O2 Monitor

Our standard Model 221R is outfitted with a complete package of electronic features and utilizes a very accurate and reliable 10-year life zirconium oxide sensor. This combination provides unmatched stability and is virtually maintenance free over its entire life.


Competitive models generally suffer from undesirable stability issues causing frequent and expensive false/nuisance alarms. The undesirable drift usually results from just a slight ambient temperature change or the unavoidable decline in electrochemical sensor outputs. Our innovative engineering and sensor technology guarantee unmatched stability and performance over a wide temperature range of 0-130 degrees F, thereby eliminating costly nuisance alarm issues.

Our sensor requires no support gases and can be easily and accurately calibrated using compressed air. A standard calibration takes approximately one minute and only needs to be performed every six months. Given the remarkable stability over an extreme temperature range, complete electronics package, and compact watertight NEMA 4X enclosure, the Model 221R is a perfect fit for a wide range of applications, including clean rooms, control rooms, confined spaces, refrigerator/freezers, and applications that are susceptible to routine hose down requirements.


  • Measurement Range: 0-25%
  • Red Backlit Digital Display: High resolution 3 ½ digit LCD. Reads full scale from 00.0% to 25.0%
  • Alarms: Two fully adjustable oxygen concentration alarms. Preset for OSHA standards, 20.0% Caution and 19.5% Danger. Dry contacts 3 A. @24VDC/115VAC
  • Status LED: Indicates Power, Safe Operation, Alarm Conditions and Loss of AC power
  • Danger Alarm: 95dB danger alarm preset for 19.5%
  • Battery Back-up: One hour
  • Analog Output Signal: Isolated 4-20mA
  • Data Logger: Logs data for 15 days @ one-minute intervals, 30 days @ two-minute intervals, etc.
  • Communications: RS-485 bi-directional
  • Power Requirements: 115 VAC< 10 watts
  • Repeatability: +/-0.1% of range or +/-0.1% of oxygen, whichever is greater
  • Operating Temperature Range: 0°-130°F
  • Diurnal Temperature Specification: < ±1% of scale over temperature range
  • 90% Full Scale Response Times for Specified Range: 0-25% < 12 seconds
  • Long Life Zirconium Oxide Sensor: 10-year life expectancy
  • Weather Tight NEMA 4X Package
  • Area Classification: Designed to meet General Purpose UL 61010-1 standard and IP 65 requirements. Approval pending.
  • Gas Connection: Diffusion screen. No pump or fittings required
  • Mounting: Wall mount or 2.0” pipe mount
  • Dimensions: 7.0″ W x 5.7″ H x 4.5″ D
  • Weight: 4 lbs
  • The Model 221R is a rugged piece of safety equipment designed for industrial applications.


    Acme Cryogenics has been delivering Excellent Quality, World Class workmanship & Customer Service for over 50 years. From Parts to Complete Plant Installation solutions. Acme cryogenics is there for all your industrial gas & liquid handling needs.
    Acme Cryogenics continues to expand and grow through the acquisition of companies that bring additional value and services to our customers. We have safe facilities across the USA to service not only the United States but globally as well. There are currently four manufacturing operations in Allentown, PA; Atlanta, GA; Lonsdale, MN; and Oxnard, CA and seven Field Service locations in Allentown, PA; Atlanta, GA; Houston, TX; Chicago, IL; Lonsdale, MN; South Plainfield, NJ; and Port St. Lucie, FL.
    As your leader in moving molecules in the industrial gas industry for over 50 years, we can offer technical assistance for your pipe system design, as well as cryogenic valves and cryogenic fittings, regardless of your level of experience. Our sales engineers have over 40 years of combined experience. Our product management, engineering, and quality departments work closely together to provide a steady flow of new features and expanded product offerings without compromising the reliability and performance that we are known for. Our manufacturing team has decades of experience and work in our newly-expanded valve-specific manufacturing area, located in our Allentown, PA headquarters.
    Acme Cryogenics specialists are readily available to assist you- Fill out a contact form, quote form or call us directly, We welcome the opportunity to deliver for you.
    Acme Cryogenics provides engineering, design, fabrication, installation, and repair services for the Food Packaging, Pharmaceutical, Semi-Conductor, Cryobiology, Medical Gas Pipe, Aerospace, and Industrial Gas industries.
    Acme Cryogenics provides an extensive suite of products and services for customers across the entire industrial gas supply and distribution chain.
    Acme has a full complement of highly trained Field Service Technicians who can expertly inspect, repair and maintain your cryogenic systems, medical gas systems, gas piping systems, (LNG) liquid natural gas fueling systems, industrial piping systems and more, assist your staff in peak times, or provide a cost-effective way to install and/or maintain your equipment. The Acme team can also assist in services such as site survey, equipment sizing, capital expenditure calculation, logistics services, and equipment supply.

We're sorry. Our site does not support your browser.

In order to view the site, you will need to upgrade your
browser. Choose one of the free upgrades below.