Servo Resolver Type TJ841 — Minispace: Technical Manual
Servo Resolver Type TJ961 Frontispiece
1
Fig.
SECTION 1
INTRODUCTION
1. © The Solartron TJ725 Servo Multiplier is a
general purpose, potentiometer-type multi-
plier for use with electronic analogue com -
puters. Itincorporatesa six-section linear
potentiometer to permit the multiplication of
five quantitiesbyacommonmultiplier. With
the exception of the input stage, the servo 2,
amplifier and its power supply system are
completely transistorised. The TJ961Servo
Resolver is driven by an identical servo
SECTION 2
system but is provided with two sine-law
graded potentiometer sections to provide
sine andcosine functions of the shaft angle.
Additionally, the TJ961 is fitted with two
linear multiplying potentiometer sections.
Both types of servo unit have the same dimen-
sions and may be used as a bench instrument,
or carried in a Servo Mounting Unit Type
TX926, which provides for mounting up to
three units in a standard 19 inch rack.
SUMMARY OF TECHNICAL DATA
3. Static Accuracy
With potentiometer centre - taps earthed
+0. 5%
With zero input +0. 25%
Dynamic Accuracy
Additional error due to dynamic response
+0. 5%
Amplitude Capabilities
Linear operation up to approximately
10c/s full amplitude. Accepting some
error full amplitude can be obtained up
to 15c/s.
Phase Shift
At 10c/s full amplitude, less than 1°.
Transient Response
Rise or fall time from zero to full-scale
not greater than 30 milliseconds with
approximately 5% overshoot.
Noise Level
Approximately 0. 25% peak-to-peak.
Temperature Limitation
Maximum ambient temperature for satis-
factory operation 40°C approximately.
Drift at 40°C 100mV approximately.
Power Requirem ents
90 - 130/200 - 240 volts, 40 - 60c/s,
single phase.
Power Consumption
NOVA,
Overall Dimensions and Weight
Height 7 in, 17. 8cm
Width 5. 6 in. 14. 2cm
Depth 17 in, 43, 2cm
Weight 17 lb 4.1kg
SECTION 3
INSTALLATION AND OPERATION
INSTALLATION
The equipment is supplied as a completely
assembled unit ready for installation. At
time of factory test, the mains voltage se-
lector panel will have been set for an in-
put of 230 volts, and a 500mA fuse cartridge
fitted in FS2 carrier. External stabilised
reference supplies of +100 volts eachat
4.0mA must be available for the operation
of the unit.
(1) Remove top and bottom covers. Set
mains input voltage selector.
(2) Check that the mains fuse FS2 is con-
tinuous and of the correct rating.
110V range mains input - 1A
220V range mains input - 500mA.
(3). Check that the printed circuit fuse FS1
* is continuous and is rated for one amp-
ere.
(4) Check that the potentiometer fuses are
continuous and each have a resistance of
approximately 150 ohms.
Note ,
The Servo Multiplier TJ725 contains six
potentiometer fuses (FS3-FS8), whilst
the Servo Resolver TJ961 contains
seven potentiometer fuses (FS3-FS9).
(5) If the unit is to be carried in aServo
Mounting Unit Type TX926, on the
MAINS IN panel LKi link the pins de-
signated VIA RACK. If the unit is to
be used bench - mounted, link the pins
designated DIRECT on the MAINS IN
panel.
(6) If the unit is to be bench-mounted, con-
nect the mains input lead at plug PL1,
pin A-line, pin B-neutral, and pin
C-earth.
(7) Refit top and bottom covers.
(8) Apply reference voltages to plug PL2
thus:-
Pini -100V
Pin 2 +100V
Pin 3 Mid-point of reference voltage
(signal ground).
OPERATION
(1) Apply mains voltage to unit.
(2) Set MOTOR DRIVE switch to ON. Check
that the OVERLOAD indicator lamp
lights, and is extinguished some 30-60
seconds after the MOTOR SWITCH is
closed.
(3) The servo should now be ready for op -
eration.
(4) Should the servo spin after the OVER-
LOAD indicator lamp goes out, set
MOTOR DRIVE switch to OFF and con-
firm that the +100V reference supplies
are applied to the servo, and that the
fuse (FS3) in the-feedback potentiometer
wiper is intact.
(5) Should the servo oscillate after the
OVERLOAD indicator lamp goes out,
set MOTOR DRIVE switch to OFF, and
check that the +100V reference supplies
are appliedto PL2 withcorrect polarity.
Pin 1 -100V
Pin 2 +100V
Pin 3 Mid-point of reference.
(6) Set MOTOR DRIVE switch to On, check
that the OVERLOAD indicator lamp
lights and is extinguished some 30-60
seconds after the MOTOR SWITCH is
closed.
(7) The servo is now ready for operation.
Operational Precautions
(1) The arms of the potentiometers must
not be earthed since the resultant high
current would destroy the potentiometers,
Some protectionis provided bythe 10mA
fuse wired in each arm.
(2) The voltage applied across any slave
potentiometer must not exceed 300
volts.
(3) The voltage applied across any section
of the tapped potentiometer must not ex-
ceed 30 volts.
z4
SE ee
Servo Accuracy Factors
(1) The +100V reference supplies must be
balanced to earth within 0. 1% if static
errors are not to be introduced.
(2) The arms of the slave potentiometers
must each be loaded with a resistance of
one megohm to an accuracy of 5%. The
other end of the loading resistor be -
ing taken to near earth potential, i.e.
computer amplifier input.
(3) The linear potentiometer centre - taps
must be earthed, and the potentiometer
fed with push-pull inputs if the greatest
accuracy is to be obtained. The servo
can be operated with non-earthed centre-
taps and single-ended inputs in circum-
stances where an error of 0.5%is ad-
missable.
Transient Performance
The transient performance of the servo
system can be adjusted according to the
application in which the servo is to beused.
At time of factory test, the servo is set-up
to a 5% overshoot. The rise time can be
increased or alternatively the overshoot re-
duced by adjustment of variable resistor
RV8 in accordance withthe directions given
in sub-paragraphs (1) to (3) following.
Note
Variable resistor RV8 must not be adjusted
during the normal operation of the equip-
ment, but only when the transient perfor-
mance of the servo is being checked or reset
to a different overshoot value.
(1) Apply a 1c/s square wave to the input
(pin 18, PL3) at the amplitude at which
the servo is to be used.
(2) Connect a d.c. potential across a slave
potentiometer, and observe the output
from the arm of the potentiometeron an
oscilloscope.
(3) From the rear panel of the unit, adjust
RV8 to give the required performance as
measured on the oscilloscope.
Note
Instability may be caused if the damping is
reduced to give more than 15% overshoot.
Multiplication
Multiplication is performed with the linear
potentiometers, six of which are fittedon
the TJ725, and designated the feedback
potentiometer and slave potentiometers A,
B, C, DandE.
Slave C is provided with nine tappings for
the connection of external padding resis -
tances if it is desired to give the winding a
non-linear characteristic forthe generation
of discontinuous functions. The multiplier,
alternatively designated the input voltage V] ,
is applied at pin 18 on plug PL3, and through
the servo system, drives the shaft of the
potentiometer gang so that the wiper of the
feedback potentiometer comes to rest ata
position which is proportional to the input
voltage Vj. If a push-pull voltage Vp is
applied across slave potentiometer A, then
the output. voltage from the arm of slave A
will be proportional to the product of the
input voltage and the voltage applied across
slave potentiometer A, or
Vo & Vy Vp.
Push-pull inputs tothe slave potentiometers
are necessary if the multiplier is to accept
inputs of both signs for V] and Vp and to pro-
vide an output voltage Vo of the correct
sign, i.e. four-quadrant operation. The
extremities, tappings and arms of all linear
potentiometers are terminated at plug PL3
aslistedin Table 1 for the TJ725 multiplier,
TABLE 1
TJ125 SIGNAL CONNECTOR PIN ASSIGNMENTS
PL3 PIN NUMBER
POTENTIOMETER
HIGH CENTRE-TAP ARM LOW
Slave A 32 16 31 15
Slave B 30 29 28 27
Slave C 26 10 25 24
Slave D 23 22 21 5
Slave E 20 4 19 3
Note
Slave C is provided with eight tappings ex-
cluding the centre-tap. These are connected
to PL3 thus:- :
Tap No. PL3 Pin No.
14
13
5 12
11
9
8
1
6
Sine and Cosine Functions
10. The TJ961 resolver is provided with two
sine/cosine potentiometers. Each of these
components will give an output of:-
Sin Vy
VR P
Cos vy! T ; | ,
VR e
Vj isthe input voltage determining
the potentiometer shaft position.
where
Vp is the voltage applied across
the sine/cosine potentiometer.
VR is the reference voltage.
Additionally, the TJ961 resolver is fitted
with two linear multiplying potentiometers.
The connections to the sine /cosine and li-
near potentiometers are made at plug PLS
mounted on the rear wall of the unit, and
are listed in Tables 2 and 3.
+100V
100V /
av
100V
-100V
RVI
TABLE 2
T3961 SIGNAL CONNECTOR PIN ASSIGNMENTS
SINE/COSINE POTENTIOMETERS
PL3 PIN NUMBER
POTENTIOME TER
V+ V- EARTH SIN cos
Slave D \ 23 5 17, 22 28 21
Slave E 20 3 i, 4 19 27
TABLE 3
TJ961 SIGNAL CONNECTOR PIN ASSIGNMENTS
LINEAR POTENTIOMETERS
PL3 PIN NUMBER
POTENTIOMETER
HIGH CENTRE-TAP ARM Low
Slave A 32 16 31 15
Slave C 26 10 25 4
Al
AV2
Electrical Method of Multiplication
emo eargeeripmerert
11.
SECTION 4 .
PRINCIPLES OF OPERATION
Multiplication by Electrical Method
Refer Fig. 2.
An accepted electrical method of multiplica-
tion is by ganged linear potentiometers. A
fixed reference voltage is applied across
potentiometer RV1, the mid-point of the
reference voltage though a constant need
not necessarily be 100 volts.
Vo = xyk
where k is a proportionality constant.
Sine/Cosine Functions
reference potential and the centre -tap of 2. Refer Fig. 3.
the potentiometer being connected to earth.
A reference potential of 100 volts is em- The TJ961 resolver is fitted with two sine/
ployed on the TJ725 and TJ961. Avoltage y, cosine potentiometers in addition to two
proportional to the quantity to be multiplied linear multiplier potentiometers. The
is applied across potentiometer RV2, the sine/cosine potentiometers are wound with
mid-point of this voltage and the potentio- sine-law graded windings, and fitted with
meter centre-tap again being earthed. If two electrically isolated arms displaced
the arm of potentiometer RV1 is now set-up from each other by an angle of 90°. poten-
to a voltage x proportional to the multiplier, tiometer RV1 is wound withalinear winding
then providing that the potentiometer gang and ganged to RV2. It is in all respects
alignment is precise, the arm of potentio- identical with potentiometer RV1 shown in
meter RV2 will take-up a coincident posi- Fig. 2, but to simplify diagrammatic
tion to that of RV1. The position of the presentation it is drawn in its circular
arm on potentiometer RV1 can be defined physical form in Fig. 3. Though the
by the ratio [§9, which since the potentio- electrical sweep angle of RV1 potentiometer
meters are identical and ganged, also wiper is restricted to 355°, the mechanical
defines the position of the arm on RV2. sweep angle is unlimited since no physical
Bearing in mind that the voltage applied stops are fitted on the potentiometer track.
across potentiometer RV2 is yV, the output A fixed reference potential, 100 volts in the
voltage Vo picked - off by the arm of RV2 TJ961, is applied across RV1, with the
must be equal to yj9g, or since the mid-point of the reference potential and the
+100V +100V
AV2
os + ARM VOLTS
4° + sov rot te +100V
+70-7¥
sin / \
7 \
\
e ov / ov
~ ¥ |. /t ¥
\ / os
: / -70-7¥
“Y" wov sv -t V4 be 4
— avi -100¥
VOUT
~To0v ~to0v “9OV “7SV =SOY -25V OY 425V +50 +73V +90V
avi RV2
Fig. 3 Derivation of Sine and Cosine Functions
centre-tap of the winding connection to earth.
A potential of 100 volts is applied across
potentiometer RV2, with the mid-point of
the supply and the diametrically opposed
winding centre-taps connected to earth.
Assuming that the ganged shafts of RV1 and
RV2 are initially in the positions shown in —
Fig. 3, then RV1 arm potential is zero,
and the potentials of the sine and cosine
arms of RV2 are respectively zero and
+100 volts. If now the arm of RV1 is set-
up to +50 volts by rotation in a clockwise
direction, the potential of the sine and co-
sine arms will be +100 volts and zero
volts respectively. Similarly, a counter-
clockwise rotation of RV1 from the zero
volts position to set-up -50 volts on the arm
will bring the potentials of the sine and
cosine arms to -100 volts and zero volts.
respectively. Considering the sine and
cosine arms as vectors rotating through
+? and - TY radians from the initial posi-
tions, then the output from those arms will
be of sinusoidal from as shown by the
curves in Fig. 3. The expressions for the
outputs from the sine and cosine arms can
be written thus:-
Sin E )
xy
100
Cos Tx
100
where x = RV1 arm voltage
y = voltage applied ac-
: ross RV2
Servo System
13. The ganged potentiometers in the TJ 725
multiplier and TJ961 resolver are motor
driven by a servo system, a block sche-.
matic diagram of which is given in Fig. 4.
The +100 volts reference supply is connected
across the feedback potentiometer, which
corresponds to RV1 in Figs. 2 and3. The
existing voltage on the arm of the feedback
potentiometer is applied to one input of a
voltage comparator. The voltage requir-
ed to be set-up on the arm of the feedback
potentiometer, hereaftercalled the input
voltage, is applied to the second input of
the comparator. The difference or error
voltage between the two inputs to the
comparator is applied as a correcting
signal to a servo amplifier to drive the
servo motor in such a direction as to re-
duce the error voltage to zero, or in other
words, to set the feedback potentiometer
arm voltage to the input voltage. It will
be seen from the block diagram that there are
two input channels to the servo amplifier.
The d.c. channel is fed from the error
voltage developed across the resistive
components of the voltage comparator,
whilst the phase-correction channel is fed
from the capacitive components. The d.c.
impedance converter stage, comprising a
valve and one transistor, serves to match
the high impedance of the comparator re-
sistors to the low impedance of the tran-
sistorised servo amplifier. The applica-
tion of an input voltage to the comparator
will cause a current to flow in resistors Rl
and R2, the magnitude and direction of
which current will be proportional to the
difference or error voltage between the
input voltage and the existing voltage on the
arm of the feedback potentiometer. This
current will develop across resistor R2a
voltage proportional in magnitude and
polarity to the error voltage, which is
applied to. the servo amplifier via the d.c.
impedance converter stage. The resultant
output from the amplifier will drive the
servo motor in suchadirection as to reduce
the error voltage. The servo motor drive
system comprises four stages, namely
power amplifier, first current control
stage, paraphase amplifier and second
current control stage. The power amp-
lifier, driven by the outputs of the d.c. and
phase correction channels, feeds the
paraphase amplifier and first current con-
trol stage. The paraphase amplifier effects
a phase reversal and drives the second
current control stage with its reversed phase
output. Each current control stage also
effects a phase reversal. The outputs
from these four stages are employed to
control the current throughtransistorsX17,
X18, X19 and X20. In the quiescent condi-
tion, each pair of transistors (X17-X18,
X19-X20) passes a current of 300 milli-
amperes. Assuming that a negative signal
appears at the input of the power amplifier
the outputs from the four stages willhave
the polarity shown in Fig. 4, with the re-
sult that transistors X17 and X20 will cut-
off, and a drive current will flow through
the motor armature and transistors X18 and
X19 in the direction shown.
; R2 =
TT]
vourace O we 2
| IMPEDANCE + +
i Rl CONVERTER
Pad gots PARAPHASE
AMPLIFIER
a - A.C.
PHASE
CONTROL + -
CURRENT
VOLTAGE CURRENT
CONTROL
COMPARATOR STAGE | are
\
-100¥ REF. —< Wy ee +100V REF
‘Kr Jl SLAVE A
vo
wy sts
Fig.4 Servo Multiplier Type TJ725 - Block Diagram
SECTION 5
PHYSICAL DESCRIPTION
General
14. The unit is built on an inverted tray type
chassis with the larger components, viz.,
transformers, smoothing capacitors, fuse
board and transistor heat sink, mounted on
top. The smaller components are carried
on two printed circuit boards fitted be-
neath the deck of the chassis. The heat
sink which carries all eight power transis-
tors and two of the intermediate power
transistors is built as an open-ended two-
piece rectangular section with the transistor
fixing nuts and connections applied from the
outside of the sink. A small blower unit is
mounted at one end of the sink, air inlet and
outlet being taken via wiremesh covered
apertures let into the paneland rear wall of
the instrument. All connections to the unit
are made at three rear - mounted plugs.
Cover plates are fitted.
Panel Fittings
15.° The panel of the unit carries one control
and one signal lamp. -
SW1 MOTOR DRIVE ON/OFF Switch
LP1 OVERLOAD indicator lamp (red)
16.
17,
ia.A41
Additionally, a potentiometer arm posi -
tion pointer is provided, which sweeps
through the electrical angle of 355° over a
dial scaled from 0 to +100.
CIRCUIT DESCRIPTION
Circuit Diagram Fig. 8
Voltage Comparator Stage
The input voltage and feedback potentio-
meter (RV7) arm voltage are compared for
error by close tolerance one megohm re-
sistors (Rl, R2) and 1500pF capacitors
(C1, C2). The input to the d.c. channel is
taken from the resistors, whilst the changing
voltage across the capacitors is differen-
tiated to provide an input to the a.c. chan-
nel in the manner described in paragraph 13
D.C. Impedance Converter
This stage, employing a pentode valve V1
and one transistor X6, serves to match the
high output impedance of the comparator
stage to the relatively low impedance of the
transistor power amplifier. The valve is
connected across the -40 and +12 volts rails,
as a cathode follower. The valve heater
is energised from the 12 volts d.c. supply
provided by the built-in power pack. The
output of the valve amplifier is taken from
across the cathode load resistor R17 and
applied between base and emitter of the
transistor amplifier X6. The bias applied
to the base /emitter circuit by the poten-
tial divider RV1, R18 controls the d.c. level
of the servo system. Output to the succeed-
ing power amplifier stage istakenfrom the
collector load resistor R76.
Power Amplifier
18, The power amplifier stage employs three
transistors X8, X7 and X16. The output
from the d.c. impedance converter is
applied directly (without attenuation) to the
base of transistor X8 so that the overall
gain of the d.c. channel is of the order of
60 times. Negative feedback is taken
from the emitter of the power transistor
X16 to the input stage via resistor R26.
The quiescent output voltage at the emitter
of X16 is-21 volts, witha maximum swing of
+14 volts about this mean value. Tran-
sistor X7is fitted witha split collector load,
the voltage developed across resistor R24
providing the drive to the power transistor
X16, whilst resistor R25 determines the
minimum output voltage of the stage. The
inputs to the Paraphase Amplifier and first
Current Control. Stage are taken at high
level from the emitter of transistor X16.
A.C. Phase Control Stage
19. The phase-correcting input voltage is deve-
loped across resistor R3 and amplified in a
four-stage amplifier employing transistors
-X1, X2, X4 and X5. The a.c. signal
appearing at the collector of X4 is divided
down by the potential divider R13, RV8, R14
to inject a negative feedback voltage into the
emitter circuit of X2 via transistor X3 and
the common emitter resistor Rll. Vari-
able resistor RV8 determinesthe amplitude
of the negative feedback voltage applied to
transistor X3 and thus controls the a.c.
gain of the stage. The drive to the power
amplifier is coupled via C7 and R19 to the
base of transistor X8. An additional in-
phase drive is taken from the collector of
X5and appliedto the power amplifier at the
emitter of X7. Variable resistor RV 2
controls the amplifier gain in the negative
direction.
20.
21,
Current Control Stage 1
The circuit consists of a two stage transi-
stor amplifier which is employed to
control the current passed by one of the
power transistors (X18) inthe motor supply
circuit. The stage is driven from the out-
put of the Power Amplifier, the input
voltage being droppedtoa suitable value by
the series resistor R27. The.d.c. level
of the amplifier is determined by resistor
R28. Overall negative feedback is applied
via resistor R29, and the effective gain of
the stage is approximately 0.2 times. It
will be noted that the two stage amplifier
produces a phase-reversal between the in-
put to the base of X9 and the output at the
emitter of X10.
Paraphase Amplifier
The Paraphase Amplifier is fed at high
level from the Power Amplifier. The stage
. has a gain just in excess of unity to give a
22,
23.
quiescent output of -21 volts. It employs
the same basic circuitry as the Power
Amplifier stage but the values of the input
and feedback resistors are suitably modi-
fied to give the reduced gain required. As
its name implies the function of the stage
is to provide a phase-reversed input to
power transistor X19 in the motor supply
circuit, and to the second Current Control
Stage.
Current Control Stage 2
This circuit is in all respects similar to
that employed in Current Control Stage 1
as described in paragraph 20. It is driven
by the phase -reversed output from the
Paraphase Amplifier, and itself effects a
phase - reversal between the input to the
base of X12 and the output at the emitter
of X11.
Power Control Stage
The Power Control Stage consists of four
power transistors X17-X20 which are em-
ployed to control the magnitude and direction
of the drive current applied to the servo
motor. In the quiescent condition, the d.c
resistances of power transistors X18 and
X20 are regulated by Current Control
Stages 1 and 2 respectively, so as to pass
currents of 300mA each. The dc. resis-
tances of power transistors X17 and X19 in
this condition are of such values as to
provide a low impedance path for these
currents with the result that no drive is
24,
25.
26.
applied to the: servo..motor.
that aninput voltage is appliedto the unit so
as to cause a negative signal to appear at
the input to the Power Amplifier, the
polarity of the resultant voltages appearing
at the outputs of the Power and Paraphase
Amplifiers, and Current Control Stages 1 and
2 will be as shown on the block schematic
diagram, Fig. 4. The collectorcurrents
passed by transistors X18 and X19 will
thereon increase, whilst the currents
passed by X17 and X20 will be correspond-
ingly decreased, causing a drive currentto
pass through the servo motor armature in
the direction shown on the block diagram.
Similarly, an input voltage of opposite
polarity will apply a reversed drive to the
servo motor.
Power Supply System
General
The unit has a built-in power pack, which
from a mains input provides regulated
supplies at -40 and +12 volts d.c. for the
operation of the amplifiers, and the servo
and fan motors.
Input Circuit
The mains transformer T1 is provided with
split primary windings capable of series /
parallel connection to accommodate a mains
input of 90, 100, 105, 110, 115, 120 or 130
volts in the lower voltage range, or 200,210,
215, 220, 225, 230 or 240 voltsinthe higher
voltage range. The primary winding is
protected by fuse FS2 rated for three amp-
eres. When the unit is mounted inthe rack
type TX926, mains input is applied at pin 6
(line) and 7 (neutral) on plug PL2. If used
as a bench-mounted unit, inputis applied at
pins A (line) and B (neutral) on plug PL1.
It should be noted that the mains input is
routed to transformer T1 via link panel
LK1, the VIA RACK pins of which must be
linked if the input is applied at plug PL2.
If input is applied at PL1 then the DIRECT
pins on LK1 must be connected.
+12 Volts D.C. Supply
The supply is stabilised by a feedback
transistor amplifier which is employed to
regulate the impedance of the seriesele-
ment, a power transistor. The output
from a14volts secondary winding on trans-
former T1 is rectified by the bridge con-
nected germanium diodes MR2, MR4, MR5
and MR6. Smoothing is effected by capa-
citor C21. Transistors X27 and X28 are
connected as a differential amplifier with the
27.
signal input from the sampling chain (R69
RV6, R70) appliedtothe base of X28. The
reference voltage is provided by the zener
diode X32, which holds the base potential of
X27 five volts positive with respect to the
zero volts rail. The value of resistor R63
is suchthat the current passed by the zener
diode is 5mA. The output from the differ-
ential amplifier is taken from the collector
of transistor X27 and applied to the base of
an emitter-follower stage (X30), whichin
turn drives the series transistor X23.
Potentiometer RV6 permits the system out-
put level to be accurately set to 12 volts.
Since the output impedance ofthe stabiliser
- increases with frequency, capacitor C25 is
connected in parallel with the loadso as to
reduce the output impedance at rising
frequencies.
-40 Volts D. C. Supply
The supply is stabilised bya feedback tran-
sistor amplifier with a variable resistance
series element provided by two paralleled
power transistors. The output from a 55
volts secondary winding on transformer T1
is rectified by the bridge-connected germa-
nium stack MR1, and appliedtoachoke input
filter circuit L1, C20. The supply is pro-
tected by fuse FS1 rated for one ampere.
The signal to the input amplifier X29 is
taken from the sampling chain R71, R74
connected across the -40 volts and stabilised
+12 volts rails, the latter serving as the
reference potential. The output from the
collector of X29 is successively amplified
by two emitter-follower stages X26 and X25,
the latter being a power transistor. The
coupling between X26 and X25 is madevia
three series-connected zener diodes X31,
_ X33 and X34.
28,
The drive to power transistors X22 and X24,
paralleled in the positive side of the supply
to form the variable series resistance, are
driven from the emitter of X25. Resis-
tors R58 and R60 connected in the collector
circuits ensure that the line current drawn
from the supply is shared approximately
equally between transistors X22 and X24.
Capacitor C23 is connected across the
supply to provide a low output impedance at
high frequencies.
Protective Devices and Other Facilities
High Temperature Cut-Out
The contacts of a thermal cut-out TCl are
wired in the positive line (common rail) of
the -40 volts supply to protect the power
transistors from damage by overheating.
Once triggered, the cut-out must be manual-
29.
30.
31.
10
ly reset after the cause of the overheating has
been found and remedied.
Delayed Power Supply Switching
The application of the -40 volts supply to the
transistor amplifiers and servo motordrive
circuit is automatically delayed by some 30
seconds so that these stages are inoperative
until the valve heater(V1) in the D. C. Impe-
dance Converter Stage has had time to warm-
up. The thermal delay switch TD1/1 is
heated from the -40 volts supply, and its
contact is employed to energise the power
switching relay RL2/2o0n the termination of
the delay period. Contact RL2. 1 will there-
on close to apply the -40 volts supply to the
transistor amplifiers and servo motor drive
circuit, and contact RL2. 2 will change-over
to reset the thermal delay switch and hold-
in relay RL2/2. It will be noted that
TD1/1 is not subject to control by the
thermal cut-out TC1.
Cooling Fan
The transistor heat-sink cooling fanis driven
by a small permanent magnet motor M 1
energised by the -40 volts supply. The
armature current is limited by series re-
sistor R57. Capacitor C16, connected
directly across the motor terminals, re-
duces high frequency radiation caused by
motor brush noise. The supply to the
motor is not subject to control by the ther-
mal cut-out TCl. Air intake is via awire-
mesh coveredaperture cut into the panel of
the unit.
Operational Facilities
Motor Drive Cut-Off
A panel-mounted MOTOR DRIVE switch
SW1 is provided to enable the amplifier and
motor drive circuits to be cut-off if it is
desired to hold the servo ready for imme-
diate use but not actually in operation.
This facility could be employed when the
servo is to be driven from an amplifier
which may have an output in excess of 100
volts during the warm-up period. The
contacts of the MOTOR DRIVE switch are
wired inthe supply line to the power switch-
ing relay RL2/2, so that the relay will drop-
out when SW1 is set to OFF. Relay contact
RL2.1 will then open to remove the motor
drive, and contact RL2. 2 will change-back
to energise the heating element of the
thermal-delay switch TD1/1. On the
32.
termination of the 30 seconds delay period
imposed by TD1/1, contact TD1. 1 will close
to permit the power switching relay RL2/2
tobe energised via SW1 when that switch is
closed to re-apply motor drive.
Overload Circuit
The overload circuit gives warning when
large errors exist in the servo system,
which condition is generally caused by de-
manding too great an accelleration from the
servo motor. The circuit consists ofa
transistor amplifier X15 connected between
the -40 volts and zero volts line, so as to
form a variable resistance shunt across the
filament of a low consumption 6 volts
indicator lamp LPl. Under normal cir-
cumstances the base potential of transistor
X15 is held at a sufficiently negative poten-
tial with respect to the emitter so that X15
passes a heavy current and shorts out the
indicator lamp. In the overload condition,
the power and/or paraphase amplifier stages
will saturate with the result that the poten-
tial at the junction of resistors R22 and R23
will go positive. This change in potential
is applied to the base of transistor X15 to
reduce the collector current and thus in-
crease the shunt resistance across indicator
lamp LP1 which will light to signal anover-
load. The a.c. component of the amplified
TABLE 4
PROGRAMME CARD CONNECTOR PIN ASSIGNMENTS
aaa CONNECTION
A Slave C - high
B SlaveC - tap2
c Slave C - tap4
D SlaveC - tap5
E No connection
F Slave C - tap7
H Slave C - tap 8 (centre)
J SlaveC - tap10
kK SlaveC - tapll
L Slave C - tap13
M SlaveC - tapl4
N SlaveC - low
P No connection
R +100V reference supply
8 -100V reference supply
33.
35.
signal is routed to the computer central
overload circuit via capacitor C19. The
germanium diode MR3 serves to prevent
low level noise voltages reaching the central
overload circuit and signalling a spurious
overload condition.
Programme Card
The Servo Multiplier Type TJ725 is fitted
with one linear potentiometer, slave C,
tapped at eight points in addition to the cen-
tre tap, to permit the potentiometer to be
used as a generator of discontinuous func-
SECTION 6
tions by the connection of resistive padding
networks. A plug-in printed circuit pro-
gramme card is provided to carry the
padding resistors, so that once a function
has been set-up, the card can be stored
ready for future use. The programme
card is fitted with 15 in-line taper pin
connections which engage with a matching
socket SK1 mounted in the base of the
multiplier chassis. Access to the socket
is by way of a rectangular aperture let
into the top dust-cover of the unit. The
supply and potentiometer tapping connections
to the programme card socket SK1 are listed
in Table 4.
INITIAL SETTING-UP PROCEDURE
General
The instructions detailed in this Section
are given to enable the operator to restore
the unit to correct working order after re-
pairs have been carried out. The complete
procedure will normally only be required
after the unit has been subjected to an exten-
sive repair necessitating the disconnection
and removal of sub-assemblies. Direc-
tions for the breakdown and re-assembly of
the unit are given in Section 8 of this hand-
book.
Test Equipment Required
The following items of test equipment will
be required.
(1) Low frequency oscillator capable of pro-
viding sinusoidal and square wave
signals over the frequency range 0.1c4
to 1kc/s.
(2) Oscilloscope.
(3) Mains variac rated for 100VA.
(4) Avometer Model 8.
Additionally, a +100 volts stable reference
supply will be required. Solartron Supply
Sub-unit AS756 is a suitable source.
rs == as
Setting-up Procedure
36. (1) Connect mains input from variac at
plug PL1, pin A being line, pin B
neutral and pin C earth.
(2) Connect DIRECT pins on link panel LK1.
(3) Check that the mains supply stands at
230V.
(4) Check that voltage selector panel is set
for a 230V input.
(5) Insert a fuse rated for one ampere in
FS1 carrier.
(6) Using the Avometer, check that the re-
sistance betweenthe OV rail and chassis
is greater than 100, 000 ohms.
(7) Check that valve V1 is firm in its base,
and of correct type (12AC6).
(8) Disconnect resistors R36 and R37 from
the OV rail.
(9) Set MOTOR DRIVE switch to OFF.
(10) Connect a load resistor, value 100 ohms
rating 50 watts, across the unswitched
-40V rail and the OV rail.
(11) Set variac to give zero volts output.
11
12
(12) Close external circuit breaker to apply
mains input to variac, and advance var-
jac to give an output of some 3-4 volts
to the servo unit under test.
(13) Confirm polarity of -40V and +12V rails.
(14) Advance variac to give an output of 230V,
(15) Adjust potentiometer RV6 to set the
potential of the +12 volts rail to +12V.
Note
Early models cannot be set to less than
+12, 8V.
(16). Check that the heater of valve V1 is lit.
(17) Check that the voltage of the -40V rail
lies between -39V and -41V.
(18) Check with oscilloscope that both the
-40V and +12V rails are free from
oscillation or excessive hum.
(19) Check that fan blades are rotating in a
clockwise direction as. viewed from the
front of the unit.
(20) Open external circuit breaker to remove
mains input from unit.
(21) Connect the 100 ohms load resistor
across the switched -40V rail and OV
rail.
(22) Close external circuit breaker, and set
MOTOR DRIVE switch to on,
(23) Check that the potential of the unswitched
-40V rail does not exceed -50V.
(24) Check that the thermal delay switch TDI
operates some 30 seconds after the ex-
ternal circuit breaker is closed,
(25) If necessary, set time delay to 30 sec-
onds by adjustment of the set screw on
TD1/1.
(26) Check that the collector voltage of Xlis
approximately -12V, and that the
collector voltage of X4 is approximately
-20V.
(27) Earth the grid (pin 1) of valve V1.
(28) Check that the links A, B, C andE are
connected.
(29) Confirm that the -40 supply is connected
to R76, R24, R21 and the collector of
X16.
(30) Check with the oscilloscope that no
oscillation is present at the emitter of
X16. -
(31) Confirm that the -40V supply is connec -
ted to R50, R52and the collector of X2L
(32) Check with the oscilloscope that no oscil -
lation is present at the emitter of X21.
(33) Confirm that the -40V supply is connec-
ted to R31 and R34.
(34) Confirm that the -40V supply is connec-
ted to R39 and R40.
(35) Openexternalcircuit breakerto remove
mains input.
(36) Solder resistors R36 and R37 in place.
(37) Remove 100 ohms load resistor from the
-40V supply.
(38) Connect a load resistor value 50 ohms
rating 20 watts, acrossthe servo motor
(M2) leads in place of the motor.
(39) Close external circuit breaker to apply
input to the unit.
(40) Check that after a period of five minutes
the outputs at the emitters of X16 and X21
are steady at -21V, and that the vol-
tages on R29 and R43 are -3V.
(41) Vary the mains input voltage between 214V
and 246V, checking that both the -40V
and +12V railsare free from oscillation,
and that the hum level on each is less
than 200mV and 80mV respectively.
(42) Set the MOTOR DRIVE switch to OFF,
and check that the OVERLOAD indicator
lamp lights and is extinguished after
some 30 seconds when the thermal de-
lay switch operates. Set MOTOR
DRIVE switch to on,
(43) Apply a 10c/s, 1V, r.m.s. sinusoidal
input to the control grid (pin 1) of V1,
and withthe oscilloscope check that both
outputs swing through 28V peak-to-peak,
and that no oscillation is present at any
time of the cycle. ;
(44) Reduce the amplitude of the sinusoidal
input until the output falls to 6V peak-to
peak. Check that the r.m.s. value of
the input necessary to give that output
is between 20 and 40mV.
(45) Apply a 300c/s, 1V r.m.s, sinusoidal
input to the control grid (pin 1) of V1,
and with the oscilloscope, check that
neither output lags the input.
(46) Apply a lkc/s, 0.2V r.m.s. sinusoidal
input at pin 18 on plug PL3 and again
check outputs for lags.
(47) Open external circuit breakerto remove
mains input from unit, and set MOTOR
DRIVE switch to OFF.
(48) Check that the resistances between all
potentiometer wipers to signal ground
and to chassis is greater than one
megohm.
(49) Disconnect the 50 ohms load resistance
_ from the servo motor leads, and re-
connect the leads to the motor.
(50) Apply the +100V reference potentials to
the unit at plug PL2, thus:-
* -100V Pin 1
+100V Pin 2
Signal ground Pin 3
(51) Close external circuit breaker to apply
mains to unit, and set MOTOR DRIVE
switch to ON.
(52) Check that after the 30 seconds delay
imposed by TD1/1, the servo pointer
moves off and finally comes to rest at
zero indicating that the servo motor is
correctly wired in circuit.
(53) Should the servo pointer oscillate, set
MOTOR DRIVE switch to OFF, and re-
verse motor connections.
ba 2S
(54) Close MOTOR DRIVE switch and check
that the servo is now stable.
(55) Should the pointer still oscillate, ensure
that the +100V reference supplies are
getting to the feedback potentiometer.
Check continuity of arm fuse FS3.
(56) With servo in operation, set the control
grid of valve V1 to OV by adjustment of
RV1.
(57) Set MOTOR DRIVE switch to OFF, and
open external circuit breaker.
(58) Remove motor/potentiometer assembly
and replace in such a position as to en-
able the pointer to be adjusted, i.e. with
the dial facing outwards.
(59) Close external circuit breaker, and set
MOTOR SWITCH to ON.
(60) Using the special tool provided, set
pointer to zero.
(61) Open external circuit breaker and set
MOTOR SWITCH to OFF.
(62) Refit motor/potentiometer assembly in
operational position.
(63) Apply a d.c. potential across one of the
linear slave potentiometers, and moni-
tor the output from the arm of this po-
tentiometer on the oscilloscope.
(64) Apply a 100V peak-to-peak, Ic/s, square
wave signal to the servo input (pin 180n
plug PL3).
(65) By adjustment of potentiometer RV8 set
the positive transient to approximately
5%.
(66) By adjustment of potentiometer RV2 set
the negative transient to approximately
5%.
13
SECTION 7
FAULT FINDING
37. The following procedure is givento assist
14
in locating any electrical fault which the .
unit may develop. Directions for dismant-
ling the equipment for repair purposes are
given in Section 8 of this manual, anda list
of quiescent test voltages is given in Table
5.
(1) Switch off supplies and disconnect all
leads from the servo unit
(2) Disconnect leads from servo motor M2,
and connect a 50 ohms, 20 watts resis-
tive load in place of the motor.
(3) Connect mains input at plug PL1, and
earth control grid of V1. Connect
DIRECT pins on link panel LK1.
(4) Apply mains voltage to unit and set
MOTOR DRIVE switch to ON.
(5) Check that the thermal delay switch
operates within 30-,60 seconds of
applying the mains input.
(6) Check that the potential of the +12 volts
railis infact +12V, and that no excessive
hum or oscillation is present.
(7) Check that the potential of the -40 volts
rail is between -39V and -40V, andthat
no excessive hum or oscillation is
present.
(8) Check that the collector voltage