Trace Moisture Gas Generators:

Span Pac™ general information
Span Pac™ 61-H2O and 261-H2O
Span Pac™ 61-W-H2O and 261-W-H2O
Span Pac™ 61-W-H2O-SD
Reactive Gases Model
Industrial-grade Models

Trace concentration moisture is an extremely important parameter in gases used in a wide range of processes. But there is no absolute analytical method that can be used in all applications.

For most sensing methods, the response to moisture is affected by the background gas and most current methods are subject to "poisoning" by certain contaminants. Basically, all trace moisture sensing systems require calibration to external standards and they must be frequently challenged with standards to demonstrate continued accuracy.

Span Pac H20 Instrument Series - Trace Moisture Gas Standards

• H2O concentration adjustable over 10:1 range with single oven; 100:1 with dual oven
• High ppm to 0.1 ppm H2O range
• Welded models (W series) can go down to about 10 ppb H2O
• Industrial models have NEMA 4 cabinets and optional purge capability
• Simple to operate

There are three special problems associated with trace moisture calibration:

• At the lowest concentration levels, there is no real zero reference point for moisture. Standards prepared by simply adding water vapor to a dry gas actually have unknown uncertainty.
• Water interacts readily with almost all materials, so changes in pressure or temperature can appear as transient concentration changes and may take a very long time to stabilize.
• Water is pervasive in our atmosphere, so even the most accurate standard may be contaminaed in the delivery process.

The Span PacT H2O systems work on a differential principal.
Calibration is based on the change in analyzer response caused by the addition of a known water vapor concentration from a Trace SourceT H20 permeation tube to a flowing stream of background gas (which may also contain some moisture). This differential method overcomes the "no zero" problem, and the problem of the background gas affecting the response. Water vapor flow from the permeation tube is measured gravimetrically, and is traceable to NIST. This technique provides a close approximation to a primary standard, even in situations where primary standards are not available.

Special care in design, construction and choice of components minimizes errors due to atmospheric contamination and interactions with other materials in the system.

As listed in menu, several Span PacT H2O models are offered to insure an economical solution to every moisture calibration problem.