Ozone Monitors & Ozone Controllers in South Africa
Fixed ozone monitors that warn your staff before ozone reaches a harmful level, and ozone controllers that switch your ozone generator to hold a room, cold store or duct at the right concentration. Eco Sensors instruments supplied from our Cape Town base to South Africa and neighbouring countries.
What is an ozone monitor? An ozone monitor is a fixed gas detector that continuously measures ozone (O3) in air, in parts per million (ppm) or parts per billion (ppb), and triggers an alarm or relay at a set concentration. An ozone controller adds adjustable set points and relays that turn an ozone generator on and off, so the treated space stays at a target level while people outside it stay below the exposure limit.
Ozone exposure limits in South Africa
Ozone is the reason ozone generators work so well: it is a strong oxidiser that kills bacteria, moulds and odours. The same property irritates the eyes, throat and lungs. Because ozone is used at concentrations well above safe breathing levels, a fixed monitor or controller is the practical way to keep people and process apart.
The Regulations for Hazardous Chemical Agents, 2021 (under the Occupational Health and Safety Act) list ozone in Table 2, Occupational Exposure Limits – Maximum Limits, with a different limit for each workload:
For comparison, the US OSHA permissible exposure limit is 0.1 ppm as an 8-hour average, and NIOSH lists 5 ppm as immediately dangerous to life or health. Outdoors, South Africa’s National Ambient Air Quality Standards set ozone at 120 µg/m³ (61 ppb) as an 8-hour running average.
What this means for instrument choice: every monitor on this page alarms at 0.1 ppm by default, which matches the strictest SA workload limit. The difference between them is what else they do, from a simple wall-mounted alarm to a controller that runs your generator.
Fixed ozone monitors and controllers from Eco Sensors
Four instruments cover the jobs most ozone users need: a low-level safety alarm (C-30ZX), a generator controller for cold stores and HVAC (OS-4), an industrial wash-down controller up to 50 ppm (OS-6), and a stand-alone digital sensor for PLC and building-management integration (SM-500).
C-30ZX Ozone Monitor
Pocket-sized alarm that anyone can read at a glance
The C-30ZX shows ozone on a colour bar graph: green is normal, yellow at 0.05 ppm means caution, and red at 0.1 ppm means danger. An audible alarm and relay contacts switch at 0.1 ppm. Its heated metal oxide (HMOS) sensor responds within tenths of a second of ozone reaching it, so staff get warning of a leak almost immediately. Wall-mount it next to a generator, in a printer room or in a treatment plant control room; there are no controls for staff to adjust.
- Range0.02–0.14 ppm (LED scale); 0.02–0.30 ppm via analog output
- Alarm0.1 ppm standard; adjustable from 0.03 to 0.14 ppm
- SensorHMOS (heated metal oxide semiconductor)
- ResponseWithin tenths of a second
- OutputsLED bar graph, buzzer, 0–3 V analog, alarm relay contacts
- Size / weight85 × 35 × 60 mm / 140 g
- Power12 VDC, 300 mA (AC adapter)
Benefits, warm-up and care
- Monitors continuously; the colour display is understood by non-technical staff.
- Normally needs no installation beyond mounting and power, and virtually no maintenance.
- The 0–3 V output feeds a data logger to record exposure over a shift.
- Allow at least one hour of warm-up on first use; about five minutes is usually enough after that if the unit has been in recent use.
- Eco Sensors recommends a function check every three months and a calibration check once a year.
- Best used indoors; the manual specifies at least 15–27 °C. Protective enclosures with heaters and 4–20 mA outputs are available for harsher locations (ask Ecotao).
OS-4 Ozone Switch
A thermostat for your ozone generator, 0.03–20 ppm
The OS-4 reads ozone from a remote electrochemical sensor module and switches your ozone generator on and off at programmable set points, the way a thermostat controls a heater. The sensor sits in the treated space on a cable while the controller stays outside it. A separate 0.1 ppm LED and relay give a safety alarm. Use it to hold a fruit cold store or ozonated HVAC system at a target level, or as a leak or failure alarm for any size of generator.
- Range0.03–20 ppm
- Accuracy10–15% (depends on application)
- SensorRemote SPEC electrochemical module, T/RH compensated, replaceable and pre-calibrated
- Control relaySPDT non-latching, 5 A at 250 VAC
- Safety alarm0.1 ppm panel LED + SPDT relay (5 A)
- Outputs0–2 V, 4–20 mA, RS-232
- Operating5–40 °C, 20–95% RH
- Size / weight127 × 64 × 42 mm / 200 g
- Power12–24 VDC, 300 mA (AC adapter)
Indicators, connections and notes
- LEDs: green = instrument on, yellow = above 0.1 ppm, red = generator on.
- Terminal blocks for relay output and DC input, plus a 2.5 mm DC jack for the AC adapter.
- Flame-resistant ABS case with mounting ears.
- Replacement sensor modules are small and pre-calibrated, so calibration is kept by exchanging the module.
- The manufacturer’s specification advises against use in the presence of strong acid gases or VOC fumes.
- Imported on order. Ask Ecotao for the current lead time.
OS-6 Industrial Ozone Controller & Monitor
Wash-down rated control up to 50 ppm, with failure alarm
The OS-6 is built for plant rooms, food processing and other wet, industrial locations. Its NEMA 4X polycarbonate enclosure resists water spray, and its backlit display auto-ranges from 0 to 50 ppm. Set MAX and MIN points to control the generator, plus a FAIL time: if ozone stays outside the control band for longer than that, a failure alarm and relay trip. A front-panel cut-off switch isolates the generator for maintenance.
- Display4-digit, 12 mm, backlit, auto-ranging 0–50 ppm
- SensorRemote electrochemical module: 0–20 ppm or 1–50 ppm
- Set pointsMAX, MIN and FAIL time, adjustable from the front panel
- RelaysGenerator control, >100 ppb safety limit, failure to control; 10 A at 25 VDC, 0.25 A at 250 VDC
- Outputs0–2 V and 4–20 mA (selectable full scale), RS-232 9600 8N1
- EnclosureWall-mounted polycarbonate, NEMA 4X
- Size160 × 166 × 118 mm (H × W × D)
- Power12–24 VDC in; +5 or +12–24 VDC out to sensor
Indicators, inputs and sensor options
- LED indicators: sensor, above MAX, below MIN, >100 ppb, generator on, failure.
- Generator-enable input (contact closure) lets a timer or BMS permit ozone generation.
- Relay rating also listed as 2.0 kVA AC (resistive).
- Sensor module: the SM-500/RME is the manufacturer’s current module in both 0–20 ppm and 1–50 ppm ranges. Existing SM-7/SM-EC modules remain compatible.
- Imported on order. Ask Ecotao for the current lead time.
SM-500 Electrochemical Ozone Sensor
Digital ozone sensor for PLC, BMS or the OS-4 / OS-6
The SM-500 is a calibrated electrochemical ozone sensor with its own replaceable RME-O3 sensing module. Wire it to an OS-4 or OS-6 as the remote sensor, or use it on its own and read ozone over RS-232 or USB into a PLC, building-management system or PC. It detects from 30 ppb with 5 ppb resolution, has little to no cross-sensitivity to VOCs, and a re-zero button for field checks.
- Range0–20 ppm or 1–50 ppm (choose when ordering)
- Detection / resolution30 ppb lower limit / 5 ppb
- SensorElectrochemical, user-replaceable RME-O3 module, T/RH compensated
- CommunicationRS-232 and USB (USB also powers it)
- Power5–30 VDC, <100 mA
- Works withOS-4, OS-6, or stand-alone
Typical applications
- Laundries using ozone and ozonated public areas.
- Agricultural and cold storage areas, farms.
- Food processing plants and large, noisy factories where a remote alarm panel or BMS alert is needed.
Ozone monitor comparison table
← Scroll to see full table →
| Feature | C-30ZX | OS-4 | OS-6 | SM-500 |
|---|---|---|---|---|
| Main job | Safety alarm | Generator control + alarm | Industrial control + failure alarm | Digital sensor / stand-alone |
| Range | 0.02–0.14 ppm (LED); 0.02–0.30 ppm (output) | 0.03–20 ppm | 0–20 or 1–50 ppm (module) | 0–20 or 1–50 ppm |
| Sensor type | HMOS | Electrochemical (remote) | Electrochemical (remote) | Electrochemical |
| Display | Colour LED bar graph | Digital readout + LEDs | Backlit 4-digit, auto-ranging | None (data via RS-232 / USB) |
| 0.1 ppm safety alarm | Yes (buzzer + relay) | Yes (LED + relay) | Yes (>100 ppb relay) | Via host system |
| Generator control | Relay contacts only | Yes, on/off set points | Yes, MAX/MIN + FAIL time | Via OS-4 / OS-6 or PLC |
| Analog output | 0–3 V | 0–2 V, 4–20 mA | 0–2 V, 4–20 mA | Ask Ecotao |
| Digital output | Ask Ecotao | RS-232 | RS-232 | RS-232, USB |
| Enclosure | Compact case | Flame-resistant ABS | NEMA 4X polycarbonate | Compact module |
| Power | 12 VDC | 12–24 VDC | 12–24 VDC | 5–30 VDC or USB |
| Best for | Printer rooms, plant rooms, labs | Cold stores, HVAC, generator rooms | Wash-down, food plants, high ppm | BMS / PLC integration, retrofits |
HMOS vs electrochemical ozone sensors: what is the difference?
Ozone monitors use one of a few sensing methods. The two on this page work differently, and that decides where each one belongs.
← Scroll to see full table →
| HMOS (heated metal oxide) | Electrochemical | |
|---|---|---|
| How it works | Ozone changes the electrical resistance of a heated metal oxide film. | Ozone reacts at an electrode and produces a current proportional to concentration. |
| Used in | C-30ZX | SM-500 (with OS-4 and OS-6) |
| Strength | Very fast response at low levels; ideal for a safety alarm | Wide range (to 20 or 50 ppm), T/RH compensated, little VOC cross-sensitivity |
| Watch out for | Chlorine and other halogens, sulfur compounds, NOx, ammonia and acid gases can affect readings; needs warm-up | Sensor module has a working life and is replaced to maintain calibration |
| Choose it when | You need to know quickly that ozone has escaped into a work area | You need to control a generator or measure the higher levels inside a treated space |
Need a reference-grade reading for validation, or a portable instrument for spot checks? UV absorption analysers and handheld ozone meters are covered on our Ozone in Air page.
How to choose an ozone monitor
Answer three questions: who or what are you protecting, what concentration will the sensor see, and does the instrument need to control anything?
-
I need to warn staff if ozone leaks into a room
The sensor will see clean air most of the time, and you need fast warning at 0.05–0.1 ppm. No control is needed.
Choose: C-30ZX -
I need to run an ozone generator in a cold store, room or HVAC duct
The sensor sits in the treated space at levels up to 20 ppm, and the instrument must switch the generator at set points.
Choose: OS-4 (with SM-500 0–20 ppm module) -
My site is wet, washed down, or runs above 20 ppm
You need a sealed enclosure, a clear display, and an alarm if the generator fails to reach or hold the target.
Choose: OS-6 (0–20 or 1–50 ppm module) -
I want ozone data in my PLC, SCADA or BMS
You already have a controller or alarm panel and need a calibrated digital ozone signal, or you are replacing an old SM-7/SM-EC module.
Choose: SM-500
Tip: most ozone installations need both. A controller (OS-4 or OS-6) inside the treated area, and a C-30ZX safety monitor in the adjoining work area or corridor where people are, gives you process control and staff protection from separate sensors.
Where ozone monitors are used in South Africa
Fruit cold stores and pack-houses
Ozone is used in cold stores to reduce mould and ethylene on stored fruit and vegetables. In South Africa’s fruit export cold chain, an OS-4 holds the store at its target level while a C-30ZX outside the door warns staff before they enter.
Water and wastewater treatment
Ozone generators, contact tanks and off-gas destructors can leak. A C-30ZX in the generator room gives an immediate alarm, and its relay can shut the generator down. See our ozone water treatment page.
Food and beverage processing
Ozonated wash water and room sanitation create wet areas with variable ozone levels. The OS-6’s NEMA 4X enclosure and failure-to-control alarm suit these wash-down environments.
Ozonated laundries, hotels and HVAC
Ozone laundry systems and ozone injected into HVAC ducts need control at the source and assurance in occupied spaces. The SM-500 sends readings to the building-management system; the OS-4 controls the generator.
Printer, photocopier and UV rooms
Laser printers, photocopiers and some UV lamps produce ozone. A C-30ZX mounted in the room shows staff the level on a simple colour bar and alarms at 0.1 ppm.
Labs, pilot plants and fumigation
Research labs and fumigation projects run short, high-concentration ozone treatments. An OS-6 with a 1–50 ppm module controls the treatment, and a C-30ZX outside confirms the area is safe to re-enter.
How to install and look after an ozone monitor
- Safety monitors in the breathing zone. Mount the C-30ZX where people work, near likely leak points such as the generator, injector or destruct unit.
- Control sensors inside the treated space. Place the OS-4 or OS-6 sensor module where it reads the room concentration, not directly in the generator outlet plume. Keep the controller itself outside the high-ozone area.
- Keep sensors dry and clean. Avoid direct spray, condensation, chlorine and acid fumes. Use a protective enclosure where splashing is possible.
- Wire the safety relay to the generator. Use the 0.1 ppm relay on any of the instruments to cut the generator or start ventilation automatically.
- Allow warm-up. Give a C-30ZX at least one hour on first use before relying on readings.
- Check and calibrate. Function-check the C-30ZX every three months and have its calibration checked yearly. For the OS-4, OS-6 and SM-500, replace the pre-calibrated sensor module as needed to maintain calibration.
Ozone monitor questions
What is an ozone monitor?
An ozone monitor is a fixed instrument that continuously measures the concentration of ozone (O3) gas in air, usually in ppm or ppb, and raises an alarm or switches a relay when a set level is reached. It protects people where ozone is generated or used, and controls ozone generators so the treated space stays at the intended concentration.
What is the safe limit for ozone in the workplace in South Africa?
The Regulations for Hazardous Chemical Agents, 2021 (Table 2, Occupational Exposure Limits – Maximum Limits) set ozone limits by workload: 0.1 ppm for heavy work, 0.16 ppm for moderate work, 0.2 ppm for light work, and 0.4 ppm for exposures of less than 2 hours at any workload. The 0.1 ppm level is also the US OSHA 8-hour limit and the default alarm point on Eco Sensors monitors.
What is the difference between an ozone monitor and an ozone controller?
An ozone monitor measures and alarms; its job is to warn people. An ozone controller also measures, but uses set points and relays to switch an ozone generator on and off so a room, cold store or duct is held at a target concentration. The C-30ZX is a monitor. The OS-4 and OS-6 are controllers that also give a 0.1 ppm safety alarm.
Which is better for ozone detection, an HMOS sensor or an electrochemical sensor?
Neither is better for every job. A heated metal oxide semiconductor (HMOS) sensor, as in the C-30ZX, responds within fractions of a second and suits low-level alarm monitoring around 0.02–0.3 ppm, but it can react to chlorine, NOx, ammonia, sulfur compounds and acid gases. An electrochemical sensor, as in the SM-500 module used with the OS-4 and OS-6, covers a much wider range (up to 20 or 50 ppm), is temperature and humidity compensated, and has little to no cross-sensitivity to VOCs, which makes it the choice for generator control and high-concentration treatment areas.
Which ozone monitor do I need for a fruit cold store or ozonated HVAC system?
Use the OS-4 Ozone Switch. Eco Sensors lists ozone monitoring in fruit, vegetable and agricultural storage and in ozonated HVAC systems as typical OS-4 applications. Its sensor module sits in the treated space on a cable while the controller stays outside it, and its relay switches the ozone generator at your set points between 0.03 and 20 ppm. For wash-down areas or concentrations up to 50 ppm, choose the OS-6 with a 1–50 ppm sensor module.
How often does an ozone monitor need calibration?
For the C-30ZX, Eco Sensors recommends a function check every three months (more often in dusty, halogen-rich or spray-exposed areas) and a calibration check once a year. The OS-4, OS-6 and SM-500 use replaceable pre-calibrated sensor modules, so calibration is maintained by exchanging the module rather than recalibrating on site.
Can I still use my SM-7 / SM-EC sensor module with an OS-4 or OS-6?
Yes. The SM-7/SM-EC electrochemical module is compatible with the OS-4 and OS-6. The manufacturer has since named the SM-500/RME module as its replacement, and the SM-500 is the current sensor for new OS-4 and OS-6 installations. Contact Ecotao to match a replacement module to your existing controller and range.
Where should an ozone sensor be mounted?
For worker protection, mount the sensor in the breathing zone where people work and close to likely leak points such as the ozone generator, injector or contact tank. For generator control, place the sensor module inside the treated space away from the direct outlet of the generator so it reads the room concentration, not the plume. Keep sensors dry and away from spray, chlorine and acid fumes.
Does Ecotao deliver ozone monitors outside South Africa?
Yes. Ecotao supplies ozone monitors and controllers from Cape Town throughout South Africa and to Namibia, Botswana, Zimbabwe, Mozambique, Lesotho and Eswatini. The OS-4 and OS-6 are imported on order; contact Ecotao on +27 21 911 5835 or sales@ecotao.co.za for current lead times.
Not sure which ozone monitor fits your site?
Tell us what you are treating, the size of the space and the ozone generator you use, and we will recommend a monitor, controller and sensor range. Supplied across South Africa and neighbouring countries.
- Head Office+27 21 911 5835
- Zak086 142 8716
- Zaid082 390 3989
- Emailsales@ecotao.co.za
aqua@ecotao.co.za