App-32
IM 760301-01E
When the Data Update Rate Is Set to 250 ms, 500 ms, 1 s, or 2 s
The measurement period is set equal to the data update interval. The measured values
are determined by computing the average of all the sampled data in the data update
interval through digital filtering. This computing method is called Exponential Average for
Measuring Period (EAMP). In this method, the measurement period is not affected by the
input signal period or the synchronization source setting. Therefore, the input signal
period does not have to be detected. In addition, the measurement period always
matches between all input elements. It is recommended that this method be used when it
is difficult to match the measurement period between the input and output signals such
as in the aforementioned example of “(3) Power Transformer with Single-Phase AC Input
and Three-Phase AC Output.” In principle, this method is superior in obtaining highly
stable measured values, because factors such as errors in period detection do not exist.
Exponential Average for Measuring Period
Yn = Yn-1 +
(Xn – Yn–1)
A
Xn:
n
th
sampled data in the measurement period.
Yn:
Output value of the n
th
exponential average in the measurement period.
Yn-1: Output value of the n–1
th
exponential average in the measurement
period.
A:
Constant
This equation is stacked several stages to derive the measured value. The last
value in the measurement period, Yn, is displayed as the measured value.
ASSP: Average for the Synchronous Source Period
EAMP: Exponential Average for Measuring Period
Data Update Rate and Averaging Method
Data update rate
50 ms
100 ms
250 ms
500 ms
1 s
2 s
5 s
10 s
20 s
ASSP
Computing
method
Setting the
Measurement
Period
EAMP
ASSP
Required
Not required
Required
Appendix 6 Setting the Measurement Period