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Oscilloscope measurment error?

K

Krunom

Jan 1, 1970
0
I measure some behaviours of ferroresonant circuit and the main goal of
measurment is to
determine for which amplitude of AC voltage source i get current with
doubled frequency compared
with frequency of source.

Well, i must determine for which E of voltage source E*sin(2*pi*f*t) i get
current with frequency 2*f...

I only can detect this behaviour with looking on oscilloscop to see waveform
of current and with increasing
of E to determine the moment (and, of course, value of E) in which frequency
of current becomes 2*f...

I made this measurments but my problem is to calculate measurment error
(unrealibility?).. If i measure something
with voltmeter i have in its specifications data about its
inrealibility/error and then i can write measurment result
something like this:

measured voltage= 5V +- 10%, or
measured voltage= 5V +- 0.5V...

But how to determine this value (+-10% or +-0.5V) for oscilloscope at which
im looking and waiting to see doubled
frequency of current...?


Thanks...

P.S. It would be easier if i had "Frequencymeter" but i dont have it and
because of that i must determine wanted value E
only with Oscilloscop-display and with my eyes waiting for 2f frequency of
current...
 
M

murgatroid

Jan 1, 1970
0
That is listed in the Oscilloscope specs, and then you have to eyeball it,
so that can be 3% too.
 
D

Don Taylor

Jan 1, 1970
0
Krunom said:
I made this measurments but my problem is to calculate measurment error
(unrealibility?).. If i measure something with voltmeter i have in its
specifications data about its inrealibility/error and then i can write
measurment result something like this:
measured voltage= 5V +- 10%, or
measured voltage= 5V +- 0.5V...
But how to determine this value (+-10% or +-0.5V) for oscilloscope at which
im looking and waiting to see doubled frequency of current...?

Many oscilloscopes have specifications for their error.
But often these depend on your having had your scope
calibrated recently, having had your scope turned on
and warmed up for a sufficient period of time, etc.

See if you have had your scope calibrated recently and
if there are accuracy specifications available for it.

Sometimes you can get a less accurate estimate of this
by using a known good amplitude calibration signal of
about the same waveform and amplitude, measure that and
determine the error, and assume the same error will be
present in your actual measurements.
 
K

Kruno Milicevic

Jan 1, 1970
0
Thanks to all for replies...
See if you have had your scope calibrated recently and
if there are accuracy specifications available for it.

Its calibrated and i have the specifications. But there is small
complication about the measurment. Ill describe shortly measurment process:
Im increasing manualy E (AC voltage source: E*sin(2Pi*f*t)) and im looking
current wave form at oscilloscope display and waiting to see that the
frequency of current equals 2*f (double source frequency) and then im
reading the value of E (at the display of some other instrument). Now should
i write result something like this:

E=10V+-0.1V.

I know that all instruments have influence on measurment error, but i want
to know what is the influence of Oscilloscope because im not using any
"numeric" values from oscilloscope, im only "looking" at display and waiting
to recognize "frequency of current" = 2*"source frequency"...

Should i simply use error-data from oscilloscope-manual or is it more
complicated because of subjective nature of measurment: "...im only
"looking" at display and waiting to recognize"... hmmm.. im waiting to
recognize... what is my "error"....? maybe is this the main question...

I hope its more clear now...

Thanks...
 
D

Dombo

Jan 1, 1970
0
Thanks to all for replies...


Its calibrated and i have the specifications. But there is small
complication about the measurment. Ill describe shortly measurment process:
Im increasing manualy E (AC voltage source: E*sin(2Pi*f*t)) and im looking
current wave form at oscilloscope display and waiting to see that the
frequency of current equals 2*f (double source frequency) and then im
reading the value of E (at the display of some other instrument). Now should
i write result something like this:

E=10V+-0.1V.

I know that all instruments have influence on measurment error, but i want
to know what is the influence of Oscilloscope because im not using any
"numeric" values from oscilloscope, im only "looking" at display and waiting
to recognize "frequency of current" = 2*"source frequency"...

Should i simply use error-data from oscilloscope-manual or is it more
complicated because of subjective nature of measurment: "...im only
"looking" at display and waiting to recognize"... hmmm.. im waiting to
recognize... what is my "error"....? maybe is this the main question...

I hope its more clear now...

Thanks...

What is the bacndwith of the scope and at which frequency are you
measering?
Do not forget that the bandwith of a scope is specified at the -3db point.
So the amplitude error could be 30% ....

-bent
 
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