Geodynamics GPS Fieldwork

The Australian National University
Research School of Earth Sciences
Geodynamics Group

Quirks of the PCON

Written by Paul Tregoning pault@rses.anu.edu.au

Decision Criteria
Time and Alarm settings
Known Problems

Criteria

Voltages

The system hibernates if the battery voltages fall below 11.5 V. From the point of view of the PCON, hibernation means not supplying power to the GPS receiver or heaters (the satellite phone can still be turned on - at the discretion of decisions made by the DSCC).

The system will wake from hibernation on 15 October or if told to do so by a command received at any of the three COM ports. The conditions for issuing such a command from the DSCC are at the discretion of the software writer. To date, the conditions are that the available integrated solar power in the previous 24 hours exceeded 300 Wh and that the battery voltages are above 12.8 V.

Temperature

Heater 1 is turned on if the average temp of probes 1 and 2 falls below 9 degrees. It remains on until the temperature rises above 11 degrees.

Heater 2 is turned on if the average temp of probes 1 and 2 falls below 7 degrees. It remains on until the temperature rises above 9 degrees.

Heater 3 is turned on if the average temp of probes 1 and 2 falls below 5 degrees. It remains on until the temperature rises above 7 degrees.

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Time and Alarm settings

The PCON maintains the time setting via an on-board Realtime clock powered by a dedicated lithium battery. We run all clocks on UT time. The PCON time can be set from the DSCC (or any of the COM ports) by sending the appropriate ASCII command to one of the COM ports.

If the PCON clock gets corrupted (ie there is an illogical time for either the real time or the alarm time) then the PCON will recognise this, set the time to 00:00:00 and the alarm time to 12:34:56. It will then power up the DSCC.

Written into the DSCC code is a check of the PCON alarm time. If it is 12:34:56 then the DSCC software assumes that it has been woken because the PCON time was corrupted. The DSCC resets the PCON time according to its own value. It sets the alarm time according to a default value listed in an input file (controllable by a user) and then shuts itself down (ie issues a PU 02 command to the PCON).

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Known Problems

If the PCON receives a command via any of the COM ports while it is in the process of logging diagnostic data it will freeze. Recovery is possible only by disconnecting ALL external power sources to the PCON (ie removing all battery connections to the card frame) or pulling out the PCON circuit board. It is therefore imperative that the DSCC software leave sufficient time between issuing a log data command (LL) and the subsequent command. At present, this is done by calling a simple FORTRAN program, which counts for X seconds, before permitting the DSCC software to continue running. To not do so is at your own peril .....

In 2001 the GPS receiver at LDBF switched itself off at the on/off switch despite our precautions of having the PCON shut down the system if the battery voltages fall to 11.5 Volts. The GPS went off during the phone call to RSES. We suspect that starting the phone and/or actual data transmission caused the battery voltage to drop below 10.4 V (the level at which the GPS will switch itself off) within 1 sec (the sampling time of the PCON). Therefore, our catch for this problem failed. Our current fix to this problem is a software fix on the DSCC - we do not send a command to power up the phone unless the battery voltage is above 12 V. We believe (but have no real proof) that the batteries will not plummet to less than 10.4 V during a normal phone call if they start out at above 12 V.

At present, the PCON decides whether the heaters need to be turned on/off. The temperatures for the decisions are hard-wired into the PCON EEPROM and only Norm Schram can change them. This is causing considerable problems at the BVLK site in 2002 where it is clear that the insulation is not working as well as it should be and the three heaters are draining the batteries, possibly resulting in less GPS data being collected than otherwise could have been. A suggested change to PCON code is that the heaters have default temperature criteria but that they are changeable by a serial port command. Alternatively, there could be a command to disable the heaters completely - or each heater individually.

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Last modified:2002 March 18 pault@rses.anu.edu.au