BLASTER TEST REPORT
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!TEST OF I/O SERIES 200 ENCODER / DECODER
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!!Equipment
* Mod 200 ENCODER, S/N: 0007 (modified with 9-pin D-sub connector and switch to select CLOCK or CONFIRMATION TimeBreak))
* Mod 200 DECODER, S/N: 0010.
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Attach:decoder-modify.png<br />''Fig.1. ENCODER Modification - you can select CONFIRMATION or CLOCK TimeBreak''
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!!Detecting Cap Current
We need to establish the relationship between Cap current and the Clock / Confirmation TimeBreak.
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We follow a tip on page 21, section 5.3.R of the "I/O Technical Manual, Series 200, Seismic Source Synchronizer System, Installation and Maintenance":
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-> <pre class='escaped'>... A more convernient way, especially when the use of explosives is to be avoided, is to use an
isolation transformer by winding ten feet of two-wire cap lead on a pencil. (The wiring length is not
critical - build up layers about two inches long). One of the cap wires forms the transformer primary,
the other wire forms the secondary. Connect the ends of one of the cap leads (same wire) to the
DECODER cap terminals. Connect the ends of the other wire pair to a galvo. When the DECODER "FIRES",
current will be induced in the galvo winding of the transformer thus causing a galvo deflection
at "FIRE" time.</pre>
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Attach:trafo-no-diode.png"Isolation transformer to measure cap current"<br />''Fig. 2. Isolation transformer to measure cap current.''
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In fig. 2, cap current runs in red and black leads in bottom right part of the picture. The isolation transformer, top, uses blue wires for the primary side, and yellow for the secondary side. The coax cable, lower left, is routed to the oscilloscope.
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In the following tests the cap wire is short-circuited; only the transformer is used.
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The cap current starts abruptly and then decreases gradually. The induced seconday voltage will reflect the rate of change in the current, so it will be large at the onset of the current.
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Fig. 3 shows the induced secondary voltage when the current starts.
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Attach:xformer-secondary.png"Transformer seconday voltage, start of cap current"<br />''Fig. 3. Transformer secondary voltage, start of cap current.''
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We limit the voltage by connecting a Zener diode (BZW06-8V5, ELFA P/N: 70-110-67) across the seconday winding. The result is shown in fig. 4.
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Attach:xformer-secondary-with-diode.png"Transformer secondary voltage, start of cap current, with diode across secondary windings."<br />''Fig. 4. Transformer secondary voltage, start of cap current, with diode across secondary windings.''
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The voltage is now reduced to a more "sensible" level.
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!!Comparing cap current and Clock TimeBreak
The cap current transformer signal is on oscilloscope channel no. 1, and the output from the ENCODER TimeBreak (see drawing) is on channel two. We take 10 readings and let the oscilloscope collect traces.
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Attach:compare-capcurrent-clock-tb.png"Ch. 1 = Cap current, ch. 2 = Clock Timebreak - 10 readings"<br />''Fig. 5. Comparison Cap current ch. 1 (DECODER) and Clock TimeBreak ch. 2 (ENCODER) - 10 readings.''
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The ten readings line up fairly good. There is a 500 usec jitter window. So we can say that there is a constant offset in time, plus/minus 250 usec. That should be acceptable.
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!!Comparing cap current and Confirmation TimeBreak
'''In this case it was impossible to have a proper trigger signal from the ENCODER. This means that demodulation / decoding of cap current signal part of the transmission from DECODER to ENCODER was unsuccesful.'''
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%red%''' WE DO NOT HAVE TIME TO FIX THIS PROBLEM RIGHT NOW. USE CLOCK TIME BREAK INSTEAD.'''%%
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