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Chapter 1 - Data Acquisition Systems
- Undo the 12 bolts around the faceplate of the reftek, store them in a secure place.
- Balance the air pressure in the DAS by pressing the schrader release valve at the bottom right of the faceplate.
- Use an air compressor attached to the air vent to pressurize the DAS, the faceplate should pop off. You may need to gently pull from underneath the faceplate to assist the air pressure. If an air compressor is unavailable, carefully try the method below.
- Use a wide slotted screwdriver to gently pry the faceplate up. Make sure you pry the lid evenly, working your way around the entire perimeter of the faceplate. Also be careful to not damage the orange O-Ring that runs around the lip of the faceplate.
- Lift the DAS cardcage and faceplate clear of the DAS case.
- Remove the two screws from each side of the card retainer.
- Put the screws back in the card retainer and put insulation and card retainer into the DAS case for temporary storage.
- You can now access the DAS cards. They are numbered as follows:
- Power Supply
- CPU
- Communications (Serial and SCSI)
- not used
- not used
- not used
- A/D and DSP card
- Filter card (channels 1-3)
- Filter card (channels 4-6)
1.1 - Reftek DAS 72A-0x General Information
1.1.1 - Specifications
1.1.2 - Opening the DAS
1.2 - Reftek DAS 72A-02 Information
1.3 - Reftek DAS 72A-08 Information
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Chapter 2 - Data Storage Systems
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The SCSI transfer rate from the DAS to SCSI storage devices it
limited by the processor speed since the CPU has to handle each packet
that is transferred. On the 72A-02s and 72A-08s, this transfer speed
is roughly 6Mb/minute or 1Mb every 10 seconds.
72A-06s and 72A-07s are clocked a little bit faster to make up for their lack of a DSP. This means that SCSI transfers happen a bit faster at roughly 8Mb/minute.
2.1 - Field Disks
2.2 - Transfer Disks
2.3 - Tape Drives
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Chapter 3 - Timing Systems
3.1 - GPS Subsystems
-
GPS satellite receivers are used mainly for accurate timing.
The TCXO clock inside of the DAS is synchronized by the GPS whenever the GPS is powered
and has its own signal lock.
The GPS can either be in continuous or cycled mode.
In cycled mode, the GPS turns on for up to 20 minutes every hour in an attempt to
get a signal lock. It turns itself off within several minutes of acquiring a lock.
The GPSs require about 3 Watts of power, which is almost as much power as the DAS
requires. So the cycled mode significantly reduces the power requirements of the
system.
One advantage of the GPS system is that it is relatively insensitive to location. And its placement restrictions are pretty obvious. The more sky that the system can see, the better.
Location information can be obtained from the GPS units. If enough samples are obtained (ie: the system is left in one place for a week or so) the locations can be averaged to obtain a pretty reasonable estimate of the location of the GPS.
The GPS system cycled on an hourly basis is the preferred timekeeping method for the PBIC. The internal TCXO clocks of the Reftek are accurate to withing 40msec a day. With 24 locks in a day, the typical drift for an hour should be <2ms. This kind of drift is only one sample at 500samples/sec. And in fact, the drift of the internal clock is usually very linear, so corrections can be applied during data processing that will get sub msec accuracy in most cases.
3.2 - Omega Subsystems
-
This low power continuously locking timing system is not used much by
the Refteks anymore. One of the disadvantages of the omega was that it was very location
sensitive. And there was no way of telling where it would work and
where it wouldn't. Sometimes the system would lose signal for days at
a time. When it was receiving signal, the omega system kept the Reftek
very tightly locked to the true time.
Another disadvantage was that the system required a lot of user interaction and knowledge. The timing was relative, not absolute. So the reftek had to be programmed to within ±5 seconds of the real time to begin with. Also, the user had to program in the approximate location of the system so that time shifts could be calculated for the ULF used by the omega. The user also had to know the leap seconds for the current year and program those into the reftek as well.
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Chapter 4 - Tranportation
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Chapter 5 - Field Housings
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Chapter 6 - ARGOS Satellite Telemetry System
6.1 - Field Setup
-
The ARGOS system is pretty straightforward to setup.
The PBIC system is set up to connect to the comm port (as opposed to the
terminal port as PASSCAL does it). This method means that the user doesnt
have to disconnect the system at a site vist, creating the possibility of
forgetting to reconnect the system. The disadvantage is that the default
settings for the comm port does not match the argos default. The easiest
solution is to change the comm port settings under FSC (F8-3). Change the
settings on port 3 to be O81 (the same settings as the terminal port). These
changes are not sent until you hit F10. Also, be aware that what is displayed
on FSC may not be how the DAS is set. So even if it looks like its O81, you
should still F10 to make sure it gets changes.
6.2 - Checking Setup
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The simplest way to get an idea of whether the system is working is to
make sure that the DAS is not in acq on (or at least not acquiring data) and
power cycle the argos system and wait 6 minutes or so. If the Reftek
disk spins up (without any input from FSC) then the ARGOS system is probably
talking to the DAS ok.
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Chapter 7 - Sensors
7.1 - L4C3D
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The L43Ds that the PBIC uses are configured with a high output coil, making them very sensitive.
These sensors are useful for detection of small earthquakes. There response is flat to velocity
above 1Hz.
7.2 - FBA23
-
These Kinemetrics Force balance accelerometers are configured so that ±2G = ±2.5V output.
These are typically recorded into Reftek channels that are configured with X1.5 Low Noise Modules (LNMs).
The LNMs amplify the output signal of the FBAs by a factor of 1.5 to use the entire dynamic range of the
16 bit reftek channels.
The LNMs also have a lower noise level than the programmable AMP01s normally used for the 16
bit channels of the reftek.
The LNMs have a low input impedence and should not be used in conjunction with a passive sensor such as
the L4s or L22s.
7.3 - CMG40T
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This active sensor has good frequency response down to about a 30 second period.
The setup is a bit more involved than for the passive sensors.
Typically they should be installed in a vault to thermally isolate them.
7.4 - L22
-
This sensor is a velocity transducer like the L4C3Ds but with a
lower output and higher corner frequency.
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Chapter 8 - Power Systems
-
While batteries seem very robust because of their bulk, they actually
require a decent amount of care.
Find out more about the technical side of battery care.
One potential problem with batteries is "Sulfation" which occurs when the battery is maintained in a discharged state for any period of time. Because of this, it is important to keep batteries charged to full capacity whenever possible.
8.1 - Flooded Batteries
-
The term "flooded" for batteries refers to the makeup of the electrolyte
contained in the battery cells. Flooded means that the electrolyte is
in liquid form.
This type of battery has a better power to weight ratio than "Gel" type
batteries.
8.2 - Gel Cell Batteries
-
The electrolyte in this type of battery is in a gelled format. The
power to weight ratio is worse than for "flooded" batteries, but
they are safer to transport due to the nature of the electrolyte.
They require little or no maintenance.
The PBIC uses several different capacities of Gel Cells depending
on the charging system to be used.
These batteries are typically more expensive than their flooded counterparts, but potentially have a longer life cycle if cared for.
8.3 - Solar Panels
-
The PBIC uses 30W frameless solar panels with an aluminum or steel backing.
One of these panels, in good sunlight conditions, can provide enough
power to keep a Reftek recharged for an indefinite period.
8.4 - Solar Charge Controllers
-
Charge controllers are required when using Solar Panels to prevent
battery discharge during periods of insufficient light (nighttime, overcast).The PBIC provides several variations of one model of charge controller.
8.5 - AC Charging Systems
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Chapter 9 - Interfacing
-
The user interface to the DAS is performed using an external
terminal of some kind. The most popular currently is the
HP 100LX palmtop computer. The PBIC also has several Zeos style palmtop computers.
In the past the Epson EHT-10 was widely used.
The palmtop computers used today with the FSC software can display
more information at one time than the older, more cumbersome EHTs.
- ctrl-brk (for communication lockup)
- ctrl-alt-del (soft reboot)
- press little gray button below on/off key (hard reset)
- remove batteries (hard reset)
- Hit return at the date and time prompts
- Use arrows to select exit at RacePen setup to EXIT and the hit return
- If you had to do a hard reset, See Note below
- Hit "Esc" button to exit RacePen and get into DOS
- FSC should start automatically
- Connect standard HP serial adaptor cable to DAS comm port cable
- reboot HP, ctl-alt-del
- hit alt to get boot options
- select option 3
- use "more..." button to get into optional software
- go into data comm
- alt f, c to get comm menu, got to settings
- set 9600,N,8,1
- make sure that cable is connected to com1 on HP and comm port on DAS
On DAS using another HP: - DAS Options (F8) 2, make sure that port 3 is set to 9600,N,8,1
- DAS Options (F8) 3, set status/diag port to port 3
The DAS should now be outputting status info to the comm port. This status logging will be disabled when ACQ is started.
9.1 - Field Setup Controller (FSC) Software
-
The user interface for PC compatible terminals/computers is the
Reftek program "fsc". The FSC software allows the user to control
all aspects of the DASs behaviour. The information displayed on the
main screen is not neccesarily the status of the DAS you are connected
to. That information corresponds to whatever parameter file is loaded
into FSC currently. You can recieve the parameters from the
DAS by using the key sequence F4-3.
The DAS status (F7-0) window is a real time connection to the DAS and does reflect information about that DAS.
The Monitor (F6-0) window allows you to look at signal from the individual channels.
Communication failures can be cleared by hitting ctrl-break. This is useful if the palmtop is locked up waiting for communication with the DAS in the event of a cable or power failure.
9.2 - Zeos style Palmtop computer
-
This palmtop tends to be much more quirky and troublesome than the
HP palmtops. It is prone to random lockups that so far have not been
explained. The following section will cover some of the information
needed to successfully reboot the Zeos palmtop.
9.2.1 - Rebooting Zeos Palmtop
-
If the palmtop locks up, try the following in order.
General procedure for reboot.
If you had to do hard reset to reboot the Zeos, you may well have to go into the setup menu (under Utilities (F10) from RacePen Main Menu). RS-232 needs to be "ON" and Power Saving needs to be "OFF". To change, use the arrow keys to select the particular setting. Hit enter. Use arrow keys to modify setting. Hit enter again. Finally, go to Quit and hit enter. Answer "Yes" to the save prompt.
9.3 - Enabling status logging to a second terminal
-
It is especially useful to see the DAS status messages during lab
testing. By default these messages are disabled or redirected
to a null device. They are disabled whenever acquisition is started.
This section assumes that the user has two HP palmtops and the
appropriate cables.
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Chapter 10 - Troubleshooting
- Run DAS info (F4-0)
- Check battery voltage
- Check battery cable connection
- Check comm cable connections to palmtop and DAS
- Connect power to DAS. Listen for power supply relays clicking on DAS power supply. May need to put ear against DAS case.
- Simple signal test
Perform monitor test in FSC. Start monitor while rubbing the appropriate input connector contacts in a circular motion. The changes in resistance should result in a monitor that looks similar to the following. Compare different channels to check for any major amplitude differences.
- Lab testing
Connect signal generator to DAS input. Compare signal levels of a 10Hz sine wave between channels. - Testing Passive Sensors for leakage
Disconnect sensor from DAS. Push one probe of DVM into ground. Set DVM to Mohms. Test resistance between each contact of sensor output and ground. Any resistance reading other than open indicates some leakage. Values below 1 Mohm or so really effect signal quality. - Lab testing
Connect scope to sensor output. Shake or stomp geophone. Use response pulse box and check uniformity of pulses. Use shake table.
10.1 - Communication problems
-
Communications failures are common with the DAS.
10.1.1 - Testing procedures
10.2 - Input signal problems
10.2.1 - Testing procedures
10.2.1.1 - Testing DAS input
10.2.1.2 - Testing Sensor output
10.2.2 - No signal seen during monitor in FSC.
| Possible Cause: | Solution |
|---|---|
| Sensor not hooked up | Connect sensor |
| Sensor cable bad | Replace sensor cable |
| Sensor component bad | Replace sensor |
| Channel turned off in params | recieve params, check channel status, turn channel on if off, resend params |
| Bad channel in DAS | receive params,init DAS, resend params |
| If channel still bad | Switch DAS |
10.2.3 - Signal distorted or weak during stomp test in FSC.
| Possible Cause: | Solution |
|---|---|
| Sensor component "leaky" | Replace sensor |
| Sensor component bad | Replace sensor |
| Bad channel in DAS | Switch DAS |