Calibration (and Autocentering) Parameters & Procedures
Note: the cal-pulse amplitude is different for STS2s and CMGs
And the use of a special plug is different.
The Reftek must have a test bus card in it to perform
a calibration or autocenter.
Instructions are given for FSC (e.g. HP Palmtop , laptop, not EHT)
I. PROGRAMMING THE DAS
The CALIBRATION menu of DAS parameters
relates to the calibration input signals and
autocentering. We suggest the following:
FSC F3 EDIT MENU / 8- CALIBRATION
Start time: 2001:125:00:00:00 (e.g. the previous day number ending in 0 or 5)
Repeat Int: 5 days
# of Cals: 0 (gives you an infinite number)
Duration: 5 seconds
Step Step: ON
Interval: 200
Width (or Step size): 201
Amplitude: 8.0 volts for STS2 *** This must be >7 volts for autocentering the STS2
0.1 Volts for CMG 3T and CMG3ESP
0.25 Volts for CMG 40T
Output to: Coil
SEND these recommended parameters to the DAS
II. CALIBRATION PROCEDURES
STS2
Requires FSC (in palmtop or laptop) and Jumper Plug
In order to record a cal signal when visiting the site, follow this
procedure:
1. Leave the DAS in Acquisition On, or Start Acquisition if it is off.
2. Check Calibration parameters in DAS. Receive DAS parms
And compare to parameters above. Send new parms, if necessary
3. Plug the STS-2 Jumper Plug into monitor port of STS-2 host box (the
green breakout box with autocenter button on it). Screw it in all the way.
4. Set DAS relays.
HP Palmtop: Main Menu/ F6 - Test
1 - Relays
Tab all the way down through to the last option (note all relays should
initially be OFF) Toggle (+/-) until the last line shows
Last option is Cal. Coil = CAL4 CAL5 CAL6
CALSIG CALSIG CALSIG
One toggle does all three channels; there are 4 options;
choose the one with all three CALSIG
F10 “to enter”
(You may turn the HP power off)
5. Wait for the sensor to respond to the cal cycle, it takes about 20
minutes. Moving around ruins the recorded signal, sit still or move
away 100 meters.
6. After callibration: Remove STS Jumper Plug and
Turn off DAS relays by resetting
Cal Coil to OFF and pressing F10 to enter it.
If you have any doubts, go back to F6 Test Menu, choose
1- Relays
to make sure the current status of the DAS is:
Cal Coil OFF OFF OFF all components
7. STOP ACQUISITION and upload data in the usual manner
More detail about the STS2 Jumper Plug:
You need an STS-2 jumper plug on the monitor port of the STS-2
host box. The jumper plug ties pin E and W together with a
10K Ohm resister and ties pins K, S, and X together.
Connecting the Jumper Plug to the monitor port of the
host box disables the autocenter function and activates the cal relays
within the sensor which connect the sensor calibration coils to the cal
input. A resistor network within the remote plug scales the DAS
calibration output so as to be appropriate for both the autocenter logic
level (i.e., 4 volts) and the cal coil inputs (approx. 4 microamp).This
resistor network also isolates the coils from one another and partitions the
current evenly between the three coils. See the sensor cable diagram for
further details, including that of the Jumper plug.
If you leave the STS Jumper plug connected, the sensor will receive a 5
second cal pulse at the scheduled times instead of autocentering.
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CALBRATION PROCEDURES -
GURALP
Requires Palmtop w/ FSC and Guralp HCU (Handheld Control Unit)
Basic steps to calibrating the sensors.
1. program the DAS (same as above, except voltages differ from STS2)
2. start acquisition
3. set relays in the DAS (same as #4 above)
4. remove autocentering plug from Guralp breakout box control port and connect
the HCU. Set CAL ENABLE on the Handheld Control Unit by turning knob from off
position to V (vertical) walk away while recording cal pulse (15-20min),
Return and turn knob to N/S and so on till all three components are complete
5. Turn off CAL ENABLE on the HCU, remove HCU, replace w/ auto-center plug
6. Reset DAS relay to regular recording mode, i.e.
Cal Coil OFF OFF OFF all components
7. Stop Acquisition
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III AUTOCENTERING
Make sure DAS “calibration” parameters are set as in item I. above
STS2
DO NOT USE the STS2 Jumper Plug
The PASSCAL cables connecting the STS-2 host box to the REF TEK DAS contain
a special wiring arrangement which can enable the sensor's autocenter
function from the calibration output of the DAS. Programming the DAS
scheduled calibration function causes the sensor to autocenter at the
desired interval.
GURALP
USE the auto-center PLUG
It works in a fashion similar to the STS2. The DAS must be
Programmed as per instructions and remember to plug the auto-centering plug into the Control port of the CMG breakout box before you leave the station.
Note that the DAS will not issue a calibration signal if any stream (except
continuous) is triggered at the scheduled time of the cal.