Re: On-topic: HP 1743A portable oscilloscope having unique feature?

Fabio Trevisan
 

Hi Raymond,
I understood what you mean!
Having myself a Tek 464 with DM44 option, when I first learned what it was
capable of doing, I was amazed, most especially because it's all analog and
it didn't need to add pretty much anything to the already existing scope's
A& B sweep circuitry. Essentially, it's only an additional multi-turn DTP
pot alternatively engaged by a flip-flop, and the voltmeter being able to
measure the voltage difference between the 2 pots' wipers... So simple and
ingenious!.
But indeed, it relies fully on both DTP's wiper voltages and, although we
can change the scope from "B SWEEP STARTS AFTER DELAY" to a NORM, or CH1 or
CH2 or any EXT post-delay B trigger event, and thus have the delta-time
alternated B Sweeps post-triggered, and see the intensified portions jump
to immediate post trigger edges, at both different times, the delta-time
reading on the voltmeter will still reflect only the position of both DTPs'
postions, irrespective of the actual time when the B-sweep was triggered.
To make the same happen on the DM44 (still in the analog realm), perhaps
one could sample-and-hold the actual A sweep's ramp voltage, by the time of
the alternated B post-trigger events, and have the volt-meter to measure
the difference of voltages between the outputs of the sample-and-holds...
But as I write this, I realize that a sample-and-hold simply just doesn't
hold the voltage forever if you don't convert it to digital! (well... maybe
long-enough with a MOSFET buffer)... Rats... I was already thinking of ways
to implement this little upgrade!.

Upon consideration, it seems that HP was really in the lead in that realm.

Rgrds,

Fabio


2017-06-29 16:16 GMT-03:00 @Raymond [TekScopes] <
TekScopes@...>:



I am not sure what you mean here. All of the oscilloscopes which
support delayed sweep and delta delayed sweep graphically show what
measurement is being made.
I think that I still haven't been able to explain what I think is unique
for a 'scope of its era and very useful.
I'll try and explain. I'll refer to the start of each B-sweep as the
marker or cursor:

With the HP 1743A set in "B-runs-after delay" mode, both markers / cursors
are placed by hand (delay knobs), each by a small amount before subsequent
rising edges of a 1 KHz (exact) square wave. Let's say that the interval
shows "0.837 ms" on the numeric display.
Now, when I switch to "B triggerable after delay" (on rising edge), not
only do the cursors jump to the first rising edges of the waveform after
their respective delay, but also the interval display now shows "1.000 ms".
If I increase the Stop delay setting beyond the next falling edge, the Stop
cursor jumps to the rising edge of the next period and the numeric display
shows "2.000 ms". Furthermore, if I slightly change the signal period
(depending on both delay settings) and I vary the input frequency, the
cursors follow and *so does the numeric display value*.
Obviously, the standard 7000 time bases don't do that, not even the delta
time setups, nor do the 2236, 2247A and others, to the best of my
knowledge.
Mind you, I'm not saying I couldn't do the measurements that I'm doing
here with other 'scopes, just not in this way and not with a display like
this. Its simplicity and non-ambiguity immediately struck me once I saw it
first.

Raymond

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