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| home >> engineering
information >> Shaker Power Amplifiers |
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| General |
| Labworks manufactures a range
of Linear Power Amplifiers primarily intended for use in driving vibration
shakers. These amplifiers are high quality, low distortion, low noise units
that can be used for any audio frequency application requiring high output
current capability. All Labworks amplifiers are designed to tolerate highly
reactive loads and will recover automatically from short circuit and over-temperature
conditions. |
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| Unlike standard public address
power amplifiers, these amps have DC output capability. The heat rejection
ability of Labworks amplifiers is between 3 and 10 times that of amplifiers
designed to drive loudspeakers. The combination of high output current,
self protection, high heat rejection, DC output, power-on interlock, and
voltage or current source capability is what sets these amps apart from
other high power audio amplifiers. It is just this combination of characteristics
that make these amplifiers suitable for use with vibration shaker and other
transducer applications. |
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| Linear Power Output Stage |
| All Labworks power amplifiers utilize
class AB1 linear power output stages. This type of output configuration
offers the maximum electrical efficiency consistent with the inherent low
noise and wide bandwidth associated with class A operation. |
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| Smaller shakers and vibration transducers
are often used in reduced force applications with sensitivity to both conducted
and radiated noise associated with Class D amplifiers. Further, these applications
will usually benefit from a highly damped voltage source amplifier. The
direct coupled solid state output of Labworks amplifiers, with no reactive
or filter components in the output signal path, provides for maximum output
damping with minimum conducted and radiated noise. |
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| These applications involving higher
frequencies, low conducted and radiated noise, and wide bandwidth make a
linear amplifier the logical choice over digitally modulated amplifiers. |
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| Heat Rejection |
| One by-product of high quality
audio and Labworks linear power amplifiers, with linear output stages, is
a higher heat rejection rate. To maintain high output currents at low output
voltages, these types of amplifiers must dissipate significant amounts of
heat. The extremely limited heat rejection rate of public address amplifiers,
along with limited or nonexistent low frequency output ability, makes them
all but unusable for shaker or high current transducer applications. These
amplifiers are designed to drive loudspeakers which are made intentionally
inefficient with higher impedance to maintain flat frequency response. Amplifiers
like these will usually falt on over-temperature or over-current when trying
to drive shakers or high current transducers. |
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| Some public address amplifiers
can be used for shaker applications if low frequency operation is not needed
and their cooling can be enhanced by adding extra cooling fins, cooling
fan packages, etc. All Labworks amplifiers come standard with oversize heat
sinks. All but our smallest amplifier, the PA-119, have low noise, variable
speed, high volume cooling fans to insure unhindered performance in high
current applications. |
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| Shaker/Transducer Protection |
| Unlike speaker applications, it
is important that the shaker amplifier never be switched on or be automatically
reset with its gain up. Uncontrolled, spurious output turn-on transients
or automatic output restoration after an amplifier or interlock fault can
result in a broken shaker. |
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| Labworks amplifiers provide for
external customer assignable shutdown interlocks as well as power-on interlock
protection. This interlock protection insures that the amplifier gain must
be fully down before the amplifier output is enabled. The external interlock
can be used in conjunction with a vibration controller or other critical
test article parameters to shut the system power amplifier down. |
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| Current Source Capability |
| In some applications involving
constant force (instead of acceleration, displacement, etc.) it is desirable
to have a completely undamped force source at the shaker. For these applications,
the most desirable amplifier output characteristic is that of a current
source instead of a voltage source. |
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| Unlike many amplifiers available,
most Labworks models have dual mode operation capability and can be simply
switched to operate as either a high frequency, highly damped voltage source
or as a high impedance, low damping current source. |
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