Model 221R


The AMI MODEL 221R has become the gold standard for oxygen deficiency & confined space monitoring throughout the US market. It is used by the thousands in US Government Laboratories, Space Agencies, Universities, and a broad range of industries, ensuring the safety of personnel. The MODEL 221R is designed for use in NON-FLAMMABLE applications and provides an incredibly accurate and stable reading over a broad temperature range (0-130°F). The Analyzer is virtually maintenance-free with its unique oxygen sensor delivering a 10-year life expectancy.

Technical Specifications

Physical & Eletrical Specifications
4.0 lbs
(1.8 kg)
Wall mountDiffusion screen. No pump, sample tubing or fittings required4-digit LCD (reads full scale from 0.0% to 25.0%)
100 –240 VAC <115 Watts.
Battery back-up provides 1 hour of power
model-221r dimensions
2-year warranty for Parts & Labor for any defects in materials or workmanship. 2-year Warranty for zirconium oxide sensors.
Operational Specifications
Method of Measurement
0 –25.0%0°F to 130°F
(17.8°C to 54.4°C)
Zirconium Oxide Sensor (10-year life expectancy)
Monitor Performance Specifications
Minimum detection limit90% UPSCALE RESPONSE TIMES
REPEATABILITYDiurnal Temperature SpecificationAPPROVALS
0.05% of Oxygen<12 sec for
0.0% – 25.0%
±0.1% of range or ±0.1% of oxygen whichever is greater<±1% of scale over temperature rangeApproved to meet General Purpose UL 61010-1 Standard and IP 65 Requirements.
CE Mark
Analyzer Key Features
2 Oxygen Concentration Alarms with Relay Contacts
ANALOG OUTPUTS4 − 20mA isolated analog output signals
COMMAND CENTERSoftware that works across AMI’s Analyzers and gives users access to advanced functions:
  • Calibration Details
  • Alarm Configurations
  • Data Logger (records O2  measurements, temperature, psig, and power)
  • Zirconium Oxide Sensor (note: sensor is not field replaceable)
  • Remote Probe (note: must be purchased from AMI)

Features & Benefits

Oxygen Deficiency Monitor in Work Environment
MODEL 221R Oxygen Deficiency Monitor installed in area with several gas cylinders

Designed for OSHA Compliance

The MODEL 221R is optimized for safety. Our standard offering provides (3) OSHA-compliant preset alarm relay contacts and a single 95 decibel audible alarm. The “Caution” alarm is preset for 20.0% oxygen, Danger for 19.5% and the Enriched Oxygen alarm for 23.5%. Both the 19.5% Danger and 23.5% Enriched Oxygen condition trigger alarm relay contacts and the 95dB audible alarm to alert personnel of the potentially dangerous situation. This Analyzer is also NRTL-certified to be compliant with UL61010-1, covering safety requirements of equipment for measurement, control and laboratory use.

Image of zirconium oxide sensor
Zirconium Oxide Sensor

Long Life Zirconium Oxide Sensor Technology

AMI’s zirconium oxide sensors are virtually maintenance-free, extremely accurate and stable over a wide temperature range without suffering from changes in barometric pressure. This unique sensor is the perfect choice for reliably measuring percent levels of oxygen in confined spaces, tank storage area, or in the workspace, ensuring personal safety. AMI’s zirconium sensor in the MODEL 221R will last up to 10 years without ever needing replacement.

MODEL 221r Oxygen Deficiency Monitor with optional remote probe
MODEL 221R Oxygen Deficiency Monitor with optional remote probe

Optional Remote Probe

The MODEL 221R is available with an optional remote probe for continuous monitoring of locations separate from the control unit. This makes it an ideal solution for making sure difficult to access locations continue to have a safe oxygen level. The remote probe comes standard with a 12 ft (3.6m) cable, but they can be extended by the customer up to 300 ft (91.4m). The probe features the same long-life zirconium oxide sensor as the standard MODEL 221R.

Command Center Software running on laptop connected to oxygen analyzer


The MODEL 221R comes standard with a 4-20mA isolated output signal and Modbus bi-directional RS485 communication. It has built-in safety features including rechargeable battery backup and tamper resistant alarms to prevent user override of safety setpoints. It also offers advanced features that can be accessed through AMI’s COMMAND CENTER Software. These includes automatic data logging that provides detailed time-stamped records of O2 measurement, and power supply voltage, as well as calibration history.

Available Accessories

Model 221R Downloads