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Re: In search of a good trigger point



Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

Hi Finn,

	I have often just used a little wire antenna.  It triggers on the powerful
and fast initial energy burst when the gap fires.  Works real good for me.

Cheers,
	
	Terry


At 08:03 PM 12/14/2000 +0100, you wrote:
>Scope jockeys!
>
>While I am modifying my new RAT (Realtime Adjustable Teslacoil) to 1500
>RPM SRSG for greater overlap and tuning range of the fixed electrodes, I
>am haunted by the experience of trying to document the results of
>different tuning and coupling issues.
>
>I seem to have a problem selecting a good trigger source. When I set the
>electrodes for equal bangsize, I have 2 inputs:
>1: the incoming 240 VAC
>2: Voltage across the primary capacitor.
>The horizontal sweep is set to 2 mS/div, and the trigger is the Channel
>that handles the incoming AC. This way I can see the relation btwn. the
>AC and the capacitor discharging, which is what I want. I have found
>that by adding HF-Reject to the trigget source, and a bit of Trigger
>holdoff, I can get a nice and steady display this way.
>
>However, when I want to watch the ringdown itself, things start to get
>nasty:
>The scope is a Tektronix 485, and it has the ability to add one more
>sweep to the display, called the B-sweep, or the B-delayed sweep. This
>sweep can run at a faster horizontal rate than the main sweep that it is
>based upon, so that a small portion of the main sweep can be scrutinized
>with greater detail. If the main sweep is set to 2 mS/div, and the
>B-Delayed sweep set to 50µS/div then the Main sweep covers the full AC
>cycle with all 6 ringdowns, (at 300 BPS) and the B-delayed sweep then
>covers the ringdown nicely proportioned within 2-3 divisions. 
>
>But due to what I expect is slightly differeft breakdown voltages of the
>gap from bang to bang, this display that zooms in on the ringdown, jumps
>back and forth on the screen, making it difficult to capture on the
>digicam, as well as counting ringdown cycles, etc.
>
>One remedy would be to make one more fiberprobe channel, hook it up
>across the primary inductor, and run it into the external trigger, to
>trigger on the nice sharp rise at each gap firing, but that way the
>relation to the 50Hz cycle would be lost. Perhaps Trigger holdoff could
>solve that problem, but I hope there is another more elegant solution.
>
>So what do you other scope jockeys use to trigger your scopes?
>Would a storage scope make this problem go away 
>Remember that I have 3 ringdowns on each 1/2 phase.
>
>Cheers, Finn Hammer
>