Model 3020M

Explosion Proof Paramagnetic Oxygen Analyzer​​​​


The Model 3020P is a versatile microprocessor-based instrument specifically designed to detect oxygen in a variety of gases. It is a precise, cost effective instrument capable of measuring percent oxygen in as low as the 0-1% range. Drawing on the solid performance of the 3000 series control platform, the 3020M provides the user with a wide variety of features and options to satisfy virtually any application.


The physical property distinguishing oxygen from other gases is its paramagnetism, which is significantly greater than other common gases. Consequently, the molecules of oxygen are attracted by strong magnetic fields which can be used in detection. The sensor consists of two spheres arranged in the form of a dumbbell suspended in a symmetrical, non-uniform magnetic field. When the surrounding gas contains oxygen, the spheres rotate out of the magnetic field by the relatively strong attraction of oxygen. A light beam focused on a mirror attached reflects asymmetrically onto two photo diodes resulting in a voltage shift. The difference of this produces a current used to drive the dumbbells back to the original position. The current flow required to maintain the null position is directly  proportional to the oxygen concentration and is shown linearly in volume percent oxygen in the display. Properly maintained sensors last for years with little or no attention making them ideal for critical measurements in the low percent range.


This unit offers three dynamic, user-configurable ranges plus auto ranging and can be calibrated in any range. It is linear on all three ranges, eliminating the need to recalibrate while switching between ranges. This analyzer comes standard with an isolated 4-20 mADC output for oxygen concentration and range identification. Additionally, a bi-directional RS-232C serial communication interface provides for remote monitoring and control of span and zero functions.

Additional Advantages

  • Linearity of analysis across three user-selectable ranges

  • Auto-ranging to follow process upsets

  • Auto-calibration electronics standard

  • No purge gas requirements


  • C       Electronically operated cal/zero valves

  • F       Flame arrestors for Class 1, Div 1, Group C/D service

  • G      Flame arrestors for Class 1, Div 1, Group C/D service with cal valves

  • H      Flame arrestors for Group B (hydrogen) service

  • I        Flame arrestors for Group B service with cal valves

Sample Gas Conditioning Requirements

  • Sample Inlet Pressure:        5 to 20 psig (regulate to fixed inlet pressure)

  • Sample Flow:                        1 to 2 SCFH

  • Sample Dewpoint:               Non-condensing at ambient temperature

  • Sample Temperature:         32° to 122°F (0° to 50°C)

  • Detector Wetted Parts:       Glass, steel, gold, Viton, acrylic glass and epoxy resin


  • Proven, robust paramagnetic sensor

  • Explosion proof NEMA 4/7 rated enclosure (Class I, Div 1, Group B)

  • Three user-selectable ranges plus cal range

  • Signal and Range ID output: 4-20 mADC

  • Programmable auto-ranging

  • Two fully adjustable concentration alarm set points with programmable relay functions, Form C contacts, 3A resistive

  • Calibration contact span/zero, Form A normally open contact, 3A resistive

  • Self diagnostics with Form C failure alarm contacts

  • Full duplex RS-232C communication link

  • Five digit oxygen concentration LED display

  • 2 x 20 alphanumeric vacuum fluorescent display for setup and diagnostics

  • Stainless steel sample passages and fittings

  • Universal power supply: 100-240 VAC / 50-60 Hz

  • Remote calibration digital inputs​

  • NEC and ATEX rated configurations



​3 user selectable ranges: typical ranges 0-5% to 0-100% auto-ranging with ID output
(lower ranges available)


​± 1% of FS at constant temperature
± 5% of FS over operating temperature range on factory default analysis ranges, once thermal equilibrium has been achieved

​Response Time

​90% of FS in < 10 seconds at 77°F (25°C)


​0.1% O2


​Zero:    0.05% O2 / 1 month
Span:   1% FS / 1 month


​0.1% / FS


​32° to 113°F (0° to 45°C)


​Two 0-1 VDC & two 4-20 mADC isolated
(concentration and range ID)


​One system-failure alarm contact to detect power failure
Two adjustable concentration threshold alarms with fully programmable set-points


​Analysis:                 5 digit red LED, 3/5" high numerals
Menu:                     20 character, 2 line vacuum fluorescent
Digital Interface:   Full duplex RS-232 communication port


​Universal AC input ranges, 100 to 240 VAC, 50/60 Hz, 70 watts max


​Explosion proof U/L and CSA listed housing for Class 1, Div 1, Groups B, C & D service;
NEMA 4/7 rated with baked powder epoxy finish for corrosion resistance

(for NEC version)​

​15.25"W x 25.63"H x 11"D
(38.73 x 65.1 x 27.94 cm)


This instrument is designed specifically for the detection of percent oxygen in petrochemical applications for process control, quality assurance and safety related purposes. Typical petrochemical plants requiring this unit are:

  • Ethyl Benzene / Styrene Monomer (EB/SM)

  • Pure Terephthalic Acid (PTA)

  • Caprolactum​

  • Phenol / Cumene

  • Polycarbonate

  • Polyethylene

  • Polystyrene

  • Ethylene Oxide / Ethylene Glycol (EO/EG)

  • Methyl Methacrylate

  • Ammonia / Urea Fertilizer

  • Refinery FCC unit and flare gas applications

  • Marine Vapor Recovery (MVR)​