WHERE TO USE

Selsyns are electro-mechanical devices used for the convenient

and accurate transmission of angular data between two or more
remote points. This transmission is accomplished electrically with-
out any mechanical connection between the two units. The data
may be furnished in terms of precise mechanical position or as an
electrical signal.
Selsyns may be used to operate equipment requiring mechanical
inputs such as dial indicators, valves, dampers, and literally hun-
dreds of other applications in manufacturing and processing
plants, municipal utilities, and steel mills. While most applications
are for measurement and position indication, the increased em-
phasis on automation has resulted in selsyns being specied for
control as well as indication.
OPERATION
Most selsyn systems consist only of two selsyns. The master unit,
called a transmitter, is operated at the sending point as a generator
and is mechanically coupled to the data source transmitting the
position change to a remote unit. The second unit, called a re-
ceiver, operating as a motor responds to this change. The two units
are electrically and physically identical except the receiver has an
internal damper which has a braking effect on the oscillation which
may develop as a result of overshoot.
When the primary excitation circuit is closed, an alternating-
current voltage is impressed on the primary of both the transmitter
and the receiver. Since the receiver rotor is free to turn, it assumes
a position similar to that of the transmitter rotor. As the transmitter
is turned (either manually or mechanically), the receiver rotor
follows at the same speed and in the same direction. This self-
synchronous action is created because the single-phase current in
the primary induces voltages in the three legs of each secondary.
The three voltages are not equal in magnitude and vary with the
position of the rotor. When the two rotors are in exactly corre-
sponding positions, the voltages induced in the transmitter second-
ary are equal and opposite to those induced in the receiver sec-
ondary, that is, they are balanced; therefore, no current ows in
the secondary windings and no torque is developed.
If, however, the transmitter rotor is moved from the original
position, the induced voltages are no longer equal and opposite
and current ows in the secondary windings. This current ow sets
up a torque which tends to return the rotors to the synchronous
position. This position corresponds to the new position of the
transmitter. Thus if the transmitter rotor is moved either mechan-
ically (by gears for example) or manually by an operator (for a
signaling or control operation), the receiver immediately assumes
a new corresponding position.
APPLICATION
Industrial selsyns are supplied in basic accuracy ratings of 1
and 5 degrees. This is static accuracy and refers to the angle of
deviation between a transmitter and receiver required to transmit
motion at no load. Accuracy is composed of two elements, electri-
cal and mechanical error. Electrical error is inherent in the wind-
ings and construction of the rotors and stators of each machine.
Mechanical error is inherent in the bearings and type of lubricant.
Selsyns of one degree accuracy have an electrical error of
1
2 degree
and a mechanical error of
1
2 degree. Selsyns of ve-degree accu-
racy have an electrical error of 1 degree and a mechanical error 2-3
degrees. The above data is for models rated 200 rpm which contain
bearings lubricated with a light coating of instrument oil.
Similar units except with grease-packed bearings, rated 1200
rpm, may have a static accuracy of 5 or 10 degrees. In normal
ambient, the grease friction will add approximately 1-2 degree
mechanical error. In all rugged applications, such as in steel
mills, or where selsyn motion is continuous, it is recommended
that grease bearing units be supplied regardless of speed in order
to achieve long bearing life.
In order to transmit motion from the transmitter to the receiver,
some angle of deviation between the two is required to develop
whatever torque is required to move the receiver load. Maximum
permissible continuous torque occurs at 20-30 degree displace-
ment and should not be confused with static accuracy ratings.
Selsyns are seldom used to transmit information further than
several hundred feet. However, greater distances can be accommo-
dated by compensating for the errors introduced by the connect-
ing lines. Resistance in interconnecting lines causes attenuation of
torque and, depending on the size of the units involved, should be
held to values ranging from 0.2 to 10 ohms per line. Excessive wire
sizes can often be eliminated by using 230-volt units.
Selsyn primaries in a given system must always be excited from
the same phase of a common power source.
Fig. 13. Schematic of selsyn transmitter-receiver torque transmission system
Fig. 14. Schematic of selsyn torque transmission system in which two receivers are
operated by a transmitter of the proper frame size
Selsyns 4-7
Type 3S9890
Data subject to change without notice
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DIFFERENTIALS
The differential transmitter selsyn rotor is mechanically posi-
tioned. It modies electrical angular information received from a
transmitter selsyn and retransmits it to a receiver selsyn or a control
transformer as electrical information corresponding to the sum or
difference of electrical input angle and its rotor position angle. In
servo control systems, the stator primary is excited by the stator
voltages of a transmitter and the rotor leads are wired to those of
another selsyn stator.
A torque differential transmitter is constructed primarily for
operation with torque receivers, control differential transmitters,
or control transformers.
A differential receiver is free to turn in order to assume a posi-
tion with respect to the stator in accordance with the sum or
difference of the electrical angular information received. This unit
is primarily constructed for operation with two selsyn torque trans-
mitters.
CONTROL TRANSFORMER
The control transformer consists of a three-phase stator and a
single-winding rotor inductively coupled. The electrical output of
the rotor is dependent upon both the position of the rotor and the
magnitude of electrical input to the stator from another selsyn.
There are several important differences between the control trans-
former unit and other selsyn units. The rotor is never connected to
an ac supply; therefore, it never induces a voltage in the stator
coils. As a result, the stator current is determined by the impedance
of its windings (which is high) and is not affected appreciably by
the rotors position.
Also, there is no appreciable induced current in the rotor, and
the rotor does not tend to turn to any particular position when
voltages are applied to the stator. The shaft of this unit is mechan-
ically driven.
SELSYN INDICATORS
When a selsyn system is used to indicate a motion taking place at
a remote location, selsyn receivers can be factory assembled in a
variety of complete packages. The output shaft is coupled to a
pointer for indication on an instrument-type dial or to a digital
readout device.
For indication, ten standard indicator dial faces are available
utilizing the GE AB-18 and AB-16 shadow-proof galvanometer-type
instruments for semi-ush panel mounting.
Permanent dials are moisture resistant with black marks etched
on photosensitive aluminum. Blank dials for calibration after in-
stallation may also be furnished. These have white paper mounted
on an aluminum plate.
DIAL MARKING
Indicators are available with the standard increment calibration
markings shown in Figs. 31, page 4-12. Customer may remove
portions of dial scale and/or assign desired numbers and descrip-
tion prior to installation.
Fig. 15. Schematic of typical selsyn differential system for torque transmission
Fig. 16. Schematic of selsyn transmitter and control transformer
Fig. 17. Connection diagram showing interconnected stator windings and rotor
windings connected to source of excitation
Selsyns 4-8
Data subject to change without notice
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ORDERING
Transmitter
1. Based on application requirements, such as accuracy, torque,
maximum speed, and size of dial, select the appropriate units from
TABLE 1.
2. If indicator also being ordered, select per transmitter used
column in TABLE 4.
3. Order by cat number. (Example: 2J55VB1)
Indicator
1. Order by 3S9890 and select form based on application require-
ments and dial face. All forms listed have blank dial face (white
paper on aluminum) suitable for customer added markings.
TABLE 2. Vertical Mounting
When vertical mounting is required, mount pulley end of
selsyn up or down as indicated below for minimum noise.
Frame
Mount with
Pulley End
Frame
Mount with
Pulley End
33 Down 65 Up or Down
35 Down 66 Up
39 Down 123 Up
55 Up or Down 55, 57, 65 Up or Down
57 Up or Down
TABLE 3. Multiple Operation
Transmitter
Frame
No. of Selsyns
in Parallel
Transmitter
Frame
No. of Selsyns
in Parallel
55 1 Frame 55 66 5 Frame 123
65 1 Frame 65 33 1 Frame 33
65 2 Frame 55 33 3 Frame 66
123 1 Frame 123 33 16 Frame 123
66 1 Frame 66 39 2 Frame 33
39 1 Frame 39
TABLE 1. Selsyn Selection
Cat. No. Function
Max. Safe
Continuous
Torque in Oz-In
Static
Accuracy
In Degrees
WK
2
(Oz-IN
2
)
Volt-
amperes
Required
Maximum
Operating
Speed
PRIMARY - 115 VOLTS, 5%; SECONDARY 57.5 VOLTS: 60 HERTZ: SINGLE-PHASE
2JD123A1 Transmitter or Receiver 2 5 2.136 55 200
2JD123A10 Transmitter or Receiver 2 10 2.136 55 1200
2J55VB1 Transmitter 3.2 1 2.72 40 200
2JD55VB1 Receiver 3.2 1 2.72 40 200
2J65FB1 Transmitter 8 1 9.92 55 200
2JD65FB1-Obsolete Obsolete 8 1 9.92 55 200
2J65HB1-Obsolete Obsolete 8 1 9.92 150 200
2JD57C2-Obsolete Obsolete 8 5
2JDA66PA5 Transmitter or Receiver 12 5 9.94 100 200
2JDA66PA10 Transmitter or Receiver 12 10 9.94 100 1200
2JA33BB1 Transmitter or Receiver 50 5 27.3 165 1200
5MJ35CB1-Obsolete Obsolete 50 5
2JA39BB2-Obsolete Obsolete 108 5 59.2 275 1200
2J5KA1 Control Transformer* . . . 1 . . . . . . 1200
PRIMARY - 115 VOLTS, 5%; SECONDARY 48 VOLTS: 50 HERTZ: SINGLE-PHASE
2JD123A7 Transmitter or Receiver 2 5 2.136 55 200
2JD123A27-Obsolete Obsolete 2 10 2.136 55 1200
2J55VB3 Transmitter 2.6 1 2.72 40 200
2JD55VB3-Obsolete Obsolete 2.6 1 2.72 40 200
2J65FB10-Obsolete Obsolete 6.5 5 9.92 55 200
2JD65FB10-Obsolete Obsolete 6.5 5 9.92 55 200
2JDA66PA30 Transmitter or Receiver 10 10 9.92 55 1200
2JA33BB27 Transmitter or Receiver 42 5 27.3 55 1200
5MJ35CB7 Differential 42 5
2JA39BB4 Transmitter or Receiver 90 5 59.2 275 1200
Sufx does not affect price. Example 2JD123A1A.
* Primary 90 Volts
TABLE 4. Selsyn Indicators
Cat. No.
3S9890
*
Dial Type
Approximate
Accuracy
in Degrees

Receiver
Used
Indicator
Parts Used
Use With
Transmitter
SINGLE-POINTER NONGEARED INDICATORS
AB100A1 4-inch dia., 1-pointer (Fig. 28) 1 2JD55VB1 AB18 2J55VB1
AA100A1 4-inch dia., 1-pointer (Fig. 28) 5 2JD123A1 AB18 2JD123A1
BB100A1 8-inch dia., 1-pointer (Fig. 25) 1 2JD55VB1 AB16 2J55VB1
BA100A1 8-inch dia., 1-pointer (Fig. 25) 5 2JD123A1 AB16 2JD123A1
AH100A1 4-inch dia., 1-pointer (Fig. 28) 5 2JDA66PA5 AB18 2JDA66PA5
*Sufx A1 designates a blank dial. Custom numbered dials no longer available.
Accuracy is the number of degrees the transmitter must rotate before the receiver begins to follow when connected electrically in a system.
Standard dial faces available.
Selsyns 4-9
Data subject to change without notice
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TORQUE
It will be noted from the curves below that the percentage of
normal synchronous torque available at the receiving unit is a
function of the interconnecting secondary leads. These curves are
for 115-volt, 60-hertz selsyns.
Fig. 18. General-purpose selsyns Fig. 19. High-accuracy selsyns
Fig. 20. Type 2JD123A
Fig. 21. Type 2JDA66PA
Fig. 22.
Cat. No.
Approximate Dimensions in Inches, Fig. 22
Keyway
Length
of Key
or Flat
A B C D E F G
Wide Deep
2JA33BB1 Flat
3
64 1
1
8 5
5
8 3
5
8 10
3
8 3 2
1
8 1
3
8
3
32
2JA39BB2 Flat
3
64 1
1
8 5
5
8 3
5
8 12
7
8 3 2
1
8 1
3
8
3
32
5MJ35CB1 Flat
3
64 1
1
8 5
5
8 3
5
8 10
23
32 3 2
1
8 1
3
8
3
32
Cat. No.
Approximate Dimensions in Inches, Fig. 22
H L M N O P U XB XC
2JA33BB1
9
32 5
1
16 3
13
16 1
1
2 5
3
4 5
1
2 0.5 3
13
16
3
4
2JA39BB2
9
32 7
9
16 3
3
16 1
1
2 5
3
4 5
1
2 0.5 6
5
16
3
4
5MJ35CB1
9
32 5
13
32 3
13
16 1
1
2 5
3
4 5
1
2 0.5 4
5
32
3
4
Fig. 23.
Cat. No.
Approximate Dimensions in Inches, Fig. 23
A B C D E F G
2J55VB-
6
1
16 3
3
32 2
7
32
3
4 0.234 2
7
32 2
27
32
2JD55VB-
2JD57C- 6
3
4 3
25
64 2
37
64
25
32 0.234 2
21
32 3
21
32
2J65FB-
7
9
32 3
31
32 2
21
32
31
32 0.350 2
7
8 3
7
8 2JD65FB-
2J65HB
Cat. No.
Approximate Dimensions in Inches, Fig. 23
H J K L M N O
2J55VB-
17
64 2
1
2 3 3
1
8
3
16 1.750 3
5
16
2JD55VB-
2JD57C-
1
4 2
1
2 3 3
1
8
3
16 1.750 3
3
8
2J65FB-
9
32 3
3
8 4 3
13
16
3
8 2.245 4
5
32 2JD65FB-
2J65HB
DIMENSIONS
Selsyns 4-10
Type 3S9890
Data subject to change without notice
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Fig. 24. 3S9890AA100A and 3S9890AB100A indicators Fig. 25. 3S9890BA100A and 3S9890BB100A indicators
Fig. 26. Selsyn Indicator (3S9890AB100A) with Type
AB18 Dial
DIMENSIONS
Selsyns 4-11
Type 3S9890 Selsyn Indicators
Data subject to change without notice
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