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PicoScope 6.0.13, trigger level mismatch

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PicoScope 6.0.13, trigger level mismatch

Postby laichh » Mon May 12, 2008 9:06 am

I am using the PicoScope 6.0.13 together with PicoScope 5204.

I am using the supplied 250MHz passive prove & I set the attenuation to x10. At the same time, I also set the "Probe Setting" to x10, so I get exactly what I input into the probe tip.

I then set the trigger to "Rising Edge Trigger".

I do not notice this problem since most of the time, the trigger level is set to 0V. Until this afternoon, I want to trigger to a level other than 0V, I notice that the trigger level do not match my probe setting.

See attachment.

When the probe is set to x10, I wish to trigger at 800mV. As I move the "Trigger Diamond" to 800mV level, the trigger level shows at the bottom of the screen actually indicate 80mV.

I can't figure out a way to make the trigger level follow my probe setting in this case.
Attachments
PicoScope 5204 Trigger Level Mismatch.PNG
This is the screen capture. Note that the "Trigger Diamond" is at 800mV level, but the display at the bottom shows 80mV.
(68.29 KiB) Downloaded 331 times
PicoScope 5204 Setup.JPG
This is how I setup an example.
(108.13 KiB) Downloaded 325 times
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Same problem on PicoScope 6.0.15

Postby laichh » Mon May 12, 2008 9:38 am

Just updated to 6.0.15, same problem exist.
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Postby markB » Mon May 12, 2008 12:39 pm

The threshold displayed on the trigger toolbar is the threshold set after your x10 probe has been applied.

When you drop your trigger point onto the scope at 800mV, the inverse of the probe scaling is applied and the scope is configured to trigger at 80mV. It is easy to imagine a probe that could have more than one solution to its inverse scaling; a modulus probe for example. If you were to drop your trigger diamond at 800mV the scope will need to be configured to trigger at both 80mV and -80mV.

Obviously the scope cannot be triggered at more than one threshold and so PicoScope displays the uncaled value to avoid confusion.
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Thank you for your reply

Postby laichh » Tue May 13, 2008 4:22 am

Hi MarkB,

Thank you for your reply. I tried with PicoScope 5.20.1 (with PicoScope 3204) and here is the screen shot.

When I set the probe to x10, & place the "Trigger diamond" to 800mV level, the botton screen shows 800mV (scaled). However, the vertical range at the top of the screen says +/-200mV (Un-scaled).
Attachments
PicoScope 5.20.1 trigger.PNG
(65.96 KiB) Downloaded 273 times
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Postby markB » Tue May 13, 2008 7:40 am

You are quite correct. PicoScope 6 does behave differently to PicoScope 5 in this instance. PicoScope 5 cannot create custom probes and as such does not suffer from the problem that I described in my earlier post.
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Will it be aligned?

Postby laichh » Tue May 13, 2008 8:00 am

Hi MarkB,

OK, I understand now. But from user point of view, is kind of mis-leading. Will this "problem" be alligned in future for PicoScope 6 release?
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Postby markB » Tue May 13, 2008 8:21 am

How would you 'fix' this problem for the modulus probe that I described earlier?

The scope cannot trigger at more than one threshold. It would be even more confusing to have different behaviour for probes that have multiple solutions to their inverse scaling.
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Suggestion

Postby laichh » Tue May 13, 2008 10:38 am

Hi MarkB,

How about we put it this way:

- the trigger threshold level, which displayed at the bottom left of the screen, should always match the vertical scale of the selected trigger source channel.

I understand that the PicoScope 6 allow user to define their custom probe with custom unit, mx+c scalling. If I want to trigger at a specific level of my custom probe (with my custom unit), I should be able to define them easily with the trigger toolbar as well as the "trigger diamond".

Actually, I don't quite understand about the "Modulus Probe" you've mention about, I've never seen any of those.
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Postby markB » Tue May 13, 2008 10:52 am

A modulus probe would use a look up table to define its behaviour similar to the one below:

-2V 2V
0V 0V
2V 2V

If you input a sine wave into this probe it will give an output like the image below.

Hopefully you can now see that the inverse scaling would yeild more than one trigger point which is impossible for PicoScope.
Attachments
output.JPG
(235.24 KiB) Downloaded 240 times
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