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IM 760301-01E
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App
Index
Faunctional Description
Types of Measurement Functions of the Motor Evaluation Function (Motor Version)
By using the motor evaluation function (motor version), the rotating speed, torque, and
output of a motor can be determined from the DC voltage (analog signal) or pulse count
signal received from a revolution sensor, which is proportional to the rotating speed of
the motor, and the DC voltage (analog signal) or pulse count signal received from a
torque meter, which is proportional to the motor’s torque. In addition, the synchronous
speed and slip of a motor can be determined by setting the motor’s number of poles.
Furthermore, the active power and frequency that are measured by the WT3000 and the
motor output can be used to compute the motor efficiency and the total efficiency.
For details, see chapter 1, “Motor Evaluation Function (Motor Version)” in the
Expansion
Function User’s Manual IM760301-51E
.
Voltage Mode and Current Mode
You can select equations for voltage (U) and current (I) from the following:
• Urms, 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
value is determined. f(t) and T represent the input signal as a function of time and
the period of the input signal, respectively.
Urms or Irms =
1
T
0
T
f(t)
2
dt
• Umn, 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 is a DC waveform, these values will differ from the true rms
values. f(t) and T represent the input signal as a function of time and the period of
the input signal, respectively.
Umn or Imn =
π
2
2
•
1
T
0
T
f(t) dt
• Udc, Idc (Simple Average, DC)
These are the average values over one period of the voltage and current signal.
This function is useful when determining the average value of a DC input signal or
a DC component that is superimposed on an AC input signal.
Udc or Idc =
1
T
0
T
f(t)
dt
• Urmn, Irmn (Rectified Mean Value)
This function rectifies one period of the voltage or current signal and determines
the average.
Urmn or Irmn =
1
T
0
T
f(t) dt
The WT3000 may use an averaging process through digital filter computation in addition
to the averaging method using the equations above to derive the measured values of
voltage (U) and current (I). For details, see “Data Update Interval” on page 2-14.
2.2 Measurement Modes and Measurement Functions