5 Practical Tips for Better SF6 Gas Analysis

Accurate SF₆ analysis is foundational for safe, reliable substation operations. Yet, several field variables can compromise data quality and lead to poor decisions. Below are five actionable insights that help improve your readings and extend the life of your equipment—especially when using the FLEX Analyzer.

1. Allow Time for Moisture Readings to Stabilize

Moisture sensors often require 1–2 tests before providing stable values. The residual moisture that can be found inside the fittings, hoses, plumbing, and in the sensor housing often need to dry out before results can be trusted. The FLEX is the only analyzer on the market with a built in heater on the tip of the capacitive polymer sensor that helps to burn off residual moisture trapped in the sensor module, making results trustworthy from the first test.

2. Watch for Leaks: They Skew Readings

Even minor leaks in the gas system reduce SF₆ purity and introduce atmospheric moisture. Leaks most often form at connection points, so check your fittings and sensor modules first. If you suspect a leak, disconnect your sample hose from the gas compartment you are testing, and run a “LEAK CHECK” function (if using a FLÉCHIR). This will pull a vacuum on the all of the plumbing and the sample hose to determine if there is a leak or not. If there is a leak, you can run it down with a SF6 Leak Detector.

3. Avoid Pump-Back Until Done Testing

Pumping gas back into a breaker can elevate moisture levels, causing artificially high readings in that compartment for up to 24 hours after reinjection. If you need to store more than a few tests, consider using a Sac de récupération de gaz that can hold more than a few samples at a time.

4. Understand Sensor Tolerances and Units

Dew point and PPMv do not scale linearly. Most moisture sensors are rated in dew point, not parts per million by volume PPMv. Know your sensor’s specified range and avoid converting without validated curves. For instance, the FLEX H2O sensor is accurate to within ± 2 °C. A range of -53°C to -51°C is a difference of 6 PPMv. A range of -37°C to -35°C is a difference of 101 PPMv. See below chart (or use our dew point calculator) to better understand how the values convert.

5. Calibration is Critical—but Not Easy

Over time, sensors drift. Most sensors can be trusted between 1-2 years. Anything that is past due might as well not be used, because the result can’t be trusted. Calibration ensures accuracy but can be logistically complex and expensive. That’s why modular replacement—like FLEX’s modular sensor design—is often the smarter solution for long-term reliability and field readiness.