Digital Power Meter

Functions

• Built-in printer (optional)
• By using the built-in printer, you can print the measurement values and the setting data. Also, when performing harmonic analysis, you can print out the measurement values in the form of a bar graph.

• Harmonic analysis function (optional)
• By installing a harmonic analysis function, you can measure voltage, current, power and harmonic content up to the 50th harmonic in accordance with IEC1000-3-2. (The analysis range can be set between the 1st and 50th harmonic, and the window width can be varied according to the fundamental frequency.)

• Voltage fluctuation and flicker measurement function (optional)
• Flicker is evaluated according to the extent of the fluctuation (flicker) of brightness perceived by the human eye. The limit value of flicker caused by electrical equipment is stipulated by IEC1000-3-3 (an international standard pertaining to the limit values of voltage fluctuation and flicker for equipment that has a rated input current per phase of no more than 16 A). This instrument measures five kinds of values covered by this standard (relative steady-state voltage change, maximum relative voltage change, time during which the relative voltage change exceeds the threshold level, long period flicker value, and short period flicker value), enabling you to judge these values with respect to the limit values
   

• MATH Function
• This function enables you to calculate the input-to-output efficiency and crest factor, perform mathematical operations between DISPLAY and A and B.
   

• Peak overload warning
• LED indicators warn you if the peak voltage or current exceeds the maximum allowable value for any element.


• Range and measurement mode selection
  • RMS: Calculation and display of the true RMS value
  • MEAN: Calculation and display of the rectified MEAN value converted into an RMS value
  • DC: Calculation and display of the DC value using a simple averaging method (with sign)
• You can select the range and measurement mode for each input element.


• Wh or Ah measurement
• You can display the results of measurements with maximum resolution even for short integration periods by varying the resolution according to the integration time. You can also perform signed DC input data integration.

• Line filter function
• The instrument has a line filter which is effective for measuring the RMS value of the fundamental wave of the output voltage which is necessary for evaluating an inverter. You can select a cutoff frequency of either 500 Hz or 5.5 kHz.
   

• Setting the display update rate
• You can set a suitable update rate for the operation frequency of the measurement object. For a display update rate of 2 seconds, you can perform stable measurements from 2 Hz.

• Display
• You can display four items simultaneously at a maximum resolution of 50000 counts. During frequency measurement, a resolution of 1 mHz can be achieved for an input at the commercial line frequency.

• Peak hold function
• By using this function, you can hold and display the maximum value (peak value) of each measurement value. (This does not apply to integration or harmonic analysis.)

• Key-lock function
• This function enables you to disable the keys so that settings are not changed if you accidentally touch the keys during measurement.

• Current inputs
• Large capacity diodes are installed to protect the internal shunt resistors from damage in the event of an input overload. The current inputs are isolated from the voltage inputs. (The maximum withstanding voltage between the voltage and current input terminals is 3700 V AC.)

• 14-channel D/A output (optional)
• Provides V DC F.S. analog outputs for V, A, W, var, PF, deg and Hz. You can freely select the items to be output on these 14 channels as well as the communication output and printer output.

New high-speed-response type digital filter

For the WT2000 series, we installed a high performance DSP and also developed a "variable attenuation type filter method" as same as 2531 to realize multiple items simultaneous measurement and high speed response which are required for electric power measurement. This filtering method enables the attenuation constant to be varied for each sampling. Compared to the conventional analog filter it has various merits including the following: (1) it has low ripple and fast response, (2) it prevents the number of calculation processing operations of the DSP from increasing, and does not significantly reduce the sampling rate, and (3) there is no need to synchronize it with the interval of the input signal. As a result, the measurement values are unaffected even if the frequency changes or a low frequency waveform is superimposed on the input signal. This method realizes a high response of 36 items of data/250 ms.

Superior noise immunity

PWM type inverter equipment which is very widely used generates a voltage waveform by switching the frequency conversion circuit, hence the output contains a lot of noise. To ensure accuracy when measuring such equipment, it is important that the measuring instrument have high noise immunity. In the design of the WT2000 series, care was taken to minimize the effect of common mode noise, power line noise and pulse noise, thus ensuring highly accurate and stable measurement.

Integration function; High speed sampling that enables the instrument

The integration method used in the WT2000 series enables the instrument to continuously acquire data by sampling the input signal at a high rate of about 110 kHz. As a result, the instrument can measure abrupt changes in input value, which was difficult to realize with conventional measuring instruments, thus enabling integrated values to be measured with very little loss of data. (There is virtually no delay or pause period due to the response of the filter.) With YOKOGAWA's conventional models, the resolution of the displayed value resulting from an integration operation is fixed by the maximum integration time, hence for short period integration, the bottom digit was not displayed and the resolution was insufficient. The WT 2000 series uses an "auto resolution method" in which the display resolution automatically changes along with the lapse of the integration time, ensuring the maximum resolution even for short period measurement.

Characteristics