YOKOGAWA WT500 User Manual page 27

2.2 Measurement Functions and Periods
2-4
Determining Voltage and Current
The following five types of voltage (U) and current (I) measurement functions are
available.
• Urms and Irms (True rms value)
These values are the true rms values of the voltage and current. The instantaneous
values over one period are squared and averaged. Then, the square root of the
average is determined. f(t) is the input signal as a function of time. T is the period of
the input signal.
T
1
Urms or Irms =
T
0
• Umn and Imn (Rectified mean value calibrated to the rms value)
This function rectifies one period of the voltage or current signal, determines the
average, and multiplies the result by a coefficient. The coefficient is a value that when
applied to a sinusoidal input signal, gives the true rms value. When the input signal is
a distorted or DC waveform, these values will differ from the true rms values. f(t) is the
input signal as a function of time. T is the period of the input signal.
π
Umn or Imn =
2 2
• Udc and Idc (Simple average, DC)
These are the average values of the voltage and current signal over one period. This
function is useful when determining the average value of a DC input signal or the DC
component that is superimposed on an AC input signal.
T
1
Udc or Idc =
f(t) dt
T
0
• Uac and Iac (AC component)
This function determines the AC component of the voltage or current. The function
calculates the square root of the square of the true rms value minus the square of the
DC component.
Uac= Urms 2 –Udc 2
• Urmn and Irmn (Rectified mean value)
This function rectifies one period of the voltage or current signal and determines the
average.
T
1
Urmn or Irmn =
T
0
Elements
Element refers to a set of input terminals that can receive a single phase of voltage and
current to be measured. The WT500 can contain up to three elements, numbered from
1 to 3. An element number is appended to the measurement function symbol for the
measured data that the WT500 displays, so that you can tell which data belongs to which
element. For example, "Urms1" corresponds to the true rms voltage of element 1.
Wiring Systems
You can specify five wiring systems on the WT500 to measure the power of various
single-phase and three-phase power transmission systems: single-phase, two-wire;
single-phase, three-wire; three-phase, three-wire; three-phase, four-wire; and three-
phase, three-wire with three-voltage, three-current method. For details, see section 2.3.
2
f(t) dt
T
1
• f(t) dt
T
0
Iac= Irms 2 –Idc
, or
f(t) dt
2
IM 760201-01E