HP 7090A, Руководство оператора, Страница: 64 / 105

Scans by ArtekMedia © 2007
Terminate the
Recording
The External-Pen
Connector
For the external and internal trigger modes, the pen is lowered and
plotting begins when the appropriate trigger is received.
6. To stop the recording for the manual trigger mode, press the STOP push­
button. This raises the pen (if it is lowered) and stops the measurement.
For the external or internal trigger mode, the recording is stopped auto­
matically when the
TOTAL TIME
has elapsed, or you can stop it at any
time by pressing STOP.
A BNC connector, labeled EXT PEN (external pen), is provided on the right
side panel ofthe HP 7090 to pennit remote-controlled penlift. The connector
is active only during manually-triggered, versus-chan3 direct recordings,
and you can use it (instead of the PEN UP and PEN ON push buttons) to
remotely raise or lower the pen.
The positive
tenninal
of
the
connector
is
pulled
high
(5-volt T'I'L level)
when a versus-chan3 direct recording is manually triggered - this holds
the pen in a raised position. A fallingTIL level or contact closure to ground
applied to the positive EXT PEN tenninal will lower the pen. Similarly, a
rising TIL level or opening the ground contact will raise the pen.
The Buffered Recording Mode
A
Channel Buffer
Each of the three input channels of the HP 7090 has its own A/D converter
and buffer. A channel buffer consists of a stack in RAM memory of 1000
memory locations -each location is used to store a digitized voltage value.
During a buffered recording, the channel input voltages are simultaneously
sampled, digitized. and stored in their buffer at a unifonn rate detennined
by the
TOTAL TIME
setting. Each channel buffer is completely filled within
that time.
rl'vvQ
INPUT
SIGNAL
AID
CONVERTER
1000 WORDS
BITS
BUFFER
Following completion of a buffered recording, the digitized data stored in
the buffers can be recalled and plotted on paper. The HP 7090 perfonns
as
a
vector plotter - the data points mapped onto the recording area
are
con·
nected by vectors during plotting to reproduce the recorded wavefonns.
Measurement graphics are created from the recorded buffers as shown by
the following plot of a Channel l input signal versus time. To draw the plot,
the
1000 voltage values stored in the Channel 1 buffer stack were pulled
from the buffer and mapped onto the recording area. The arrow in the
figure points to a single Y-axis voltage value that has been plotted against
the appropriate time element (each €Qual to
TOTAL TIME/lOOO)
on the X-axis.
44
Perfonning Direct and Buffered Recordings
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