NOVUS DigiRail-VA - Manual (Page 8)

DigiRail-VA
NOVUS AUTOAMTION 8/19
The transformer ratio should be informed in DigiRail-VA settings so you can make the correction of the measured value,
adjusting to reality. Similarly, if the use of a transformer produces a phase shift between current and voltage in the
secondary, can be corrected through the option "Allow the Correction of Phase" in the "Diagnostics" tab for DigiConfig.
Example 1: Using a voltage transformer with 1000 V input and 300 V output.
In this case, you must inform on DigiConfig that be used a voltage transformer, selecting the appropriate box. You
must then inform the transformation ratio (in = 1000 V, out = 300 V).
Example 2: Using a current transformer with 50 A input and 4 A output.
In this case, you must inform on DigiConfig that be used a current transformer, selecting the appropriate box. You
must then inform the transformation ratio. As the input range is 0 to 5 A, and in this example the current transformer
to be used does not match the specification, adjust the parameter of the input current of the current transformer, so
that the ratio transformation is maintained.
50 / 4 = 12,5
12.5 x 5 = 62.
5 → Input = 62,5 A
MEASUREMENT OF FREQUENCY AND POWER FACTOR
The frequency measurement is performed by the voltage input. In case the voltage value is close to zero, the frequency
calculation may be inaccurate and wrong values may happen. That is why the DigiRail-VA inhibits the frequency
measurement when voltage is near zero, typically below 0.5% of full scale. The inhibition of the frequency measurement,
indicated as "0 Hz", also happens when it is not performing the voltage measurement, as in the case shown in Fig 06.
Measurement of power factor there need voltage and current being measured by DigiRail-VA, it is a calculated value
based on the phase shift of these two quantities. If one of the values of the voltage or current is near zero, the calculated
value of power factor may result in wrong values. That is why the DigiRail-VA inhibits power factor measurement when
the voltage or current showing very small values, typically 0.1 % of full scale. This inhibition of measuring power factor,
denoted as "0", also happens when it is not performing the measurement of voltage or current, as in the cases illustrated
in Fig. 06 or 05.
4-20 mA OUTPUT
The 4-20 mA output can be used to transmit any of the measures in the AC input:
•
RMS Voltage
•
RMS Current
•
Active Power
•
Apparent Power
•
Reactive Power
•
Power Factor
•
Frequency
This output can be disabled if necessary.
Transmission is based on the full scale of the desired variable (e.g. 0 to 300 V for the rms voltage) or based on a
reduced scale (e.g. transmit a value of rms voltage on the range from 80 to 140 V, where 80 V corresponds to 4 mA and
140 V to 20 mA).
Finally, you can select the behavior of the 4-20 mA output in case of error: current lower than 4 mA or higher than 20 mA.
Fig. 09 – Connecting the 4-20 mA loop output.