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

[tinman]

Today i made a some what confusing discovery that could have large ramifications.
Yes-another look at the humble pulse motor.

For all those that think you can measure some pulsed systems accurately-think again,as it aint just cut and dried.

In this thread,i will show you that using a CVR and scope will not always lead to accurate measurements. I mentioned some time back,that using resistors(CVR's) dose not always give accurate result's,and in some system's your scope could be leading you up the garden path.

The simple pulse motor can be a real bitch to measure P/in and P/out accurately-unlike some of the EE guys may tell you.

In my video series to come,i will show you (using an incandescent bulb) how our scope shows us one thing,and our incandescent bulb shows us the opposite.

Simply by placing a cap within the pulse circuit,we can throw accurate power measurements out the window-->even though our CVR remains on the input side. With pulsed systems,we can increase the current flowing through an incandescent bulb,raise the voltage across that incandescent bulb,but have the bulb dissipate less power-as in the way of heat and light. This is the opposite as to what should be seen across a resistor,as an incandescent bulb is just that-->a resistor. The only way to increase the heat and light output of an incandescent bulb is to increase the current flowing through it,and this in turn will show a higher voltage across it-as the resistance rises as the heat (and light) increases.

This is very important to know,and i will show you that it is wrong. This also means that what you may see on your scope across your CVR may not be actually what is really happening-->the incandescent bulb shows this to be true.

Or is there really some truth to the claim of radiant energy,or some form of cold electricity within the humble pulse motor?.
!! Dose ohm's law always apply with pulsed system's?.

I will post the first video here as soon as it is uploaded.


Brad.

[lasersaber]

Sounds interesting.  I am looking forward to watching your video.

[gyulasun]

....
With pulsed systems,we can increase the current flowing through an incandescent bulb,raise the voltage across that incandescent bulb,but have the bulb dissipate less power-as in the way of heat and light. This is the opposite as to what should be seen across a resistor,as an incandescent bulb is just that-->a resistor. The only way to increase the heat and light output of an incandescent bulb is to increase the current flowing through it,and this in turn will show a higher voltage across it-as the resistance rises as the heat (and light) increases.
....

Hi Brad,

This is surely going to be a good topic. 
Why I put in bold above your statement is that I think an incandescent bulb is a nonlinear resistor, unfortunately and this fact can indeed lead a tinkerer up the garden path, especially when the duty cycle of the pulse motor current also changes. 

EDIT I added the voltage-current curve of an incandescent lamp, taken from this video at random:
https://www.youtube.com/watch?v=rNsykkSR3wg     Ohm's law is not valid of course.

Gyula

[fritz]

.... even changing (+) and (-) tips of your multimeter may completely change the scene. (-) is connected with the shield and has higher capacitive load to ground as the (+) tip.

[tinman]

Hi Brad,

This is surely going to be a good topic. 
Why I put in bold above your statement is that I think an incandescent bulb is a nonlinear resistor, unfortunately and this fact can indeed lead a tinkerer up the garden path, especially when the duty cycle of the pulse motor current also changes. 

Gyula

Hi Gyula

Both voltage and current will rise together with an incandescent bulb,in that the more current flowing through it,the higher the voltage across it.. This makes them linear. The incandescent bulb is just a resistor,and ohms law should tell us how much power that resistor is disipating when we know the voltage across it,and the current flowing through it--which we do !! apparently !!
With an LED,voltage will hit the rated voltage,and then the current will continue to rise,while the voltage remains close to the same. This makes the LED a non linear device.


Brad