OS-4 Ozone Monitor

The OS-4 Ozone Switch is a powerful device in a compact package. The SM-7 sensing module plugs into the OS-4 with included wire and can be mounted up to 100 meters away from the OS-4.

The OS-4 is a 0-20.0 ppm Electrochemical sensor.  Read full description below to learn more about what range may be right for you.

Ozone Information


The OS-4 Ozone Switch is a remote mount ozone sensor that uses the SM-EC sensing module to detect ozone up to 100 meters away from the base unit.  The easy to read LCD screen with indicator lights easily displays the ozone levels, and control status of your equipment. 

Acts like a thermostat to control ozone generators and alarms based on adjustable ozone concentration set-points. Ozone ppm readout via digital meter. Simple and effective.


     -Easy to install. Minimal adjustments.

     -Sensor is in a replaceable pre-calibrated module. Separated by a cable, the instrument is not in the high ozone area.

     -Sensor reading is temperature and relative humidity compensated.

     -Replacement sensor is miniature, low cost, pre-calibrated and also fits our A-22.

     -Operates from 12-24 VDC or from AC adapters available worldwide.

     -Alarms, data loggers, and other accessories available.

     -Programmable turn-on and turn-off set-points.

     -Indication when .1 ppm safety standard exceeded.

Typical Applications:

     -Monitor ozone levels in treatment storage areas for fruits, vegetables, and other agricultural products. Monitor ozonated HVAC systems. General monitoring at .03-20 ppm.

     -Control the output of ozone generators using the set-point controlled relay in the OS-4.

     -Use as either ozone leak alarm or ozone failure alarm for all sizes of ozone generators.


     -Range: .03-20 ppm Electrochemical sensor.

     -Accuracy: 10-15% (Depends on application).

     -Temperature and humidity: 5-40°c 20-95% RH

     -Measurement Principle: HMOS (heated metal oxide semiconductor) sensor.

     -Size: 127 × 64 × 42 mm (5 × 2.5 × 1.625 in).

     -Weight: 200 gr (7 oz)

     -Power Requirements: 12-24 VDC, 300 mA. AC adapters available.

     -Output control: SPDT non-latching relay. Contacts rated at 5 amps, 250 VAC.

     -.1 ppm danger alarm: Panel LED and SPDT relay 5 amp contacts.

     -Connections: Terminal blocks for relay output and DC input. 2.5 mm DC power jack for AC adapter.

     -Indicators: Green LED: instrument on. Yellow LED: >.1 ppm. Red LED: generator on.

     -Outputs: 0-2 V, 4-20mA, RS-232 digital.

     -Case: Flame-resistant ABS with mounting ears.

        *Not recommended for use in the presence of strong acid gases or VOC fumes.


Range Selection:

The OS-4 is available in a SM-EC Electrochemical Sensor 0-20 ppm range.  Each sensor is pre-calibrated with all calibration data contained on the sensor itself.  The SM-EC sensor chip is used and is replaced at a very low cost when calibration is necessary for these applications.

For many ozone control applications for odor, food, or other industrial applications the 0-20 ppm sensor will suffice and work well.

The OS-4 is now only available with the newest SM-EC sensor integrated into the SM-7 Sensor Module.  This is an electrochemical sensor with a range of 0-20 ppm.  This sensor has great advantages in high humidity environments, or areas where there may be high VOC's or other gasses.  While the HMOS sensors can be extremely accurate, they are typically more cross-sensitive than an electrochemical sensor.  The 0-20 ppm range will not be suitable for most human safety applications, but will be great for industrial ozone generator control.


SM-EC Replacement Sensor:

The OS-4 and OS-6 Ozone Monitors can be confusing when ordering and when buying replacement parts.  This explanation will help you understand the various parts.  The OS-4 consists of a base unit, the OS-4 itself.  This is attached to the SM-7 remote sensor using a 3-wire cable up to 100 meters long.  The SM-7 is a sensor module that detects the ozone and sends that signal back the OS-4 base unit.  The OS-4 base unit includes relays, voltage outputs, and a display.  The SM-EC sensor chip is installed in the SM-7 sensor module.  The SM-EC is a replaceable sensor chip that is pre-calibrated and can be plugged in and out without any other modification. 


SM-X Replacement Sensor:

The SM-X was the older version replacement sensors for the SM-6 remote sensor.  This is no longer available for purchase. If you have the old SM-6 with an SM-X sensor you will need to purchase the new SM-7 which contains a SM-EC sensor.


Summary, there are three main components:

  • OS-4 base unit includes the relays, voltage output, and display
  • SM-7 Sensor module houses the ozone sensor and measures ozone
  • SM-EC sensor chip is the replaceable sensor chip itself

All three of these pieces are included when you buy an OS-4.

The newest configuration uses the OS-4, with the SM-7 sensor module that uses the SM-EC sensor. 



Remote Sensor:

The OS-4 is shipped standard with a cable length between the OS-4 base and the SM-7 sensor of about 6 feet.  This is sufficient to place the sensor in a room, and the base unit outside the door with the wire running up the wall, and back down again.  For any other longer purposes longer wire will be required.

Simple telephone wire is used and shipped with the OS-4 sensor.  This is sufficient and will work well for distances up to 100 feet. 

We have tested the accuracy and capabilities of the OS-4 up to and beyond the manufacturer's suggested 100 meters (328 feet) max distance.  In our testing cable lengths greater than 100 feet should use shielded cable with at least a 22 gauge wire.  We have tested an 18 gauge 18-3 high quality shielded cable at distances up to 1,000 feet with good results.  If you are looking at using an OS-4 remote sensor at lengths greater than 100 meters give us a call, we would be glad to help you with your application.


Wireless Monitoring & Data Logging Kit:

Use the Wireless Monitoring & Data logging Kit with your fixed mount monitor to connect it to the internet allowing access from anywhere. Receive Instant notifications with free text and email alerts. This is a great addition for your fixed mount gas detector.


Use this kit to connect your Fixed mount gas detector to the internet allowing remote access from anywhere.


Ozone Information

More Information
Manufacturer Eco Sensors
Call For Price No
Gas Ozone (O3)
Resolution 0.01 ppm
Integrated Relays Yes
Response Time 1 second
Sensor type Heated Metal Oxide (HMOS)
Sampling Method Fan
Operational Temperature Range 35 - 100 deg F
Operational RH Range 0 - 85% RH
Power Requirements 12 VDC with supplied adapter
Size 127 × 64 × 42 mm (5 × 2.5 × 1.625 in).
Field Replaceable Battery No
Warranty 1 Year
Audible Alarm No
Calibration Replace with Pre-Calibrated Sensor Annually
Sensor Life 1 Year
Range 0-10 ppm
Unit Features

-Remote Sensor Standard

-Backlit LCD Display

-3 Integrated Relays

Sensor Range

0-20 ppm

0-50 ppm

Sensor Range

0-20 ppm (O3)

0-50 ppm (O3)

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