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Timers

The Flexcharge programmable DC timer is a two-way switch (a single-pole, double-throw relay) that can be used to schedule the power provided to electronic devices. The timer consists of an electronic clock, powered by a small rechargeable internal battery, and an electromechanical relay powered by the same batteries or the DC power supply that runs the station equipment. For PBO, there are two fundamental purposes for using such a timer:

1) Conserving power. The typical case is a relatively high-consumption communication system, such as a VSAT, running on limited power, usually solar/photovoltaic. In this case, the timer should make power available to the high-consumption device for relatively short, usually daily, intervals.

2) Maintaining system health. Some components, such as CDMA modems, might require occasional power cycling to reconnect to the cellular network. The timer should switch off the component in question for short intervals on a daily or weekly schedule.

These two cases lead to subtly different timer setups. A timer failure would presumably mean that, due to mechanical failure of the relay contacts or coil, it is stuck in a "non event" mode (explanation below), although this might not be certain. The timers have proven themselves quite reliable in field installations, but in the event that the timer should fail, the desired outcome depends on power availability:

1) Limited power. In the case of limited power it is desirable for a timer failure to result in an open circuit, with the high-consumption device powered off, so that the system can continue to run the GPS receiver. Otherwise, the communication system will drain the batteries and cause the entire system to shut down (or run intermittently when there is adequate solar power). This means that the "normally open" terminal should supply power to the communication device, and that an "on event" will schedule its operation.

2) Unlimited power. In this case, a timer failure would result in a closed circuit, leaving the communications device running without its regular power cycling. Eventually the device might go offline because it hasn't been hard rebooted, but until then, the station will stay online. To make this happen the "normally closed" terminal should supply power to the communications device, and an "on event" will schedule its non-operation.

 

For more information about timers, please see the UNAVCO Knowledge Base on Digital Timers.

Last modified: Friday, 01-Apr-2016 23:56:18 UTC

 

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