The Span Pac H2O trace moisture gas standard provides:

  • H2O concentrations adjustable over 20:1 range with single oven; 400:1 with dual oven system; 10,000:1 with secondary dilution mass flow
  • Concentrations within 0.01 to 10,000 ppm H2O range depending on model selection
  • H2O concentrations below 100 ppb with welded model
  • Industrial models have NEMA 4 cabinets and optional Z or X purge capability
  • Uses KIN-TEK Trace Source disposable and refillable water permeation tubes

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.
There are three special problems associated with trace moisture calibration:

  1. 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.
  2. 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.
  3. Water is pervasive in our atmosphere, so even the most accurate standard may be contaminated in the delivery process. 

The Span Pac H2O instrument works on a differential principal. Application of this principle is meaningful when the moisture content of the background diluent gas exceeds 10 percent of the minimum concentration to be generated. Calibration is based on the change in analyzer response caused by the addition of a known water vapor concentration from a KIN-TEK Trace Source water permeation tube to a flowing stream of the diluent gas. This differential method overcomes the "no zero” problem, and the problem of the background gas affecting the response.
The permeation tube emission rate is certified by the Factory traceable to NIST by gravimetric weight loss over time. This provides a close approximation to a primary standard, even in situations where primary standards are not available. 
KIN-TEK takes special care in design, construction and choice of hardware components to minimize errors due to atmospheric contamination and interactions with other materials in the system.
KIN-TEK manufacturers several Span Pac H2O models to insure an economical solution to every moisture calibration problem.

A. Single Oven (Span Pac 61-H2O)

The single-oven model can produce moisture concentrations over a 20:1 range within an overall bounds of 0.1 to 10,000 ppm (depending on the permeation tube emission rate and dilution flow rate) in nitrogen and other inert background gases. The standard primary dilution mass flow rate range is 0.25 to 5 l/min. Other flow range options are available.
The component flow path features all electropolished stainless steel tubing with heat tracing. 
A cabinet purge port is available to:

  • Purge the cabinet with dry inert gas to minimize outboard-to-inboard contamination from atmospheric moisture when generating low moisture concentrations. Dry nitrogen or zero air is recommended.
  • Maintain an acceptable nitrogen level within the cabinet when using hydrogen as the diluent gas to eliminate any possibility of an explosive mixture. The user must supply a continuous controlled flow of nitrogen to the purge port.

B. Dual oven (Span Pac 261-H2O)

The dual-oven model is similar to the single-oven model, but can generate concentrations over a 400:1 range depending on selection of permeation tube emission rates. 

C. Single oven with Secondary Dilution (Span Pac 61-H2O-SD)

The single-oven instrument with secondary dilution (SD) is our most versatile moisture system (as shown in the picture above). This instrument provides both primary and secondary dilution. The secondary dilution step allows generation of extremely low concentrations over a very wide concentration range (up to 10,000:1), and generation of variable concentrations into a fixed total output flow rate.
The component flow path features all electro-polished stainless steel tubing with heat tracing. 
A cabinet purge port is available to:

  • Purge the cabinet with dry inert gas to minimize outboard-to-inboard contamination from atmospheric moisture when generating low moisture concentrations. Dry nitrogen or zero air is recommended.
  • Maintain an acceptable nitrogen level within the cabinet when using hydrogen as the diluent gas to eliminate any possibility of an explosive mixture. The user must supply a continuous controlled flow of nitrogen to the purge port.

D. Welded Models Available for Trace Moisture Below 100 ppb 

Single Oven (Span Pac 61-W-H20) 
Single Oven with Secondary Dilution (Span Pac 61-W-H2O-SD)

The welded (W) instrument is required for applications that generate one or more moisture concentrations below 100 ppb. (Welded models can also be used for higher moisture concentrations.)

In single-oven models with only primary dilution (i.e., no secondary dilution), the minimum moisture concentration of 5 ppb is set by the minimum practical permeation tube emission rate and maximum allowed dilution flow rate. The secondary dilution model can generate moisture concentrations much lower.
The welded model has the same features and functions as the non-welded model including purge port and heated electro-polished stainless steel tubing. In addition, the tubing is seamless with orbitally-welded joints to further reduce the possibility of outboard-to-inboard atmospheric moisture contamination. The addition of special hardware components insures high-purity service.

E. Industrial-grade Models 

All non-welded models are also available in NEMA 4 enclosures for use in industrial environments. Optional capabilities include (1) Z-purge for Class 1, Group C or D, Division II and (2) X -purge for Class 1, Group C or D, Division I.