Measurement Processor Signals - Tektronix 2246 1Y Service Manual

selects a pot to be scanned by connecting it
to Comparator U2306 in the d -to -a circuitry.
The Measurement
successive-approximation a -to -d conversion
on each pot, using the DAC (U2302) to out­
put the search values to the Comparator. Pot
values are scanned, processed, and con­
verted to analog control values by the DAC.
The analog levels from the DAC are output to
the controlled devices via sam ple-and-hold
circuits (U2304, U2305 on Diagram 11).
5. Sets up the hardware state of the instrument,
including shift registers 0 and 1, BEAM FIND,
and the operating states of U600 (SLIC) and
U602 (FLIC). This setup takes place as
needed for every change of a front panel
m om entary-contact
switch.
6. Keeps track of trigger status and controls the
trigger levels when in AUTO LEVEL mode. It
uses FLIC (U602) to find the A Trigger status
(writing to FLIC to reset the A Trigger latch,
and reading from it to get the status). It uses
SLIC (U600) to find the B Trigger status
(writing to SLIC to reset the B Gate latch, and
reading from it to
reacquire the trigger level
negative peaks of
waveform) it uses the Trigger ICs (U421 and
U431), and the Trigger Comparators in FLIC
(it writes to FLIC to reset the Trigger com ­
parator latches, and reads from FLIC to get
the status of the latches). To switch between
free-running and triggered mode in AUTO
LEVEL and AUTO trigger modes, it writes to
the control register in FLIC; it switches to trig­
gered mode when
sufficiently high and to free-run mode when
too low.
7. Tracks the trigger level and ground with cur­
sors. The cursors are displayed by directing
the Readout system to display cursor charac­
ters, and using the DAC system to set the
REF CURSOR and DELTA CURSOR level to
match the trigger or ground point on the
waveform.
8. Does automated measurements.
measurements are knob-driven. They are:
k- SEC -M
k- 1/SEC-H
k- PHASE-M
k- VOLTS-H
r,h VOLTS-H
Theory of Operation—2246 1Y and 2246 Mod A Service
Processor does a
or rotary-contact
get the status). To
(positive and
the trigger source
trigger frequency is
Some
When these measurements are running, a new
digital value is displayed,
delay-zone position is changed only when the user
changes the setting of one of the continuous-
rotation CURSOR/TIME POSITION controls. Other
measurements are waveform -driven. They are:
DC
+PEAK
-PEAK
PK-PK
GATED +PEAK
GATED -PEAK
GATED PK-PK
When these measurements are running, a new
digital value is displayed and the cursor position is
changed each time a measurement cycle occurs.
These measurements use the B trigger system; and,
for DC, the low-pass circuit formed by U1101B and
associated filter components (Diagram 3).
9. Calibrates the measurement system. The
vertical and horizontal gains of the instrument
are set by manual potentiometer adjust­
ments; therefore, the Processor does not
control the match between the waveform dis­
play and the graticule. However, it does
adjust the measurement results to compen­
sate for any error in the vertical or horizontal
gain. (An example of this is that there could
be more than 0.5% error in matching a time
base signal to the graticule, but less than
0.5% error in a time measurement done on
that signal).
In the Time Base calibration routine, the Measure­
ment Processor uses the TB Cal signal, the Trigger
circuitry, the A Sweep system, and U602 (FLIC) to
find the match between the delay levels (REF DELAY
and DELTA DELAY) and edges of the calibration
signal. In the Vertical
Processor uses the Voltage Reference Generator
(U931, Diagram 7), the
Vertical Preamplifiers, the Delay Line Driver, and the
Vertical Comparator (U702)
between Readout REF CURSOR and DELTA CURSOR
levels and vertical outputs generated by the pre­
amplifiers. It uses the Voltage Reference Generator,
the Vertical Preamplifiers, and the Trigger circuitry
to find the match between trigger levels and trigger
signals picked off from the Vertical Preamplifiers.
MEASUREMENT PROCESSOR
3-26 is a listing of signal name and function of the

Measurement Processor signals.

and the cursor or
System calibration, the
Readout System, the
to find the match
SIGNALS. Table
3-43