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GPS 100  EXTERNAL TIME REFERENCE INTERFACE

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
    multiple SER cards to an external time reference with an
    accuracy of 1 millisecond.

The card provides a means of synchronizing the Time of Day
    clock in the PLC with an IRIG-B time code signal or a GPS 300
    GPS receiver.

 


 

 

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
    industry standard time code interface. This 1kHz amplitude modulated signal is
    connected through a coaxial cable connector on the ETR card. The ETR card presents
    a high impedance load to the IRIG-B signal so that it can be looped between multiple
    devices.

GPS 300 GPS Receiver interface. The GPS 300 is a low cost rugged design that
    integrates the receiver and antenna into a single weatherproof housing suitable for
    outdoor mounting. The GPS 300 receiver is powered from the GPS 100 card. The
    interface between the GPS 100 and the GPS 300 receiver is a multiple conductor cable
    carrying RS-232 signal levels. Since the receiver and the antenna are integrated into a
    single unit, the GPS 300 receiver can be mounted as much as 250 feet from the GPS
    100 card.

In the absence of either of the two synchronizing signals the ETR card will maintain the time based on an internal crystal controlled oscillator.
 


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