Model 303B Moisture Analyzer

The Model 303B offers a simple solution to the problem of measuring the moisture content of gas streams.


The Model 303B offers a simple solution to the problem of measuring the moisture content of gas streams. Using an electrolytic (P2O5) sensor, the Model 303B can be used to monitor nearly all gases. It is compact, lightweight, and suitable for both portable use and permanent installation in Class I Div. 2 areas. With the optional carrying bag and lightweight design, the 303B is truly portable.

Every 303B is equipped with the following:

  • digital display
  • rugged moisture cell
  • bypass flowmeter
  • 4 to 20 mA output
  • internal battery and recharging system
  • AC and 12VDC power inputs


The 303B is designed to measure moisture content in gases such as air, nitrogen, argon, natural gas, and others with comparable characteristics. Typical applications are:

  • Monitoring natural gas pipelines and gas treatment processes
  • Monitoring air humidity in dry boxes
  • Continuous monitoring of atmospheres in simulated space chambers
  • Sensing elements in humidity control systems
  • Monitoring inert protective atmospheres in brazing or sintering furnaces
  • Monitoring moisture in many fluorocarbon gases
  • Constant measurement of batch and continuous driers to assure quality control without the expense of overdrying
  • Monitoring anhydrous batch chemical processes at startup
  • Quality control of transistor and diode backfill gas
  • Instrument air systems
  • Cryogenic processes
  • Radar waveguides



  • UL/CSA General Safety Requirements
  • UL/CSA Class I, Division 2, Groups A, B, C, D T4A
  • Complies with all relevant European directives


Dynamic Range 0 to 1000 ppmv at 100 mL/min sample flow through cell at 25ºC and 101.4 kPa (0-2000 ppmv range possible with reduced sample flow
Sensitivity 0.1 ppmv
Accuracy +0.5 ppm or +5.0% of the display reading, whichever is greater
Response Time 63% response to a stepwise change in either direction between 50 ppm and 1000 ppm will occur in 30 seconds or less
Utility Requirements 100 to 130 VAC or 200 to 260 VAC and optional 12 to 14 VDC operation, 20W maximum
Analog Output 4-to-20 mA DC proportional to range selected, compatible with 625-ohm maximum load
Alarms Rated for 1 A, 24 VDC, normally open and normally closed contacts; user-settable to fail-safe or low-power operation
Sample Temperatures up to 52ºC (125ºF)
Ambient Temperature 0º to 52ºC (32º to 125ºF)
Temperature Stability 0.5% per ºC of selected range
Sample Pressure 69 to 690 kPa (10 to 100 psi) gauge
Electrolyte Cell The electrolyte sensor is in a self contained assembly for quick and easy replacement
Front Panel Controls Analog ranges 0 to 10, 100, 1000, and 2000 ppm; 0 to 0.5, 5, 50, 100 lb/mmscf
-Display light
-Standby power
-Electrical test
-Cell test
-Sample and by-pass flow adjust
External Connectors Gas IN and OUT fittings for 1/8 inch OD tubing. Internal connections for output and alarms; relay jumper changes operation to failsafe mode
Materials of Construction Sample comes in contact with P2O5 stainless steel, TEFLON® fluorocarbon resin, gless, platinum, and Viton
Weight 6.4kg (14 lb)
Cabinet Dimensions (LxWxH) 34.3 x 23.5 x 12.7 cm (13.5 x 9.25 x 5.0 in)


Model 303B Productsheet
Carbon Dioxide Gas
Drying Plastic Resin Pellets
Natural Gas Process Instrumentation