Eaton Vickers EM-A-10 Mounting instructions

Revised 09/01/87 I-3081-S
Single Ended Linear DC Servo Amplifier
EM-A-10
Vickers®
Servo Valves
Service Data

B. Specifications
Input Impedance Min. Typ. Max. Units
4
5
Input Signal Level
Gain: Continuously
Adjustable: Input 5
Input 4
Output
Output Current
20 Ω load
Output current limits
Dither current adjustable
Output drift at max. gain
During warm-up (30 min.)
vs. temperature
vs. time (after 30 min.)
vs. supply voltage
4.95
49.5
–100
2
0.20
20
–20
3
Frequency Response
DC - 300 Hz max.
gain full load
Single ended with respect to common
5
50
0
200
5.05
50.5
+100
20
2
400
500
100
30
1
10
1
–3
KΩ
KΩ
V-peak
Amps/volt
Amps/volt
MA
MA
MAp-p
MA
MA/_F
MA/24 hrs.
MA
DB
Regulated Output
Supply into 500 Ohm load
Pin 7 to common
Pin 8 to common
Temperature Range
Operating
Storage
Power Supply Req’mnt
Voltage Range
+9
–9
–29
–40
+14
–14
+10
–10
+19
–19
+11
–11
+71
+85
+20
–20
Vdc
Vdc
_C
_C
Vdc
Vdc
Mechanical Specs
Module
Module Size
Module Weight
Controls
Special printed circuit card
5.0” x 3.5” x 1.0”
8 ox.
Screwdriver adjusted
Dither
Gain
Table 1. Electrical and Mechanical Specifications for the EM-A-10.
General
This manual is written primarily to establish a logical trouble-
shooting procedure for the solid state EM (electronic modular)
amplifier. Complete systems are beyond the scope of this manual
and will not be covered. Adequate information is presented for an
Electrical Technician to repair the EM-A-10 amplifier.
EM-A-10 (308118) Linear Servo Amplifier
A. Description
The EM-A-10 is a special purpose DC servo amplifier designed
specifically for a Vickers SE3 or SF4 flapper type servo valve.
The EM-A-10 consists of a high gain summing amplifier, a low
gain DC amplifier and a power output stage.
The amplifier module also contains a 10 volt regulated power
supply which may be used for development of input signals
through an external 5000 ohm potentiometer.
The complete amplifier and power supply are contained on a
plug-in module whose approximate dimensions are 3-1/2 x 5
inches. Refer to table 1 for electrical and mechanical
specifications.
C. Installation
The EM-A-10 servo amplifier is designed for mounting
on a power supply plate such as the EMP-A-11. Input
and output connections to the amplifier circuitry are
provided by printed circuit pin connections on the
module. These pin connections, when installed into a
plug-in receptacle, must be connected as shown in Table
2. TB2 wiring interconnections, located on the EMP-A-11
power supply plate, are shown for convenience.
Portions of the EM–A-10 servo amplifier are of the
incapsulated construction and must be replaced as
complete assemblies. Amplifier A1 and A2 shown on the
schematic diagram Figure 1 are examples of this type of
construction. Replacement of A1 and A2 require factory
adjustments to be performed to the resistance values
designated by an asterisk (*). Therefore, should
replacement of either amplifier be required, it is
recommended that the installation be accomplished by
Vickers. Replacement EM-A-10 amplifiers are available.
EMP-A-11
TB2
(J)A
(J)B
(J)C
Plug-in
receptacle
pin
conn’tions
Plug-in
module
pin
conn’tions
Signal
–
–
–
4
5
6
7
8
–
–
1
2
–
–
3
a
b
c
d
e
f
h
j
k
l
m
n
p
r
s
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Dither (13 Vac)
N.C
–19 Vdc input
Input #1
Input #2
Summing Junction
Regulated +DC output
Regulated –DC output
N.C.
N.C.
Negative output to coil
Positive output to coil
+19 Vdc input
Slotted for polarizing
key
Common
Table 2. The EM-A-10 Plug-in Receptacle and
Terminal Board Interconnecting Wiring
D. Circuit Description
Amplifier Section - The EM-A-10 is a DC amplifier,
consisting of a high gain summing pre-amplifier feeding a
unity gain buffer amplifier which drives a power output
stage.
The output stage is statically adjusted to produce 200
Milliamperes (MA) of current through the 20Ωservo
valve coil. (Vickers type SE3/SF4 servo valve) and varies
from this 200 MA value with variations in input signal.
An explanation of the circuitry follows: Refer to the
pictorial diagram, Figure 1, the simplified schematic
diagram Figure 2, and the complete schematic diagram
schematic diagram Figure 3.

Command and feedback signals are connected through R1 and
R2 to the input of amplifier A1. Resistors R1, R2, and amplifier
A1’s input resistance form a summing network which permits a
difference potential to be developed across amplifier A1’s input
resistance. The amplitude of this potential is determined by the
polarity and amplitude of the input signals, the input coupling
resistance R1 and R2, and the input resistance of amplifier A1.
Under normal operating conditions, the junction of R1 and R2
is maintained at ‘‘virtual ground’’ within a few millivolts by A1.
Diodes D8 and D9 limit amplitude extremes at the input of A1
to approximately .5 volt minimum, if the amplifier output
saturates. Amplifier A1 inverts the output signal with respect to
the input signal, permitting gain adjustment to be obtained by a
negative feedback arrangement through resistors R3 and R4.
A portion of the inverted output is allowed to develop across
the input resistance of amplifier A1. This negative feedback
subtracts from the input signal subsequently reducing the gain
of the amplifier.
The output of A1 is used to drive amplifier A2 which in turn pro-
vides the current necessary to drive power transistor Q5 and
Q6. (Shown on the complete schematic diagram Figure 1).
Amplifiers A1 and A2 are of the same type. But amplifier A1’s
gain differs from that of amplifier A2, due to wiring arrange-
ment. Amplifier A1’s gain is essentially the ratio of feedback
to input resistance or:
A1 Gain - Input 1
(Approx. gain of 2)
A1 Gain - Input 2
(Approx. gain of 20)
=
=
R3 +
R1
R2
R4 SR4a
R4 + R4a
R3 + R4 SR4a
R4 + R4a
Amplifier A2 is connected to provide a non-inverting, unity
gain amplifier characteristic. Unity gain amplifiers (gain of 1)
provide isolation between circuits (buffer action) and will per-
mit a source with low current capacity (A1) to drive a heavy
load (Q5 and Q6).
Transistor Q5 and Q6 develop the necessary output current
for the servo coil. Resistors R20 and R20a bias amplifier A2
and establish the 200 MA null current through Q6, D6, the
servo coil, and resistor R26 (the current sensing resistor).
A voltage is developed across R26 directly proportional to the
current through it. The voltage is reduced through voltage
divider action by R23 and R21, and is fed to pin two (2) of the
unity gain amplifier A2 reducing its gain. This gain reduction
(negative feedback) improves the linearity of the driver stage
A2 and the output transistor circuit Q5 and Q6. R25a and
R25b are adjusted to limit the maximum current. When the
voltage across R25a and R25b exceeds the threshold voltage
of D4 and D5, the diodes conduct limiting a further current
rise in the output circuit.
Dither - The dither signal (60 to 400 Hertz) is connected to pin
1 of the plug-in module. A variable resistive divider network
R16 and R18 provide adjustment of the value of the dither.
The dither is applied to pin two (2) of amplifier A2 through
resistor R17. Dither signal is used to keep the servo flapper in
constant motion, thus preventing the flapper from magnetizing
in a locked condition against the orifice. Constant motion of
the flapper will also reduce the effect of silting (the particle
build-up around the orifice).
Power Supplies - Four regulated power supplies are
provided on the plug-in module. Refer to the schematic
diagram figure 1. The amplifier section utilizes both a
positive ten (+10) and a negative ten (–10) volt supply for
operation. A positive ten (+10) and a negative ten (–10)
volt supply is also available for external use.
The externally connected supplies may be used for
amplifier control circuitry if desired, thus providing the
control voltage and amplifiers necessary for a complete
system in one plug-in module.
All the regulated supplies operate in a similar manner,
therefore, explanation of only one will be presented.
Upon application of negative nineteen (–19) volts DC to
pin 3 of the plug-in module, Zener Diode Z2 conducts
through R7 establishing a regulated source voltage for
the base of Q2. A portion of this regulated voltage is
applied to Q2 through the voltage divider network of R9,
D2, and R11. Diode D2 and resistor R11 shunt the base
resistance of Q2 and reduce the base drive as the
temperature rises. This reduction in drive prevents
thermal runaway of transistor Q2. Emitter resistor R13
swamps the emitter base junction resistance and
prevents a large increase in emitter current, particularly
at low temperatures. Q2 and R13 act as a variable
voltage dropping resistor for Zener Diode Z4, and
maintain a constant current through Z4 with varying input
voltages. The combined action of Q2 and Z4 provide a
regulated -10 volt source at pin 8 of the plug-in module.
E. Troubleshooting Procedure
Determine if the EM-A-10 module is functional. Refer to
the schematic diagram figure 1 and the pictorial diagram
Figure 2.
Note
The EMP-A-11 power supply or its equivalent must
be used to perform the following test. Minor wiring
changes may be required if an equivalent supply is
used.
1. Remove electrical power from the system.
2. Remove the input signal connections 4, 5, 6, 7, and
8. Tape the wire ends and symbolize to prevent
error.
3. Connect a linear taper, 5000 ohm test potentiometer
as shown in figure 4.
4. Remove the EM-A-10 plug-in module. Use the ohm-
meter on the low ohm scale to check the resistance
of the load as follows:
Connect the ohmmeter between J* - m & n. A read-
ing of approximately 20 ohms is considered normal.
If the reading is normal, reinsert the plug-in module
and proceed with the test.

Com
–D.C.
Note
The characteristics of this amplifier are such that once
conduction starts, a very small change in input signal level
will cause a very large change in output current. There-
fore, the 5000 ohm command test potentiometer (shown in
figure 4) will seem to have no effect on the measured out-
put voltage level until the center of the control is reached,
then the voltage level will change rapidly from 0 to –1.5
volts. To obtain –0.6 volts (200 MA) reading, the control
must be varied very slowly when the center of the control
is reached.
5. Connect a volt-ohmmeter between TB2*-2 and TB2*-3
(common ground reference). Apply power and mea-
sure for negative .6 volts (200 MA). The voltage
should vary from approximately zero (0) volts at one
end of the test potentiometer adjustment range to
approximately 1.5 volts at the other. If the amplifier
performs as indicated, it is operating normally.
6. Remove AC power from the system.
7. Connect symbolized wiring removed in step E. 2.
12
11
6
5
7
4
8
3
21
3
8
15
7
13
1
2
5
4
6
–D C Supply In
R15R13
2.2K
R11
Z2
Q4
Q2
D 2
2.7K
R7
1.5 K Z 4
Z 6
Z 5
Supply Out
R9
1.5 K
R6
Supply Out
2.7 K
R8
Z1
6
5
7
4
8
3
21
ALL RESISTORS + 5%, 1/4 W
UNLESS OTHERWISE SPECIFIED
*FACTORY ADJUST
+D.C.
Z 4 R26
3Ω
3W
POS
OUT
Q5
R24
470 Ω
R23
3.3K
0.1 µf
C2
D3
D4
D5
R25b R25a
R25
2.0 Ω
3W
Q 6
C5
Summing Junction
Sig. Input 1 R1
DITHER
50K
Sig. Input 2
DITHER
+ D.C. Supply In
+1%,5W R2
5K
+1%
5 W
R16
15K
R10 R12 R14
Q3
2.2K 220Ω
D1
Q1
D8 D9
A
1
R17
22K
R271%1/10W
a
*
R3
10 K
R2
C4
.0068 µF
200K
R4 a
GAIN
R 4
470PF
R18
1 K
R20aR20
82 K *
DITHER
R21
3.3K
A2 NEG
OUT
D 6
*
*
Figure 1. Complete Schematic Diagram for EM-A-10
68Ω
220Ω68Ω
b

Figure 2. Pictorial Diagram of the EM-A-10
Figure 3. Simplified Schematic Diagram of the EM-A-10
+10 Vdc
R16
22K
R17
22K
DITHER
R18
1K
*R20a
R20 82K
50K
R1
R2
5K
A1 A2
R21
3.3K
10/1 INV.
4
5
R4
200K
R3
10K
R23
3.3K
12
15
R26
3 Ω
Load
11
*Factory Adjust

EMP-A-11
TB2-*
Load Neg. Out
Load Pos. Out
Volt-Ohm Meter (VOM)
Servo Coil
20Ω
Remove signal
wiring at
terminals 4 & 5.
Symbolize the wires
removed to prevent error.
Common ground
Input signal
Test Potentiometer
5000 Ohm Linear
Potentiometer
Note
If the EMP-A-11 power supply is not used,
connect the power source as shown to
test the EM-A-11 amplifier.
Figure 4. Test Potentiometer Wiring Diagram
1
2
3
4
5
6
7
8
+DC
–DC