BRUEL & KJAER System V User manual

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vvww. aef .se -
Instruction Manual
Vibration Exciter System V
• Exciter Body
Type
4801 with
General Purpose
Head Type
481 2
• High g Head
Type
4811
• Mode Study Head
Type
4814
• Permanent Magnet
Body Type 4805
with Calibration
Head Type 481 5
• Big Table Head
Type
4813
This Vibration Exciter System can be used
over a large range
of conditions for vibra-
tion tests of instruments and structures . It
consists
of two exciter bodies and five exci-
ter Heads.
The
exciter employed is driven by a Power
Amplifier 2707 and can deliver a peak
force
of 380 to 445 N with Body Type
4801 or 267 to 310 N with the Permanent
Magnet Exciter Body Type 4805. The Exci-
ter is protected mechanicalIy and electri-
cally. Cooling
of the Exciter is performed by
a
built-in fan in the ca se of the 4801 and
by an externaI
extractor fan (not supplied) in
the case of the 4805 . Any angle of opera-
tion through 360
0
may be chosen, the body
being locked in position by a
handwheel .
~ Bruel & Kjcer
033-0070

VIBRATION EXCITER SYSTE M V
EXCITER BODY 4801
EXCITER BODY 4805
HIGH g HEAD 4811
GENERAL PURPOSE HEAD 4812
BIG TABLE HEAD 4813
MODE STUDY HEAD 4814
CAlIBRATION HEAD 4815
(Applicable to 4801 from serial no. 807327)
Revision February 1980

CONTENTS
1. INTRODUCTION ...... . ............. .. ........... ............ .. ....... .. ..... . ...... .. :................ ........................... 5
2.
INSTALLATION ........................... .... . ....... . ........................ .......... ...... ... ................................. 7
2.1.
MECHANICAL INSTALLATION OF EXCITERS USING
TYPE
4801 BODY ..... ............. ........... .............. ......... ...... ......... ........ ...... 7
Direct Mounting .. ............. ....... .. ...... .. ..... ......... .. ........ .... .... ............. ...... 7
Mounting upon a seismic block................ ............ .. ..... .. .. .. ... ..... ... ..... .... .. .. 7
2.2 . ELECTRICAL INSTALLATION OF EXCITERS USING
TYPE
4801 BODY .......... .. ................ ...... .. ................ .. .......... ..... .. ........... 9
System Interconnection ...... ...... . ......... .. .. ........................ .... ........ .. ..... ..... .. 10
Fan Motor Fuses .. .. ............... .. ....................... ... ....... .... ...... .. ..... ....... ....... 10
2 .3 . INSTALLATION OF EXCITERS USING
TYPE
4805 BODY ................................................. .... ............... .. .. .. 12
3. OPERATION ..... .......... ...... .... . .......... ......... .... .......... .. ...... ....................... ................. .. .. ..... .... 13
3.1. PRINCIPLE OF OPERATIOI\J ....... .. ........ ..................... .... ..... .. .. ..... ..... ...... ... 13
3.2 . SELECTION OF APPROPRIATE B & K EXCITER HEAD ............... ... .. .. ......... 13
Brief Description ........... ............................... .. .. .. ........ ......... ...... .............. 14
3.3. MOUNTING AND REMOVAL OF EXCITER HEAD ... .. ........... .... .. .. ............ .. .. 15
4801 Body . .............. ..... ........... ...... ...................... .......... .............. .. ........ 15
4805 Body ........................... ........... ............ ...... ............. ..................... 16
3.4 . INSERT INSTALLATION AND REPLACEMENT ... .. .......... . ............ . .. . ...... 16
3.5. FIXTURES ....................................... .. ......... ..... .. .. .............. .. .. .. .... 16
3.6. MOUNTING THE FIXTURE AND TEST OBJECT ............. .. .. .. . .. .. ........ .. ........ .. 17
Bolt Patterns and Mounting Screws ... ............ ..... .. ..... .... ....... .... .. ..... ......... 17
Positioning the test object ....................................... .. .. ......... ...... .. .... .. . 18
Externai Supports ............... .. .... ............... .... .. .. ................ .... ...... .......... .. .. 18
Electrical connections to test objects . ....... ... .. ......... .. ........... .. ... ...... . .......... 19
3.7. POSITIONING THE EXCITER .... ........... .. .... .. ............... ........ ........ .. .............. 19
3.8 . STATIC LOAD LIMITATIONS ....... .... ...... ... ............ .. .... . ....... ..... ...... ........ .. .. 20
3.9. PUSH RODS ............................. .. ..... .... ..... .... .............................. ...... ...... 23
3.10. START-UP PROCEDURE ... ........ ...... ....... ....... .. ....... .. ....... ..... ........ . ...... .... 24
3.11. "EXCITER" LAMP INDICATION ........................... ... ..... .. .... . ...... . ...... .. .. .. .... 25
3.12 . OPERATION IN HIGH AMBIENT TEMPERATURES ... .......... .. ...... ................ 25
4801 Body ..... .... ............... ..... .. .... .... ............. ...... . .......... ........ ........ 25
4805 Body ........ .................................. . ............. .... ........ .. ...... .. ... .... ...... 25
3. 13. REDUCTION OF RESIDUAL MOTION ..... ... .......... . .... ... ....... . ............. .. .... .. . . 25
4. DESCRIPTlON OF 4801 EXCITER BODy ........... .. ................ ..... ... .... ..... .............. ...... ........... 26
4.1. THE MAGNET ASSEMBLy .................. .. ...... .. .. .... ...... ..... ... ..... .... .. ... .. ..... ... 27
Field Coils .... .. .......................... .. ............................ ....... .. ........ . .. ... .... ... .. 27
Secondary Bands .. ...... .. ... . .. .. .......... .......... .. .. .. .. ............ ...... .. .. .. .... .. ........ 27
Stem ............ . .......... .. .. . ..... .. .. ....... .. .. ....... ........... ................ .. .. . ............. 27
Centre Bowl .. . .. ............. ....... ........ .............. ...... .. ................... .. ............... 27
Upper Wheel ............ .. .... ........ .......... ....... ... .... ..... ...... ..... ..................... ... 27

4.2. THE FIELD SUPPLY AND COOLlNG ASSEMBLY .. ...... .... ...................... ........ 27
The Head and Field Cooling Fan .. .......... ....... . ...... ...... .... ......... .. .. ....... .. ..... 28
Blower Motor . ...... .. .... .. ....... .. . .. ....... ........ . .. ............. .. ... ... .. ..... . .. ... ........ . .. 29
Field Supply ........ ... .. .. .. ...... .. .. ... .. ..... .. ...... ..... .. ............ ........ .. ...... . .......... 29
4.3 . EXCITER SUPPORT ...... .. .. ......... .... .. .. ................ ... .. .. .. .. .. .. ..... .. ... ...... ...... . 30
Base ...... .. .. ........ ...... . ................. .. . '" .... ....... .. .... .. .... .. ...... . ...... ... ........ . .. 30
Side Supports ...... .. . .. .................. .... ..... ...... .. .. ... .. ...... .... .. ..... .. ... .. .. .. .. .... 30
Trunnion Springs .. ...... .. .. .. .......... ... ........ ..... ........ .... .. ..... .. .... .. ... . 30
High Frequency Suspension Engagement Knob .. ...... .......... 30
Rotation Bearing / Brake. ........... ...... .. ...... ........ .. ...... .. 30
Rotation Clamp Knob .............. .. .... .. .. ........ ... .... ...... .. ........ .. .. .. ..... .. ... .... . . 31
4.4. 4801 (S) .................... .. .. .. .. .. .. .... .. ....... .. ... .... .. .. ..... .. ..... ... .... ...... .... ..... 31
5. PERMANENT M
AGNET BODY , TYPE 48 05 ...... .. .... .... ... .. .. .. ........ ....................... ...... ...... .. .... 32
6. DESCRIP TION OF EXCITER HE ADS ...................... .. .......................... .... ..................... . .. ...... 33
6.1. HEADS WITH SQUARE TABLES, TYPES 4811, 4812, 4813 .... .. . ....... ........ .. 33
Table and Mounting Surface ................................................. ........ . .. .. ...... 33
Flexure System . ...... .. ...... .. . ............. .. .. .... .......... .. .. ... .. ........ ... .............. . 33
Stray Magnetic Field ... .. ............ ........ .. .. .. .. ........... .. .. ... .. .......... .. .. .. .. .. 35
M
echanic al Ov er-trave I Stops ...... .. ............. .......... ........ .. .......... ............. ... 36
Split Hub .. .............. .... .. . .. ......... .. ........ .. .... .. .... .. . .. .... .... . .. ... . ... . 36
Driver Coil ......... .. 36
Side
Overload Pads ......
37
Moving Element Skeleton . . .. ...... .. .. .. .. ..... ....... .... . .. ..... .. .. .. ....... .... .... .. .. .. 37
Boot . .
........... ... 38
Protective Can an d Guidance Pins for the Head ..... .. .. .......... ....... ............. ..
38
6.2.
THE MO DE STUDY HEAD TYPE 4814 .. ..... .. .. .... .. ... ....... ..... ..... ... ... .. ........ .. .
38
6.3.
THE
CA lI BRATION HEAD TY PE 4815 .. .. ... .. .. ... ... .. .... .. .. ..... .. 39
Reference Accelerometer ......... ... .... .. ... ........ .. .. .. .. .. .... .... .. ........... ....... . 40
Mounting the Accelerometer .. .. ... ..
4 1
Other Features Specific to the Type 4815
42
7. CHARACTERISTICS ........... .... .. .. . ....................... .. ............ .. ................... .. .. . .. ................. .. .... 43
7.1.
S
QU ARE TABLE HE ADS ..................... .. .. . .... ....... ........ .. ..
43
Frequency Response and Resonance .......... .. . .. .... .. ....... ....... .... .. .. ..... ...... ...
43
Rated Force and
Limits ....................... ... ...... .. .. .... .. ... ... .. ....... .. . ... . .. .. .... . 44
7.2 .
MO DE STUDY HE AD ................................. .. .. . .... ... .. ... .... .. . 45
7.3.
CALlBRAT ION HEA D TYPE 4815 .......... . .. . ..... ...... .. .. ........... .. .... ... .. .. .. ... .
49
Frequency Response of the Head .................................... .. .. .. ......... .... .... . 49
Frequency Response of the Standard Accelerometer Type 8305 ......... .. ... .. . . 50
Acceleration vs. Load . ................... .. .......... .. .... .... .
50
C ross-Motion .. . ... ... ...... ................ .. .......... .. ... .... ...... .... . 51
Errors in Ca libration .. ..... .. .. .. ....... .. ......... .. ...... . ..... .. ..
....... ................ 51
8. CARE AND MAINTENANCE ............. ................................................................................... 54
8 .1 . PERIODIC C LE ANING ... ........ .. ................. .. .. ........... .... ...... .......... ...... .. ...... 54
8.2 . CARE OF EXCITER BO Dy .. .......... .. ....... ... ....... ........ .. .... .. ...... .. .................. 54
Exc iter Body Cover .. . ....... . .. ................... ............ .... .......... ... ........... .. ...... .. 54
Clea nli ness of Exciter Body .......... .. .. .. .. .... .. . ....... .. ...... .... .. .... .. ...... ... .. ........ 55

Field Coil Cleaning .......... ....... .. ...... .. ...... .. ..... . .... . ..... ..... .................. .. .... 55
8.3. CARE OF EXCITER HEAD ........ .. ........ .. . .. ..... .... .... . ........ .... ...... .. ..... .... .... . 55
Removal of Cable ... .. . ..... .......... .... ... .. .. ...... .................... .. ............ ...... .... 55
Cleaning of Exciter Head .. .. ...... .. ..... .. ... ....... ....... .... ....... .. ....... ........ .. .. .. .. 56
Clean Workbench Surface .. .. .. . .. ...... ..... .... .. .... .. .. .. ....... .. ..... .... ......... ... .... 56
Care of Mounting Surface ... .... ...... .. .. ... .. .. .. ......... .... ...... ... ...... ... ..... .. .. .... 56
Exciter Head Inspection and Repair ...... .... .............. ..... .... .. ....... ....... ..... .... 56
8.4. CARE OF EXCITER BODY 4805 ...... .... ......... ....... .. ......... .. . .... .. .. .. .. .. ........ 56
9. SPECIF ICA TIO NS ................. ...... ........ .......... ...................................................... . ........ ... .. .. 57
9.1. EXCIT ER BODY 4801 .. .... ........... .. ....... ...... .. ..... ..... .. .... ....... ..... .. .. .. ..... ... 57
4801 T ... .. ............. ...... ....... .. . .... .. .. .. .... .. .. .... ........ .... .. .... .. .... .. ...... ..... ... 57
4801 S .. ........... ..... ........ ................. ..... ..... ....... .. ... .. .. . .. ........ .......... .. .... 57
9.2. EXCITER BODY 4805 .. ..... ...... ...... ....... .... ........ ..... .. ....... .. ....... . .. ............ 58
9.3. EXCITER HEADS .......... .. . .. ... ..... .. ...... .. ..... .. ..... .. . ...... ............... .... ........ .. 58
High g Head Type 4811 .... ............. ... .. .. .. .. .......... .. .. ... .. .. .. .......... ........ .. .. 58
General Purpose Head Type 4812 ...... .. ....... ...... .. . .. .. .... .. .. ......... .............. 59
Big Table Head Type 48 13 ........ . .. ..... ... .. ........... ......... ..... .. .. ......... ... .. ..... 60
Mo de Study Head Type 48 14 ............. .. ...... .. ... .. ... .. .... .. ... .. ...... .. ............. 61
Ca libration Head Type 4 8 15 .. .. .. .. .... ...... . .. ............ .. ........ .. ....... .... .. . .. . ..... 62
9.4 . NOTES TO SPECIFICATIONS .. ... .. .. .... .. .. ... ........ ............. .. ... .. .. .. .... .. .... .. .. 62
9.5. EXTERNAL DIMENSIONS .... ... .......... .. . ........... .... ...... ... .. .. .. ..... .. .. .... .. .. 63

1. INTRODUCTION
Until recently, all electrodynamic vibration exciters, or shakers as they are of ten called,
looked like the one shown in the sketch in Fig.1.1a. A drive coil, carrying an alternating
current. was suspended in a gap in a concentric magnetic field. The drive coil was sus-
pended by upper and lower flexures, which allowed it to move up and down in the gap
and kept its motion rectilinear. Because the drive coil was built into the shaker, the char-
acteristics of a particular shaker were fixed. It could be a heavy-duty type, a light-weight
type, or a large displacement type .
With the advent of the B & K Exciter Systems, it is now possible to have as manyas five
different shakers in one system. The difference is that the B & K exciters have set both
sets of flexures up above the drive coil (Fig.1 .1 b) .
Upper Flexure ---,
low er Flexu re --_,
;::;il~~--- Field Coil
Lower Flexure
la) Ib)
272173
Fig. 1. 1. Construction principles of Vibration Exciters
The flexures and drive coil therefore form a Head which can be lifted off the Body con-
taining the magnetic field and exchanged for another Head. Hence, specialized Heads can
be
built which all fit the same Body The V System of Exciters has five such specialized
Heads and two bodies. Each Head can be used on either the electromagnetic Exciter Body
4801 or the Permanent Magnet Exciter Body 4805. The force range available is from
155t0445N.
There are three square table Heads, varying from a light-weight, high acceleration type to
a large heavy-duty one. There is also a Head with a single, centrally located mounting
point for structural excitation, and a Calibration Head with a built-in reference acceler-
ometer.
For the electromagnetic Exciter Body 4801 , a choice of two different types of base are
also available, under the designations 4801 T and 4801 S. The 4801 T is a spring su-
5

spension arrangement which provides isolation at most frequencies and has the facility of
full 360
0
positioning . The 4801 S is a simplified base upon which the Exciter is fixed in
one position . Uniess otherwise stated, in this book the 4801 T is the Body referred to.
For
same applications, it could be preferable to use a Permanent Magnet Exciter Body
4805. It has the advantage of quieter operation since it can be operated without cooling,
but the disadvantage of reduced force rating . Use of the permanent magnet bodies re-
duces the power available to 70% of that available with the 4801.
6

2. INSTALLATION
2.1. MECH ANIC AL INSTALLATION OF EXCITERS USIN G TYP E 48 01 B OD Y
The technique used to install the Exciter Body 4801 depends upon the usage. For most
applications , the Base of the exciter may be placed directly upon the floor. For more criti-
cal applications , other mounting techniques may be preferred.
2. 1.1. Dir ect Mo untin g
The easiest way to mount the Exciter Body 4801 is to place the Base directly on the
floor. This technique is suitable whenever the forces transmitted from the exciter to the
floor do not produce objectionable results and when the motions coupled to the exciter
from the floor do not affect the usefulness of the exciter. Motion transmitted to the exci-
ter through its body is likely to be insignificant for operation frequencies over 30 Hz and
when an appreciable fraction of the available force is used.
The forces transmitted to the building are seldom bothersome when the exciter is placed
on a substantiai masonry floor. If the exciter is placed on a thin wooden floor , the forces
transmitted from the exciter to the building are likely to cause annoyance , in the form of
vibration and noise . For some situations, an adequate reduction in the irritation leveiover
that obtained with direct mounting can be achieved by placing an inch or two of soft re-
silient material under each corner of the Base.
2. 1.2. Mo unting upon a seis mic block
Vibration isolation better than that provided by the trunnion springs of the exciter usually
is obtained only by use of a seismic block.
A
seismic block consists of a large mass, typically reinforced concrete supported by a rel-
atively soft spring system . The mass is typically ten times as large as the mass of the ex-
citer itself. Hence the block characteristics dominate and the entire complex of exciter
and seismic block may be treated as a simple mass on a spring, i. e., a single degree of
freedom system . Such a system has a resonant frequency corresponding to
f=_l_~ k
2TT m
where k equals the overall spring stiffness of the system and m is the total mass.
Since the mass of the V System Exciter is about 85 kg (187 Ib), depending on which head
is chosen, its seismic block should have a mass of about 850 kg (1870 Ib) This corre-
sponds to 0,35 m3 (12,5 ft
3)
of reinforced concrete . If the Exciter should work down to
1 Hz, then the spring stiffness of the suspension system should be
k =
(2 TT) 2 m = 33,4 N/ mm (190 Ib/ in)
7

272 182
Fig.2. 1. Typical seismic block system
A sketch of a typical seismic block system is shown in Fig.2.1.
The block either stands above the lab floor or is mounted in a pit. In the example shown,
the springs are in compression. In another type of mounting, each corner of the block is
hung from a matched pair of springs in tension (Fig.2.2).
Note that in either case the coupling of mass to springs is done in the plane of the cen-
ter of gravity .
The mounting bolts for the exciter trunnion can be set into the concrete during pouring,
but a better matching of bolt-holes is achieved if the bolts are welded to a plate and the
plate anchored to the concrete. This can be done as shown In Fig.2.3.
The bolt is pushed through the location hole in the plate from underneath and the head is
welded to the plate. J-bars of suitable dimension can be welded on, to anchor the plate
8
2

-----
Springs Waund in
o pp osite Directi
ans
Eye · B alt
Bracket Wel ded to Plate
Nut
--
(j})
.-dl J
C
~
--
-
~
~
C{Y
]b
Steel Frame
~
:)
~
or
Steel
Plane
of
--
r---
- -
Pl ate
G. G. of Mass
I----i
Sp ac
V
ers
271180
Fig .2.2. Tension support for a seismic block
into the concrete . The bolts should project up 75 mm from the plate, in order to clear the
base plate of the Exciter.
Fig.2.4 shows the dimensions of the base plate of the Exciter and the location and size of
the bolt holes. Each dimension applies to all four sides.
2.2. ELECTR IC AL INST A LLATION OF E XCITERS USING TYPE 4801 BODY
It is recommended that all mains installation and connections be made by a qualified
electrician .
S urf ace of
100mm
Concrete
_L ___
")
J
J J J
) Steel J J
J
Pl ate J J )
)
')
)
')
')
J
')
J
J J
')
')
')
J
J J
')
J
')
')
J
')
J
J J
J J J J J
J J
J J J
J J
J J
J J J
') ')
')
J
') ')
J
272185/1
Fig.2.3. Plate anchor details for mounting blocks
9

381 mm (15 ini
l'
'I
I
---$-- -
-- -$- --1-.
E
E
o
'"'
M
I
-- ~ --
I
70 mm (2,75 ini
15 mm (0.59 i ni
212181 / 1
Fig.2.4. Bas e p/ate dime nsio ns for 4801 T
2.2.1. System Interconnection
The Type 4801 Exciter Body is supplied with two captive cables. One of these is a five-
core cable,
which carries three-phase mains power to the Exciter Body. It includes a neu -
tral and an earth . The other is the safety trigger cable. When the 4801 is used with a
suitable B & K amplifier such as Types 2707 or 2708, this cable is used to initiate shut-
down in the event of overheat ing of the field coil, loss of a supply phase or blowing of
one of the fuses on the safety circuit board. Shutdown includes removal of both the exci-
tation and the three-phase supply f rom the Exciter.
For
connection of these cables to a B & K Amplifier Type 2707 or 2708 , refer to the in-
struction manuals for these instruments . If the 4801 is to be connected to an older am-
plifier Type 2707 , having single-phase power requirements, consult your B &K represen-
tative . Remember to reduce CURRENT LIMIT to alevei appropriate to the head in use,
especially
with the more powerfu l Amplifier Type 2708 .
For maximum operating safety the green / yellow conductor in the power cable must be
connected
to a suitable earth, such as the protective earth contact of a mains socket out -
let. The use
of extension cables without protective conductor sha.1I be avoided.
Connection of th e Exciter Head to the power amplifier is made via drive cable AQ 0026 ,
which has a 3-pin connector at each end. Either end may be connected to the Exciter
Head.
2.2.2 . Fan Motor Fuses
The
three fan - motor fuses are situated on the safet y circuit board. To gain access to
them remove th e base cover of the Exciter, which is held in place by four screws. See
lO

Fig .2.5. Details of the fuses are given in the Specifications. Mak e sure that only fuses
with the required rated cur rent and of the specified type are us ed for replace me nt. The
use
of mended fuses a nd th e sh ort - circu iti ng of fus e-holders is prohib it ed.
F an Molor F uses 11 A sl ow·blowl ----,
Cab le E nlr y -- --- --,
Sa fety Cir cuit Board
Ea rth
Fan o lor --- ;::;
8OOJ59
Fig. 2.5 . Exciter Body with base cover re moved
2.3. INSTALLATION OF EXCITERS USING TYPE 4805 BODY
The cable connection between the Power Amplifier 2707 and the Exciter Head is made
as in se
ction 2.2 . In order to complete the electrical loop which operates the EXCITER IN -
TERLOCK, a
connection must also be made from the Exciter Body back to the Power Am -
plifier For this reason a single conductor cable has been provided (AO 0103). which
should be connected as shown in Fig.2.6. The banana plug is inserted in the hole pro-
vided
in the 4805 Body. On Power Amplif i ers wi th single -phase mains supplies the tree
end is connected to terminals 1 and 2 of the terminal board. For connection to Power
Amplifiers with 3-phase mains supplies , refer to the Instruction Manual for the Ampli -
fier .
Terminal Board
2707 740410
Fig 2.6. E xciter inter/ock connections for 4805 Body
11

In order to get the maximum power possible out of the permanent magnet system it is
necessary to supply a cool air flowaround the drive coil. This air flow should be
0,42 m3 / min at 0,008 kg/cm
2
pressure. An ordinary vacuum cleaner will suffice . The
hole in the base of the PM Body is made to receive a vacuum cleaner nozzle. Note that
the vacuum cleaner should be used to suck air from the Shaker rather than blow air in.
The air blown from vacuum cleaners is generally t oo war m for use as a cool ant.
It should also be noted that the base of the B ody is op en. Th erefore if the S haker is used
in other than the upright position, for instance if it is sim ply laid on its side, it will be
necessary to fix a plate to the bottom in order to ensure an adequate cooling flow. If the
Shaker is suspended by using a plate fixed to the mounting holes in the bottom (see sec-
tion 3.7) then there is no problem . Fig. 2.7 is a bottom view of the 4805, showi ng the
placement of the mounting holes .
~ 121 ± 0,2
~ 83 ± 0,3
8 x 11 mm ~ Air ·holes
7404 12
Fig.2 .7. Boltom of the 4805
12

3. OPER ATION
3.1. PRINCIPLE OF OP ER AT ION
The forces generated in an electrodynamic exciter are due to the interaction between an
alternating current in a coil and a magnetic field. This is illustrated in Fig. 3.1.
Test
Obj ec t
Signal
Source Power
Am p li fi er 1-------------,
211056
Fig.3 . 1. Principle of operation of an Electrodynamic Exciter
, is the current in the coi', B the flux density of the magnetic field and F the force gener-
ated by the coil. The magnitude of the force is given by
F = BIL
where
F = Force in newtons
B = Ma gnetic flux, in webers
I = Current in coil, amperes
L = Length of conductor in magnetic field, metres
The current for the exciter is provided by a power amplifier. A signal source , such as a
sine-wave or random generator, is connected to the input of the amplifier. As the signal is
fed to
the coil, a fluctuating force and hence a vibratory motion is imparted to the test ob-
ject. Of course, the coil itself is wound about a moving element and this has a certain
mass. Hence the acceleration due to an applied force F will be
F
a m + me
where m is the mass of the test object and me is the moving element mass .
3. 2. SELECTION OF APP ROPRIATE B & K EXCITER HE AD
The user is urged to read the detailed specifications for each of the currently available
B & K Exciter Heads. He should select the Exciter Head having specifications best suited
to his p articular application. A brief summary of typical specifications is shown in
Table 3. 1.
In Table 3.1 the first thr ee lines list the force a vailabl e fro m each of 5 B &K E xciter
13

B & K Exc it er Head Ty pes
4811 4812 4813
4814 4815
Force,
with 48 01
N (Ibf ) 370 (85) 445 (100)
445 (100) 370 (85)
370 (85)
Force,
with 4805
and cooling N (Ibf) 248 (56)
310 (70) 283 (64) 267 (60) 267 (60)
Force,
with 48 05,
no cooling N (l
bf) 124 (28) 155 (35) 142 (3
2) 133 (30) 133 (30)
Moving Element
Ma ss
Displacement
Limit
Resonant
Frequency
Mounting Point
Locations
kg (lb)
mm (in)
Hz
Circle,
Diameter
mm (in)
Square,
Side
mm (in)
0,18 (0,4)
13 (0,5)
8500
50,8
(0,2)
35,9
(1,414)
0,45
(1,0)
13 (0,5)
7200
76,2
(3,0)
53,9
(2,13)
0,79
(1 ,6)
13 (0,5)
5400
114,3
(4,5)
80,8
(3,18)
0,23 (0,5)
25 (1,0)
64
00
Threaded
hole in
center
of
19 mm
(0,75)
diamet
er
tab le
0,32 (0,7)
13 (0,5)
10000
Reference
accel erometer
Table 3. 1. V System Exciter Heads
Heads when connected to the 4801 Body, and when connected to the 4805 Body with
and without cooling . This force is the force F described in Section 3.1 .
T
he fourth line lists the mass of the moving elements . Exciter Heads 4811, 4814 and
4815 are wound with aluminum wire and 4812 and 4813 with copper wire . The copper
winding permits greater current flow per cross-sectional area and therefore greater force .
Use
of the aluminum winding lightens the total moving element weight . 3.3
The fifth line lists the available peak-to-peak displacement. A displacement of 13 mm
(0 ,5 in) is adequate for almost all environmental vibration testing and calibration applica-
tions . The larger displacement of the 4814 is useful when testing structures or modeis.
3.3
The sixth line lists the resonant frequencies of the moving elements . For environmental
vibration testing and calibration applications, operation below the resonant frequency
provides low distortion and low cross motion . Although operation at frequencies up to
100 kHz is possible, the available force is considerably reduced .
Exciter Heads 4811 , 48 12 and 4813 have a centre m ountin g insert and four equally
spaced outer inserts . Line seven gives both the dia me ter of the circle formed by the four
outer inserts and the side of the equivalent square .
3. 2. 2. Brie f D escription
The High g Head Type 4811 has an 380 N (85 Ibf) force rating, a light-weight moving
element and high resonant frequency . It is especially weil suited to the environmental vi-
bration testing of small objects, either to very high vibratory acceleration levels or to high
freq uencies .
The Big Table Head Type
4813 has a 445 N (100 Ibf) force rating, a large, stift table, and
14

extra strong fle xure s, to resis t large applie d mome nt s. E nvironm e ntal testi ng of lar ge de-
vices, of unb alance d o bjects, and of objects w ith se vere t ransv erse resonances, is b est
don e with this he ad.
The
General Purpose Head Type 4812 has a 445 N (100 Ibf) force rating . The table is
larger than the 4 811 but smaller than 4813. T he moving element weight, moment limit,
and resonant freq u ency are intermediate in value between the 4811 and the 48 13. The
Exciter Head Type 4812 is tr u ly a "Gener al Purpo s e" head, suit able for a wide ra ng e of
appl ications.
The Mode S tudy Head Type 48 14 has a 25 mm (1 in) pe ak -to-peak di splacement cap abil-
ity, co mpl ia nt springs a nd a light-weight mo vi ng eleme nt . T he ta bl e is ro u nd , 19 mm
(0,75 in) in diameter, with a centre insert. B oth me tr ic and in ch inse rts ar e p rovid ed.
This head is intended to be used either sing ly or in m ultiple exciter arra ys as a for ce gen-
erator . In most stru ct ural vib ration testin g ap pli ca tions , eit her a pu sh rad or a t ension
wire is connected betwee n the exc iter table top and th e te st obj e ct to mini mi ze th e c ou-
pling of skew for ces from the test object to t he e xcit er. Ty pic al struc tur al testi ng ap plica-
t ia ns would incl ud e the det er mi natio n of th e frequ ency and damp ing for each of the reso-
nant modes of ai rcr aft elements, suc h as con troi surfa ces, wi ngs , or land in g gear. Hy-
drodynamicists and ae rodyn am icists may find t he Exc it er He ad Type 4814 use ful fo r cavi-
tation or vortex shed ding stu di es . Chemists and Chemi cal Engin eers may use this head
to vary the rate of chemic al r eactions or to vibr ate pla stic e xtru sion di es.
The Ca
libration Head Type 481 5 is design ed for the cal ibration of a ccele rom eters. A R ef-
erence St andard Acc elerome ter (included) is fi xed to a mou n ting blo ck in the ce nt re of
the table . The accelerometer to be cali br ated is sc rewed into the top of t he refe r en ce ac-
cele rometer . The skele ton of the E xciter Head Type 481 5 is sti ff , p rov id ing a reson ant
frequency of 10kHz w ithou t an attached ac ce le rom e ter , and more th an 8,5 kHz w ith
mo st types of accele ro m eters . A dequate force is pro vid ed for cali bration at l evels to
100 g at fre quen cies up to 10 kHz. Calibr at ion at l ev els as l ow as 0, 01 g is also possi-
ble,
either by disco nnecti ng the cooling sy ste m in the 4801 or by usin g a 480 5 Exciter
Body.
3.3. MOUNTING AND REMOVAL OF EXCITER HEAD
3.3.1. 4801 Body
With the power to the Exciter Body turned off , place the Exciter Head on top of the Exci-
ter Body with the connector to t he rear (the cableto the Exciter Body is also to the rear).
The lower edge of the Head Protective Can w ill slip over the Upper Wheel of the Exciter
Body and
the Head Alignment Pins will rest on the upper s urface of th e Upper Wheel .
Rotate
the head until the Head Alignment Pins drop into the holes in the Upper Wheel
an d l ower the head until it is fully engaged . The Split Hub of the Head will provide close
concentricity guidance . Engage and press down th e Head Latche s in any order . Attach
the cable from the Power Amplifier to the connector on the Head. The Exciter is now
ready for operation.
To r emove an Exc it er Head, fi rst turn off the power swit ch on the Power Amplifier , w hich
co nt rols the power for the magneti c fi e ld of th e E xcit er. Next , dis c onne ct the ca ble from
the Exc iter Head, to e limin ate the possib ili ty of burning out the Driver Co il wh en th e Exci-
te r Head is re mov ed from the Exciter Body. Lift the Ex c iter Head ev e nl y a nd smoot hly
straight upward , being care f ul n ot to lift one side before the other . tf one side is p ulled up
before the other , it is possible to jam the head with two pins out of their holes and one
p in cocked and jammed inside its hole . If this happens , agentle tap upward with a
wooden block on the lower edge of the Head Pro tective Can or in a handle hole will re-
lease
the jammed pin . Place the head on a smooth clean surface with the table upward.
being sure that there is nothing on the surface that might d amage the Driver Co il.
15

3.3.2. 4805 Body
Place the Exciter Head on top of the Exciter Body with the connector to the rear (the cool-
ing
air hole is also to the rear). The lower edge of the Head Protective Can will slip over
the Upper Wheel of the Exciter Body and the Head Alignment Pins will rest on the upper
surface of the Upper Wheel. Rotate the head until the Head Alignment Pins drop into the
holes in the Upper Wheel and lower the Head until it is fully engaged . The Split Hub of
the Head will prov ide close concentricity guidance. The magnetic field should be suffi-
cient to hold the Head in place, but 3 x 4 mm screws are also provided, which can be
screwed into the space normally used for the Head Latches .
Attach the cable from the Power Amplifier to the connector on the Head. The Exciter is
now ready for operation.
To remove an Exciter Head, remove the hold-down screws from the Head Latch slots .
Place
your feet against the base on either side, take hold of the Head and jerk it upwards
a few centimeters. This will pull the Driver Coil free of the magnetic field, after which the
Head can be lifted off easily and smoothly.
3.4. INSERT INSTALLATION AND REPLACEMENT
Exciter Heads which use inserts are supplied with a mounting tool, a bott le of thread
locking cement, and two boxes of inserts. One box contains inserts with metric internai
threads and the other contains inserts with imperial internai threads.
To install an inser!, the insert is placed on the tool, with the pin of the tool inside the in-
sert internai thread and with the blade of the tool in the slot of the insert. Both the insert
and the hole should be thoroughly cleaned with a solvent to remove all traces of oil or
contaminants from fingerprints. A drop of cement is placed on the insert· externai
threads, and the insert is screwed into the hole.
If properly installed, the upper surface of the insert should be about 0,1 mm (0,005 in)
below the surface. If an insert is damaged, it can be unscrewed with the same tool. It is
advisable to heat the insert with a soldering iron to weaken the cement before unscrew -
ing
the insert.
3.5. FIXTURES
It will almost always be necessary to prepare some sort of fixture to act as a transition
from the Exciter to the test object. This is because the test object is usually attached at
those places where it will be fixed in service, in order to duplicate field conditions, and
these attachment points will seldom match those of the Exciter.
The fixture may be a simple plate with holes for bolting to the Exciter and for mounting
the test object, or it may be a very complicated structure. Whether simple or complex, its
main function is to convey the force generated in the Exciter to the test object, and there-
fore its performance can be crucial to the test .
It is
beyond the scope of this book to do a comprehensive study of fixtures . However, if
there are enough interested persons in a given geographical area, courses in fixture de-
sign can sometimes be arranged. Contact your B & K representative for more informa-
tion.
16

3.6. MOUNTING THE FIXTURE AND TEST OBJECT
3.6.1 . Bolt patterns and mounting screws
In Table 3.2 are shown the bolt patterns and other pertinent data for the three square
table heads in the V Series.
Mounting screws are used to fasten the fixture to the table surface . A steel socket head
screw with a large hexagonal socket and good threads is recommended .
Check each screw before it is used to determine:
a) That the threads are smooth, dean and undamaged,
b) that the socket is dean and undamaged, and
c) that the screw is the right length to engage all of the threads of the insert but not
bottom in the hole.
It may be necessary to use a steel was her under the screw head either to avoid crushing
the fixture or to adjust the length of the screw to avoid bottoming . The mounting screws
should be tightened to the torque shown on the label on the Exciter Head. The use of a
torque wrench is highly recommended.
A
o
B
O O
4811
4812
4813
A mm
in
B
mm
in
Depth
af Hale
Thread Size
mm
in
mm
in
44,7
1,76
35,9
1,41
7,5
0,30
M4
8-32 UNC
66,5
2,62
53,9
2,12
7,5
0,30
M5
10-32 UNF
100,0
3,94
81,0
3,18
15,9
0,63
M6
1/4-20 UNC
Thread
Depth
mm
in 5,6 ,216
3,9
,165 4,7
,185
740508
Table 3.2 . Fixturing detal'fs of the three square table Heads
17

3.6.2 . Positioni ng the te st o bject
3.6.
If possible, the effective ce ntr e of gravity of the test object should be placed on the axis
of the moving element. close to the table surface, and should remain fixed in position
throughout the frequency range . For same specimens, this is not possible.
If the centr e of gravit y is not on the axis of the m oving ele m ent, a mo ment is ap plied to
the table , of mag n it ude e qu al to the produc t of the for ce needed to accelerate the test ob -
je ct and the di stance between the movi ng eleme nt axis a nd the centre of gr a vity . This
moment may deflect the moving element to the side and, if deflection is excessive, the
sid e overload pads on the moving element will rub on the centre post. This probl em c an
be mi nimize d by providin g a counterweight so that the centre of gravity of the combina-
tia n is on the axis.
The test object is likely to have resonances of its own . These resonances may apply mo-
ments to the moving element or cause an effective shift in the location of the centre of
mass . If the problem is serious , and if only part of the force capability of the exciter is
needed to vibrate the test object to the desired leve!, a judicious addition of mass to the
moving system may be help fu!.
3.7.
3. 6.3. Exte rnai Supports
The flexur e systems of B & K Exciter Heads ar e de signed to operate with side loads larger
than commonly are encountered . If, however, it is necessary to vibrate objects that are
likely to apply unusually large side forces to the moving element. it is advisable to use
same form of externai support to reduce these loads. An externa I support should not be
used
uniess it is necessary, si nc e it can lead to pr ob l ems caused by additio nal mass ,
cross motion, distortion and / or ali gnment.
The pr obl em of e xcessive side loads is most co m mon wh en vi br at ing large ob je cts in the
hor iz onta l dir ecti on. The p ro bl em is most seve re whe n th e c entre of gravit y of the object
is
remote fr om the mo un t ing s urfac e.
M any techniques have been devised to reduce the side force s on the moving element . A
few of these tec hniques are:
a) Provide one or more wires or elastic cords from
the gravitationa l force.
an overh ead support to counteract
b) Place the object on a slip table to counteract the gr av itat ional force . Most of these
slip tables are esse ntially a flat plate supported by a thin fi lm of oil on a flat granite
block .
c) Drive the object through a flexible link that is stif fax ially b ut bends rela tively easily.
A
thin rad, t hi n ned do wn regions on a larger diameter rad, or a wire in tension may
be a suitable solution for a particular problem .
d) S
upport the load with linear bearings. If syste ms using ball or roller bearings are
used , same means shou ld be pro vid ed to pre-Ioad every ball or r oller, or ra ttl ing and
excessiv e d istortion will res ult. Air bea rin gs are smooth , and typically free of distor-
tion , but the low stiffn ess may cause ratatianal resonance pro bl ems . High pressure
linear oil be arings wo rk weil if carefully made an d w eil maintained . However, they
tend to be heavy and expensive and ca n be ru ined by a li ttle dirt in the oi!.
18

3.6.4. Electrical connections to test objects
The test object mounted on the Exciter Head may have electrical connections made to it.
F
or example, cables may be run from accelerometers m ount ed on the test object for
measurement or contro i p urposes . Where suc h conn ectio ns ar e made, it is important to
avoid making an earth (ground) connection to the Exc iter H ead through these connec-
ti on s. Such an earth can in te rfere with the proper fu nct io ni ng of t he inte rlock system
( whi ch depends on the earthing of the Head vi a the E xciter Body) and can cause meas-
urement or contr oi errors owing to the creation of earth loops . In t he case of accelerome-
ters mount ed on the test object, this earth co nne c tion can be avoided by insulating the
bodies of the accelerometers from the test object. using for example insulated stud s YP
0150 and mica washers YP 0534 . If the test object is a piece of electrical equipment
with its frame permanently connected to an energiz ed circuit. then the test object itself
should be insulated from the Exciter Head.
3.7. P OS ITION I NG TH E EX CITER
For testing of structures and structural models it is quite of ten necessary to use th e Exci-
ter in a position other than its upright position . The Exciter Body Type 4801 can, in face
be moved through a full 360
0
circle .
To
rotate the Exciter Body, loosen the large hand wheel on each trunnion, rotate to the
desired angular position, and re-tighten the hand wheel.
The technique of mounting the Exciter will vary with the type of structure . If, for in-
stance , a flexible structure is to be set in motion and the Exciter used in the horizontal
position to move il. it would be desirable to bolt the Exciter Body directly to the floor or to
a seismic block . On the other hand, it is sometimes useful to hang the Exciter in some
position facing the test object. In this case, the entire Exciter could be suspended with
elastic ropes. The Exciter Base can be removed , if desired and the Body and Head sus -
pended by an eye-bolt arrangement screwed into the threaded holes in the lower bowl .
When working directly over a structure, the exciter can be slung from ordinary ropes.
." tE = 3
--
-~ .. -...., ..
Fig .3.2. Using the 4805 1 14 in an infrasonic ex periment
19