Stop the Noise: How to Fine-Tune Waveshape Triggering for Distorted Loads

If your power monitoring system is capturing more events than you can make sense of, incorrect settings might be to blame.

Dranetz waveshape triggers are a powerful tool to detect step load changes, negative transients, harmonics, and other intermittent fast changes in voltage or current that can affect your power system. Waveshape triggers continually look for cycle-by-cycle changes in voltage and/or current. Regardless if your power is ‘clean’ or ‘dirty’, if it’s consistent, and not changing, waveshape triggers will not occur. Waveshape triggers look for changes in each AC cycle that may be harmful, and if not applied correctly can create nuisance triggers.

Varying distortion or loads—such as notching, load changes, Silicon-Controlled Rectifiers (SCR)—can create such changes. These aren’t necessarily faults, but to a monitoring system that isn’t properly configured, they can look like one.

The result? A flood of unnecessary waveshape triggers and bloated data files. You get buried in noise, when what you really need is clarity.

This post explains how waveshape triggering works in the Dranetz HDPQ series, what causes it to trip unnecessarily, and how to configure your settings to focus only on the events that matter.

Understanding the Two Trigger Types

Dranetz HDPQ instruments come equipped with two primary ways to detect waveform anomalies:

1. Waveshape Difference Trigger

This is the more sensitive and granular of the two methods. It breaks each 50/60 Hz AC cycle into smaller windows, defined as a percentage of the total cycle (for example, ten windows at 10% each). Each of these segments from the current cycle is then compared to the same segment from the previous cycle. If the difference exceeds the user-defined threshold, an event is recorded.

This method excels at identifying short-duration changes that occur mid-cycle, such as electronic notching or micro-transients. However, in environments with ongoing distortion, this can easily become oversensitive if not tuned correctly.

2. RMS Deviation Trigger

This method takes a broader approach. It compares the entire waveform cycle from start to finish, subtracting the previous cycle from the current one on a sample-by-sample basis. If the resulting deviation crosses a set threshold, the trigger activates.

This method is better suited for identifying more sustained or consistent waveform changes, such as voltage sag or swell events, rather than brief or localized distortions.

Both methods are useful, but when you’re monitoring a system with built-in distortion, the Waveshape Difference Trigger can trip repeatedly if not set properly.

Before You Start Monitoring

Always check your waveform in real-time scope mode before you start monitoring. This gives you a live look at what your voltage and current waveforms actually look like under load. If the waveforms are constant and not varying, default settings usually work fine.

But if you see varying waveshapes or harmonic content, you’ll want to adjust your settings depending on your monitoring needs before leaving the instrument to run. This is especially the case when monitoring current which tends to vary greatly as loads change. Otherwise, you risk collecting too much low-value data.

How to Adjust Your Settings

In the Dranetz HDPQ Wizard setup:

Navigate to the Trigger Limits tab.
Select Set Waveshape Transients.
Adjust the Magnitude Limits to reflect a more realistic threshold for your system.
If you want uniform settings across all three phases, use the Set ABC the SAME button.

If the distortion you’re seeing is part of your system’s normal operation and not relevant to your monitoring goals, you can choose to disable the Waveshape trigger altogether using the Disable button.

A Real Example in Dran-View

In one case, a Dranetz HDPQ unit recorded repeated events due to a voltage peak-to-peak distortion of 66.3 V. The Waveshape Magnitude threshold was set at 48.0 V, which was too low for this environment. Adjusting the threshold reduced unnecessary event recordings while still preserving relevant data.

Dran-View 7’s zoom and measurement tools made it easy to inspect and validate these changes.

What to Do Before Every Deployment

The ability to fine-tune your Waveshape trigger thresholds is what allows the Dranetz HDPQ to adapt to different environments and deliver relevant, clean data.

Before every deployment: