Trial, Error, and Physics: The Story Behind the G3's Saturator

When Bob Hardy sat down to design the G3 Low Frost Point Generator, he wasn't looking to give a sales pitch. He wanted to tell a story—a story about the technical "headaches" that have plagued humidity generation for decades and how a little trial and error in Arizona led to a breakthrough in primary methods.

"I had worked on frost point generators for many years," Bob explains. "There were always things I wanted to do differently—things I knew were a problem. We found some better ways through experimentation. Some things worked, some didn't, but we solved a few big problems."

Here is the "layman’s guide" to the physics and the "why" behind the G3.

The Fundamental Physics: The Hybrid Approach

In metrology, there are two classic ways to generate humidity. Bob decided the best way forward was to stop choosing between them and instead combine them.

1. The Two-Temperature Technique: You saturate gas at one temperature (T1​) and measure it at another (T2​). If the pressures are equal, the saturator temperature is effectively your frost point.

2. The Two-Pressure Technique: You saturate gas at a high pressure (P1​) and then expand it to a lower pressure (P2​) in a test chamber. The ratio of those pressures gives you your humidity.

The G3 Solution: A hybrid system. By independently controlling both temperature and pressure in the saturator and the chamber, the G3 uses integrated math to provide rock-solid accuracy across a massive range.

Building the "Perfect" Saturator

The "heart" of any generator is the saturator—the place where gas and water (or ice) reach equilibrium. Bob experimented with several designs before finding the winner.

• The Failures: Bob first tried stainless steel, but it didn't conduct heat well enough without a massive fluid bath. He then tried nickel-plated copper, but the brazing process was so difficult it destroyed the plates. He even tried copper-nickel, but the small amount of nickel ruined the thermal conductivity.

• The Winner: A solid copper stacked-plate design. Copper is the ultimate thermal conductor, allowing the system to reach equilibrium without bulky circulating fluids.

• The Seal: Instead of standard rubber O-rings (which allow water vapor to leak in), the G3 uses Indium seals. Indium is a soft metal that creates a literal "metal-to-metal" barrier against the outside world.

Stirling Coolers & The "Cold Foot"

Bob never liked traditional cooling systems involving messy fluids. For the G3, he turned to Stirling Coolers. These are powerful, refrigerant-free coolers that use a "cold finger" (or what Bob calls a "cold foot") to directly contact the copper saturator.

"With a Stirling cooler at -80 °C, I’ve still got about 45 Watts of lift," Bob says. The result? The G3 can drop from room temperature to -80 °C in about 30 minutes—an unheard-of speed in the world of low frost point generation.

Obliterating Permeation with a Vacuum

The "secret weapon" of the G3 is that the entire saturator and its critical valves are housed inside a vacuum chamber.

In low-humidity work, water vapor from the room is constantly trying to "permeate" through seals and tubing into your dry gas. By surrounding the system with a vacuum, Bob eliminated the problem at the source. If there’s no water vapor outside the valve, no water vapor can leak in.

Why It Matters

For Bob, the G3 wasn't about making a fancy machine; it was about making a maintenance-friendly, high-speed tool for the people doing the hard work in the lab. By combining copper's thermal conductivity, the power of Stirling coolers, and the protection of a vacuum, RHS has turned a "24-hour wait" into a "30-minute stroll."