Tait TB8100 Installation And Operation Manual

Contents

Tait TB8100 Installation And Operation Manual Manual pdf 32 page image

32 Operation T801-4 Installation and Operation Manual© Tait Electronics Limited September 20072.8 AlarmsAll six T801-4 alarms are available on the I/O PORT on the rear panel. Fourof these alarms are generated by the Satsync 7 module. The alarms aredescribed in the following table. Refer to “I/O PORT” on page 18 for fulldetails on these outputs.GPS Alarms The GPS alarms will be activated whenever the Satsync 7 module detectsthat the 1PPS signal has become invalid or is missing. For example:■ When the Satsync 7 module is programmed for PPS timing source withNMEA data, the GPS alarm will be activated if the 1PPS signaldisappears or the NMEA data indicates that the 1PPS signal is invalid.■ When the Satsync 7 module is programmed for PPS-only timing source,the GPS alarm will be activated if the 1PPS signal disappears.Take care when providing the T801-4 with an external PPS-only source,such as a TTL or RS-485 signal. In this case the NMEA data is not availableto the Satsync 7 module, and it must be programmed for a PPS-only timingsource. Although the GPS alarm will be activated if the 1PPS signaldisappears, some GPS receivers do not disable the 1PPS signal when thereceiver loses its GPS fix, and consequently the GPS alarm will not betriggered. This is the case with the QS 2 RSU GPS receiver. It is importantin this situation to monitor the correct alarms. This is covered in more detailin the relevant parts of “System Configuration” on page 49.Pin Signal Name Notes1 OSC ALRM OSC1 Activated by the Satsync 7 module(s) when the master oscillator accuracy isbelow the ±1 part in 108 threshold. For example, when:■ the T801-4 is first powered up and the oscillator has not yet stabilised■ the 1PPS signal is lost and the 24 hour “frozen” period has elapsed■ the Satsync 7 oscillator circuitry has a fault.The front panel MASTER OSCILLATOR LED is red when this alarm is activated.2 OSC ALRM OSC23 GPS ALRM OSC1 Activated by the Satsync 7 module(s) when the 1PPS signal is missing ordeemed invalid. For example, when:■ GPS reception is lost (no GPS fix)■ the 1PPS signal path is broken■ the GPS receiver has failed.The front panel GPS LED is red when this alarm is activated.4 GPS ALRM OSC25 GPS RX IND This output indicates which GPS receiver is selected. The output states are asfollows:■ high = internal GPS receiver or external PORT B GPS receiver selected■ low = external GPS receiver selected (PORT A).9 1PPS VALID OUT Activated (high) when the 1PPS signal becomes invalid. It also reflects the stateof the applied QS 2 RSU 1PPS VALID signal.