Accurate Measurements on pulsed system's harder than you think.

[tinman]

EMJ
Look at the scope shots below.
First is the current trace of a pulsed incandescent bulb
Second is the current trace of the same as above,but with inductor in series--in case anyone thought that the inductor would skew the trace in any way.
Third is a screen shot of the current trace we have in our DUT

See a problem yet?

Brad

[EMJunkie]

Can you raise or lower the voltage across that resistor without raising the current flowing through it?.
Can you increase the temperature of the bulb element without increasing the total current flowing through it? Current is what increases the element temperature,and an increase of temperature means an increase in resistance,but the increase in current must happen before the increase of resistance can exist. We decreased the average current flowing through the bulb,but increased the temperature-thus resulting in an increase of resistance-->but to what extent. Look at the scope shot's again,dose the current trace not tell you that the resistance is rather constant during the on time?-->in fact,is it not opposite to the shape of the trace curve that should exist if the resistance was increasing during that current pulse?. Draw a current trace of a pulse of current that has an increasing resistance during that pulse,and then compare that with the current trace in the scope shot. And remember,we are at low frequencies here.


Brad

I think we are going around in circles.

   Chris Sykes
       hyiq.org

[tinman]

I think we are going around in circles.

   Chris Sykes
       hyiq.org

I am trying to show you that things are opposite to what they should be.
Look at the scope shots i posted in my last post. The first two show what the current trace should look like across the CVR. But in the scope shot from the DUT,the current wave form is opposite to what it should be. This is showing the bulbs resistance is decreasing during the pulse--not increasing as it should be. As i have been trying to say,the incandescent bulb is showing/doing opposite to what it should be. Measurements being taken from something that dose not act as it should can only lead to measurement error.

Now you have to figure out why the current trace is opposite to what it should be-->then we can start talking about correct measurements.

Brad

[EMJunkie]

EMJ
Look at the scope shots below.
First is the current trace of a pulsed incandescent bulb
Second is the current trace of the same as above,but with inductor in series--in case anyone thought that the inductor would skew the trace in any way.
Third is a screen shot of the current trace we have in our DUT

See a problem yet?

Brad

@Brad, thanks for your time posting scope shots.

I see, under different Circuit conditions we see different wave forms. But nothing I see is alarming.

What is it that you see that is of importance?

   Chris Sykes
       hyiq.org

[EMJunkie]

EMJ
Look at the scope shots below.
First is the current trace of a pulsed incandescent bulb
Second is the current trace of the same as above,but with inductor in series--in case anyone thought that the inductor would skew the trace in any way.
Third is a screen shot of the current trace we have in our DUT

See a problem yet?

Brad

@Brad, if I may suggest, although this is simple, a Circuit when presenting information would be very helpful.

Is this current circuit something like this:

   Chris Sykes
       hyiq.org