The External Time Reference
(ETR) interface card is designed to synchronize multiple SER cards to an
external time reference such as an IRIG-B time code signal or a GPS
receiver. The ETR card can also be used to synchronize the PLC’s time
of day clock. By using GPS time synchronization, event recorders located
hundreds of miles apart can be synchronized to within 1 millisecond of
each other. The ETR cards have a Modulated IRIG-B time code input
as well as a direct interface to a GPS 300 GPS Receiver.
The GPS 100 ETR card is designed to operate as a standard I/O card for the Modicon Quantum PLC. The GPS 100 card provide two important functions in the SER system:
The card provides the timing pulses necessary to synchronize
The card provides a means of synchronizing the Time of Day
The GPS 100 card communicates with the SER cards over an RS-485 bus. The GPS 100 card will send out a synchronization message to all of the SER cards every second. The GPS 100 card has a hot standby feature for redundant operation. When the card is first powered up, it will listen on the bus for time sync messages from another GPS 100 card. If it detects that another GPS 100 card is active, it will continue to monitor the bus until it detects the other card has failed, at which time it will start sending synchronization messages.
The ETR cards have two time synchronization inputs:
Modulated IRIG-B time code interface.
The Modulated IRIG-B interface provides an
GPS 300 GPS Receiver interface. The
GPS 300 is a low cost rugged design that
the absence of either of the two synchronizing signals the ETR card will
maintain the time based on an internal crystal controlled oscillator.