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PCE Americas Inc.
Instruction Manual
PCE-VM 31
Vibration Meter
711 Commerce Way
Suite 8
Jupiter
FL-33458
USA
From outside US: +1
Tel: (561) 320-9162
Fax: (561) 320-9176
info@pce-americas.com
www.pce-instruments.com/english
PCE Instruments UK Ltd.
Southpoint Business Park
Hampshire / Southampton
United Kingdom, SO31 4RF
info@pce-instruments.com
www.pce-instruments.com
Units 12/13
Ensign way
From outside UK: +44
Tel: (0) 2380 98703 0
Fax: (0) 2380 98703 9
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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......................................................................................13
4.4.2.1. Whole-Body Measurement with RMS Values...............................13
4.4.2.2. Whole-Body Vibration Measurement with VDV Values...............17
4.4.2.3. Seat Effective Amplitude Transmissibility (SEAT)........................18
5. General Vibration Measurement..........................................................................18
6. Frequency Analysis..............................................................................................21
7. Data Memory.......................................................................................................21
8. Keypad Lock........................................................................................................ 22
9. Device Settings....................................................................................................22
9.1. Sensor Calibration........................................................................................22
9.2. Time and Date.............................................................................................. 22
9.3. Shut-off Timer..............................................................................................23
9.4. Battery Type................................................................................................. 23
9.5. Display Brightness........................................................................................23
9.6. Menu Language............................................................................................23
9.7. Default Settings............................................................................................24
10. Reset Key...........................................................................................................24
11. Connection to a PC............................................................................................24
12. Data Transfer to a PC.........................................................................................25
12.1. Opening the Excel File vm31.xlsm.............................................................25
12.2. Data Import to Excel..................................................................................26
12.3. Calculation of Vibration Exposure A(8) and VDV(8)................................26
12.4. FFT Data Import to Excel...........................................................................27
13. Firmware Update............................................................................................... 28
14. Calibration.........................................................................................................29
15. Technical Data...................................................................................................31
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3. Fundamentals of Human Vibration Measurement
3.1. Introduction
Vibrations affecting the human body are called human vibration. The main purpose
of measuring human vibration is the prevention of health risks 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 buttocks, the back and the feet of a sit -
ting person, the feet of a standing person or the back and the head of a recumbent
person. Such vibrations may cause backache 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 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 6954 - Guidelines for the measurement, reporting and evaluation of vibra-
tion 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 workers protection.
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3.2. EU Occupational Health Directive 2002/44/EC
The following text is an abstract of Directive 2002/44/EC of the European Parliament 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 workers from
the risks arising from vibrations. Manufacturers of machines and employers should
make adjustments regarding risks 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
Exposure limit
2.5 m/s² 0.5 m/s² 9.1 m/s
5 m/s² 1.15 m/s² 21 m/s
Table 1: Limits to EU directive 2002/44/EC
Once the exposure action value is exceeded, the employer shall establish and implement a program of technical and organizational measures intended to reduce to a
minimum exposure to mechanical vibration, taking into account in particular:
• Other working methods that require less exposure to mechanical vibration
• Appropriate work equipment of ergonomic design, producing the least possible
vibration
• Provision of auxiliary equipment that reduces the risk of injuries, such as protec-
tive gloves or special seats
• Appropriate maintenance programs for work equipment
• Design and layout of workplaces
• Adequate information and training to instruct workers to use work equipment
correctly and safely
• Limitation of the duration and intensity of the exposure
• Work schedules with adequate rest periods
• Provision of clothing to protect workers from cold and damp
In any event, workers shall not be exposed above the exposure limit value. If this
should be the case, the employer shall take immediate action to reduce exposure be low the exposure limit value.
The methods used may include sampling, which must be representative of the personal exposure of a worker 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 eighthour work period. For the determination of A(8) it is not necessary to measure over
eight hours. It is sufficient to make short-term measurements during representative
work steps. The results are normalized to eight hours. Daily exposure is calculated
as follows:
1,75
1,75
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A(8)=a
we
√
T
e
T
0
Equation 1
aw=√a
wx
2
+a
wy
2
+a
wz
2
A(8)=
√
1
T
0
∑
i=1
n
a
wi
2
T
ei
Ax(8)=
√
1
T
0
∑
i =1
n
a
wxi
2
T
ei
where
A(8) is the daily exposure
a
is the energy equivalent mean value of the frequency weighted acceleration
we
during exposure, which means
- For Hand-Arm Vibration the X/Y/Z vector sum of Wh frequency-
weighted RMS values (Equation 2)
Equation 2
- For Whole-Body Vibration the highest of the three RMS values
awx, awy and a
- X and Y with weighting filter Wd and weighting factor 1.4
- Z with weighting filter Wk and weighting factor 1.0
Te is the total duration of exposure during one work day
T
is the reference duration of 8 hours
0
Daily exposure may consist of several partial exposures with different vibration
magnitudes. This can be the case if there are longer interruptions in the work
process, if the work 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:
with the following frequency and magnitude weightings:
wz
Equation 3
where
A(8) is the daily exposure
a
is the energy equivalent mean value of the Wh frequency weighted acceleration
wi
of partial exposure section i
n is the number of partial exposure sections
T
is the duration of exposure i
ei
T
is the reference duration of 8 hours
0
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.
Equation 4
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Ay(8)=
√
1
T
0
∑
i=1
n
a
wyi
2
T
ei
Equation 5
Az(8)=
√
1
T
0
∑
i=1
n
a
wzi
2
T
ei
VDV (8)=VDV⋅
4
√
T
exp
T
meas
VDVx(8)=
4
√
∑
i=1
n
VDV
xi
4
⋅
T
iexp
T
imeas
VDVy(8)=
4
√
∑
i =1
n
VDV
yi
4
⋅
T
iexp
T
imeas
VDVz(8)=
4
√
∑
i =1
n
VDV
zi
4
⋅
T
iexp
T
imeas
Equation 6
where
A
(8) are the daily exposures of directions X/Y/Z
x/y/z
a
are the energy equivalent mean values of the frequency weighted accelerations
wx/y/zi
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 Wk and weighting factor 1.0
n is the number of partial exposure sections
T
is the duration of exposure i
ei
T
is the reference duration of 8 hours
0
The calculations shown above are based on RMS values. An alternative method uses
fourth-power mean values called Vibration Dose Value (VDV) with the measuring
1,75
unit m/s
VDV based daily exposure VDV(8) is calculated:
where
VDV(8) is the daily exposure value
VDV is the frequency-weighted vibration dose value
T
exp
T
meas
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.
. Table 1 also includes VDV based limit values.
Equation 7
is the duration of exposure
is the duration of VDV measurement
Equation 8
Equation 9
Equation 10
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where
VDV
VDV
(8) are the daily exposures of directions X/Y/Z
X/Y/Z
are the frequency-weighted vibration dose values of directions X/Y/Z dur-
x/y/zi
ing exposure section i
T
T
is the duration of exposure section i
iexp
is the duration of VDV measurement during exposure section i
meas
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 alkaline batteries 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
back cover of the device and open the battery compartment (Figure 2). When inserting the batteries, please ensure that their polarity is correct, (see the engraved
markings inside the compartment).
Important:
• Always use three batteries of the same type and same date of manufacture.
Figure 2: Batteries
• Remove old batteries from the device, and take out the batteries if the device will
not be used for a long period of time. Otherwise leaking 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 9.4.
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If the VM31 is connected to a USB interface, it will be powered via USB to save the
GND
X
Y
Z
batteries. In this case “Extern” is shown instead of the battery symbol.
4.2. Switching on and Connecting the Sensor
Switch on the VM31 by pressing the ON/OFF key. The
unit can be switched off again by pressing and holding the
ON/OFF key 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.
Figure 5:
Hand-Arm accelerometer KS903.10
Figure 4: Seat pad accelerometer KB103SVD
Figure 3:
TEDS detection
The sensors KB103SVD and KS903.10 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 9.1).
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 broken sensor
cable. Sensor condition is detected by means of the bias voltage at the sensor output:
< 0.7 V: short circuit
0,7 – 14 V: normal
>14 V: open, e.g. broken cable
Please note that settling time after connecting a sensor is
about 1 minute.
Figure 6:
Sensor socket
(view from outside)
1 TEDS = Transducer Electronic Data Sheet
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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.
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 work 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, we offers some mounting accessories for curved surfaces.
Figure 7: Handle adapter 141 Figure 8: Hand-held adapter 143
The adapter model 141 is attached with a plastic cable strap. Model 143 is pressed
onto the handle by the hand.
Close contact between the sensor and the machine is of great importance. Any motion of the sensor would distort the measurement.
Figure 9 shows the axis directions for attaching the sensor to the handle. For cylindric handles the Y direction points in the direction of the handle axis. The Z axis is
approximately the extension of the third metacarpal bone.
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Figure 9: Coordinate system of the hand (from ISO 5349-1)
1 10 100 1000 10000
0,0001
0,001
0,01
0,1
1
10
Wh min ISO 8041
Wh max ISO 8041
Wh VM31
Hz
4.3.2. VM31 Settings
For the evaluation of hand-arm vibration it is recommended 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 Vibration Value, MTVV) which may indicate the presence of shock 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.
Figure 10:
Hand-arm measurement
Figure 11: Hand-arm weighting filter Wh
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Press the F3 key to open the main menu and select “Human vibration” / “Hand-Arm
ISO 5349”/„Health“. After returning to the measurement screen (Figure 10) you can
check the settings by pressing F1.
Measurement can begin when the sensor and the worker's hands have been placed
on the handle of the object carrying out the operation. To start the measurement
press the key ► (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 conditions.
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 takes. After a while short shock 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 magnitude
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 af ter the date. This warning can be deleted by pressing the key ► (Reset).
After measurement you may save the results by pressing the key ▼. Measurement should be continued or
finished immediately before pressing the key. Otherwise the measuring values will drop slowly. You will
be asked to enter two lines of ten capital letters or
numbers as a comment (Figure 12). Use the keys
◄▲▼► to select characters and to change the input
position. Press F1 to change the input line. Measure ment can be finished before entering the comment because the results have already been saved when press ing the key ▼.
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 “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 Excel macro file vm31.xlsm is provided.
The fourth channel (A) of the VM31 is not active when hand-arm vibration is mea sured.
Figure 12: Comment
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4.4. Whole-Body Measurement with the VM31
Z
Y
Z
Y
Z
X
Y
Z
X
X
Y
X
Y
Z
X
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 shocks 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 back 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 13 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
column. The vibration sensor has to be placed accordingly. A special case is measurement at the backrest (see notice below Table 2 on page 13).
Figure 13: Coordinate systems for whole-body vibration to ISO 2631
Table 2 shows the weighting filters and factors to be used for different postures and
positions.
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Whole-Body Health Evaluation
Posture Position Direction
sitting seat surface
X / Y
Z
Frequency
weighting
W
W
d
k
Weighting
factor (k)
1.4
1
Whole-Body Comfort Evaluation
seat surface
sitting
feet platform
backrest
standing feet platform
recumbent
under pelvis
under head X (vertical) W
X / Y
Z
X / Y
Z
X*
Y
Z*
X / Y
Z
X (vertical)
Y / Z (horizontal)
W
W
W
W
W
W
W
W
W
W
d
k
k
c
d
d
d
k
k
d
j
1
1
0.25
0.4
0.8
0.5
0.4
1
1
1
1
1
In railway vehicles:
standing
sitting
recumbent
feet platform
seat/backrest/feet
support. surface, pelvis/head
X / Y / Z W
b
1
In buildings:
undefined in buildings X / Y / Z W
m
1
Table 2: Weighting filters and factors for whole-body vibration
* Please note that the Z axis points along the backbone for all measurements. For measure ments at the backrest with a seat pad accelerometer the sensor will always be in a vertical position with Z perpendicularly to the backbone. However, to compensate this the VM31 automatically swaps the X and Z axis for backrest 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 recommended 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 Vibration Value, MTVV) which may indicate
the presence of shock vibration.
The following section explains the measurement of
whole-body vibration in terms of health risks. Health
evaluation is done with weighting filter Wd for X/Y
and Wk for Z and with weighting factors 1.4 for X/Y
and 1.0 for Z. Figures 15 and 16 show the frequency
response curves of the filters Wd and Wk in VM31
and the tolerance bands in compliance with
ISO 8041.
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Figure 14:
Whole-body measurement
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Figure 15: Whole-body weighting filter Wd
0,1 1 10 100 1000
0,0001
0,001
0,01
0,1
1
10
Wd min ISO 8041
Wd max ISO 8041
Wd VM31
Hz
0,1 1 10 100 1000
0,0001
0,001
0,01
0,1
1
10
Wk min ISO 8041
Wk max ISO 8041
Wk VM31
Hz
Figure 16: Whole-body weighting filter Wk
In addition to health evaluation the VM31 also supports measurements regarding
comfort. This type of measurement uses other postures, sensor positions and different frequency weightings but the general procedure is the same.
Figures 17 to 20 show the frequency response curves of the weighting filters for
comfort measurements.
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Figure 17: Whole-body weighting filter Wb for passenger trains
0,1 1 10 100 1000
0,0001
0,001
0,01
0,1
1
10
Wb min ISO 8041
Wb max ISO 8041
Wb VM31
Hz
0,1 1 10 100 1000
0,0001
0,001
0,01
0,1
1
10
Wc min ISO 8041
Wc max ISO 8041
Wc VM31
Hz
Figure 18: Whole-body weighting filter Wc for the backrest of seats
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0,1 1 10 100 1000
0,0001
0,001
0,01
0,1
1
10
Wm min ISO 8041
Wm max ISO 8041
Wm VM31
Hz
Figure 19: Whole-body weighting filter Wj for the head of recumbent persons
0,1 1 10 100 1000
0,0001
0,001
0,01
0,1
1
10
Wj min ISO 8041
Wj max ISO 8041
Wj VM31
Hz
Figure 20: Whole-body weighting filter Wm for persons in buildings
To start whole-body vibration measurement for the assessment of health risks 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 measuring screen (Figure 14). You may press F1 to check your settings.
Press the key ◄ to switch from VDV to RMS if necessary.
If the worker being tested is sitting in the right position and vibration exposure has
started, press the key ► key (Reset) to:
• 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 conditions.
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The RMS values of X/Y/Z and the vector sum are averaged over the entire measur -
VDV =
4
√
∫
o
T
a
w
4
(t )dt
ing time. That's why fluctuation becomes less the longer the measurement takes. After a while short shock pulses have almost no influence on the the displayed results
anymore.
The recommended measuring time for hand-arm vibration is at least 2 minutes. To
alert you, the timer in the upper right corner remains red until 2 minutes have
elapsed.
“OVERLOAD” is indicated instead of the measuring values if the current magnitude
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 af ter the date. This warning can be deleted by pressing the key ► (Reset).
After measurement you may save the results by pressing the key ▼. Measurement
should be either continued or finished immediately before pressing the key. Otherwise the measuring values will drop slowly. You will be asked to enter two lines of
ten capital letters or numbers as a comment (Figure 12, page 11). Use the keys
◄▲▼► 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 key ▼.
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 “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 now do further measurements (see section 3.2).
For the calculation of vibration exposure A(8) and to store results on a PC the Excel macro file vm31.xlsm is provided.
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 fourth power mean values. VDV is more sensitive to peaks.
The measuring unit of VDV is m/s
1,75
.
Equation 11
Press the key ◄ to switch from RMS to VDV and
vice versa (Figure 21).
The same weighting filters and factors as for RMS
measurement are used. You may press F1 to
check your settings.
The device displays VDV values for the directions X/Y/Z. In addition the highest of the three
Figure 21: VDV measurement
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axis values (Max. VDV) and the highest VDV since the last reset (Max. abs.) are
displayed.
VDV measurements need to be started by pressing the key ► (Reset).
Measurements can be saved by pressing the key ▼ (see page 17).
The Excel file vm31.xlsm also allows the calculation of vibration exposure based on
VDV measurements.
4.4.2.3. Seat Effective Amplitude Transmissibility (SEAT)
The Seat Effective Amplitude Transmissibility (SEAT) value is the ratio of the vi bration experienced on top of the seat and the vibration that one would be exposed
to when sitting directly on the vibrating floor. Both vibration magnitudes are measured in the vertical direction (Z) only. SEAT values are widely used to determine
the vibration isolation efficiency of a seat.
The fourth channel (A) of the VM31 in combination
with a uniaxial accelerometer can be used to deter mine SEAT values. Metra recommends the TEDS
accelerometer KS78.100 for this purpose. It is connected via a sensor cable VM31-A to the left socket
(see 1). The fourth channel is named “A” on the display. The sensitivity of the KS78.100 will be auto matically detected. With a non-TEDS sensor it
needs to be entered manually (see section 4.2).
Select “Whole-body ISO 2631” / “Unweighted” for
channels X/Y/Z. Channel A does not have frequency weightings. Its frequency range (-3 dB) is
0.8 to 250 Hz. The RMS or VDV of channel A is
displayed below channels X/Y/Z (Figure 22).
Figure 22: SEAT measurement with channel A
5. General Vibration Measurement
In addition to its human vibration ranges the VM31 can measure:
• Vibration acceleration from 0.2 to 1500 Hz and
1 to 1000 Hz,
• Vibration velocity from 1 to 100 Hz,
2 to1000 Hz and 10 to 1000 Hz (for the measurement of machine vibration to ISO 10816),
• Vibration displacement from 5 to 200 Hz.
Press F3 to open the menu, select “Measuring
mode” and use the keys ▲▼ to select the vibration
range.
You can switch the measuring screen from RMS to
peak display by pressing the key ◄. Please note
that the RMS and peak values in the general vibration ranges are computed over the last display cycle
(not over a long period). A disp2lay cycle can be
between 1 and 4 seconds, depending on the frequency range.
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Figure 23: 4-channel display
with velocity measurement
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RMS or peak values are shown for X/Y/Z. There will also be an RMS or peak value
0,1 1 10 100 1000 10000
0,01
0,1
1
10
a: 1Hz – 1kHz
a: 0,1 Hz – 2 kHz
for channel A if you have connected a sensor to this input. Channel A always measures acceleration. Its frequency range depends on the mode selected for X/Y/Z
(Figure 3).
Mode X/Y/Z Frequency range X/Y/Z Frequency range A
Acceleration 0.2 to 1500 Hz 0.2 to 1500 Hz
Acceleration 1 to 1000 Hz 3 to 1000 Hz
Velocity 1 to 100 Hz 1 to 250 Hz
Velocity 2 to 1000 Hz 2.5 to 750 Hz
Velocity 10 to 1000 Hz 2.5 to 750 Hz
Displacement 5 to 200 Hz 1 to 250 Hz
Table 3: Frequency ranges of channel A
Vibration velocity is computed by single integration of the acceleration signal, displacement by double integration. Due to integration there is a strong attenuation at high frequencies which limits the measurable frequencies, particularly for displacement. Low frequencies, including noise, are strongly amplified. High pass filtering is inevitable. The
frequency response curves of the general vibration ranges can be seen in Figures 24, 25
and 26.
Figure 24: Frequency ranges of vibration acceleration
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Figure 25: Frequency ranges of vibration velocity
1 10 100 1000 10000
0,0001
0,001
0,01
0,1
1
10
v: 1Hz – 100Hz
v: 2Hz – 1kHz
v: 10Hz – 1kHz*
1 10 100 1000
0,0001
0,001
0,01
0,1
1
10
Figure 26: Frequency range of vibration displacement (upper end due to resolution)
Vibration quantity and frequency range can be checked by pressing F1.
Below the 3 (or 4) RMS or peak values you can see two combined values which are
calculated from X/Y/Z. These are:
• in RMS mode the vector sum of X/Y/Z (aw(Vec)) and the highest RMS value
(Max. abs.) since the last press of the Reset key ►.
• in peak mode the highest of the currently displayed XYZ peak values (Max.
XYZ) and the highest peak value (Max. abs.) since the last Reset ►.
Maximum values are displayed in the color of the channel where they occurred.
Pressing the Reset key ►
• deletes the maximum values and
• restarts the measuring timer.
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Measurements can be saved by pressing the key ▼ (see page 17).
The Excel file vm31.xlsm can be used to transfer the measurements to a PC.
6. Frequency Analysis
The VM31 provides a simple FFT function for the
detection of main frequencies. It displays a 125 line
peak spectrum of acceleration.
Press F3 and select “Frequency analysis” to open
the FFT screen (Figure 27). You see the frequency
components of channels X/Y/Z2 in their respective
channel colors.
The line above the diagram shows frequency and
magnitude of the longest spectral line.
The keys ◄► move the cursor. Below the diagram you can see the cursor readout.
Press F1 or F2 to change the frequency range. Four
ranges are selectable:
• 3 to 244 Hz
• 7 to 488 Hz
• 15 to 977 Hz
• 30 to 1954 Hz
Pressing the key ▼saves the spectrum. The VM31 memory can hold 1000 FFTs.
To view stored FFTs press F3 to open the menu and select “Data memory” /
“View/delete FFT data”. Use the keys ▲▼ to select the desired FFT. A cursor function using the keys ◄► is also available.
Stored FFT data can be transferred to a PC using the Excel macro file vm31.xlsm.
The file also provides a graphical output.
Figure 27: Frequency analysis
7. Data Memory
The VM31 memory can hold 10,000 data records. A record includes:
• Date and time
• Comment (20 characters)
• Filter and measuring mode
• Measuring values X/Y/Z and, if available,
channel A and 2 combined values (vector sum
and maximum value)
Saved data can be viewed on the screen. Press F3
and select “Data memory” / “View/delete measurement”. Use the keys ▲▼ to navigate
through the records (Figure 28).
Single records can be erased by pressing ◄. Erasing means the record is not displayed anymore.
2 There is no FFT function for channel A.
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Figure 28: Data memory
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Its memory position, however, will not be released until the entire memory is erased.
This can be done in the menu “Data memory” / “Delete memory”. Please note that
the FFT records will also be erased.
Stored measurement data can be transferred to a PC using the Excel macro file
vm31.xlsm.
8. Keypad Lock
To prevent manipulation during ongoing measurement, it can be advantageous to activate the key lock. This function can be found in the main menu under “Key lock”
To release the key lock press all four arrow keys ◄▲▼► simultaneously, until the
device displays “unlocked”.
9. Device Settings
9.1. Sensor Calibration
If a connected sensor is not TEDS compatible, the
VM31 will automatically open the menu “Transducer calibration” (see section 4.2). It can also be
opened from the menu “Device settings” to check
or to change the entered sensitivities.
Sensitivities are entered one after another for chan nels X/Y/Z and, if connected, for channel A. The
sensitivity value is a five-digit number with the
measuring unit mV/ms-2. You find the correct values in the transducer calibration sheet. The decimal
point can be shifted by pressing F1. The allowed
sensitivity range is 0.800 to 12.000 mV/ms-2 or
8.00 to 120.00 mV/ms-2.
9.2. Time and Date
When saving measurement values the date and
time need to be correctly recorded. To set the date
and time, open the main menu by pressing F3 and
select “Device settings”. Within this sub menu select “Date and time”. Using keys ▲▼ you can adjust the chosen value. Upon reaching the maximum
value, e.g. in the 23rd hour, the counter starts again
from the beginning. Press ◄► to skip between
hour, minute, month, day and year. The date takes
account of the leap year. It is, however, important
to ensure that no invalid day-month combinations
are entered.
Additionally, clock inaccuracy can be corrected.
This can be done using the setting at “Cal.” in ppm
(parts per million). The clock frequency can be in creased with positive values and decreased with negative. The sign changes to minus
at +254 ppm.
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Figure 29: Sensitivity
Figure 30: Time and date
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9.3. Shut-off Timer
The VM31 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, select “Device settings” and “Shut-off timer”. Press keys ▼▲ to select the timer duration from the options 1, 5, 15 and
60 minutes. To deactivate the timer select ('none').
The switch off timer starts to run after the last press
of a button. If a button is pressed the timer will
restart the count down for the set duration.
9.4. 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 VM31 battery indicator can be adjusted to both voltages. To adjust the voltage, open the main
menu by pressing F3, select “Device settings” and
“Battery type”.
Within the sub-menu select “Battery type” (Figure
32) pressing ▼ selects between “Alkaline” (nonrechargeable, 1.5 V) or “NiMH” (rechargeable, 1.2
V).
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 device specifica tions. At this point the battery level indicator is
completely empty and the device switches itself off
automatically.
Figure 31: Shut-off timer
Figure 32: Battery type
9.5. Display Brightness
In the menu “Device settings”/ “Display brightness”,
press the keys ◄► to adjust the display settings according to your working environment. The main
purpose of reducing display brightness is to save
battery power. Current consumption increases by approximately 20 % between the minimum and maximum setting. The difference can be even higher, de pending on the display content.
9.6. Menu Language
Open the menu “Device settings” / “Menu language”
to change the display language. The available lan guages depend on the firmware installed.
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Figure 33: Brightness
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our webside.
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12.2. Data Import to Excel
Open the worksheet “Import”. If previous measurement data appears in the table,
please save the file under another name and then click “Clear tables” to erase all
measurements from the tables. Connect the VM31 to a USB port on the PC and
switch it on. If not done before, install the device driver (section 11). Click “Import
measurements from VM31”. The device with its virtual COM port will be automatically detected. In rare cases detection may fail, due to other connected USB hard ware using virtual COM ports. It may be necessary to disconnect such hardware be fore data transfer.
The messages in the “Status” field inform you about import progress. Data import
may take between a few seconds and some minutes depending on the amount of
data. When the transfer is completed Excel will automatically sort the data into the
following worksheet columns: record number, date, time, comment, mode, filter and
the measurements of X/Y/Z and A. Columns B and C contain the combined values.
Figure 38: Excel import
12.3. Calculation of Vibration Exposure A(8) and VDV(8)
Vibration exposure A(8), and alternatively, VDV(8), are both used for the risk assessment of human vibration. They can be calculated based on hand-arm (H/A) and
whole-body measurements (W/B). Use the check boxes in the left column of the import worksheet to select the data to be included in the vibration exposure calculation. Alternatively, you may click “Select all”. After selecting the data, click the but ton “Transfer selected data to daily exposure worksheets”. This will transfer the relevant records to the worksheets. These worksheets are available for RMS based handarm and whole-body measurements and VDV based whole-body measurements.
A message box will show you how many records have been transferred.
Select and open a worksheet according to the type of calculation you require “A(8)
RMS H-A”, “A(8) RMS W-B” or “Daily VDV W-B”.
Vibration exposure can be calculated for several persons and activities, i.e. partial
exposures. For this purpose there are two drop down menus for each record. The ten
cells “Person” and “Activity” above the table may be overwritten with your own
text. The changes you have made will be shown in the drop down menus the next
time you transfer data.
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Figure 39: Daily exposure calculation in Excel
Click “A(8) calculation” or, in the case of VDV, “Daily exposure calculation” to
calculate the vibration exposure (Figure 39). The result(s) will be compared with the
limits stated in the EU directive 2002/44/EC and are displayed in various colors:
black: below exposure action value
purple: between exposure action value and exposure limit
red: above exposure limit
During vibration exposure calculation a report is generated automatically. You can
find it in the worksheet “... Report”. It includes tables with the measured values and
the partial exposure values for each person and activity. Below you will find the vibration exposure results for each person (Figure 40).
Figure 40: Example report (part)
12.4. FFT Data Import to Excel
The FFT data stored on the VM31 can also be transferred to the Excel macro file.
Switch to the worksheet “FFT Import”. If previous FFT data is appears in the table,
please save the file under another name and click “Clear FFTs” to clear the table.
Then click “Import FFTs from VM31”.
The frequency steps along with the respective amplitudes of X/Y/Z are sorted into
table rows. You will see the date, time and comment for each record. Tick the check
boxes on the left hand side of each record to select which FFTs should be displayed
in the three diagrams above the table (Figure 41).
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Figure 43: Firmware Updater
5. Click on “Load” in the “Firmware Updater” and enter the path to the file where
the downloaded firmware file vm31.hex is located.
6. In the VM31 “Device Settings” select the option “Firmware update” and confirm the warning and subsequent hint messages by pressing OK. By carrying out
this step the old firmware is deleted. The VM31 will then indicate that it awaits
new firmware data from the USB interface (Figure 44).
Figure 44: Firmware update
7. Click on “Send” in the “Firmware Updater”. Transfer of the Firmware data has
now begun. The transfer progress is displayed as a time bar on the PC and also
on the VM31. When the update is finished the VM31 will start up and the
“Firmware Updater” will close. Please do not interrupt the update process. Following transfer failures the update can be restarted at point 3.
14. Calibration
The VM31 is supplied with a factory calibration. In this way it is assured that the in strument measures accurately if a calibrated transducer is connected and its sensitiv ity entered (see section 9.1). Month and year of the last calibration are shown on the
start screen (Figure 42).
The standard ISO 8041 lays down the requirements of electrical and mechanical cal ibration of human vibration meters.
Figure 45 shows the connections for calibrating the VM31 with electrical signals.
The signal generator needs to be connected via the shown R-C combination to the
inputs X/Y/Z and A. The 4.7 kΩ resistor serves as a sink for the IEPE constant currents. The 1000 µF capacitor keeps the resulting DC voltage drop away from the
generator. The electrolytic capacitor must be rated for at least 25 V. Please make
sure that the generator output can handle the resulting load of approx. 1 kΩ.
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Figure 45: Connections for electrical calibration
GND
X
Y
Z
+
4k7
1000µ
Generator
GND
X
+
4k7
1000µ
GND
Y
+
4k7
1000µ
GND
Z
+
4k7
1000µ
GND
A
GND
A
Plug for X/Y/Z: Binder 711 series, 4 pins, order no. 99-0079-100-04
Plug for A: Binder 711 series, 8 pins, order no. 99-0479-100-08
The maximum input voltage without overload indication is ± 1150 mV.
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15. Technical Data
Inputs 4 Low-power IEPE inputs, 1 mA / 17 V,
transducer sensitivity range 0.8 to 120 mV/ms
TEDS support for template 25 to IEEE 1451.4
Display functions
Human vibration
Interval RMS
Vector sum
Maximum running RMS (MTVV)
Vibration dose value (VDV)
General vibration
(acceleration /
velocity /
displacement)
Running RMS
Maximum running RMS
Vector sum
Peak value
Maximum peak value
Measuring ranges
Acceleration
Velocity
Displacement
Sensor with 1 mV/ms
1100 m/s²
100 - 10 000 mm/s (1 kHz /1 Hz)
250 - 15 000 µm (5 Hz / 250 Hz)
-2
Sensor with 10 mV/ms
110 m/s²
10 - 1000 mm/s (1 kHz /1 Hz)
25 - 1500 µm (5 Hz / 250 Hz)
(zero-to-peak values)
Display resolution
Acceleration
Velocity
Displacement
Sensor with 1 / 10 mV/ms
0.01 m/s²
0.1 mm/s
1 µm
-2
Sensor with 100 mV/ms
0.001 m/s²
0.001 mm/s
0.1 µm
Linearity range > 75 dB (for < ± 6 % error)
Noise < 0,003 m/s²
Filters
Human vibration
Weighting filters Wb, Wc, Wd, Wh, Wj, Wk, Wm
Unweighted: 6.3 - 1259 Hz (hand-arm); 0.4 - 100 Hz (whole-body)
Acceleration
Velocity
Displacement
0.2 Hz – 1.5 kHz; 1 Hz – 1 kHz
1 Hz – 100 Hz; 2 Hz – 1 kHz; 10 Hz – 1 kHz
5 Hz: – 250 Hz
Frequency analysis 125 line FFT for X/Y/Z; Peak spectrum of acceleration
Frequency ranges: 3 - 240, 6 - 480, 12 - 960, 24 - 1920 Hz
Refresh rate: 0,5/s; Windowing: Hann
Data memory Flash; 10 000 measurements; 1000 FFTs
Display OLED, colored, 128×160 pixels
USB interface USB 2.0, full-speed, CDC mode, via cable VM2x-USB
Batteries 3 cells size AAA or Alkaline (LR03) or rechargeable NiMH (HR03)
Battery oper. time 10 - 14 hours
Oper. temperature - 20 – 60 °C
Dimensions 125 mm x 65 mm x 27 mm (without connectors)
Weight 140 g (with batteries, without sensor)
-2
-2
-2
31
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