Overview
The eGauge can calculate Total Harmonic Distortion (THD) on a given CT or voltage reference. Each THD measurement will use one physical register. The eGauge can measure up to the 10th harmonic.
THD is a measurement of the harmonic distortion of a signal given it's fundamental frequency, and thus may be larger than 100%. If there is insufficient amperage on a CT or the circuit is not active, the noise may calculate to high percentages.
THD is typical on current waveforms which, depending on the type of load is not always a cause for concern.
Prerequisites
To complete the steps in this article you will need:
- Access to the eGauge interface
- Valid login credentials to change settings.
Instructions
Step 1: Access the eGauge Installation settings by navigating to: Setup → Other Settings, then click Installation to the left.
Step 2: Under Registers, click the Add Registers button.
Step 3: Name the register as appropriate, and using the dropdown menu change the register type from P to =
Step 4: A second dropdown menu will appear. Select the unit type to total harm. dist or THD [%]
In the formula field, enter the following: THD(Hz, chan("XX")) where Hz is the system frequency in Hz and XX represents either a CT or Voltage Sensor (S1, S2, S3, etc) or a voltage reference (L1, L2, L3 or ldc).
Step 4: Click Save at the bottom of the page when finished (valid credentials required)
- In firmware 4.0 and earlier Sensor channels were referred to as “CT” rather than “S”. Thus, instead of using
chan("S1"), usechan("CT1")on earlier firmware. Configuration is otherwise identical.
Additional Resources