PA8HF power amplifier
Operating guide
Wilcoxon Sensing Technologies
20511 Seneca Meadows Parkway, Germantown MD 20876, USA
Amphenol (Maryland), Inc d/b/a Wilcoxon Sensing Technologies
97012 Rev D 8/17
Tel: +1 (301) 330-8811
Tel: +1 800 WILCOXON
Fax: +1 (301) 330-8873
www.wilcoxon.com
Contents
Safety section
Safety summary
1.0 Product description
1.1 Front panel
3
4
5
5
1.2 Rear panel
2.0 Operation of the power amplifier
2.1 Using the power amplifier with an electromagnetic shaker
6
8
8
2.2 Using the power amplifier with a piezoelectric shaker
2.3 Matching networks
3.0 Initial system setup
3.1 AC line power
9
9
11
11
3.2 Signal input
3.3 The power amplifier, matching network, and shaker cables
4.0 Operation
4.1 Applying power
11
11
12
12
4.2 Test operation
5.0 Maintenance
6.0 Technical assistance
6.1 Technical assistance
6.2 Customer service
14
15
16
16
16
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WARNING: OPERATION OF THIS AMPLIFIER IS SAFE WHEN THE INSTRUCTIONS IN THIS
MANUAL ARE READ THOROUGHLY BEFORE THIS SYSTEM IS CONNECTED TO ELECTRICAL
POWER.
PARTICULAR ATTENTION MUST BE PAID TO THE SAFETY SECTION OF THIS
MANUAL.
IT IS THE ULTIMATE RESPONSIBILITY OF THE USER TO SAFELY SET UP,
OPERATE AND MAINTAIN THE SYSTEM. REPLACE FUSES ONLY WITH THE SAME TYPE AND
RATING AS INDICATED IN THIS OPERATING GUIDE.
WARNING: TO PREVENT FIRE OR SHOCK HAZARD, DO NOT EXPOSE THIS EQUIPMENT TO
RAIN OR MOISTURE.
WARNING:
LETHAL VOLTAGES ARE PRESENT IN THE AMPLIFIER AND MATCHING
NETWORKS. THE AMPLIFIER CONTAINS ENERGY STORING DEVICES. THEY MUST BE
ALLOWED TO DISSIPATE ENERGY BEFORE OPENING THE AMPLIFIER ENCLOSURE.
Safety section
The power amplifier can be safely operated when the instructions in this manual are carefully followed.
This section summarizes the safety considerations. Reminders, in the form described below, will
appear in the detailed instructions to assure operator awareness of these safety considerations.
Qualified personnel should operate and maintain this power amplifier only after becoming thoroughly
familiar with this manual.
WARNING: This symbol is used in the instruction manual where operator safety must be
considered. The instruction manual should be consulted and read carefully.
CAUTION: This symbol is used when caution is needed to prevent damage to equipment.
It is used where careful attention to certain procedures described in the instruction manual
is needed. This symbol is also used to emphasize procedures other than normal operating procedures.
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Safety summary
1. Make sure that the power amplifier is properly grounded to a good earth ground.
2. Make sure that any piezoelectric shaker being driven is properly grounded to a good earth ground.
3. Disconnect the power cord at its source before connecting or removing power amplifier cables.
4. To reduce the risk of electric shock, do not remove the power amplifier cover. No user-serviceable
parts are inside. Refer all servicing issues to Wilcoxon Sensing Technologies.
5. Do not attempt to operate a power amplifier without the protective covers secured.
6. All cables must be connected between the power amplifier, matching network and shaker before
electrical power is connected. Inspect for frayed or cut cables prior to operation.
7. Hearing protection devices are highly recommended in the vicinity of a piezoelectric shaker
whenever the shaker is being driven at high output levels.
8. Do not expose this equipment to rain or moisture.
9. Lethal high voltage may be present at the power amplifier output connector.
10. When using the D125L piezoelectric shaker, it requires pressurization (minimum 1800 PSI) from a
source of dry, inert gas. The D125L shaker must be electrically connected to the matching network
and power amplifier, or the shaker terminals should be shorted together, prior to pressurization or
de-pressurization. Pressure must be applied or released slowly (1 minute) to prevent excessive
voltages at the shaker connecting terminals. Use extreme caution when handling pressurized
cylinders.
11. Use common sense and avoid haste!
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1.0 Product description
The PA8HF is a single-channel, rack-mountable power amplifier designed to high performance
standards. The PA8HF develops a maximum of 800 watts of power into a 4 Ohm load. The amplifier
will drive the full range of Wilcoxon shakers, with the ability to drive the larger shakers to the full
performance limits of the shakers.
The PA8HF combines the latest power amplifier technology with uniquely simple circuit technology to
reduce distortion of all types, and at all power levels, over the full frequency range. In addition to
performance achievements, the power amplifier is designed for long-term reliability and exceptional
resistance to abusive operating conditions.
The power amplifier has circuit breaker protection for AC power input and fuse protection for the output
of the power amplifier.
Specifications
PA8HF
Power output
800 Watts, maximum, into 4Ω load
Power bandwidth
0.5 Hz to 100,000 Hz
Output fusing
12 Ampere, type 3AG or AGC, fast-blow
Input sensitivity
2.5 Volt peak, for full output
Input impedance
50 kΩ, nominal
Dimensions
19” wide, 17.5” deep, 5.25” high
Weight
50 lb
Power requirements
2,000 Watts, maximum
1.1 Front panel
1.1.1 Power switch: The power switch is located on the lower center of the front panel and serves to
energize the power amplifier from the AC power line. The switch is a membrane type and latches the
power when depressed to place the power in the “ON” or the “OFF” condition.
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1.1.2 Power indicator: The PA8HF has an LED indicator above the power switch to monitor the
following conditions:
Unlit - indicates the amplifier has no power.
Red - indicates the amplifier is muted (power-up)
Green - indicates the amplifier operation is normal.
Flashing red - indicates the amplifier clipping.
Orange - indicates channel thermal shutdown.
1.1.3 Output fuse: One output power amplifier fuse is located in the upper right corner of the front
panel. This fuse is connected in the power amplifier output circuit to aid in protecting the power amplifier
or shaker from excessive current. The PA8HF power amplifier is supplied with a 12 Ampere fuse. The
recommended fuse type is 3AG or AGC. Manual section 2.1 lists other values of fuses that may be
used when driving electromagnetic shakers.
CAUTION: To prevent damage to equipment, NEVER replace a fuse with anything other
than the type and value specified. Using values other than those specified will void the
equipment warranty and may cause fire or injury to personnel.
1.2 Rear Panel
1.2.1 Line cord socket: The power amplifier is powered from the AC line using a standard power cord
terminating in an IEC320 socket in the power amplifier chassis.
1.2.2 Power/circuit breaker (mains): The PA8HF amplifier uses a magnetictrip circuit breaker to protect the amplifier. This switch should be ‘OFF’ during
the time the shaker test system is being connected. When switched ‘OFF’, all
A/C power is removed from the amplifier, including standby power. The circuit
breaker is not the power switch and should be switched to and left ‘ON’ after all
test connections are complete. Use the power switch or an external control voltage to power-up or
power-down the amplifier.
1.2.3 Output connector: There is a four-pin SPEAKON connector providing output to drive the shaker
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or matching network.
1.2.4
Input connector: A BNC coaxial connector located on the rear panel provides the input
connection for the power amplifier.
1.2.5 Piezo filter switch: This is a toggle switch located on the rear panel. This switch allows the user
to enable the 500 Hz (-3 dB point) high pass filter required when driving piezoshakers using matching
networks. When the switch is in the “IN” position, the 500 Hz high pass filter is selected. When the
switch is in the “OUT” position, the 0.5 Hz high pass filter is selected.
Note: The piezo filter should be set to the “OUT” position when driving electromagnetic shakers (such
as the F3, F4, F5B, or the F10). Check the position of this switch if you have low output from your
electromagnetic shaker.
1.2.6 Auto/local switch: In “local” position either the front panel power switch or an
external voltage controls the power-up of the amplifier. “Auto” is used when the
amplifier is powered from a switched power outlet. The ‘POWER’ switch and / or control
voltage will function normally after the initial power up.
1.2.7 External/local switch: To power-up the amplifier using an external control
voltage, supply a 4V to 12V AC or DC control voltage to the ‘IN’ terminals of the control voltage
connector. By selecting the switch to the “external” position, the amplifier will power-up only when the
control voltage is present (on). Immediately following power up, the control voltage will appear at the
’OUT’ terminals of the control voltage connector for the control of other equipment. The removal of the
control voltage (0V) causes the amplifier to turn ‘off’ and the control voltage at the ‘OUT’ terminals will
be interrupted. In the “Local” setting, the amplifier will ignore the control voltage, and power up only by
using the front panel power switch. If a control voltage is present at the ‘IN’ terminals it will still be
available at the ‘OUT’ terminals after the power-up sequence.
1.2.8 Ground terminal: The ground terminal in the lower right corner is available to ensure proper
ground of the test system components. Matching network ground connection can also be made to this
terminal.
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2.0 Operation of the power amplifier
Meggitt Sensing Systems manufactures a comprehensive line of vibration generating systems,
including electromagnetic and piezoelectric shakers. Electromagnetic shakers are powered directly
from the output of the power amplifier. However, piezoelectric shakers require a matching network
between the power amplifier and the shaker. A signal source to drive the power amplifier is not part of
the system and must be supplied by the user. This guide describes the operation of the PA8HF power
amplifier. Other guides describe the operation of the matching networks and shakers. For all vibration
generating systems a customer supplied signal generator is necessary to operate the vibration
generating system. A piezoelectric accelerometer to monitor vibration output is strongly recommended.
2.1 Using the power amplifier with an electromagnetic shaker (models F3, F4, F5B,
F10)
2.1.1 Piezo filter switch: The power amplifier drives electromagnetic shakers directly. The switch
should be set to the “OUT” position.
2.1.2 Output fuse: The output fuse is used to protect the shakers and matching networks attached to
the output of the amplifier. Users may wish to replace the 12 Amp fuse shipped with the amplifier with a
smaller value to insure excessive current is not applied to the electrodynamic shakers. Use AGC or
3AG type fuses. The maximum safe current to each shaker is as follows:
Model Current
F5B
0.1 Amp
F3
0.75 Amp
F4
1.5 Amp (no cooling unit)
2.5 Amp (with cooling unit)
F10
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4 Amp
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2.2 Using the power amplifier with a piezoelectric shaker (models F7, F7-1, D60L,
D60H, D125L)
The power amplifier will drive piezoelectric shakers, but must have a matching network between the
power amplifier and the shaker. High pass filtering at 500 Hz (-3 dB point) is selected by setting the
piezo filter switch to the “IN” position.
Note: The amplifier requires external fan cooling when operated at or near maximum power for
extended periods. The fan aids the dissipation of heat from the heat sink cooling fins. Operating with no
fan may allow the thermal shutdown of the amplifier to engage during testing.
CAUTION: In these modes of operation power amplifier must be used with a Wilcoxon
matching network. Do not attempt to operate the power amplifier without the appropriate
matching network.
CAUTION: The impedance matching transformers used in the matching networks are not
designed for use at low frequencies. NEVER attempt to drive the matching networks at
frequencies less than 500 Hz. Piezoelectric shakers have little or no useful output at low frequencies.
2.3 Matching networks
The operating guide for the particular matching network used will provide detailed information for the
proper use of matching networks. However, information in this section is presented to aid the user in
understanding and applying matching networks.
While an electromagnetic shaker presents a low, relatively constant, largely resistive impedance, a
piezoelectric shaker is essentially capacitive.
This means that the impedance presented by the
piezoshaker will decrease almost linearly with increasing frequency.
A piezoshaker creates a
displacement proportional to the voltage input for frequencies below its resonance. Therefore, in order
to get maximum displacement and consequently maximum acceleration levels at low frequencies, the
voltage must be stepped up significantly.
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The impedance matching network normally consists of a step-up transformer and an
output tap switching arrangement. A variety of output voltages are then available to
maximize the voltage delivered to the piezoshaker at different frequencies. Due to the capacitive nature
of the piezoelectric shaker, the output impedance of the power amp, and the impedance transformation
of the matching network’s transformer, the voltage at the piezoelectric shaker rolls off at 20dB per
decade after the corner frequency (exactly like an RC filter). As the voltage switch setting on the
matching network is switched from highest to lowest setting, the bandwidth of the system will increase.
In general, piezoshakers can be operated at their lower frequencies with the matching network switch in
its highest voltage position.
The relatively low load (high impedance) of the piezoshaker at low
frequencies is not demanding and the power amplifier can maintain the high voltage swing for
maximum shaker output, however as the operating frequency increases, lower output voltage taps
become more efficient. The greatest power requirements for the Power Amp will occur at the corner
frequencies of the matching network and shaker system and at the resonant frequency of the shaker.
CAUTION: The piezoshakers can be damaged by internal heat build up when run at
high levels for extended periods. This is due to the dielectric loss tangent of the
piezoceramic material that generates heat. When driven at high power levels this heat
buildup will raise the temperature of the piezoceramic to the Curie temperature where it
will depolarize itself.
Please contact
Wilcoxon Sensing Technologies for
assistance when extended high output
testing will be performed.
CAUTION: Do not change switch settings of the matching network when there is a signal present as
this may cause the contacts to arc and destroy the switch.
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3.0 Initial system setup
Note: All cables should be installed and connections should be completed before switching the
power/circuit breaker switch to "ON."
3.1 AC line power
The power amplifier is wired at the factory for either 120 VAC or 230 VAC. This
AC voltage power wiring is not changeable by the user. The AC power source
should be capable of providing a minimum of 20amps at 120 VAC or 13 amps at
230VAC. A power cord terminating in an IEC320 plug should be connected from
the power amplifier to the AC power line socket.
3.2 Signal input
A laboratory grade low-noise oscillator should be used as a signal source. Use a coaxial cable to
provide the input signal to the BNC connector on the rear panel of the power amplifier. To avoid hum
and noise pickup, avoid running the signal cable parallel to power line cords. Any cabling near power
line cords should be crossed at right angles. The driving signal amplitude is controlled by the signal
generator amplitude control. It is recommended that the signal generating amplitude control be preset,
considering the signal generator’s capability, to eliminate the possibility of overdriving the power
amplifier.
3.3 The power amplifier, matching network, and shaker cables
Electromagnetic shakers do not require a matching network and are connected directly to the power
amplifier with the indicated cable type. Piezoelectric shakers require a matching network between the
power amplifier and shaker; therefore two cables will be necessary to complete the connections. Table
1 describes the cable types required for completing all shaker system connections.
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Table 1 – Interconnecting cables
Cable connecting to
Matching
Cable connecting to shaker
Shaker model
matching network
network
None
None
R1-22-J93-10F3
F3
None
None
R4M-22-J9B-10F4
F4
None
None
R2-22-J9C-10F5
F5B
None
None
R4M-22-J9B-10F10
F10
R22-22-J9B-5
N7FS
R4-4M-J9-10
F7
R22-22-J9B-5
N7FS
R7-7M-J59-12
D60L
R22-22-J9B-5
N7FS
R7-7M-J59-12
D60H
R22-22-J9B-5
N8FS
Integral Cable
D125L
R22-22-J9B-5
N8HFS
R4-4M-J9-10
F7-1
4.0 Operation
4.1 Applying power
Verify the AC voltage is correct and all necessary cables are securely attached.
1 – On the back panel of PA8HF, before plugging the unit into an AC power source make certain the
‘Main Switch/Breaker’ is in the off position. Proceed to step 2.
2 – After plugging the AC power cord into an AC power source, turn the ‘Main Switch/Breaker’ to the
‘on’ position.
3 – The rear panel Status light should initially
flash red. After a few seconds it should turn
green. This is your indication that the amplifier
is ready to be used. If it does not turn green,
turn the ‘Main Switch/Breaker’ to the off
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position and repeat step 1 and 2. See photo of rear panel. If this condition persist, contact Wilcoxon
Sensing Technologies as the unit is most likely damaged.
4 – Once the Status light is green, connect the oscillator cable making certain the oscillator output is set
to its lowest (0 volts) output. You need to wait to increase the oscillator output until after the power
amplifier is operational. Attaching the oscillator cable with the signal level set to something other than
zero volt output sets up the potential of generating a transient signal that could potentially damage the
shaker.
5 - Push the front panel power switch (this is the 7B/SST marking as shown in the adjacent photo) and
observe the LED turning from unlit to red (mute). When the power supply has stabilized the amplifier will
come out of mute and the LED will change to green (normal operation).
Note: If the power indicator color remains red, a fault condition exists within the power amplifier or
output circuit. Turn off the power, repeat the steps in the initial system setup (section 3.0) then re-apply
power. If the fault persists, contact Wilcoxon Sensing Technologies. The LED, when unlit, indicates no
AC mains power is present and the amplifier probably needs only to be powered on or the rear panel
circuit breaker is switched off. The amplifier will need to be unplugged from the AC power source and
steps 1 and 2 must be followed to correct this condition.
Clipping occurs when the channel output level no longer can follow the level increase at the input
(overdriven input condition). When the PA8HF is driven into clipping the LED will change from green to
red then back to green when the level is reduced (flashing red). Momentary clipping can be tolerated,
however it indicates that maximum output power has been surpassed and potential amplifier or shaker
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damage may result if overload conditions persist. Any amplifier that is constantly clipping indicates a
more powerful amplifier is needed for that application. A different (larger force output) shaker may be
required
The PA8HF has thermal shutdown circuitry to prevent damage due to overheating. Should thermal
shutdown occur, the amplifier will mute and the LED will turn orange – indicating this condition. When
the amplifier has cooled to a safe operating condition the PA8HF will return to normal operation.
Persistent thermal shutdown indicates a cooling fan may be necessary to increase airflow across the
PA8HF’s heat sink. The end user should investigate cooling fans for this.
4.2 Test operation
Follow the procedures below to test the operation of the power amplifier.
1.
Verify the amplitude level of the signal source is set to its minimum position.
2.
While monitoring the shaker force output level, or acceleration level, gradually increase the signal
output level of the signal generating system.
3.
Verify that the shaker force being applied to the test structure is adequate to continue testing.
Large test levels are not normally necessary. The minimum signal level necessary to conduct your
test should be used as sudden changes in the mechanical impedance of the test object can
adversely the amplifier’s output causing overloads or shaker damage. A current monitoring device
is suggested for electrodynamic shaker applications to ensure the maximum current to the shaker
is not exceeded.
4.
If there is no force output from the shaker after increasing the signal level to the PA8HF, reduce the
signal generating system output signal to its minimum, turn off all power, check all instrumentation
components, check all system fuses, and check all cabling before re-applying power.
5.
If it appears that there is a problem with the power amplifier, please refer to maintenance (section
5.0) for assistance. If the shaker is producing adequate force, the system is ready to use for
testing.
6.
At the completion of all testing operations, reduce the signal generating system output signal to its
minimum and turn off power to all test system components.
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5.0 Maintenance
WARNING: Lethal voltages are present within the chassis of the power amplifier
whenever AC power is connected. Users should not attempt repair operations on
components of the power amplifier.
A great deal of care has gone into every power amplifier to verify that it meets or exceeds all its
specifications before it is shipped to you. If you are certain the problem lies in the power amplifier,
check first to determine if the power indicator is illuminated. If it is not, the main AC mains breaker has
likely tripped. Reset the breaker.
After resetting the AC mains breaker, the amplifier may immediately cause another breaker trip. If this
should occur, there could be an amplifier power supply problem and the power amplifier requires
service.
CAUTION: To prevent damage to equipment, NEVER replace a fuse with anything other
than the type specified. Using types other than those specified will void the warranty and
may cause fire or injury to personnel.
The output fuse (located on the front panel) should only be replaced with AGC or 3AG types as
supplied with your system. When removing this fuse, ensure that power is not applied to the power
amplifier.
The output fuse, because of its construction, may interrupt the circuit before a circuit breaker on a
matching network opens. DO NOT substitute a higher value or a different type of fuse. Decrease the
matching network output voltage tap or decrease the level of the signal generator. Consult Wilcoxon
Sensing Technologies for more information about inductive tuning or other special application
assistance.
For piezoelectric shaker systems employing matching networks, there may be another current-limiting
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device (such as a fuse, circuit breaker, or thermal cutout) to the amplifier’s output within the matching
network. Consult the matching network’s manual for details.
CAUTION: The power amplifier contains no user serviceable components. Service or
repair of the power amplifier should not be attempted by anyone other than Wilcoxon
Sensing Technologies employees or designated representatives.
6.0 Technical assistance
6.1 Technical assistance
For technical assistance, please contact Wilcoxon Sensing Technologies customer service at 301-330-8811 or
email info@wilcoxon.com.
6.2 Customer service
To obtain a return materials authorization number, please email info@wilcoxon.com using ‘RMA request’ in the
subject line. Please provide return contact information including name and phone number or contact customer
service directly at 301-330-8811.
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