background image

 

 

Since  the  Back-to-Back  Calibration  technique  relies  on 
each  sensor  experiencing  an  identical  acceleration  level, 
proper  mounting  of  the  test  sensor  to  the  reference 
standard  is  imperative.    Sensors  with  mounting  holes  are 
attached  directly  to  the  reference  standard  with  a  stud 
tightened  to  the  recommended  mounting  torque.  A 
shouldered mounting stud is typically used to prevent the 
stud  from  “bottoming  out”  in  the  hole.  Both  mounting 
surfaces  are  precision-machined  and  lapped  to  provide  a 
smooth,  flat  interface  according  to  the  manufacturer’s 
specification.    A  thin  layer  of  silicone  grease  is  placed 
between the mating surfaces to fill any imperfections and 
increase  the  mounting  stiffness.    The  cables  are  stress-
relieved by first routing them to the shaker head, then to a 
nearby stationary location.  This reduces cable motion and 
helps to prevent extraneous motion or stresses from being 
imparted  into  the  system.    A  typical  set-up  is  shown  in 
Figure 12.  
 

 

Figure 12.

 Typical Calibration Set-Up 

 
Adhesively  mounted  sensors  use  similar  practices.  
However,  in  this  case,  a  small  portion  of  quick-bonding 
gel,  or  similar  temporary  adhesive,  is  used  to  attach  the 
test sensor to a reference standard designed with a smooth, 
flat mounting surface. 
 
In  addition  to  mounting,  the  selection  of  the  proper 
equipment  is  critical.    Some  of  the  more  important 
considerations  include:  1)  the  reference  standard  must  be 
specified  and  previously  calibrated  over  the  frequency 
and/or amplitude range of interest; 2) the shaker should be 
selected  to  provide  minimal  transverse  (lateral)  motion 
and  minimal  distortion;  and  3)  the  quality  of  the  meters, 
signal  generator,  and  other  devices  should  be  selected  so 
as to operate within the limits of permissible error. 

 
8.4 COMMON MISTAKES 

Most  calibration  errors  are  caused  by  simply  overlooking 
some of the fundamental principals of dynamics.  This section 
attempts to address some of the more common concerns. 
 

For  stud-mount  sensors,  always  mount  the  accelerometer 
directly  to the reference standard.  Ensure that the mounting 
surfaces are smooth, flat, and free of any burrs.  Always use a 
coupling  fluid,  such  as  silicone  grease,  in  the  mounting 
interface  to  maintain  a  high  mounting  stiffness.    Mount  the 
sensor  according  to  the  manufacturer’s  recommended 
mounting torque. 
 

 

 

 

 

Figure 13.

 Stud Mounting 

 
For  adhesive  mount  sensors,  use  a  thin,  stiff  layer  of 
temporary adhesive such as quick-bonding gel or superglue.  
DO  NOT  use  excessive  amounts  of  glue  or  epoxy,  as  the 
mounting  stiffness  may  be  reduced  and  compromise  high-
frequency  performance.    It  may  also  damage  the  sensor 
during removal. 
 

 

 

Figure 14

.

 Incorrect Adhesive Mounting 

 
Triaxial  accelerometers  should  always  be  mounted 
directly to the reference standard. Use of adaptors may be 
required for calibration of three individual accelerometers 
oriented in a triaxial arrangement. The vibration at the test 
sensor’s sensing element may differ from the vibration at 
the reference standard due to a “cantilever” effect, seen in 
Figure 15. 
 

 

 

Figure 15.

 Mounting Triaxial Sensors (Incorrect) 

 

 

Summary of Contents for 3741E1225G

Page 1: ...elerometer Installation and Operating Manual For assistance with the operation of this product contact PCB Piezotronics Inc Toll free 800 828 8840 24 hour SensorLine 716 684 0001 Fax 716 684 0987 E ma...

Page 2: ...ty regimen When in doubt about a calibration cycle a good rule of thumb is to recalibrate on an annual basis It is also good practice to recalibrate after exposure to any severe temperature extreme sh...

Page 3: ...rchase Order should include authorization to proceed and return at current pricing which can be obtained from a factory customer service representative Contact Information International customers shou...

Page 4: ...isclosure Table Pb Hg Cd Cr VI PBB PBDE O O O O O O PCB X O O O O O O O O O O O X O O O O O O O O O O O O O O O O O O O O O O O O O X O O O O O O O O O X O O O O O O O O O O O X O O O O O X O O O O O...

Page 5: ...e O O X O O O Wires O O O O O O Cables X O O O O O Plastic O O O O O O Solder X O O O O O Copper Alloy Brass X O O O O O This table is prepared in accordance with the provisions of SJ T 11364 O Indica...

Page 6: ...e applied acceleration The sensor element is electrically connected in a Wheatstone bridge circuit The integral amplifier provides a low impedance output to follow on instrumentation These particular...

Page 7: ...ssembly With each conductor being 30 AWG Teflon coated The supplied cable length for a standard DC accelerometer is 10 ft or 120 in 3 m Custom cable length requirements should be specified at time of...

Page 8: ...and stiff adhesives provide the best high frequency response METHOD 1 Adhesive Mounting Base This method involves attaching a base to the test structure then securing the sensor to the base This allow...

Page 9: ...es to reduce the effects of EMI and RFI that is present near electrical motors and machinery Teflon jacketed cabling may be necessary to withstand corrosive environments and higher temperatures Feel f...

Page 10: ...its provide the capability for continuous monitoring Note High sensitivity DC Accelerometers feature on board differential amplification 7 0 OPERATING NOTE Always operate the accelerometer within the...

Page 11: ...s and costly errors Therefore in an effort to prevent the common mistakes associated with customer performed calibration this document includes a broad overview of the Back to Back Calibration techniq...

Page 12: ...usly calibrated over the frequency and or amplitude range of interest 2 the shaker should be selected to provide minimal transverse lateral motion and minimal distortion and 3 the quality of the meter...

Page 13: ...eturn policies and instructions When unexpected measurement problems arise call our 24 hour SensorLineSM to discuss your immediate dynamic instrumentation needs with a factory representative Dial 716...

Page 14: ...tegral Cable Integral Cable Electrical Connection Position Side Side Cable Termination Pigtail Ends Pigtail Ends Cable Type 010 4 cond Shielded 010 4 cond Shielded Cable Length 10 ft 10 ft Mounting Th...

Page 15: ...MIN POWER RED POWER SIGNAL GROUND BLACK OUTPUT WHITE OUTPUT YELLOW MODEL 081A103 MOUNTING SCREW ASSEMBLY 2 SUPPLIED FOR M OPTION MODEL M081A103 MOUNTING SCREW ASSEMBLY 2 SUPPLIED POWER RED CONNECT TO...

Page 16: ...rmation disclosed hereon Neither it nor any reproduction thereof will be disclosed to others without the written consent of PCB Piezotronics Inc REVISIONS REV DESCRIPTION DIN SEE SHEET 1 FASTEN CABLE...

Reviews: