MMF VM31-M User manual

Instruction Manual
Manfred Weber
Metra Mess- und Frequenztechnik in Radebeul e.K.
Meissner Str. 58 - D- 1445 Radebeul
Tel. [phone] Fax [phone]
Email: [email protected] Internet: www.MMF.de
Human-
Vibration
Analyzer
VM31
(Valid from version 003.023)

Published by:
Manfred Weber
Metra Mess- und Frequenztechni in Radebeul e.K.
Meißner Str. 58
D-01445 Radebeul
Tel. [phone]
Fax [phone]
Email [email protected]
Internet www.MMF.de
Note: The latest version of this manual can be found at http://www.mmf.de/prod-
uct_literature.htm
Specification subject to change.
© 2014 Manfred Weber Metra Mess- und Frequenztechni in Radebeul e.K.
Full or partial reproduction subject to prior written approval.
Nov/ 22 #194

Contents
1. Purpose.................................................................................................................2
2. The Device at a Glance.........................................................................................2
3. Fundamentals of Human Vibration Measurement................................................3
3.1. Introduction...................................................................................................3
3.2. EU Occupational Health Directive 2002/44/EC............................................4
4. Human Vibration Measurement with the VM31...................................................7
4.1. Batteries.........................................................................................................7
4.2. Switching on and Connecting the Sensor......................................................8
4.3. Hand-Arm Measurement with the VM31......................................................9
4.3.1. Measuring Points for Hand-Arm Vibration............................................9
4.3.2. VM31 Settings.....................................................................................10
4.4. Whole-Body Measurement with the VM31.................................................12
4.4.1. Measuring Points for Whole-Body Vibration......................................12
4.4.2. VM31 Settings.....................................................................................14
4.4.2.1. Whole-Body Measurement with RMS Values..............................14
4.4.2.2. Whole-Body Vibration Measurement with VDV Values..............18
4.4.2.3. Seat Effective Amplitude Transmissibility (SEAT)......................19
5. General Vibration Measurement.........................................................................19
6. Data Logger........................................................................................................22
7. Frequency Analysis............................................................................................23
8. Data Memory......................................................................................................24
8.1. Measurement Data Memory........................................................................24
8.2. Logger Data Memory..................................................................................24
8.3. FFT Data Memory.......................................................................................25
9. Keypad Loc ......................................................................................................25
10. Device Settings.................................................................................................25
10.1. Sensor Calibration.....................................................................................25
10.2. Time and Date...........................................................................................25
10.3. Shut-off Timer...........................................................................................26
10.4. Battery Type..............................................................................................26
10.5. Display Brightness....................................................................................26
10.6. Menu Language.........................................................................................26
10.7. Default Settings.........................................................................................27
11. Reset Key..........................................................................................................27
12. Connection to a PC...........................................................................................27
13. Data Transfer to a PC........................................................................................28
13.1. Opening the Excel File vm31.xlsm...........................................................28
13.2. Data Import to Excel.................................................................................29
13.3. Calculation of Vibration Exposure A(8) and VDV(8)...............................29
13.4. FFT Data Import to Excel.........................................................................30
14. Firmware Update..............................................................................................31
15. Calibration........................................................................................................33
16. Technical Data..................................................................................................34
Appendix: Warranty
Declaration of CE Conformity
1

Thank you for choosing a Metra Vibration Measurement device!
1. Purpose
The VM31 has been developed, particularly, for the measurement and analysis of
human vibration. Other fields of application include machine condition monitoring,
building vibration measurement and quality control.
In combination with a triaxial accelerometer, hand-arm and whole-body vibrations
can be measured in compliance with ISO 5349, ISO 2631 and the EU Directive
2002/44/EC. A fourth measuring channel can be used, for example, for SEAT mea-
surements (seat effective acceleration transmissibility).
The VM31 meets the requirements for human vibration meters in compliance with
ISO 8041. In the development of the VM31 value was placed on simple operation
and compact design.
In addition to its application as human vibration meter the VM31 can also measure
machine vibration according to ISO 10816-1/2/3/5/6/7. Measuring ranges for accel-
eration, velocity and displacement are available.
2. The Devi e at a Glan e
2
Figure 1: Controls, connectors and display

3. Fundamentals of Human Vibration Measurement
3.1. Introdu tion
Vibrations affecting the human body are called human vibration. The main purpose
of measuring human vibration is the prevention of health ris s and the evaluation of
comfort, for example in vehicles.
Two categories are distinguished:
•Hand-Arm Vibrations, which are induced via the hands into the body. They
may cause, for example, circulatory disorder, bone, joint or muscle diseases.
•Whole-Body Vibrations, acting via the buttoc s, the bac and the feet of a sit-
ting person, the feet of a standing person or the bac and the head of a recumbent
person. Such vibrations may cause bac ache or damage to the spinal column.
Both types of human vibration measurement are described in international standards:
•ISO 5349 - Measurement and evaluation of human exposure to hand-transmitted
vibration
•ISO TR 18570 – Measurement and evaluation of human exposure to hand-trans-
mitted vibration – Supplementary method for assessing ris of vascular disorders
•ISO 2631 - Evaluation of human exposure to whole-body vibration
(also ASA/ANSI S3.18)
•ISO 8041 - Human response to vibration. Measuring Instrumentation
•ISO 8662 - Hand-held portable power tools - Measurement of vibrations at the
handle
•ISO 20283-5 - Guidelines for the measurement, reporting and evaluation of vi-
bration with regard to habitability on passenger and merchant ships
•ISO 10056 - Measurement and analysis of whole-body vibration to which pas-
sengers and crew are exposed in railway vehicles
•ISO 10326 - Laboratory method for evaluating vehicle seat vibration
•ISO 28927 - Hand-held portable power tools - Test methods for evaluation of vi-
bration emission
Practical advice for measurement and evaluation of human vibration can be found in
VDI 2057.
The subject of human vibration has gained particular importance in Europe since the
directive 2002 44 EC came into effect. It specifies the duties of employers with re -
gard to wor ers protection.
3

3.2. EU O upational Health Dire tive 2002/44/EC
The following text is an abstract of Directive 2002/44/EC of the European Parlia -
ment and of the Council dated June 25, 2002. The complete text can be downloaded
from http://eur-lex.europa.eu/
The directive specifies minimum requirements for the protection of wor ers from
the ris s arising from vibrations. Manufacturers of machines and employers should
ma e adjustments regarding ris s related to exposure to vibration.
The directive lays down the following limit values:
Hand-Arm, RMS Whole-Body, RMS Whole-Body, VDV
Exposure action
value
2.5 m/s² 0.5 m/s² 9.1 m/s1,75
Exposure limit 5 m/s² 1.15 m/s² 21 m/s1,75
Table 1: Limits to EU directive 2002/44/EC
Once the exposure action value is exceeded, the employer shall establish and im-
plement a program of technical and organizational measures intended to reduce to a
minimum exposure to mechanical vibration, ta ing into account in particular:
•Other wor ing methods that require less exposure to mechanical vibration
•Appropriate wor equipment of ergonomic design, producing the least possible
vibration
•Provision of auxiliary equipment that reduces the ris of injuries, such as protec-
tive gloves or special seats
•Appropriate maintenance programs for wor equipment
•Design and layout of wor places
•Adequate information and training to instruct wor ers to use wor equipment
correctly and safely
•Limitation of the duration and intensity of the exposure
•Wor schedules with adequate rest periods
•Provision of clothing to protect wor ers from cold and damp
In any event, wor ers shall not be exposed above the exposure limit value. If this
should be the case, the employer shall ta e immediate action to reduce exposure be-
low the exposure limit value.
The methods used may include sampling, which must be representative of the per -
sonal exposure of a wor er to the mechanical vibration in question.
The assessment of the level of exposure to vibration is based on the calculation of
daily exposure A(8) expressed as equivalent continuous acceleration over an eight-
hour wor period. For the determination of A(8) it is not necessary to measure over
eight hours. It is sufficient to ma e short-term measurements during representative
wor steps. The results are normalized to eight hours. Daily exposure is calculated
as follows:
4

A(8)=awe
√
Te
T0
Equation 1
where
A(8) is the daily exposure
awe is the energy equivalent mean value of the frequency weighted acceleration
during exposure, which means
- For Hand-Arm Vibration the X/Y/Z vector sum of Wh frequency-
weighted RMS values (Equation 2)
aw=
√
awx
2+awy 2+awz 2
Equation 2
- For Whole-Body Vibration the highest of the three RMS values
awx, awy and awz with the following frequency and magnitude weightings:
- X and Y with weighting filter Wd and weighting factor 1.4
- Z with weighting filter W and weighting factor 1.0
Te is the total duration of exposure during one wor day
T0is the reference duration of 8 hours
Daily exposure may consist of several partial exposures with different vibration
magnitudes. This can be the case if there are longer interruptions in the wor
process, if the wor equipment or its way of use is changed. A partial exposure sec-
tion should have a roughly constant magnitude and less than 10 % interruptions. Re-
sulting daily exposure is calculated as follows:
Hand-Arm Vibration:
A(8)=
√
1
T0
∑
i=1
n
awi
2Tei
Equation 3
where
A(8) is the daily exposure
awi is the energy equivalent mean value of the Wh frequency weighted accelera-
tion of partial exposure section i
n is the number of partial exposure sections
Tei is the duration of exposure i
T0is the reference duration of 8 hours
Whole-Body Vibration:
Separate daily exposures need to be calculated for X/Y/Z. The highest value is used
for the evaluation, i.e. compared with the limits of Table 1.
Ax(8)=
√
1
T0
∑
i=1
n
awxi
2Tei
Equation 4
5

Ay(8)=
√
1
T0
∑
i=1
n
awyi
2Tei
Equation 5
Az(8)=
√
1
T0
∑
i=1
n
awzi
2Tei
Equation 6
where
Ax/y/z(8) are the daily exposures of directions X/Y/Z
awx/y/zi are the energy equivalent mean values of the frequency weighted accelerations
in the directions X/Y/Z during partial exposure section i with the following
frequency and magnitude weightings:
- X and Y with weighting filter Wd and weighting factor 1.4
- Z with weighting filter W and weighting factor 1.0
n is the number of partial exposure sections
Tei is the duration of exposure i
T0is the reference duration of 8 hours
The calculations shown above are based on RMS values. An alternative method
uses fourth-power mean values called Vibration Dose Value (VDV) with the mea-
suring unit m/s1,75. Table 1 also includes VDV based limit values.
VDV based daily exposure VDV(8) is calculated:
VDV (8)=VDV⋅4
√
Texp
Tmeas
Equation 7
where
VDV(8) is the daily exposure value
VDV is the frequency-weighted vibration dose value
Texp is the duration of exposure
Tmeas is the duration of VDV measurement
Daily exposure may consist again of several partial exposure sections. Separate
daily exposure values are to be calculated for X/Y/Z. The highest one is compared
with the limits of Table 1 for evaluation.
VDV x(8)= 4
√
∑
i=1
n
VDV xi
4⋅Tiexp
Timeas
Equation 8
VDV y(8)= 4
√
∑
i=1
n
VDV yi
4⋅Tiexp
Timeas
Equation 9
VDV z(8)= 4
√
∑
i=1
n
VDV zi
4⋅Tiexp
Timeas
Equation 10
where
6

VDVX/Y/Z(8) are the daily exposures of directions X/Y/Z
VDVx/y/zi are the frequency-weighted vibration dose values of directions X/Y/Z dur-
ing exposure section i
Tiexp is the duration of exposure section i
Tmeas is the duration of VDV measurement during exposure section i
Model VM31 measures Hand-Arm and Whole-Body vibration, the latter as RMS or
VDV values. For the calculation of daily exposure an Excel sheet with a data import
function is provided.
4. Human Vibration Measurement with the VM31
4.1. Batteries
The VM31 is powered from three standard al aline bat-
teries size AAA (LR03). Alternatively rechargeable
NiMH batteries of type HR03 can be inserted. Precise
operation is guaranteed until the batteries are almost
completely discharged.
Please note that date and time need to be adjusted after
replacing the batteries. All other settings, including
saved measurements, remain stored after removing the
batteries.
To insert the batteries, remove the two screws from the
bac cover of the device and open the battery compart-
ment (Figure 2). When inserting the batteries, please en-
sure that their polarity is correct, (see the engraved
mar ings inside the compartment).
Important:
•Always use three batteries of the same type and same date of manufacture.
•Remove old batteries from the device, and ta e out the batteries if the device will
not be used for a long period of time. Otherwise lea ing battery acid may cause
severe damage to the device.
Please use your local collection point to dispose of batteries.
Batteries do not belong to the household waste.
A battery indicator can be found in the upper left corner of the display. A green
filled battery symbol indicates a fully charged battery. When the symbol becomes
red only a small portion of power remains and the unit will switch-off soon. Please
also read section 10.4..
If the VM31 is connected to a USB interface, it will be powered via USB to save the
batteries. In this case “Extern” is shown instead of the battery symbol.
7
Figure 2: Batteries

4.2. Swit hing on and Conne ting the Sensor
Switch on the VM31 by pressing the ON/OFF ey. The
unit can be switched off again by pressing and holding
the ON/OFF ey for one second.
If the sensor has not yet been connected, plug the sensor
cable into the right connector. The VM31 will start
TEDS1 detection each time it is switched on or a sensor is
connected. It supports IEEE 1451.4 TEDS template no.
25 (with or without transfer function). The sensitivities of
X/Y/Z and channel A are displayed for some seconds
(Figure 3). For each channel also the user text of TEDS
(ID) is displayed.
The sensors KS963B100-S and KS963B10 supplied by Metra feature TEDS.
Should a connected sensor not have TEDS or an incompatible TEDS version, the
VM31 will open a menu for entering the sensitivities manually (see section 10.1.).
The sensitivities entered remain stored as long as the sensor is connected, even if the
batteries are removed.
The warning “SENSOR!” indicates a missing or defective sensor or a bro en sensor
cable. Sensor condition is detected by means of the bias voltage at the sensor out -
put:
< 0.7 V: short circuit
0,7 – 14 V: normal
>14 V: open, e.g. bro en cable
Please note that settling time after connecting a sensor is
about 1 minute.
The VM31 is suitable for connecting any low power IEPE
accelerometers which can be operated with a 1 mA supply
current. The internal compliance voltage of the current
sources is 18 VDC.
1 TEDS = Transducer Electronic Data Sheet
8
Figure 3:
TEDS detection
Figure 4: Seat pad accelerometer KS963B100-S
Figure 5:
Hand-Arm accelerometer KS963B10
Figure 6:
Sensor soc et
(view from outside)

Figure 6 shows the contact arrangement of the 4 pin female sensor connector of type
Binder 711.
4.3. Hand-Arm Measurement with the VM31
This section will give you basic instructions for the measurement and evaluation of
hand-arm vibrations based on the standard ISO 5349 and the guideline VDI 2057,
Part 2. Please consult the original documents for detailed explanations.
4.3.1. Measuring Points for Hand-Arm Vibration
The sensors should be attached as close as possible to the gripping points of the
hand, however, they must not interfere with the wor process. Measurement should
be performed with the same hand pressure force as used under normal operating
conditions.
Since most machine tool handles do not provide surfaces for the adhesive or screw
attachment of sensors, Metra offers some mounting accessories for curved surfaces.
The adapter model 141B is attached with a plastic cable strap. Model 143B is
pressed onto the handle by the hand.
Close contact between the sensor and the machine is of great importance. Any mo-
tion of the sensor would distort the measurement.
Figure 9 shows the axis directions for attaching the sensor to the handle. For cylin-
dric handles the Y direction points in the direction of the handle axis. T he Z axis is
approximately the extension of the third metacarpal bone.
9
Figure 7: Handle adapter 141B
Figure 9: Coordinate system of the hand (from ISO 5349-1)
Figure 8: Hand-held adapter 143B

4.3.2. VM31 Settings
For the evaluation of hand-arm vibration it is recom-
mended to measure both the interval RMS values of
X/Y/Z and their vector sum aW. The VM31 measures
these four values simultaneously. In addition it shows
the maximum running RMS (Maximum Transient Vi-
bration Value, MTVV) which may indicate the pres-
ence of shoc vibration.
The frequency weighting for hand-arm vibration is Wh.
Figure 11 shows the filter of the VM31 and the toler-
ance bands to ISO 5349.
10
Figure 10:
Hand-arm measurement
Figure 11: Hand-arm weighting filter Wh to ISO 8041
1 1 1 1 1
, 1
, 1
, 1
,1
1
1
Wh min ISO 8 41
Wh max ISO 8 41
Wh VM31
Hz

The VM31 supports in addition measurements with frequency weighting Wp accord-
ing to ISO/TR 18570 (Figure 12). It was developed for assessing the ris of vascular
diseases (vibration white finger). However, there are no mandatory limit values yet
for this type of measurement.
Press the F3 ey to open the main menu and select “Human vibration” / “Hand-Arm
ISO 5349”/„Health“. After returning to the measurement screen (Figure 10) you can
chec the settings by pressing F1.
Measurement can begin when the sensor and the wor er's hands have been placed
on the handle of the object carrying out the operation. To start the measurement
press the ey ► (Reset). This will result in the following:
•the RMS values of X/Y/Z, the vector sum aW and MTVV reset to zero
•the measurement timer restarts.
Pressing Reset before a measurement is mandatory to establish defined start condi-
tions.
The RMS values of X/Y/Z and the vector sum are averaged over the entire measur-
ing time. That's why fluctuation becomes less the longer the measurement ta es. Af -
ter a while short shoc pulses have almost no influence on the displayed results .
Recommended measuring time for hand-arm vibration is at least 30 seconds. The
measuring timer in the upper right corner remains red until 30 second have elapsed.
“OVERLOAD” is indicated instead of the measuring values if the current magni-
tude is too high. Even if the overload condition was of short duration the measured
interval RMS value may become invalid because of missing samples. An overload
event during the entire averaging time is indicated by “OVL!” in the upper right
corner after the date. This warning can be deleted by pressing the ey ► (Reset).
11
1 10 100 1000 10000
0,0001
0,001
0,01
0,1
1
10
Wp min ISO
Wp max ISO
Wp VM31
Hz
Figure 12: Hand-Arm-weighting filter Wp to ISO/TR 18570

After measurement you may save the results by
pressing the ey ▼. Measurement should be contin-
ued or finished immediately before pressing the ey.
Otherwise the measuring values will drop slowly.
You will be as ed to enter two lines of ten capital let-
ters or numbers as a comment (Figure 13). Use the
eys ◄▲▼► to select characters and to change the
input position. Press F1 to change the input line.
Measurement can be finished before entering the
comment because the results have already been saved
when pressing the ey ▼.
Measurements can only be saved if a sensor is de-
tected at X/Y/Z and if there is no overload condition.
In these cases the VM31 will display “Sensor error”
or “Overload occurred” instead of saving in order to avoid invalid recordings. If an
overload occurred since the last reset (“OVL!” in upper right corner) the instrument
will show a warning “Overload occurred after last reset! Save anyway?”.
If you want to measure several partial exposures you may do further measurements
(see section 3.2).
For the calculation of vibration exposure A(8) and to store results on a PC the Ex-
cel macro file vm31.xlsm is provided.
The fourth channel (A) of the VM31 is not active when hand-arm vibration is mea-
sured.
4.4. Whole-Body Measurement with the VM31
This section will give you basic instructions for the measurement and evaluation of
whole-body vibrations based on the standard ISO 2631 and the guideline VDI 2057,
Part 1. Please consult the original documents for detailed explanations.
The described method is suitable for all vibrations acting on the human body. It is
not suited for vibration containing occasional shoc s or for impacts such car
crashes. Vibrations transmitted via the hands are described separately in the previ-
ous section.
4.4.1. Measuring Points for Whole-Body Vibration
Whole-body vibration is usually measured with seat pad accelerometers. These are
triaxial piezoelectric sensors built into a flat rubber pad, which adapt themselves to
the interface between the vibration source and the test person (Figure 4).
The following measuring points are suitable:
On the seat surface under a seated person
On the bac rest behind a seated person
Under the feet of a seated person
Under the feet of a standing person
Under the pelvis of a recumbent person
Under the head of a recumbent person
Figure 14 shows the coordinate systems for whole-body vibration to ISO 2631. As
can be seen from the drawing, the Z axis always points in the direction of the spinal
12
Figure 13: Comment

column. The vibration sensor has to be placed accordingly. A special case is mea-
surement at the bac rest (see notice below Table 2 on page 13).
Table 2 shows the weighting filters and factors to be used for different postures and
positions.
Whole-Body Health Evaluation
osture osition Direction Frequency
weighting
Weighting
factor (k)
sitting seat surface X / Y
Z
Wd
W
1.4
1
Whole-Body Comfort Evaluation
sitting
seat surface X / Y
Z
Wd
W
1
1
feet platform X / Y
ZW
0.25
0.4
bac rest
X*
Y
Z*
Wc
Wd
Wd
0.8
0.5
0.4
standing feet platform X / Y
Z
Wd
W
1
1
recumbent under pelvis X (vertical) Y / Z (horizontal)
W
Wd
1
1
under head X (vertical) Wj1
In railway vehicles:
standing
sitting
recumbent
feet platform
seat/bac rest/feet
support. surface, pelvis/head
X / Y / Z Wb1
In buildings:
undefined in buildings X / Y / Z Wm1
Table 2: Weighting filters and factors for whole-body vibration
13
Figure 14: Coordinate systems for whole-body vibration to ISO 2631
Z
Y
Z
Y
Z
X
Y
Z
X
X
Y
X
Y
Z
X

* Please note that the Z axis points along the bac bone for all measurements. For measure -
ments at the bac rest with a seat pad accelerometer the sensor will always be in a vertical po-
sition with Z perpendicularly to the bac bone. However, to compensate this the VM31 auto-
matically swaps the X and Z axis for bac rest measurement.
4.4.2. VM31 Settings
4.4.2.1. Whole-Body Measurement with RMS Values
For the evaluation of hand-arm vibration it is recom-
mended to measure both the interval RMS values of
X/Y/Z and their vector sum aW. The VM31 measures
these four values simultaneously. In addition it
shows the maximum running RMS (Maximum Tran-
sient Vibration Value, MTVV) which may indicate
the presence of shoc vibration. MTVV is not al-
ways the maximum value of the three single RMS
values of X/Y/Z since these are multiplied with
weighting factors (see table 2) which is not the case
for MTVV.
The following section explains the measurement of
whole-body vibration in terms of health ris s. Health
evaluation is done with weighting filter Wd for X/Y
and W for Z and with weighting factors 1.4 for X/Y
and 1.0 for Z. Figures 16 and 17 show the frequency response curves of the filters
Wd and W in VM31 and the tolerance bands in compliance with ISO 8041.
14
Figure 15:
Whole-body measurement
Figure 16: Whole-body weighting filter Wd
,1 1 1 1 1
, 1
, 1
, 1
,1
1
1
Wd min ISO 8 41
Wd max ISO 8 41
Wd VM31
Hz

In addition to health evaluation the VM31 also supports measurements regarding
comfort. This type of measurement uses other postures, sensor positions and differ-
ent frequency weightings but the general procedure is the same.
Figures 18 to 21 show the frequency response curves of the weighting filters for
comfort measurements.
15
Figure 18: Whole-body weighting filter Wb for passenger trains
,1 1 1 1 1
, 1
, 1
, 1
,1
1
1
Wb min ISO 8 41
Wb max ISO 8 41
Wb VM31
Hz
Figure 17: Whole-body weighting filter W
,1 1 1 1 1
, 1
, 1
, 1
,1
1
1
Wk min ISO 8 41
Wk max ISO 8 41
Wk VM31
Hz

16
Figure 20: Whole-body weighting filter Wj for the head of recumbent persons
,1 1 1 1 1
, 1
, 1
, 1
,1
1
1
Wj min ISO 8 41
Wj max ISO 8 41
Wj VM31
Hz
Figure 19: Whole-body weighting filter Wc for the bac rest of seats
,1 1 1 1 1
, 1
, 1
, 1
,1
1
1
Wc min ISO 8 41
Wc max ISO 8 41
Wc VM31
Hz

To start whole-body vibration measurement for the assessment of health ris s open
the main menu by pressing F3, and select “Measuring mode” / “Human vibration” /
“Whole-body ISO 2631” / “Health”. From this menu you will return to the measur-
ing screen (Figure 15). You may press F1 to chec your settings.
According to ISO 2631-1 there are two evaluation methods for whole body vibra -
tion: basic evaluation and additional evaluation. Basic evaluation is performed by
interval RMS measurement. Additional evaluation can be the running RMS method
(MTVV) or the fourth power vibration dose method (VDV) whereupon the latter is
more common. One of the two additional evaluation methods should be applied for
occasional shoc s or transient vibration since the basic evaluation methods may un -
derestimate their effects. A measure for the shoc content of vibration is the crest
factor, i.e. the ratio of pea and RMS. If the crest factor exceeds 9 the additional
evaluation method should be applied.
If the wor er being tested is sitting in the right position and vibration exposure has
started measurement can begin.
Select crest factor mode by pressing the ◄ ey and start crest factor measurement
by the ► ey (Reset). This will
•reset the RMS values of X/Y/Z, the vector sum aW and MTVV to zero
•restart the measurement timer.
Always press Reset before a measurement to establish the defined start condi-
tions.
If the displayed crest factors X/Y/Z are below 9, switch to Interval RMS mode by
pressing the ◄ ey. At crest factors above 9 you should measure in addition vibra -
tion dose as shown in the next section.
Interval RMS values and crest factors are calculated based on the elapsed measuring
time since the last pressing of the ey ► (Reset). This means that the fluctuation of
the displayed values becomes lower the longer the measurement lasts. Single pea s
will have less influence than at the beginning. Relevant for evaluation is only the
value at the end of measurement. The recommended measuring time for whole-body
17
Figure 21: Whole-body weighting filter Wm for persons in buildings
,1 1 1 1 1
, 1
, 1
, 1
,1
1
1
Wm min ISO 8 41
Wm max ISO 8 41
Wm VM31
Hz

vibration is at least 2 minutes. To alert you, the timer in the upper right corner re -
mains red until 2 minutes have elapsed.
The displayed interval RMS for X/Y/Z and vibration total values aw include the
weighting factors ( ) according to table 2. The weighting factors are set to 1 for
maximum RMS (MTVV) and vibration dose value (VDV).
“OVERLOAD” is indicated instead of the measuring values if the current magni-
tude is too high. Even if the overload condition was of short duration the measured
interval RMS value may become invalid because of missing samples. An overload
event during the entire averaging time is indicated by “OVL!” in the upper right
corner after the date. This warning can be deleted by pressing the ey ► (Reset).
After measurement you may save the results by pressing the ey ▼. Measurement
should be either continued or finished immediately before pressing the ey. Other-
wise the measuring values will drop slowly. You will be as ed to enter two lines of
ten capital letters or numbers as a comment (Figure 13, page 12). Use the eys
◄▲▼► to select characters and to change the input position. Press F1 to change
the input line. Measurement can be finished before entering a comment because the
results will have already been saved by pressing the ey ▼.
Measurements can only be saved if a sensor is detected at X/Y/Z and if there is no
overload condition. In these cases the VM31 will display “Sensor error” or “Over-
load occurred” instead of saving in order to avoid invalid recordings. If an overload
occurred since the last reset (“OVL!” in upper right corner) the instrument will
show a warning “Overload occurred after last reset! Save anyway?”.
If you want to measure several partial exposures you may now do further measure -
ments (see section 3.2).
For the calculation of vibration exposure A(8) and to store results on a PC the Ex-
cel macro file vm31.xlsm is provided (see section 13.3.).
4.4.2.2. Whole-Body Vibration Measurement with VDV Values
The VM31 also allows whole-body vibration to be measured as vibration dose val-
ues (VDV). These are integrated fourth power values. VDV is more sensitive to
pea s. The measuring unit of VDV is m/s1,75.
Equation 11
Press the ey ◄ to switch from RMS to VDV (Fig-
ure 22).
The same weighting filters as for RMS measurement
are used. You may press F1 to chec your settings.
The device displays VDV values for the directions
X/Y/Z. In addition the highest of the three axis val-
ues (Max. VDV) and the highest VDV since the last
reset (Max. abs.) are displayed.
VDV measurements need to be started by pressing
the ey ► (Reset).
18
Figure 22: VDV mode
VDV =4
√
∫
o
T
aw
4(t)dt