memory” (Figure 30). In the sub-menu “View
K(t) base memory” you can scroll through the saved start values using the ▼▲ keys. Press F1 to delete an entry.
In the sub-menu “Erase K(t) memory” all saved K(t) start values can be deleted as a whole.
Figure 30: K(t)-base memory menu
6.9. Frequency Analysis
6.9.1. Settings
In addition to the measurement of RMS and peak values the PCE-VM 25 has a simple frequency analysis function. To access this function, switch to the main menu by
pressing F3 and select the menu option “Frequency analysis (Figure 31).
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