Differences between measurements in the same test point.

[ereides]

Hello,

I noted that in some test points I have different measurements results on the same board (taken as reference).
When I do on this test point a real time measurement I can see that the result is moving until the point when stabilizes and the result is allways the same.

May be that some capacitive effect is present and produces this phenomena.

My question is what can I do in order to define a more precise measurement, is it possible to delay the results until the stabilization point? or may be another solution?

How can I be sure that my reference is good?, Is there some method in order to refine the results and improve the reference?

Thank you all and best regards.

Ernesto Reides

[admin]

You are seeing a classic example of charging effect where a capacitance on the circuit board is charging as the Tracker signal is applied. The charging causes the signature to change as it being is sampled. The Workstation software has two features that may help.
- Delay: You can set a delay time in the Range tab of the signature pane. It will cause the signal to be applied but not actually sampled until the delay time has passed.
- Drain: This feature will connect the Tracker probe to Common for a short time (set in the Tools/Options/General tab) therefore "draining" built up charge at the test point. This does not stop the charge but tries to set the level of charge at the test to zero before testing.

Hopefully this information is helpful.

Curtis
(Admin)

[ereides]

Thank you Curtis for your quickly respponse.

Today I tried with the delay (in the Tree pane), and seems to me that the results are better. What method do you prefer? delay or drain?

[admin]

Delay and Drain serve a fairly similar function but that said I usually start with setting the Drain. The Drain is probably a more repeatable function by discharging the test point BEFORE the signature is captured.