HP 202A Service manual
SPECIFICATIONS
r
FREQUENCY RANGE:
DIAL ACCURACY:
FREQUENCY STABILITY:
OUTPUT WAVEFORMS: Sinusoidal, square, and triangular. Selected by panel switch.
MAXIMUM OUTPUT VOLTAGE:
FREQUENCY RESPONSE:
lNTE RNAL IMPEDANCE
DISTORTION:
0.008 to 1200 cps in five decade ranges with wide overlap at each
dial extreme.
Within
Within
*lo%.
At least 30 volts peak-to-peak across rated load (4000 ohms) for
three waveforms. (10.6 volts RMS for sinewave.
Constant within
and load.
Approximately 40 ohms over the entire range.
:
Less than 1% on
*2% from "1. 2" to "121q on dial; *3% from ". 8" to "1.2".
4%
including warm-up drift and line voltage variations of
)
*0.2 db over entire frequency range at rated output
all
ranges except X100. Less than 2% rms on
all
X100.
OUTPUT SYSTEM:
HUM LEVEL:
SYNC PULSE
POWER: Operates from
DINENSIONS: Cabinet Mount: 20-314" wide, 12-112" high, 14-112" deep.
WEIGHT: Cabinet Mount: 48 lbs; shipping weight, approximately 84 lbs.
ACCESSORIES AVAILABLE:
Can
be
operated either balanced or single-ended. Output system
is
direct-coupled; dc level of output voltage remains stable over
long periods of time. DC adjustment available on front panel.
Less than
10 volts peak negative, less than 5 microseconds duration. Sync
:
pulse occurs at crest of
on other waveforms.
17 5 watts.
Rack Mount:
Rack Mount:
For rack mount style: End Frames with handles for bench use.
Specify
0.05%
@No. 17 End Frames.
at
rated output.
sinewave and with corresponding positions
ll51230V
19" wide,
36 lbs; shipping weight, approximately 74 lbs.
-+lo%,
10-l/21qhigh, 14-11 4" deep.
5011000 cycles source. Requires
CONTENTS
SECTION I GENERAL DESCRIPTION Page
SECTION
SECTION
II
m
1 . 1
OPERATING INSTRUCTIONS
2
.
2
.
2 . 3 230-Volt Operation
2
.
2 . 5
.
2
.
2
THEORY OF OPERATION
3
-1
3 . 2 Bi-Stable Circuit
3 . 3 Linear Integrator
3
.
3 . 5
3
.
3-7 Powersupply
General
1 Inspection
2 Controls and Terminals .
4
Operation ..........
Single-Ended Output
6
Balanced Output
7
Sync Out 11-2
General
4
Sine Synthesizer and Function Selector Switch
Output System
6
Sync Pulse Output
...........
..........
.........
.
..........
...........
.........
.........
1-1
II . 1
II
.
11
II
II
II
III
III
III
III
III
III
III
.
.
.
.
......
.
\
.
........
........
.
.
........
1
1
1
2
2
SECTION IV MAINTENANCE
General
Power Supply
Function Generator (bi-stable circuit and integrator) .
Sine Synthesizer and Function Selector
Output Amplifier
sync Out
Tube Replacement
Tube Replacement Chart
Power Supply Regulator Adjustment
Theory of DC Balance and Distortion Adjustments
DC Balance and Distortion Adjustments . . .
Adjust Squarewave Amplitude .
Frequency Ratio and Calibration Procedure . . IV-8
Replacement of R58 Potentiometer .
SECTION
V
TABLE OF REPLACEABLE PARTS
5
.
1
Table
...........
.........
. IV
........
.......... IV
........
.
.
.
of
Replaceable
Parts
.
IV-1
IV
.
1
IV
.
2
.
2
IV
.
3
.
3
IV . 3
IV
.
4
N
.
4
IV
.
5
lV
.
5
IV
.
8
IV
.
9
V
.
1
Sect. I Page 1
1-1
GENERAL
The Model 202A Low Frequency Function Generator
is
a compact, convenient, and versatile source of
transient-free test voltages between 1200 and
cycles per second. It
purpose low frequency testing application and
particularly valuable in the testing
geophysical equipment, vibration and stability characteristics of mechanical systems, electro-medical
equipment, and for the electrical simulation of
mechanical phenomena. Three types of output wave-
form are available; sine, square andtriangular.
Also, a sync output pulse
The Model 202A Low Frequency Function Generator
contains a type of relaxation oscillator that
ticularly advantageous for the generation of very low
frequencies. Both a triangular and
voltage function of time are inherent in the oscillating
system. Also, a
by synthesis from the triangular wave.
Output amplitude and distortion are virtually in-
dependent of the frequency of operation. This type
is
useful for any general
of
servo systems,
is
available for external use.
sinewave function
a
squarewave
is
.008
is
is
par-
produced
SECTION
GENERAL DESCRIPTION
of oscillating system in
plitude device so that no A.
sociated delay in stabilization after frequency changes,
is
required
The frequency range from
second
is
The output system
system designed for either single ended or balanced
output. It has good stability with respect to
current in the output and very low hum level. Both
the FUNCTION
control are so arranged that the characteristics of
the amplifier are independent of their position. The
internal impedance of the output amplifier
imately 40 ohms, and the unit
at least 30 volts peak-to-peak to a 4000 ohm load.
A negative peak sync pulse of 10 volts into a 2500
ohm load
than
sinewave and at corresponding positions with the
other functions.
is
covered in 5 bands. The frequency dial
linear.
selectro switch and the AMPLlTUDE
is
also provided.
5
microseconds and occurs at the crest of the
inherent^^
V.
.008 to 1200 cycles per
is
a direct-coupled amplifier
It
a constant am-
C. system, with as-
is
approx-
is
rated to deliver
has
a duration of less
direct
I
Sect.
I1
Page 1
2-1 INSPECTION
After the instrument
should be carefully inspected for damage received
If
in transit.
the procedure outlined in the "Claim for Damage in
Shipment" page at the back of the instruction book.
2-2
CONTROLS AND TERMINALS
any shipping damage
is
unpacked, the instrument
is
found, follow
RANGE
This switch
range to be covered
FUNCTION
This switch
types of output waveform.
FREQUENCY
This dial
for the
knob just below the dial escutcheon
nected to the frequency varying element. The lower
knob
is
of the frequency.
AMPLITUDE
This control adjusts the amplitude
voltage admitted
output
0 to 100 in arbitrary units.
from
is
used to select the desired frequency
by
the frequency dial.
is
used to select any one of the three
is
calibrated directly in cycles per second
X1 frequency range of the oscillator. The
is
directly con-
a
mechanical vernier for fine adjustment
of
the oscillator
to
the amplifier and, therefore,
of
.the instrument. This control
is
calibrated
the
SECTION
II
OPERATING INSTRUCTIONS
OUTPUT
This group consists of three terminals. The one
marked "G"
chassis.
are the OUTPUT terminals. With respect to the
ground terminal each of these outputs has equal
magnitude of signal, but they are 180" out of phase
with each other. The internal impedance between
the two OUTPUT
SYNC OUT
The Sync Out terminals are single-ended and have
an internal impedance of about 2,000 ohms.
Power Cable
The three-conductor power cable
a three-prong plug. The third prong
off -set pin which provides
adapter may be obtained to permit use of this plug
with two-conductor receptacles.
2-3 230-VOLT OPERATION
This instrument
the power transformer primaries connected in
parallel for
on
ified
primaries will have to be connected in series
shown in "Transformer Details" on the schematic
wiring diagram
is
connected directly to the instrument
The
other two terminals, vertically aligned,
115
v operation, unless otherwise spec-
the order.
terminals
is
If
of
the Power Supply Section.
is
appmximately
is
supplied with
a
chassis ground. An
shipped from the factory with
230 v operation
is
40
ohms.
is
a round
desired,
the
as
POWER
This toggle switch controls the power supplied to
the instrument from the power line.
FUSE
The fuseholder, which
tains the power line fuse. Refer to the Table
Replaceable
Parts
is
located on the panel, con-
for the correct fuse rating.
of
2-4 OPERATION
The following step-by-step procedure should
used
as
a
guide when operating this instrument.
1) Turn the POWER switch
seconds for oscillations to start. The instrument
will operate nearly within specifications after
few minutes warm-up.
30
cations after
minutes.
It
to
ON. Allow thirty
will
be within specifi-
be
a
Sect.
I1
Page 2
2) Set the
desired frequency. The frequency dial scale must
be
multiplied by
the RANGE switch setting to obtain the oscillator
frequency. Example: 4 (on dial scale)
plying factor indicated by RANGE switch setting)
=
.4 cycles/sec.
3)
Set the FUNCTION switch for the desired output
waveform.
4)
Connect the equipment under test to the OUTPUT
terminals.
5) Adjust the AMPLITUDE Control for the desired
output voltage. Because the frequency response
is
rated k0.2 db, the output amplitude may
sured
level will be correct (within these limits) for any
other frequency.
RANGE
at
any convenient frequency and the output
and FREQUENCY controls for the
the
multiplying factor indicated by
x
.l
(multi-
be
NOTES
mea-
be
must
and the strapped pair will then be the ground side of
the output.
2-6
Connect the two OUTPUT binding posts
ment being supplied. The
then
being driven. Under these conditions the internal
impedance of the Model 202A from either OUTPUT
terminal to ground
capacitor (C29). A maximum dc voltage of 400 volts
may
and the
capacitor (C29). The 40 ohms internal impedance
(resistive) will shunt the impedance existing between
the two signal inputs of the system being driven.
Under circumstances where the connection places
the Model
rent, distortion of the Model
if
through the Model 202A output system.
connected
BALANCED
be
connected to the chassis of the equipment
be
applied between either OUTPUT terminal
"G" terminal without damaging the 1 pf
202A
greater than 10 ma peak current
to
one of the OUTPUT terminals,
OUTPUT
to
the equip-
"G" binding post may
is
7900 ohms in series with a 1 pf
in
series with a path carrying cur-
202A output will occur
is
caused to flow
When small output voltages are required it may
an
desirable to use
because the hum and noise
constant with output amplitude.
To
minimize distortion in the output waveform,
always use the lowest RANGE when the overlap
of
the FREQUENCY dial permits a choice.
external attenuator. This
in
the output
is
be
is
nearly
-------------
2-5
SINGLE-ENDED
The terminal
OUTPVT terminals. For single-ended operation
FYgwe
marked
2-L Single-Ended
"(3"
OUTPUT
is
isolated from the actual
0
EQUIPMENT
BEING
SUPPLIED squarewave.
-
-
Output
Co~ections directly connected to the chassis.
"(3'
RO
@
Figure 2-2. Balanced Output Connections
2-7
SYNC.
The SYNC. OUT
5 microseconds duration and
a
2,500 ohm load.
into
and triangular crests and at the rise
respect to one of the OUTPUT terminals and at the
negative crest of the other. Therefore,
changed by 180" with respect
by reversing connections to the two OUTPUT terminals, which are otherwise completely interchange-
able. The SYNC. OUT terminal marked
OUT
is
a negative pulse of less than
It
It
occurs at the positive crests with
0
EQUIPMENT
SUPPLIED
ground or no
-
at
occurs on one of the sine
to
signal point
least 10 volts peak
orfall of the
it
can
be
the output system
"G1'
is
Sect.
111
Page
1
3-1
GENERAL
Figure 3-1 depicts the general scheme of the @Model
202A
and indicates the waveforms produced. The bistable circuit consists of a flip-flop circuit capable
of producing a square-wave output at point
vided
it
is
triggered at the proper time. This
done by including in the bi-stable circuit, a two-way
comparator circuit which produces the proper triggers for the flip-flop whenever the switching signal
becomes equal to either the
or the "minus switching reference". The triangular
switching signal returned to the bi-stable circuit
"plus switching reference"
A,
pro-
is
SECTION
Ill
THEORY OF OPERATION
is
that seen between points B and
of square wave to triangular wave takes place in
the integrator unit which
produce an accurate integral of the applied square
wave. The bi-stable circuit and linear integrator
are loop coupled in such a manner that the resulting
is
relaxation oscillator
quency operation.
sinewave output
The
the triangular voltage at point
level at point
is
fixed, and the network between C and
D.
suitable for very low fre-
is
taken from a point C between
The resistance between B and
D.
The conversion
is
carefully designed to
B
and the average
D
C
is
a
+
SWITCHING REF
+
SWITCHING SIGNAL
-SWITCHING REF
-
+
1
OUTPUT
Figure 3-1. Model
=
CR12
CRlO
CRIl
CR13
202A
-
8+
Function Generator
0
@
AVE
FtfH
,
-
OUTPUT
AMPLIFIER
vOLT4GE FROM
@TO
@
VOLTAGE FROM
, ,
Sect.
III
Page
2
non-linear system which synthesizes a
sinewave
from the triangular wave. This network consists
of a group of biased diodes arranged in such a manner that at certain predetermined voltage levels they
begin to conduct, therefore, providing shunt paths
D.
from C to
Each additional shunt path reduces
the slope of the triangle in the proper amount so
that the wave
This approximation
which a
is
shaped to approximate a sinewave.
is
as shown, and the degree to
sinewave may be approached depends on
the number of diodes. Thus there are available
the
sinewave C, triangular wave B, and squarewave A functions with respect to D to be selected
and brought to the OUTPUT terminals through the
output amplifier. The output amplifier has a differ-
ential input and push-pull output.
3-2
BI-STABLE CIRCUIT
Figure 3-2 shows the details of the bi-stable circuit
and includes the integrator in block form in order
to indicate the bilateral connection from integrator
output to comparator input.
The portion of the diagram composed of
V1, V2
and V3 is the "bi-stable circuit". Actually, this
circuit
citors
is
to cathode of
is
a combination of two circuits.
If
capa-
C10 and C13 are disconnected so that there
no possibility of inductive coupling from grids
V1 and V2, the remaining circuit
is
the well-known "flip-flop" or Eccles-Jordan trigger
circuit. The other circuit which appears in the bi-
is
stable circuit
"Multiar". The multiar
a voltage comparator known as the
is
a circuit which employs
a regenerative loop to produce a pulse when the
of
two input voltages are equal. There are two
is
in the bi-stable unit. One multiar
V3A and T2, and the other of V2, 3B and T1.
V1,
composed of
these
The cathode of V3A and the plate of V3B are connected to reference voltages derived from the voltage regulator tubes V5 and V6. The triangular.
is
wave
of
applied
V3B. As the voltage on the plate of V3A rises
towards the plus switching reference,
to
the plate of V3A and the cathode
V1
is
con-
ducting, but when V3A conducts, a negative pulse
is
formed on the grid of V1 which flips the Bi-Stable
Unit to its other stable state and starts the voltage
on the cathode of V3B towards the minus switching
Bf
-
$
4
I
SEC13
-
~'j1133!
V3B
IE
+REF
T
+
-
-REF
-
T
-
.-.
*
LINEAR
INTEGRATOR
R20
.0-"-,,
*
B-
Figure
3-2.
Details
of
Bi-Stable Circuit
and
Switching System
reference. When V3B conducts the Bi-Stable Unit
is
flipped back to its original state, completing one
cycle of operation.
Voltage regulator tubes V5 and V6 are connected
by a voltage divider from which the switching reference voltages are taken. They also provide the
limiting voltages applied to tubes
V7 and V8 which
are seen to be a push-pull clamping system. Inasmuch as the integrator output
is
to the input, it
seen that the magnitude of square-
is
directly related
wave applied must be carefully controlled. Although only the squarewave appearing at the plate
of Vl
is
needed to drive the integrator, the clamp
is
made push-pull to prevent excessive current
variations in the regulator tubes. The action of
V7B and V8B
is
such that if the applied waveform
has peak excursions in excess of the potentials on
the remaining cathode and plate, these being deter-
by
mined
regulator tubes V5 and V6, a current will
flow through R20 which drops the voltage to very
nearly the potential of the regulated element of the
conducting section of the diode. The action of the
is
other diodes
the same, but 180" out of phase,
inasmuch as they are coupled to the plate of V2.
In
this way, waveforms appearing on the clamped
sides of R21 and
magnitude as well as
the average of dc level of the squarewave
R20 are assured to be of equal
180" out of phase, and further
is
ac-
curately controlled.
3-3
LINEAR INTEGRATOR
Consider the block diagram of the linear of feedback integrator as shown in Figure 3-3. Starting
with the output voltage
of the amplifier
at the junction of R and
be
small. For a fixed output Eo as the gain
E,,
it
is
seen that
is
high, then the signal appearing
C
(the amplifier input) must
if
the gain
is
in-
creased the resultant signal at the input of the am-
plifier becomes arbitrarily small. Since the voltage
C
is
at the junction at R and
arbitrarily small, a
squarewave applied to the input will cause a constant
current in R. Because the current charging and dis-
charging C
is
constant, except for direction, the
voltage across C will be triangular. Since there
Sect.
III
Page 3
is
virtually no signal at the junction of R and C the
output voltage must also be triangular.
In this case the frequency of the applied
signal
is
so
low that the amplifier used must be direct coupled.
is
There
a net voltage rise between input level and
output level in a dc amplifier. In this particular
application the average output level
is
determined
as the average of the "plus reference" and "minus
reference" levels, since the output excursion
limited to these levels.
B
this
level does not coincide
is
with the average level of the applied squarewave,
then the positive and negative excursions of the
squarewave will not be equal,
resulting in unequal
rise and fall rates of the output triangle. Because
squarewave input
the
is
generated from the triangular
output by the bi-stable circuit, the net result is that
is
under such conditions the squarewave
really a
rectangular wave. The resulting rectangular wave
has an average value just equal to that demanded
by
of the amplifier input
virtue of the pre-set output
level. The average levels of the input and output
are stabilized by the use of a differential amplifier
that has high gain to the difference between the voltage applied to its inputs but little or no gain to any
voltage change common to both inputs.
is
Figure 3-4 shows how this
grid of the differential amplifier
is
input and
driven through R by the rectangular
wave appearing on the FREQUENCY control.
average voltage of this rectangular wave
done.
The right hand
V15,
is
the signal
is
The
depen-
dent on the clamping levels and the ratio of "on" to
is
"off" time. When the system
on-off times (squarewave) the average
adjusted for equal
is
just the
average of the clamping levels. The left hand grid
has no signal because the voltage divider which in-
is
cludes the balance control
connected to the nosignal sides of the clamping tubes. However, any
change in the clamping level changes the average
level appearing on both input grids in the same
amount. Due to the large common cathode resistors
of V15 and V16 a common mode change has very
little effect. The input to the left hand grid has
another function.
If
the balance control R60,
is
varied slightly, the output of the amplifier will show
a
considerable change in average level; and therefore
-
€9,
t
-
-
AMP
-
-
Eour
a
Figure 3-3. Generalized Miller or Feedback Integrator
ID-"-5.
Sect.
III
Page
4
Figure 3-4. Simplified Linear Integrator
the average level of the output can be adjusted to
exactly the voltage midway between the "reference"
This
levels.
control then serves adequately to adjust
the triangular wave balance which in turn equalizes
the on-off time of the squarewave.
The signals
appearing at the plates of the first tube V15, are
180" out of phase and nearly equal in magnitude.
These signals are also very nearly the difference
between the inputs on the two grids. Since there
is
no signal on the left grid, the only signal into
is
the amplifier
is
the condition originally required. The second
is
stage
a push-pull amplifier employing the signals
that at
the
junction
of
R and C, which
from the plates of the previous stage. Again the
common cathode resistance
is
very little degeneration of the push-pull input.
is
very high, but there
The gain of the system to changes common to both
is
grids
appearing between the input grids
250. Finally C
the cathode
about one-half while the gain to voltages
is
something over
is
fed back to the signal grid from
of
V17A which
is
180" out of phase with
the signal input.
is
The cathode follower
used as an isolation stage
between the integrator and the bi-stable circuit.
This completes
oscillating loop with
its
inherent
the
production of both square and triangular functions.
3-4
The triangular wave from the linear integrator
connected
TION selector switch (53) the other end of R94
connected to the sine synthesizing diodes and
R93B, one half of the dual
meter. The synthesized
as the difference signal between points C and
SINE SYNTHESIZER AND FUNCTION
SELECT OR
to
R94.
SWITCH
In
the
SINE position
AMPLITUDE
of
the
FUNC.-
potentio-
sinewave signal appears
D,
is
is
to
but an error signal which appears at D with respect
to
B-
also appears at C with respect to
composite signal
is
applied
to
a differential amplifier
B-.
This
in the output circuit.
The plus and minus switching references in the
bi-stable unit are adjusted so that the ratio of the
triangular wave amplitude to the conduction voltages
the
synthesizer diodes produces
of
the
least distortion
of the sinewave. This adjustment also fixes the
is
equal
to
average voltage at C and
the average
of the plus and minus switching references.
at
The dc voltages
D, and the cathode of V4 are
adjusted to be the average of the plus and minus
switching references. Since
there
is
no change in DC level applied to the Output
as
Amplifier
the AMPLITUDE control
these
voltages are equal
is
varied.
El-STABLE
f
225
VDCREG
.
Sect.
111
Page 5
t75
VDC
REG AMPLIFIER
Figure 3-5.
Sine Synthesizer and Function Selector
(A)
TO OUTPUT
Waveform from integrator output to B-. Triangular
regardless of function selector position.
(B) Waveform from@to B- with selector switch in sine
position. Note distortion especially at peaks.
w
(C) Waveform from@to B- with selector switch in sine
position.
in waveform (B) above.
This
t75
VDC
REG.
is
the distortion component present
ID.I.6M
RO
Figure
(D) Waveform fromato@ (i. e.
(C)
waveforms (B) and
above. ) This
mated sinewave.
3-6.
50
IL
Waveforms
:
difference between
is
the approxi-
Sect.
111
Page 6
sinewave
The
resistance across
is
approximated by varying the shunt
R93B
is
steps determined by the
diode synthesizing network. The waveform slope,
is
at first,
just that determined by R94, R93B and
the input waveform. When the first diode conducts
is
R93
shunted by a predetermined amount, decreasing the slope. Each diode in turn decreases the
slope until all the diodes are conducting and the
triangular wave
has
reached
its
crest. The triangular
wave starts down, the diodes stop conducting in turn
until the triangular wave has reached its crest. The
triangular wave
starts
down, the diodes stop conduct-
ing in turn until the triangular wave reaches the
average level. The other half-cycle is formed in
the same manner, but by the diodes that are biased
to shape the negative excursion.
It can
be
shown that using seven segments to approx-
imate one half cycle of the
sinewave results in ap-
proximately 11 6% rms distortion. However, variations
in the diodes limit the practical result to about
1%
rms distortion.
In
the triangular wave position of the FUNCTION
selector switch the non-linear load consisting of
is
the diode network
combination R94 and R95
for all voltage levels. It
replaced by R95 so that the
is
a simple linear divider
is
adjusted to give equal
sine and triangular wave peak magnitude.
is
squarewave
connected to the FUNCTION selector
The
switch through the divider R59 and R22 which adjusts
the average voltage of the squarewave to the voltage
at the cathode of V4. In the squarewave position
of the selector switch, R63 parallels
R93B to adjust
the amplitude of the squarewave to be equal to the
amplitude of the
3-5
OUTPUT
sinewave and the triangular wave.
SYSTEM
The output system consists of three stages as shown
in Figure 3-7. The first Stage V18
acting
as
a pair of separate cathode followers.
is
a dual triode
These
cathode followers isolate the signal input from the
output stage. Any dc unbalance at the output terminals can be corrected by varying R65.
The second stage
V19
is
a differential amplifier.
The difference between the two signals at its grids
appears at both plates in nearly equal magnitudes
is
and 180" out of phase. This effect
due to the large
common cathode resistance. In this stage ampli-
fication takes place and also the signal difference
E
minus F
third stage V20
The signals appearing at the plates of
is
converted to push-pull voltages. The
is
another pair of cathode followers.
V19 are
Figure
3-7.
Output Amplifier System of Model
202A
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