Manual Number: 38704
Manual Revision: C
3991 Series Piezoresistive Shock Accelerometer Operating Guide
3
8.0
Sensor Verification
Generally the ZMO of a PR transducer is a good measure of
the health of the transducer. Input Resistance (from Red to
Black) or Output Resistance (from Green or Yellow to White),
is less commonly used to check the condition, since resistance
changes with temperature. A thorough check of the health
(suggested both before and after an expensive test) must
include calibration of the sensitivity.
In some laboratories which use piezoresistive transducers, it is
customary to check the continuity and gain of the conditioning
and data acquisition system using a technique called “Shunt
Calibration”. By temporarily unbalancing the bridge with a
shunt resistor placed in parallel with a leg of the bridge
(usually between the “+ Sig” wire and either the “+ Exc” or “–
Exc”), dc shifts of the offset are created. Whereas the process
does not calibrate the transducer, it is a check of system gain,
with accuracy of the resultant dc shift in output dependent on
the degree that the resistances of both the leg of the bridge and
the shunt resistor are accurately known. Among other sources
of variability, temperature can change the value of the
resistors, and therefore the Shunt Calibration output. The user
should be aware that because the sensors are full bridge
transducers, all legs are active and will have temperature
coefficients typical of piezoresistive sensors (approximately
+0.1%/degree C).
9.0
Sensor Calibration
For shock accelerometers, the most appropriate, accurate and
reliable calibration is with a comparison shock using a back-
to-back reference and pneumatic exciter, as described in ISO
16063-22, “Methods for the calibration of vibration and shock
transducers — Part 22: Shock calibration by comparison to a
reference transducer.” PCB offers this calibration as a service.
10.0
Maintenance and Repair
Because of the sophisticated nature of PCB instrumentation,
field repair of the equipment is not recommended. Most PCB
sensors are of modular construction and are factory repairable.
A repair or replacement quotation is available at no charge.
Before returning equipment for repair, it is recommended that
the user confer with a factory application engineer (or inter-
national representative) to first troubleshoot the problem.
11.0
Return Procedure
To expedite the repair process, contact a factory application
engineer to obtain a Return Material Authorization (RMA)
number prior to sending equipment to the factory. Please have
information, such as model number, serial number and
description of the problem, available.
Customers outside the U.S. should consult their local PCB
distributor for information on returning equipment. For
exceptions to this guideline, please contact the International
Sales department to request shipping instructions and an RMA.
For further assistance, please call (716) 684-0001 or fax us at
(716) 684-0987. You may also receive assistance via e-mail at
or visit our web site at
12.0 Customer Service / Warranty
The employees of PCB strive to provide superior, unmatched
customer service. Should you at any time find yourself
dissatisfied with any PCB product for any reason, consult a
factory Application Engineer or local representative/distributor
to discuss repair, refund, or exchange procedures.
When unexpected measurement problems arise, call our 24-
hour Sensor Line
TM
at (716) 684-0001 to discuss your
immediate dynamic instrumentation needs with a Factory
Representative.
