Why no delayed trigger on newer DSOs? - sci.electronics.design

Message from discussion Why no delayed trigger on newer DSOs?

Joerg

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More options Aug 14 2007, 11:27 am

Newsgroups: sci.electronics.design

From: Joerg <notthisjoerg...@removethispacbell.net>

Date: Tue, 14 Aug 2007 15:27:44 GMT

Local: Tues, Aug 14 2007 11:27 am

Subject: Re: Why no delayed trigger on newer DSOs?

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Mike Harrison wrote:
> On Mon, 13 Aug 2007 12:19:48 -0700, Joerg <notthisjoerg...@removethispacbell.net> wrote:

>>Hello Folks,

>>Question: It seems that most portable DSOs in the 200MHz/1GSPS class
>>don't offer delayed trigger anymore which makes pulse-echo measurements
>>a real pain. Why don't they?

>>After all it's just a simple counter that is needed. Same for hold-off
>>which typically ain't there either :-(

>>Beats me but IIRC I used delayed trigger on a lower end TDS220 although
>>its data sheet said that it could not do it. However, that scope had
>>some other serious issues (noise) so I asked the client to obtain a used
>>2265. Old Faithful, of course, always has delayed trigger but sure
>>enough the plastic clutch for that function fell apart right away.
>>Designing a trigger delay into an analog scope is no small feat but for
>>a DSO it should be really easy.

> Is it that it isn't there, or is no longer an explicit feature - you just scroll the display..?.
> I find it hard to believe that any digital scope doesn't have holdoff.... can you name specific
> models?

In my case it's the Instek GDS-2204 but when looking at competitor
models such as the Tektronix TDS-2024 it seems that it is a similar
situation there. John Larkin would know for sure because he's got one.

No hold-off. Here is the real puzzler: I've got the 4-ch model and the
less expensive 2-ch model does contain delayed trigger (!). Snooping
around in the firmware I saw that it's still in the control set but
somehow not engaged, IOW I can access delayed trigger but not tie it
into any of the channels which renders it useless. Plus it isn't
available via the scope's buttons, only if I enter via the doggie door
with HyperTerminal Wrote to Instek about it but no answer yet. Hopefully
they'll realize that disconnecting delayed trigger on their most
expensive flagship was not such a great idea, and maybe they'll fix that
in the firmware.

Scrolling the display gets you a few usec on Tek, and a few tens of usec
on the Instek. But even the 25K on mine will eventually run out,
precisely at 25usec when using the highest sample rate. Ok, on the Hameg
2008 with its Megabyte buffer I could understand this strategy but not
on the others. Even 25usec is nothing on pulse-echo jobs.

I do have to say that the advanced trigger features of these scopes are
really great. For example, this Instek can trigger on stuff like "only
when pulse exceeds x usec" and this feature goes to 10 seconds. But of
course then it waits for the slope so I can't hitch a delay-trigger ride
here. So they've got a long counter in there already and implementing a
delay feature should almost be a no-brainer.

--
Regards, Joerg

http://www.analogconsultants.com

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