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OPERATION
3.13.1 Average
The average of the samples in the measurement buffer can
be displayed by pressing SHIFT AVG (or simply AVG if
not in the data entry mode). The instrument
will then
display the average of the samples in volts stored in the
measurement
buffer
in accordance with
the following
formula:
n-1
c
vi
i=O
V"",
= _____
n
Where: Vi = voltage amplitude
of individual
sample
i = individual
sample number (0 through
n-l)
II = number of samples in the measurement
Thus, the average is determined
simply by adding up all
the samples and then dividing
by the number of samples
in the measurement.
Typically,
the display might show:
1.2235 V AVG 1
In this case, the average of samples in channel 1 is being
displayed.
'The average function
can be applied to measurements
"f
any sire, although
taking the average of a single-sample
measurement
sequence makes no sense because the
average is the same as the sample.
Example:
As an example, assume that the data listed in Table 3-10
has been taken during
a measurement
sequence. The
average value is simply the sum of the samples divided
by the number of samples (11). Thus, the average of this
measurement
would be:
v,,,;
= l30.65111
V rlVG = 11.877V
3.13.2 True RMS
The true RMS value of a voltage waveform is that value
which would produce the same heating effect as an equal
3-30
DC voltage. For a sine wave, the TRMS value equals 0.707
times the peak value.
To determine
the true RMS value of the measurement,
press SHIFT TRMS (or simply TRMS if not in the data cn-
try mode). The instrument
will respond by displaying
the
TRMS value in volts of the samples in the measurement
buffer. Although
TRMS can be applied to measurements
of any
number
of samples,
it is usable
only
for
meaSurcme"tS
of two or more samples.
A typical display in the TRMS mode is as follows:
2.Y875 V RMS 2
In this instance, the TRMS value of the channel 2 measure-
ment buffer is being displayed.
TRMS values are calculated as follows:
"-1
c
v;
VTM
=
I--
i=O
"
Where: Vi = voltage amplitude
of individual
sample
i = individual
sample number (0 through
n-l)
n = number of samples in measurement
Example:
As an example, let us determine the TRMS value of the
measurement with samples listed in Table 3-10. WC can first
determine
the sum of the squares of all 11 samples as
follows:
i=n-1
E
= 1576.5825
i=O
The TRMS value can then be easily calculated by using
the above value as follows:
1576.5825
vTM
=
F-
11
K,,,
= 11.97V
.-
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