External Signal Control Group

External signal control provides the interface for automatic operation of the system in response to non isolated signals from process instruments, motor armature voltages, line tachometers, tachometer followers or other signals within the ranges listed. All external signal control options (except the tachometer followers) contain a built in signal isolator. Note that Option S-21 isolates and conditions the standard Polyspede O-6 VDC speed reference for all types of multiple drive systems.

A Signal isolator eliminates the need for AC line isolation when a signal that is referenced to AC ground is connected to an SCR DC drive. It is smaller than an isolation transformer and it generates no heat, but it does not provide any AC line surge or spike suppression.

Where the external signal from a tachometer or other source is already line isolated, the Tachometer Follower option, which contains no isolator is used.

The external signal control is a field or factory installed printed circuit board assembly. In contains an optically coupled voltage frequency - frequency voltage signal isolator with a polarity insensitive, rectified and filtered input circuit, Scaling registors a MANUAL AUTO relay and indicator light a field adjustable RATIO pot, plus factory adjusted CAL and ZERO pots are also standard features.

In the AUTO mode, the MANUAL speed pot is by passed by the MANUAL AUTO relay and the isolated and processed external signal is fed to the SCR DC drive. In the MANUAL mode, the relay selects the speed potentiometer for control if a jog option is also selected, the external signal option is disabled during jogging and speed is controlled by the jog pot setting.

In all cases, the external signal control output is positive and increases as the input signal increases.

Example:

4ma to 20ma input = 0 to max output

0 VDC to 90 VDC input = 0 to max output

Maximum output is determined by the setting of the HATIO pot.