Page 18 - Prosig Catalogue 2005

HARDWARE PRODUCTS
MADE TO MEASURE

change and are the most fragile The reason the impact hammer is sometimes referred to as a Modally
strain gauge type. Tuned® hammer is that the structural design of the hammer has been
optimized so that the structural resonances of the hammer during the
Training & Support use for strain gauges is in Impact hammers are used in many fields from automotive and aerospace
Strain gauges are used in
‘hit’ will not affect the frequencies of interest in the structure and will
many disciplines of science
therefore not corrupt the test data.
and engineering, the classical
material and structural fatigue
design and development through to bridge health assessment.
prediction, but strain gauges
Pressure Transducers
are also used in areas as
diverse as medicine, biology,
Most pressure transducers as used in industry today are of a similar
aircraft structures and even
appearance; they normally take the form of a cylindrical steel body with a
bridge design.
Torque Sensors
A pressure transducer is a transducer that converts pressure into an
electrical signal. There are various types of these transducers on the
Torque measurement is the measurement of the angular turning moment pipe fitting on one end and a cable or connector at the other.
at a particular location and instantaneous time in a shaft. market, but the most widely used is the strain gauge based transducer.
The conversion from pressure into an electrical signal is achieved by
Condition Monitoring effects of this deflection. From the measured deflections it is possible to relationship of applied pressure to diaphragm deformation, that is the
Torque is usually measured in one of two ways: either by sensing the
the deformation of a diaphragm inside the transducer that has been
actual shaft deflection caused by the shaft twisting or by measuring the
instrumented with a strain gauge. It is then possible, knowing the
sensitivity, to deduce the pressure.
calculate the torque in the shaft.
Classical torque sensors, normally based on strain gauges, are used
Pressure transducers are used in any application where the pressure
to measure the deflection in a shaft. These gauges are mounted at 90
in a gas or fluid is being monitored. Sometimes this monitoring is over
degrees to each other. One is mounted in parallel to the main axis of the
long periods, water pressure for example; sometimes it is for very short
shaft the other perpendicular to this.
durations, for example an automotive airbag.
Torque transducers based on strain gauges are often foil types, but can
also be diffused semiconductor and thin film types. However, any strain
the IEPE constant current types are increasingly becoming standard.
gauge based device will be subject to temperature variations. Unless the Pressure transducers normally provide a direct voltage output. However,
These types of transducers are used in situations where electromagnetic
change due to temperature is sensed and accounted for then corruption of noise is present or when long cabling is required.
results can occur. In order to correct for this effect bridge supply sensing
is required. Force Transducer
A force transducer is a device for measuring the force exerted upon a
Software inductive, capacitive or optical types. These types use a slightly different particular structure. The force
There are also more modern types of torque transducer; these include
transducer usually measures the
method to measure the torque in which the angular displacement between
deflection in the structure that
two positions on a shaft is measured and the torque deduced from the
has been caused by the force,
amount of twist.
Torque transducers are used to measure many parameters such as the not the force itself.
amount of power from an automotive engine, an electric motor, a turbine However, some materials used
or any other rotating shaft. in the construction of force
transducers, when compressed,
Recently torque sensors have been used increasingly as part of hand tools actually change in electrical
on a production line. This enables the measurement of torque as screws characteristics. These materials
or bolts are tightened, which can be used to improve quality control. measure the force directly; they
are active sensing elements and
Impact Hammer have a high frequency response.
Hardware test specimen or material. The force gauge that is built into the hammer withstand small amounts of force before damage occurs. The material in
They can however only normally
The function of an impact hammer is to deliver an impulsive force into a
question is a certain quartz based crystalline material. These transducers
measures the magnitude and frequency content of this excitation.
are sometimes called piezoelectric crystal transducers. Electronic charges
An impact hammer is usually used in conjunction with at least one
accelerometer. These accelerometers would normally be single axis,
that force being applied to the crystal. There are other types of force
however tri-axial accelerometers can also be used. These accelerometers are formed in the crystal surface in proportion to the rate of change of
transducer available, for example the ceramic capacitive type.
measure the response of the impulsive force in the material. From the
combined measurements of the excitation and response a frequency Typically force transducers are used for bench testing and for monitoring
function can be calculated. It is possible to change the frequency quality during reshaping or bonding operations on a production line.
characteristics of the impulse by changing the type of ‘tip’ on the hammer Force transducers are heavily used in the aerospace industry, they are
System Packages Impact hammers, sometimes called Modally Tuned® impact hammers, force being applied to the control system.
head. A harder tip will generally produce a shorter impact time, and will
often used as part of a pilot controls. It is important in these situations
often be used for situations where higher frequency analysis is of interest.
not just to have positional information on the pilots’ controls, but also the
are normally applied manually. These devices often resemble common
Load Cell
everyday hammers. They would be used in classical structural or modal
A load cell is basically a transducer that converts a load into an electronic
analysis situations, although they can also be used for acoustic testing.
signal. The majority of load cells in the market are strain gauge based,
To use an impact hammer it is necessary to ‘hit’ the structure with the
however there are some other alternatives. In almost any modern
hammer. The weight and the type of hammer head must be correctly
selected for the amount of force required to excite the structure. The
application that involves weighing, a load cell comprised of strain gauges
bigger and heavier the structure the larger the mass of the hammer head
in a Wheatstone bridge configuration is used.
must be and greater the force used.
Load cells based on strain gauges consist normally of four strain gauges
18 http://prosig.com +1 248 443 2470 (USA) or contact your
+44 (0)1329 239925 (UK) local representative
sales@prosig.com
A CMG Company