Industrial CO2 Sensors & Transmitters

• A CO2 monitor displays the reading on the device itself for a person to read. It works standalone and does not need to be wired into anything. The COMET T5000 and U8415 are monitors.
• A CO2 transmitter converts the reading into a standard signal — 4-20mA, 0-10V, RS232 or RS485 — for a PLC, building management system or controller to act on. A display is optional. Most of this range are
transmitters.
• A CO2 sensor is the general term. On this range it usually means a networked unit (Ethernet, PoE or WiFi) that publishes readings to software or a browser rather than down a signal wire.
• Relay-output models sit slightly apart: they act on the reading themselves, switching a fan, damper or alarm directly at a set threshold with no controller in between.

If you only need to see the number, buy a monitor. If something else needs to act on the number, buy a transmitter or a networked sensor. Note that these are complete instruments — PST does not supply bare OEM sensing modules for embedding into your own product.

• 4-20mA — the default for long cable runs and electrically noisy plant rooms, because a current loop is unaffected by voltage drop over distance. T5140, T5141, T5145, T8148.
• 0-10V — simpler and cheaper over short runs to a controller in the same room or panel. T5240, T5241, T5245.
• RS485 — a multidrop digital bus, so several devices share one cable pair and each is individually
addressable. T5440, T5441, T6445, H5421, H5424, H6420.
• RS232 — point-to-point serial to a single device or PC. T5340, T5341, T6340, H5321, H5324, H6320.
• Ethernet or PoE — where the device should sit on the building network and be read by software or a web browser. PoE also removes the need for a separate power run. T5540, T5541, T5545, T5640, T5641, T6540, T6541, T6545, T6640, T6641, H5521, H5524, H6520.
• WiFi — retrofit installations where no cable can be run. W4710, W5714.
• Relay only — where there is no controller at all and the sensor must switch ventilation or an alarm directly. H5021, H5024.

If you are not sure, tell us what the sensor is connecting to and we will confirm the right output before you order.

• Outdoor air sits at roughly 400-420 ppm. That is the practical floor for any indoor reading.
• Below 800 ppm — well ventilated.
• 800 to 1,000 ppm — generally acceptable for occupied offices and classrooms.
• Above 1,000 ppm — the most widely used trigger to increase ventilation, and around the point where complaints of stuffiness and drowsiness typically begin.

It is worth separating comfort from compliance. Safe Work Australia’s workplace exposure standard for carbon dioxide is far higher — 5,000 ppm as an 8-hour time-weighted average and 30,000 ppm short-term. Those are asphyxiation-risk limits, not air-quality targets: an office sitting at 2,000 ppm is legally compliant and still ventilating badly. For occupant wellbeing and productivity, design to the 800-1,000 ppm band, not to the exposure standard.

For a concrete reference point, the COMET U8415’s factory traffic-light thresholds are green up to 1,000 ppm, amber from 1,001 to 1,400 ppm, and red above 1,400 ppm. Demand-controlled ventilation systems usually modulate against a setpoint in the same band, and PST’s relay-output models (H5021, H5024) can switch a fan or damper directly at a configurable threshold without a controller.

Every CO2 device on this page uses NDIR — non-dispersive infrared. It works by measuring how much infrared light at CO2’s absorption wavelength is absorbed as air passes through the optical path. Nothing is consumed in the measurement, and that single fact drives the practical differences: long-term stability with low drift, a service life measured in years rather than months, and no scheduled cell replacement.
Electrochemical cells work by reacting with the target gas, so they are gradually consumed and need periodic replacement. They remain the right technology for gases NDIR cannot see — carbon monoxide, hydrogen sulphide, oxygen — which is why PST’s gas detection products sit in a separate category. For a fixed installation in a duct or on a wall that has to run unattended for years, NDIR is the correct choice, and it is why the entire range uses it.

No. Every product on this page measures gaseous CO2 in air, reported in ppm. Dissolved CO2 measurement — carbonation levels in beer, wine or soft drink, usually expressed in g/L or volumes — is a different instrument class using inline or immersion probes, and PST does not stock it.
If what you actually need is to monitor CO2 gas in a brewery, cellar, cool room or bottling hall — for staff safety or leak detection rather than product quality — then the products on this page are appropriate, and the extended-range 0-10,000 ppm models are usually the right starting point.

No. Carbon dioxide (CO2) and carbon monoxide (CO) are different gases and require different sensing technology. Everything on this page is NDIR CO2 only and will not respond to CO.
Carbon monoxide is acutely toxic and needs a dedicated detector — see PST’s gas detection range. Where a site needs both, such as a car park, plant room or any space with combustion equipment, they are two separate devices, not one dual-gas unit.