Research School of Earth Sciences
Geodynamics Group
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The Australian National University
Research School of Earth Sciences Geodynamics Group |
The information below is intended to provide an overview of the various
pieces of equipment, hardware, electronics etc that comprise my remote
Antarctic GPS installations. Photographs below can be viewed at full size
and resolution by clicking on the images.
The solar panel cables are 3 m long and are terminated with a male "buccaneer" connector. The outer metallic sheath of the cables is earthed to a metal plate on the ground.
The advantage of this setup is that the solar panel cables can be connected easily to the solar panel bracket in the Antarctic environment (ie with gloves on!).
The solar panel regulators we are using have been designed in-house by the RSES Electronics Group. They are specifically tailored for gellcell batteries in that they adjust their charging voltage according to the temperature, based on the published "ideal" charging voltages for the batteries. Our systems are designed for 6 solar panels and three batteries. Therefore, two panels (hence two regulators) charge each battery. The regulators are housed in small plastic boxes which are placed on top of each battery so that the measured temperature used by the regulator to decide the optimal charging temperature is as close to the temperature of the battery as possible.
The Card Frame is the metal case in which we hold the electronic circuit boards which control the whole system. The circuit boards can be inserted and removed relatively easily and are protected from damage in transit and during installation and upgrades.
All electrical connectors are fitted on one vertical face of the card frame, while all computer connections (monitor, keyboard etc) are made on the top horizontal surface.
The frame currently houses three cards: the PCON, the PSC and the DSCC (see below for descriptions). There is space to include a fourth circuit board in the card frames. At present we don't have need for this (nor are the card frames wired up to accommodate a fourth).
The internal wiring of a partially completed card frame can be viewed here.
The Power Controller (PCON) is the heart of the whole system. It is responsible for monitoring the battery and solar panel voltages, internal temperatures, external temperature and pressure and for making decisions about whether to hibernate the system, turn heaters on/off etc. It is also the interface between the computer and the hardware, powering on/off specific devices such as satellite phones.
The PCON runs continuously and consumes about 0.6 Watts. Every second it reads the battery voltages and internal temperatures. If the temperatures fall below preset levels during normal operation then the PCON switches on heaters to warm the equipment box. Once the temperatures rise again the heaters are switched off automatically. Similarly, if the battery voltages fall below critical levels then the PCON will shut down the power supply to the GPS receiver and will turn off the heaters - effectively putting the system into a hibernation state. The PCON will wake the system from hibernation either upon receipt of a command to do so from the computer (see below) or on the 15 October, when there should be sufficient solar power available to power continuous operations. Further details of the automatic operations of the PCON and the default decision-making criteria can be found here.
The PCON has three serial ports. COM1 is linked to the computer (DSCC), COM2 is dedicated to talking to the fuel cell (a lonely, one-sided conversation at this stage ...!) and COM3 is a "monitor" port that was used for testing. COM3 is still useful for field personnel because they can talk directly to the PCON by connecting a PC to COM3 and using any terminal program (e.g. procomm). Communication settings are 9600,n,8,1. The PCON listens continuously for contact on any of the comm ports. Note: it doesn't listen if it is logging diagnostic data!!! In fact, talking to it while it is logging generally results in the system hanging
Every 20 minutes the PCON records system diagnostic data - battery and solar panel voltages, temperatures and pressure, heater and hibernation status. The logging cycle takes only a few seconds. The PCON has an alarm time setting and, once per day at the alarm time, irrespective of the hibernation status, the PCON powers up the computer. It will provide power for 45 minutes (unless instructed otherwise) at which time it will shut off the power to the computer. While the computer is powered up the PCON continues to monitor the whole system as well as responding to commands from the computer. Such commands include transferring the diagnostic data which has been logged since the last transfer, turning on/off devices, changing some of its internal settings (e.g. alarm time, remaining time to shutdown of the computer etc).
Additional information on the PCON is available from a document written by Norm Schram (RSES Electronics) who designed and programmed the logic of the PCON.
The circuit board of a PCON can be viewed
here.
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The DSCC has several important functions
The DSCC is typically powered up for 5 or 50 minutes per day depending on whether the system is hibernating. The difference is the time to convert the GPS data to compressed rinex and to make the phone call. The control of the operation of the DSCC is the responsibility of the scientists - that is, we write the software that runs on the DSCC and it is up to us to interface with the PCON (via commands through the serial port) to get the PCON to control the system. Further details of the automatic operations of the DSCC and the default decision-making criteria can be found here.
The DSCC has three serial ports. COM1 is linked to the PCON, COM2 is dedicated to talking to the GPS receiver and COM3 is connected to the satellite phone. COM3 can also be used for talking directly to a field laptop computer if required. Again, the DSCC will do whatever it is programmed to do - this is our responsibility. The actual computer is a PC-104 card model TB486 (ie a 486 without a math co-processor). We are considering changing to a TD310 model with a co-processor but this draws considerably more power. The decision has not yet been made .... if we can get the TB486 to do all that we require then we will stay with it!
The DSCC has the capability of telling the PCON to shut down its power, simply by issuing a PU (power up) command through COM1. For example, PU 50 will reset the PCON timer to shut down the DSCC power in 50 minutes (used to prolong the life of the DSCC waking) whereas PU 02 will shut down the power in 2 minutes (used to turn off the DSCC).
Additional information on the DSCC is available from a document written by Paul Tregoning (Geodynamics Group) who has programmed the operation of all DSCCs to date.
The circuit board of a DSCC can be viewed here.
The PSC contains the electronics to actually switch on/off some devices. The user never interacts directly with this circuit board; rather, commands to/from the DSCC and PCON direct the PSC to perform certain tasks.
The circuit board of a PSC can be viewed
here.
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The AIB was an additional piece of electronics added in 2001 to expand the capabilities of the system. It acts as an interface between the PCON and peripheral devices such as the air pressure sensor, satellite phone and fuel cell. There are also additional power and control lines (currently wired but not being used) to permit further additions to the system if required.
A system without a satellite phone or fuel cell does not require an AIB. If the pressure sensor is connected directly to the card frame it will work correctly - therefore, there is no need for an AIB. However, if one wants to add a satellite phone at a later time one can simply change the order of connections slightly, add the AIB and insert the satellite phone into the system.
The circuit board of an AIB can be viewed
here.
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The air pressure gauge is a SenSym SDX 15A2 sensor which has been mounted on a circuit board and connected either to the AIB or to the card frame directly. Every time the PCON records diagnostic data, the pressure gauge is powered up, a reading is taken and the gauge is then powered down. Tests have shown that the gauge reaches stability in milliseconds so powering it up temporarily does not cause any problems.
There is some hysterisis evident in the pressure gauges. To date, this has not concerned me - in fact, the pressure data have not yet been used to estimate precipitable water in the troposphere above the GPS sites but that is the long-term intention. Also, the pressure sensors are rated to only 0 deg C and data from Davis in 2000 shows a clear linear variation with temperature below zero.
It is well known that atmospheric pressure loading affects the vertical estimates of geodetic heights. A combination of pressure measurements made by our equipment and the Antarctic Division automatic weather stations will allow such effects to be modelled and removed from the height time series.
The circuit board of an air pressure sensor can be viewed
here.
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Last modified:2002 March 17 pault@rses.anu.edu.au
