Elgar 251 User manual
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MODELS 251 &
501A
AC POWER SOURCES
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ELGAR ONE-YEAR WARRANTY
Elgar Electronics Corporation (hereinafter referred to as Elgar) warrants its products to be free from defects
in
material and workmanship. This warranty is effective
for
one year from the date
of
shipment
of
the product
to the original purchaser. Liability
of
Elgar under this warranty shall exist provided that:
the Buyer exposes the productto
normal
use and service and provides normal maintenance on the
product;
Elgar is promptly notified
of
defects by the Buyer and that notification occurs within the warranty period;
the Buyer receives a Return Material Authorization (RMA) numberfrom Elgar's Repair Department prior to
the return
of
the product to Elgarfor repair, phone 800-73-ELGAR (800-733-5427), ext. 2295;
the Buyer returns the defective product in the original,
or
equivalent, shipping container;
if, upon examination
of
such product by Elgar it is disclosed that,
in
fact, a defect
in
materials and/or
workmanship does exist, thatthe defect in the product was notcaused by improper conditions, misuse,
or
negligence; and,
that Elgar
QA
seal and nameplates have not been altered
or
removed and the equipment has not been
repaired or modified by anyone other than Elgar authorized personnel.
This warranty is exclusive and in lieu
of
all other warranties, expressed
or
implied, including, but not limited
to, implied warranties
of
merchantability and fitness
of
the product to a particular purpose. Elgar, its agents,
or
representatives shall in no circumstance be liable for any direct, indirect, special, penal,
or
consequential
loss
or
damage
of
any nature resulting from the malfunction
of
the product. Remedies under this warranty
are expressly limited to repair
or
replacement
of
the product.
CONDITIONS
OF
WARRANTY
To
return a defective product, contact an Elgarrepresentative
or
the Elgar factory for an RMA number.
Unauthorized returns will not be accepted and will be returned at the shipper's expense.
For Elgar products found to be defective within thirty days
of
receipt by the original purchaser, Elgar will
absorb all ground freight
charges
for the repair. Products found defective within the warranty period, but
beyond the initial thirty-day period, should be returned prepaid to Elgarfor repair. Elgar will repair the unit
and return it by ground freight pre-paid.
Normal warranty service is performed at Elgar during the weekday hours of7:30 am to 4:30 pm Pacific
time. Warranty repair work requested to
be
accomplished outside
of
normal working hours will be subject to
Elgar non-warranty service rates.
Warranty field service is available on an emergency basis. Travel expenses (travel time, perdiem expense,
and related air fare) are the responsibility
of
the Buyer. A Buyer purchase order is required by Elgar priorto
scheduling.
A returned product found, upon inspection by Elgar, to be
in
specification is subject to an inspection fee and
applicable freight charges.
Equipment purchased
in
the United States carries only a United States warranty for which repair must be
accomplished atthe Elgar factory.
Committed
to
Quality...Striving for Excellence
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MODELS
251
and 501A
1-1
1-3
1-9
1-14
1-16
2-1
2-3
2-5
2-8
2-17
3-1
3-3
4-1
4-6
4-8
5-1
5-3
5-5
5-7
5-9
5-12
5-14
Introduction . . •
General Description .
Physical Description
Performance Specifications •
System Applications . • .
TABLE
OF
CONTENTS
SECTION I
GENERAL
DESCRIPTION
SECTION II
INSTALLATION
Introduction . . . . . . . .
Unpacking
and
Receiving Inspection
Rack Mounting
Installation
Checkout
.•
Introduction • • • .
Controls and Indicators
SECTION
Ill
OPERATION
SECTION
IV
THEORY
OF
OPERATION
Circuit Description • • • . . . . . . .
Power Supplies . . . . . . . . . . .
Interconnections
for
Multi-Phase Operation
Introduction .
Factory Repair
·.
Test Points . .
Output
Regulation Adjustment
Current
limit
Adjustment
Periodic Maintenance
Troubleshooting . . . .
SECTION V
MAINTENANCE
Table
of
Contents
1-1
1-1
1-1
1-2
1-2
2-1
2-1
2-1
2-2
2-2
3-1
3-1
4-1
4-1
4-5
5-1
5-1
5-1
5-1
5-1
5-2
5-2
iii
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Table
of
Contents
6-1
6-3
7-1
7-3
1-1
1-2
3-1
TABLE
OF CONTENTS (Continued)
Introduction
Spare Parts .
Introduction
Diagrams
..
SECTION
VI
PARTS LIST
SECTION
VII
DIAGRAMS
LIST
0 F
TABLES
Model
251
Performance Specifications .
Model
501
A Performance Specifications .
Controls
and
Indicators . . . . . .
·.
LIST
OF
ILLUSTRATIONS
Power
Output
Derating . . . . . • • . •
Typical Harmonic Distortion at Rated Power •
Models
251
and
501A
Rear
Panel
Connections
Controls
and
Indicators
and
Front
Panel
Connections.
Models
251
and
501
A, Block Diagram. . . . . . .
Interconnections
for
Multiphase Operation
(page
1
of
2)
Open-Delta Hook Up . . . . .
Quasi-Square
Wave
. . . • . . .
Models
251
and
501A Top View
..
Models
251
and
501A Bottom View
Model
251
Volts Select Board . . .
Model
251
Overall Schematic, Dwg. No. 520-101-6X
Model
501
A Overall Schematic, Dwg. No. 505-002-6X
MODELS
251
and
501A
6-1
6-1
7-1/7-2
7-1/7-2
1-3
1-3
3-1
1-4
1-4
2-3
3-2
4-2
4-3
4-5
4-6
1-1
1-2
2-1
3-1
4-1
4-2
4-3
4-4
5-1
5-2
5-3
7-1
7-2
7-3 Models
251
and
501A
Amplifier
Board Assembly, Parts Layout Dwg. No. 620-210-00
5-2/5-3
5-4
5-5
7-3/7-4
7-5/7-6
7-7/7-8
iv
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MODELS
251 and
501A
SECTION I
SECTION I
GENERAL
DESCRIPTION
1-1.
INTRODUCTION
1-2. This manual
has
been
prepared
for
use
with
the Elgar Models
251
and
501A
AC Power Sources.
The
information
it
contains
is
intended
for
use
by
operators and trained technicians. The manual pro-
vides
information
regarding the installation,
theory
of
operation and maintenance
of
the AC Power
Source. Also included
is
a parts
list
and schematic
diagrams
to
aid in maintaining the
unit
at
optimum
performance.
1-3.
GENERAL
DESCRIPTION
1-4. The Elgar Models 251 and
501A
Power
Sources provide AC power
at
precise frequencies
for
testing,
motor
operation, and frequency con-
version.
1-5. The basic power amplifier consists
of
two
DC
power
supplies and a
direct~coupled
amplifier
driving a tapped
output
transformer. The
output
transformer
of
the Model 251 provides nominal
output
voltages
of
28, 115, and
230
VAC,
that
are
adjustable between 0-32, 0-130, and 0-260 VAC.
The
output
transformer
of
the Model 501 A provides
nominal
output
voltages
of
0-65,0-130,
and 0-260
VAC. The
total
available power
for
the Model 251
is
250VA
and
500VA
for
the Model
501
A at the
rated
output
voltages.
1-6. Power
at
less
than full-rated
output
voltage
is
derated
as
shown in Figure 1-1. Figure 1-2 shows
a typical harmonic
distortion
curve over the fre-
quency range
of
both
units. The
input
power
for
both
units
is
115
or
230
VAC
±10%, 47-53Hz,
10.
1:1.
Output
power frequency
is
established by
a plug-in oscillator module.
Output
frequency
range
of
the Model
251
at
full
power
is
45
Hz
to
5KHz and
at
rated
half
power
is
5KHz
to
10KHz.
The
output
frequency
range
of
the Model
501A
is
45
Hz
to
5KHz
at
full
power. A variety
of
fixed
and variable frequency plug-in oscillator modules
are available
with
frequency tolerances up
to
.0001%. (Refer
to
the specific oscillator manual.)
1-8. The basic power source
output
is
single
phase.
Multi
phase
power can
be
obtained, how-
ever,
by
stacking
two
or
three power sources, all
driven
by
a multi-phase plug-in oscillator module.
1-9.
PHYSICAL
DESCRIPTION
1-10. The Elgar Models 251 and
501A
are
each
contained in
an
all-steel enclosure designed
with
a
standard 19-inch rack-mounting and slide-out
capability. Refer
to
paragraph 2-4, Section
II
for
mounting
instructions. The
front
panels
of
the
Models 251 and
501A
each
contain a voltmeter,
avoltage amplitude control, a power
circuit
breaker
and indicator lights.
1-11. The wind tunnel contains the
output
power
heatsink assemblies, which comprise a two-section
power amplifier. The voltage amplifier and
control
circuitry
is
contained on a plug-in
circuit
board
with
test points and adjustment controls available
at
the
top
of
the board. The Model 251
has
a
special plug-in board which selects anyone
of
four
output
voltage configurations 0-32, 0-130, 0-260
or
auxiliary. The auxiliary position supplies the
nec-
essary
connections
for
using
two
amplifiers
to
gen-
1-1
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SECTION I
erate three-phase-wye
output
power,
or
tandem out-
put
connections using
two
amplifiers in
series
for
two
times the
output
power single
phase.
Output
power
of
both units
is
available at the
output
pow-
er terminal block located on the rear
of
the
chassis,
and at the red
and
white binding posts on the
front
panel.
1-12. The Elgar Plug-In Oscillator module (sup-
plied separately) mounts in the blank
space
located
on the
front
panel
of
both power sources. In most
cases,
however, the power source
will
already
be
equipped
with
this module; depending on the
original purchase order.
If
removal
of
the oscil-
lator
assembly
is
necessary, the
two
thumb
screws
will
facilitate its removal or installation.
1-13. The grill assemblies located on the
front
panel and rear panel provide the fan
with
the nec-
essary
air intake and
outlet
locations
for
proper
operation. The air
is
drawn
into
the
front
grill and
exhausted through the rear grill.
CAUTION
Under no circumstances should the
front
or
rear grill
assemblies
be
blocked or serious
damage
to
the
power source may occur.
1-14. PERFORMANCE SPECIFICATIONS
1-15. The performance specifications
for
the
Model
251
and 501Aappear in Tables
1-1
and 1-2,
respectively. A graph illustrating
output
power de-
rating appears in Figure 1-1, while still another
graph illustrating the typical harmonic
distortion
of
both power sources at rated power appears in
Figure 1-2.
1-16. SYSTEM APPLICATIONS
1-17. The Models
251
and
501
A
can
be
connect-
ed
in
two's
or
three's
with
a common oscillator
to
provide double power, single-phase, two-phase and
three-phase power. The various standard system
model numbers available
are
as
follows:
1-18. Model
251
Systems
1. System 500-1
1-2
MODELS
251
and
501A
This system consists
of
(2) Model 251's,
(1)
Modei400BT
Signal-Routing Plug-In
and (
1)
interconnecting cable.
Not
in-
cluded with the system
but
necessary
to
complete
it,
is
(
1)
400(T) plug-in oscilla-
tor. This system provides
500VA
single-
phase,
output
power, at 65VAC, 130VAC,
or
260VAC
output
voltage.
2.
System 500-2
This system consists
of
(2) Model
251
's
(
1)
4008
Signal-Routing Plug-In,
and
(
1)
interconnecting cable.
Not
included with
the system,
but
ne~essary
to
complete
it,
is
(1) Elgar
2-phase
plug-in oscillator.
This system provides
250VA
output
pow-
er per
phase
at 32VAC, 130VAC
or
260
VAC
output
voltage.
3. System 500-30
This system consists
of
(2) Model 251's,
(1)
Modei400B
Signal-Routing Plug-In,
and (
1)
interconnecting cable.
Not
in-
cluded
with
the system
but
necessary
to
complete
it,
is
(
1)
Elgar 3-phase plug-in
oscillator. This system
is
connected in a
3-phase, open-delta configuration. The
output
power per
phase
is
166
VA
at 32
VAC, 130VAC or
260VAC
output
volt-
age.
4. System 500-3Y
This system consists
of
(2) Model
251
's,
(1)
Modei400B
Signal-Routing Plug-In,
and (
1)
interconnecting cable.
Not
pro-
vided
with
the system,
but
necessary
to
complete
it
is
(1) Elgar 3-phase plug-in
oscillator. This system
is
connected in a
3-phase, phantom-wye configuration.
The
output
power per
phase
is
166VA
at 32VAC, 130VAC
or
260VAC
output
voltage.
5. System 750-3
This system consists
of
{3) Model 251's,
(1)
Modei400B,
(1)
Modei400C,
and
(1)
interconnecting cable.
Not
provided
with
the system,
but
necessary
to
complete
it
is
{1) Elgar 3-phase plug-in oscillator.
This system
is
connected in a three ampli-
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MODELS
251
and
501A
Table 1-1. Model
251
Performance Specifications.
OUTPUT
Power:
(VA)
Power Factor@ Full
VA
Voltage
Ranges
(VRMS)
Frequency
Range
(Hz)
Distortion%@
FL
-
INPUT
Voltage (VAC)
Phase
Frequency (Hz)
Power (approx. max. W
.)
PHYSICAL
Height (in & mm)
Width (in & mm)
Depth {in & mm)
Weight, net (
lbs.
kg.)
shipping (lbs. kg.)
45-200 Hz
200-1000
Hz
1000-5000 Hz
5000-10000 Hz
250
±0.7
0-32, 0-130,0-260
45-10000
0.6
0.4
0.6
0.9
115
or
230
Single
47-63
800
5.25
19
16
70
80
133
482
406
32
36
Table 1-2. Model 501A Performance Specifications
OUTPUT
Power:
(VA)
Power Factor@ Full
VA
Voltage
Ranges
(VRMS)
Frequency
Range
(Hz)
Distortion%@
FL
-
INPUT
Voltage (VAC)
Phase
Frequency (Hz)
Power (approx. max.
W.)
PHYSICAL
Height (in & mm)
Width (in & mm)
Depth (in & mm)
Weight, net (lbs. kg.)
shipping (
lbs.
kg)
45-200 Hz
200-1000 Hz
1000-5000
Hz
5000-1 0000
Hz
500
±0.7
0-65, 0-130, 0-260
45-5000
0.6
0.4
0.6
0.9
115
or
230
Single
47-63
1700
7
19
17
100
115
178
482
432
46
52
SECTION I
1-3
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SECTION I
251
501A
250
500
-+------
225
450
1
-~
200
400
J
.!!! I
~
I
a:
175
350
~
'E
I
~
150
300
~
I
'-
I
~
125 250 j
i
100
200
~
0 75 150
-l
c:
0
.....
,_
0
-
"'
0
50
100
25
50
0 0
.6
.4
.2
32
130
260
27
120
110
240
220
22.1
100 90
200 180
17.2 12.3
80 70 60 50
40
160 140 120 100
80
Output
Voltage
Figure 1-1. Power
Output
Derating
MODELS
251
and
501A
6.2
30 20
60
40
2.46
10
20 0
0
(251
only)
ol~
--~~----~----J
10
45
100
1000
10,000
Frequency
(Hz)
Figure 1-2. Typical Harmonic Distortion
at
Rated Power
1-4
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MODELS
251
and
501A
fier, 3-phase, wye configuration. The
output
power
is
250VA
per
phase
at
32VAC, 130VAC
or
260VAC
output
voltage.
1-19. Model
501A
Systems
1.
System 1000-1
This system consists
of
(2) Model
501
A's
(1)
Modei400BT
Signal-Routing Plug-In,
and (1) interconnecting cable.
Not
in-
cluded
with
the system,
but
necessary
to
complete
it,
is
(1) 400(T) plug-in oscilla-
tor. This system requires the
two
power
sources
be
connected in tandem thus pro-
viding 1
OOOVA
(1
KVA)
single-phase
output
power
at
130VAC
or
260VAC
output
voltage.
2.
System 1000-2
This system consists
of
(2) Model 501A's
(1)
Modei400V,
and (1) interconnecting
cable.
Not
included
with
the system,
but
necessary
to
complete
it,
is
(1) Elgar
2-phase plug-in oscillator. This system
provides 500VA power
output
per
phase
at 65VAC, 130VAC
or
260VAC
output
voltage.
3.
System 1000-30
This system consists
of
(2) Model 501A's,
(1) Model
400V,
and
(1)
interconnecting
cable.
Not
included
with
the system,
but
necessary
to
complete
it,
is
(
1)
EIgar
3-phase plug-in oscillator. This system
is
connected in a 3-phase open-delta con-
SECTION I
figuration. The
output
power per
phase
is
333
VA
at 65VAC, 130VAC
or
260
VAC
output
voltages.
4. System 1000-3Y
This system consists
of
(2) Model 501A's,
(1) Model 400V Signal-Routing Plug-In,
and (1) interconnecting cable.
Not
in-
cluded,
but
necessary
to
complete the
system,
is
(1) Elgar 3-phase plug-in oscil-
lator. The system
is
connected in a 3-
phase,
phantom-wye configuration and
has
333
VA
power
output
per
phase
at
65VAC, 130VAC
or
260VAC
output
voltage.
5.
System 1500-3
This system consists
of
(3) Model
501
A's,
(1)
Modei400V,
(1) Mode1400C,
and
(1)
interconnecting cable.
Not
included
with
the system,
but
necessary
to
complete
it
is
(
1)
Elgar
3-phase
plug-in oscillator. The
system
is
connected in a three-amplifier
3-phase wye configuration. The
output
power per
phase
is
500
VA
at
output
voltages
of
65VAC,
130VAC
or
260VAC
output
voltage.
1-20. Whenever astandard Elgar System
has
been
ordered
with
a cabinet, the system model
number
will
be
preceded
with
the letter
C.
Infor-
mation concerning the
output
connections
of
any
of
the standard systems
appears
in Section II
of
this instruction manual. Information concerning
calibration
of
Systems 500-1 and 1000-1 appears
in Section V.
1-5
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MODELS
251
and 501A SECTION
II
SECTION
II
INSTALLATION
2·1. INTRODUCTION
2-2. The Models
251
and 501A
AC
Power Source
units
have
been
calibrated
and
quality
tested prior.
to
shipment. The units, therefore, are ready
for
installation
and
operation upon receipt. Instruc-
tions in this section must be followed
to
ensure
proper inspection upon receipt
of
the
unit
and
correct installation.
2-3. UNPACKING
AND
RECEIVING
INSPECTION
2-4. The
unit
has
been
packed in accordance
with
industrial standards
for
safe
shipment. Upon
receipt
of
the unit, unpack
and
inspect the
unit
as
described in the following steps:
1.
Visually inspect the
unit
exterior
for
any
signs
of
damage,
such
as
dents,
scratches, or distortion.
2.
Check the
front
panel controls
for
ease
of
operation.
3. Ensure that the
front
panel indicators
are
not
damaged.
4.
Inspect the
front
panel mounted meters
and
ensure they
are
not
damaged.
5.
Remove
the top cover and ensure all
circuit boards
are
securely
seated
in
their respective connectors. Re-install
top cover.
2-5.
6.
If
the power source
has
been
equipped
with
aplug-in module, remove
and
in-
spect
it
for
any
signs
of
<;lamage.
Re·
install the plug-in module. Removal
and reinstallation
of
the plug-in module
is
facilitated by the
use
of
two
thumb·
screws
located on the
front
of
the plug-
in module.
NOTE
If
any
·physical damage
is
evident, file a
claim for concealed damage with the
carrier agent
and
save
all
shipping
materials for inspection. Forward a report
of
damage
to
the ELGAR Repair
Department. Elgar will provide
instructions for repair
or
replacement of
the instrument.
ELGAR
Repair Department
9250
Brown
Deer
Road
San
Diego,
CA 92121-2294
1-800-733-5427
Tel: (858) 450-0085
Fax:
(858) 678-4482
www.elgar.com
RACK MOUNTING
2-6. Both power
sources
have
been
designed
to
allow rack mounting
in
a standard 19-inch instru-
ment rack. The physical dimensions
of
both
units
are
given in Tables
1-1
and
1-2 in Section
I.
2-7.
For slide-out capability, the power sources
have
been
built
with threaded screw holes on both
2-1
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SECTION II
sides
of
the units
to
allow
for
installation
of
the
Zero Mfg. Co.
chassis
slides, part number CTN-120.
CAUTION
When
mounting the Model
251
or
501
A, ensure
that
the
flow
of
air
into
the fan intake
or
outlet
is
not
obstructed
or
serious damage may
occur
to
the
unit.
2-8.
INSTALLATION
2-9.
Power Requirements
2-10. Both AC Power Sources operate
from
either
115VAC
or
230VAC, single phase, 47 Hz
to
63
Hz
input
power. The maximum
input
power (approxi-
mately)
of
the Model 251 and
501A
is
800 watts
and
1700
watts, respectively.
2-11.
For
115VAC
input
voltage operation
of
the
Model
2~
1
or
501
A, connect jumpers
to
input
transformer
T1
as
follows: pin 1
to
pin 3 and
pin
2
to
pin
4. For
230VAC
operation, connect a jum-
per
from
pin
2
to
pin 3 and remove the jumpers
for
the
115VAC
operation. (Refer
to
Figures
7-1
and 7-2, Overall Schematics in Section
VII.)
2-12. Plug=ln Modules
2-13. In most
cases,
the Model
251
or
501A
will
already have a plug-in oscillator, signal-routing
plug-in
or
a blank panel installed. However, in the
event installation
of
one
of
these plug-in modules
is
necessary, the
two
thumb
screws
will
facilitate
their
installation or removal.
2-14. External Oscillators, Programming and
Synchronization
2-15. In some applications
it
may
be
desirable
to
use
an
external oscillator rather than
an
Elgar plug-
in module.
If
this situation exists, the blank
space
in the
front
panel should contain a blank
filler
panel (supplied separately).
2-2
MODELS
251
and SOlA
2-16. When using
an
external oscillator, all
input
and
control
signals should
be
connected
to
J
1,
a
12-pin Cinch-Jones connector. J 1
is
located on the
rear panels
of
the Models
251
and
501
A. (Refer to
Figure 2-1.) Connector J1 may
also
be
used
for
external amplitude programming and synchroniza-
tion
of
the internal Elgar plug-in oscillator
to
an
external
timing
source.
It
is
important
to
know
that
when
an
external oscillator
is
used, the
input
impedance must
be
matched
to
the
input
opera-
tional amplifier
to
obtain again
of
1.
2-17. CHECKOUT
2~18.
The Models
251
and
501A
may
be
checked
out
as
follows:
1.
Inspect the plug-in oscillator.
2. Connect the load
to
the appropriate ter-
minal
of
the rear panel power
output
ter-
minal block
(See
Figure 2-1).
For
bench-
mounted applications, the
front
panel
binding posts may
be
used
for
28V,
115V,
or
230V
output
on the Model 251 and
115V
or
230V
output
on the Model
501
A.
3. Connect the
input
power cord on the
rear panel
to
an
appropriate source
of
single-phase power.
4. Set the
front
panel power switch
to
the
ON position. The indicator lamp
that
lights indicates the
output
voltage
range
as
selected
by
the plug-in volts select
board.
If
the other
range
is
desired,
re-
move
top
cover
of
the
unit
and plug
opposite
end
of
volts select board
into
the connector (Model 251
only).
Re-
install
top
cover.
5.
Adjust
front
panel
AMPLITUDE
con-
trol
for
the desired
output
voltage
as
indicated on the
front
panel voltmeter.
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MODELS
251
and
501A
MODEL
251
OUTPUT POWER
TERMINAL
K TB2
INPUT
POWER
LINE
CORD
MODEL 501A
Figure 2-1. Model
251
and 501A
Rear
Panel
Connections
SECTION II
B1
Ref.)
B1
(Ref.)
2-3
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MODELS
251
and 501A SECTION
Ill
SECTION
Ill
OPERATION
3-1. INTRODUCTION
3-2. This section
describes
the controls
and
in-
dicators
of
the Models
251
and
501A, respectively.
The controls
and
indicators
are
called out in Fig-
ure 3-1. The functions
of
the controls
and
indica-
tors
are
given
in Table 3-1. (Refer to Oscillator
Instruction Manual
for
adescription
of
the con-
trols
on
the oscillator plug-in module.)
3-3. CONTROLS AND INDICATORS
3-4. The controls
and
indicators
of
Models
251
and
501
A
are
described
in Table 3-1.
TABLE 3-1. CONTROLS AND INDICATORS
Control and Indicator
Input
Power Circuit Breaker
CB
1
Indicator Lamp
DS1
(Model 501A)
Indicator Lamp
D51
(Model 251)
Indicator Lamp D52 (Model 251)
Indicator Lamp D53 (Model 251)
AC Voltmeter M1
AMPLITUDE Control Potentiometer R1
Function
Applies
AC
input power to unit.
Lights
to
indicate power
has
been
applied
to
unit.
Lights when output voltage
is
selected at 0-32 volts.
Lights when output voltage
is
selected at 0-130 volts.
Lights when output voltage
is
selected at 0-260 volts.
Monitors output voltage in AC
ranges:
0-35 (Model 251)
0-150 (Model
251
and
501A)
0-300 (Model 251)
Adjust input
signal
amplitude
of
oscillator.
3-1
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SECTION
Ill
3-2
AC
VOLTMETER
Q-30, Q-130,
0-260
AMPLITUDE
CONTROL
MODEL
251
EXTERNAL
OSCILLATOR
JACK
MODEL
501A
CONTROL
R1
MODELS
251
and
501A
SELECTABLE
PLUG-IN
OSCILLATOR
MODULE
POWER
BINDING
POST
CONNECTIONS
THUMB.SCREW
FASTENER
Figure 3-1. Controls
and
Indicators
and
Front
Panel
Connections
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MODELS 251 and 501A SECTION
IV
SECTION
IV
THEORY OF OPERATION
4-1. CIRCUIT DESCRIPTION (Refer
to
Figures
4-1, 7-1, and 7-2.)
4-2. The input signal, approximately 3 VRMS,
is
provided by the plug-in oscillator. For most
oscillators,
the
input signal amplitude
is
controlled
by
front
panel AMPLITUDE control, R1. The
sig-
nal
is
applied
to
the first amplifier stage consisting
of
differential amplifier
01
and
02.
The differen-
tial amplifier provides high
DC
stability. The
emitter currents are supplied by
R6
from a +12V
supply regulated by CR5. The
output
of
01
is
coupled
to
the
base
of
05
which provides drive
signals
to
the
complementary driver stage,
06
and
07.
06
operates
as
an emitter-follower
to
drive
emitter-follower
08,
which provides base drive
sig-
nals
to
the
upper half
of
the push-pull class Bpow-
er amplifier.
07
is
operated
as
a common emitter
stage
to
provide phase inversion
of
the
drive signals
to
the
lower half of
the
poweramplifier. The out-
put
of
07
is
applied
to
emitter-follower
016
which
provides base drive signals
to
the
lower half
of
the
power amplifier.
4-3. The power amplifier consists
of
a number
of
power transistors mounted on two heatsinks.
The .22 ohm emitter resistors ensure equal current
sharing
of
the
output
transistors. The driver and
output
stages are operated from nominal ±42VDC
supplies. Thermal switch
S1
shown on heatsink
No. 1 turns drive signals
off
to
the power amplifier
in
the event
the
power amplifier overheats from
excessive load
or
restricted airflow through the
wind tunnel.
4-4. The power amplifier
is
also protected from
overloads
or
short circuits on
the
output
by current
limit transistors
03
and
04.
The current
in
the
upper half
of
the power amplifier
is
sampled by
R32 and applied across upper limit adjustment
potentiometer R24. The current signal
is
then
applied
to
the base of
03
through R21. When
the voltage
at
the base
of
03
reaches
03's
con-
duction threshold (approximately 0.6V}
the
drive
signal
is
diverted from the base
of
06,
preventing
any further increase
in
output
current. Simultane-
ously, the current
in
the lower half
of
the power
amplifier
is
sampled across R32 and applied across
lower limit adjustment potentiometer R25. This
signal
is
then applied
to
the base
of
04
through
R22. When the voltage at the base
of
04
reaches
04's
conduction threshold,
the
drive signal
is
diverted from the base
of
07
preventing a further
increase
in
output
current.
4-5. Amplifier
output
(TP2)
is
connected
to
out-
put
transformer T2, which steps up
the
amplifier
voltage
to
the
required
output
level. Negative
AC
feedback path
is
from TP2 through R13
to
the
base
of
02.
Capacitor C6 across R13
is
used
to
pre-
vent high-frequency osciUations
in
output.
load
regulation
is
accomplished by passing
the
TP2 wire
from the heatsink plugs through a current trans-
former T3. Positive current feedback
is
taken
across the secondary through regulation adjustment
potentiometer R14 and
to
the
base
of
02
through
R11. R12 and
C4
are used as a high-frequency
regulation boost network.
4-6.
POWER
SUPPLIES
4-7. Plus and minus 42VDC for the amplifier
is
. developed by
the
full-wave bridge rectifier on the
secondary
of
T1. Filter capacitors and supply
4-1
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f'
.....,
J1-4
EXT.
OSCillATOR
INPU'T
ElGAR
PlUG-IN
OSCillATOR
R1
AMPLITUDE
CONTROL
REGULATED
FEEDBACK
AC
FEEDBACK
Figure 4-1. Models
251
and 501A, Block Diagram
OUTPUT
J
en
m
0
-1
0
z
<
s:
0
0
m
,...
en
.....,
en
...
Qj
::l
Q.
en
0
...
)>
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MODELS
251
and
501
A
CONFIGURATION SECTION
IV
OUTPUT CONFIGURATIONS FOR MODEL
251
CD
®
--
-----
3-PHASE
OPEN
DELTA
130
VAC
L-L
3-PHASE
WYE
(2
AMPLIFIER 130 V L-N)
NO.TE: VOLTS SELECT BRO. IN WYE
POS.
3-PHASE WYE (3 AMPLIFIERS)
I I
A0
N
B0
C0
A0
B0
C0
N
HI
NOTE:
28V
0 R 230V OUTPUTS
ARE ALSO
AVAILABLE
FOR
ALL
CONFIGURATIONS EXCEPT 3
AND
5,
BY ROTATING VOLTS
SELECT CARD TO DESIRED
OUTPUT VOLTAGE POSITION
20-100-20
1,
2,
3, 4
20-102-20
1,
2, 3, 4, 5
NO
260V OUTPUT WITH
20-102-
20 VOLTS SELECT CARD
TANDEM
251
ONLY
SPECIAL VOLTS
SELECT CARD
REQUIRED
#20-102-20
Figure 4-2. Interconnections
for
Multiphase Cperation
(Page
1
of
2)
4-3
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