Ex-Proof Temperature & Humidity Sensors
Safe Measurement for Air Ducts and Industrial Areas with Explosion Risk
Ex-Proof Temperature & Humidity Sensors are industrial measuring devices that continuously measure temperature and relative humidity values in air ducts or controlled process environments and transmit them to automation systems.
In areas where explosive gases, vapours or combustible dust may be present, special transmitter models with ATEX or IECEx certification and flameproof or intrinsically safe protection principles can be used.
The duct-type probe design allows the sensing element to be positioned inside the airflow. Measured temperature and humidity values can be transmitted to a PLC, DCS or building management system via 4–20 mA, 0–10 V or an appropriate digital communication protocol.
ATEX / IECEx Options
Certified product configurations suitable for areas containing explosive gases or combustible dust can be provided.
Duct-Type Probe
The probe extends into the air duct to measure air temperature and relative humidity directly.
IP66 / IP67 Enclosure
High protection against dust, humidity and water exposure can be achieved with suitable enclosures and cable entries.
Automation Integration
Connection to PLC, DCS and building management systems is possible through analogue or digital outputs.
What Is an Ex-Proof Temperature and Humidity Sensor?
Ex-proof temperature and humidity sensors are transmitters designed to safely measure ambient temperature and relative humidity values in hazardous areas where an explosive atmosphere may occur.
Unlike standard field transmitters, the device enclosure, electrical connections, energy levels, surface temperature and cable entries are designed and certified for hazardous-area use.
While the measuring probe is inserted into the air duct, the electronic transmitter enclosure can remain outside the duct. This allows temperature and humidity to be measured inside the duct while electrical connections are kept within a protective enclosure.
How Do Temperature and Humidity Sensors Work?
The Probe Is Installed in the Air Duct
The measuring probe is mounted at a suitable point that represents the airflow within the duct.
Temperature and Humidity Are Detected
The sensing element continuously measures air temperature and relative humidity.
Converted into a Measurement Signal
The electronic circuit converts the measured values into an analogue or digital output signal.
Transferred to Automation
Temperature, humidity and device status information are transmitted to the control system for monitoring and recording.
Ex-Proof Protection Options
Electronic components are housed in a certified enclosure designed to limit the spread of an ignition occurring inside the enclosure to the external environment. The permitted zone is determined by the device’s Ex marking.
Electrical energy supplied to the field is limited to a level that will not cause ignition through sparking or heating. It should be used with a suitable Zener barrier or galvanic isolator.
Terminals, connection elements and cable entries are arranged to reduce the risk of arcing or excessive temperature during normal operation.
Certified models suitable for Zone 20, Zone 21 or Zone 22 applications can be selected with dust-tight enclosures and controlled surface temperature.
Hazardous Area Zone Classification
| Environment Type | Zone | General Definition | Selection Note |
|---|---|---|---|
| Gas and vapour | Zone 0 | Areas where an explosive atmosphere is present continuously or for long periods. | A specially certified model with an equipment protection level suitable for Zone 0 is required. |
| Gas and vapour | Zone 1 | Areas where an explosive atmosphere may occur during normal operation. | Flameproof or suitable intrinsically safe devices may be used. |
| Gas and vapour | Zone 2 | Areas where an explosive atmosphere is not expected during normal operation or occurs only for a short time. | The category and protection level on the device label must be verified. |
| Combustible dust | Zone 20 | Areas where a cloud of combustible dust is present continuously or for long periods. | A certified model suitable for the highest level of dust protection is required. |
| Combustible dust | Zone 21 | Areas where a combustible dust atmosphere may occur during normal operation. | The dust group and permitted surface temperature must be checked. |
| Combustible dust | Zone 22 | Areas where a combustible dust atmosphere may occur infrequently or for short periods. | The device’s dust protection marking must be suitable for the area classification. |
General Technical Features of Temperature and Humidity Sensors
| Technical Feature | Option / Construction | Description |
|---|---|---|
| Measured parameters | Temperature and relative humidity | Two separate measurement outputs can be provided in a single sensor enclosure. |
| Mounting type | Duct type or ambient type | The duct probe should be selected at a length suitable for ambient conditions. |
| Enclosure material | Cast aluminium or 316L stainless steel | Selected according to corrosion, chemical environment and washdown conditions. |
| Protection rating | IP66 or IP67 options | The final rating must be verified against the product data sheet and installation method. |
| Hazardous-area certification | ATEX or IECEx | The device certificate, label marking and certificate schedules should be reviewed together. |
| Protection principle | Flameproof or intrinsically safe | The selected model’s suitability for zone, gas group and temperature class must be verified. |
| Analogue output | 4–20 mA or 0–10 V | Separate outputs can be used for temperature and humidity. |
| Digital communication | Digital protocol depending on model | Enables data transfer to PLC, DCS or building management systems. |
| Probe material | Stainless steel | Should be suitable for in-duct temperature, humidity and chemical conditions. |
| Probe length | According to project and duct dimensions | The probe tip should reach a representative airflow within the duct cross-section. |
| Sensor protective element | Sintered metal filter | Protects the sensor from particles and mechanical effects; it does not replace Ex certification on its own. |
| Cable entry | Certified Ex cable gland | The gland should be compatible with the cable type, enclosure protection and Ex marking. |
Measuring range, accuracy, response time, supply voltage, output signals and Ex certificate marking vary according to the selected product model. Final technical specifications should be verified through the manufacturer’s certificate and technical data sheet.
Gas Group and Temperature Class Selection
The suitability of equipment for IIA, IIB or IIC gas groups should be determined according to the ignition characteristics of the flammable gas or vapour present on site.
The device’s permitted maximum surface temperature should be safely below the ignition temperature of the flammable substance present in the environment.
The permitted ambient temperature range stated on the certificate should be compatible with the site temperatures where the device will be installed.
In combustible dust applications, the conductive or non-conductive dust classification, minimum ignition temperature and dust layer conditions should be assessed.
Installation and Electrical Connection
A certified gland suitable for the enclosure’s Ex protection type, IP rating and cable construction should be used at cable entries.
In intrinsically safe circuits, the field device should be powered through a Zener barrier or galvanic isolator compliant with certificate parameters.
Enclosure earthing, shielding and equipotential bonding should be completed in accordance with product instructions and the site electrical design.
The probe should be installed at a suitable distance from elements such as elbows, dampers, fans and heaters that may disturb the flow or temperature profile.
The connection between the probe flange and the duct should be sealed to suit process and hazardous-area conditions.
A flameproof enclosure cover must not be opened while energised or when a hazardous atmosphere is present. Manufacturer safety instructions must be followed.
Application Areas for Temperature and Humidity Sensors
Advantages of Temperature and Humidity Sensors
Temperature and Humidity Sensor Selection Criteria
Technical Selection and Safety Note
Describing a device only as “Ex-proof” does not mean that it can be used in every hazardous area. The device zone classification, equipment protection level, gas or dust group, temperature class and ambient temperature range must be evaluated together with the site classification.
Equipment to be used in Zone 0 applications must be explicitly certified for that zone. While flameproof enclosure models are commonly used in Zone 1 and Zone 2 applications, suitable intrinsically safe measuring circuits may be preferred for Zone 0.
A sintered metal filter can protect the sensor from particles and mechanical effects; however, it does not make the device explosion-protected on its own. Ex compliance is determined by the complete device design and certification scope.
Installation, commissioning and maintenance must be carried out by trained and authorised personnel for hazardous areas in accordance with the product certificate and installation instructions.
Get Technical Support for Temperature and Humidity Sensor Selection
Sensor selection should be based on site zone classification, gas or dust group, temperature class, measuring range, probe length and automation infrastructure.
You can receive technical information about ex-proof duct-type temperature and humidity transmitters, certified cable glands, galvanic isolators, Zener barriers and automation integration.
