3S9890 General Electric Selsyn

WHERE TO USE

General Electric 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 without any mechanical connection between the two units. The data may be furnished in terms of precise mechanical position or as an electrical signal.

General Electric Selsyns may be used to operate equipment requiring mechanical inputs such as dial indicators, valves, dampers, and literally hundreds of other applications in manufacturing and processing plants, municipal utilities, and steel mills. While most applications are for measurement and position indication, the increased emphasis on automation has resulted in selsyns being specified 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 receiver, 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 corresponding positions, the voltages induced in the transmitter secondary are equal and opposite to those induced in the receiver secondary, that is, they are balanced; therefore, no current flows 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 flows in the secondary windings. This current flow 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 mechanically (by gears for example) or manually by an operator (for a signaling or control operation), the receiver immediately assumes a new corresponding position.

GENERAL ELECTRIC 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-flush panel mounting.

Permanent dials are moisture resistant with black marks etched on photosensitive aluminum. Blank dials for calibration after installation may also be furnished. These have white paper mounted on an aluminum plate.