491M - Specifications

Principle of Operation

  • Dilution of constant component vapor emission from permeation or diffusion tubes 
  • Delivery of precise, adjustable, low concentration dynamically blended gas mixtures. Trace concentrations - ppmv, ppbv, pptv     
  • Manual front panel controls for oven temperature and dilution flow rate adjustment and standby, zero and span selection      

Permeation Tube Oven 

  • High thermal mass oven with electronic PID control in Vertical orientation
  • Oven temperature range (heat only):     30-150 °C
  • NIST-traceable oven temperature     
  • Oven setpoint resolution and control:     ±0.1 °C
  • Temperature digital indication and adjust via front panel

Diluent Gas (customer-supplied)      

  • Uses inert, non-reactive, non-hazardous dry gas (Nitrogen, zero air, Argon, etc.) 
  • Mass flow meter subsystem is factory-calibrated in Nitrogen; contact factory for calibration in other type gas           

Primary Dilution Mass Flow Controller     

  • Dilution flow rate set by manual valve on front panel; measured by mass flow meter     
  • Standard dilution flow rate range: 0.25 to 5 l/min
  • Optional flow rate ranges available (0.5-10, 0.1-1, 0.1-0.5 l/min)     
  • Mass flow rate accuracy ±1% FS
  • Mass flow rate indication via front panel     
  • Mass flow calibration method: Analog zero/span adjust

Accepts Vapor Emissions from the Following Devices (A single oven can hold only one of the above tube types at a time)    

  • Liquid-filled disposable tubes up to 15 cm in length (maximum of 8 tubes)     
  • Liquid-filled high rate (LFH) permeation tubes (maximum of 1 tube)     
  • Factory pre-filled gas-fed permeation tubes (maximum of 1 tube)     
  • Diffusion tubes (maximum of 4 tubes)  

Standard Component Flow Path      

  • Component contacts only glass, Teflon and stainless steel     
  • Glass permeation tube holder     
  • Suitable for reactive component gases       

Optional Component Flow Path (specified at time of order)      

  • Heated output lines     
  • Stainless steel     
  • Electro-polished stainless steel     
  • Sulfinert-coated stainless steel     
  • Teflon only     
  • Teflon permeation tube holder      

Standard Modes of Operation      

  • Standby (oven venting at approx 75 cc/min flow rate)     
  • Zero (with user-specified flow rate)     
  • Span-by-flow; flow rate set by manual valve on front panel and measured by mass flow meter with front panel digital indication     

Output Concentration Range      

  • Below 1 ppb to over 1000 ppm depending on tube emission rate and dilution flow rate; low ppb and ppt concentrations with secondary dilution 


  • Additional permeation ovens (via up to five 491M-PM modules)     
  • Customer-refillable gas-fed permeation oven option (via 491M-GF modules)     
  • Secondary dilution flow rate option (via 491M-SD module): 0.5 to 5 l/min (other ranges available)
  • Overall output gas stream dilution ratio with both primary and secondary dilution: up to 10000 to 1
  • Direct gas blending module option (via 491M-DGB)     
  • Humidified gas module option (via 491M-HG)     
  • Gas stream output Interface Module option via 491M-IM module: ambient to 276 kPa (40 psig). (If 491M-SD secondary dilution module is installed, subtract 69 kPa (10 psig))       

Instrument Housing (specified when ordering)      

  • Carrying case (standard)     
  • Expansion chassis (optional); desktop or rack-mount, maximum 2 cases,  maximum 3 modules per case
  • Maximum 6 modules in a single 491M system:

Power Requirements (specified when ordering)      

  • 115 VAC, 50/60 Hz     
  • 230 VAC, 50/60 Hz       

Dimensions and Weight      

  • Dimensions (Base module as packaged in carrying case): 18.4 W x 34.3 H x 50.8 D cm3
  • Weight (Base module as packaged in carrying case): 14.5 kg


  • European CE Mark (230 VAC, 50 Hz): 491MB (Base), 491M-PM, 491M-SD, 491M-HG, 491M-GF, 491M-DGB     
  • UL (site-specific)

Speciality Applications (Please contact us)      

  • Special diluent (carrier) gases other than inert gases     
  • Trace moisture     
  • Chemical compatibility issues     
  • Heat tracing requirements