ATEX vibration sensors for hazardous areas

Explosion-protected versions in the catalogue

• Intrinsically safe accelerometers (Ex i) — AC accelerometer versions (100 mV/g as standard), including HS-100I, HS-150I and HS-170I, side-exit versions (e.g. HS-100IS), and triaxial (HS-173I), high-temperature (HS-105I) and low-power (HS-104I) versions. Category: accelerometers for Ex zones.

• Intrinsically safe 4–20 mA transmitters — vibration velocity (HS-420I/M), acceleration (HS-422I/M), versions with an additional AC output (HS-421I) and with a temperature output (HS-420IT, HS-422IT). Category: intrinsically safe 4–20 mA transmitters.

• Ex tb — an accelerometer with protection by enclosure, designed for dust zones (HS-150tb).

• Ex d — a 4–20 mA transmitter with a flameproof connection head (HS-420d).

• Accessories — intrinsically safe connection boxes and an intrinsically safe display unit with a vibration switch function (HS-517I) for HS-420I and HS-422I series sensors.

The manufacturer offers intrinsically safe versions with ATEX certification, and some of them also with IECEx certification. The scope of approval of a specific model — Ex marking, ambient temperature range and circuit parameters — is given in its specification and certificate.

How to recognise an Ex version

In the model designation, an intrinsically safe version is identified by the letter “I” (e.g. HS-100I), or by “IS” in side-exit versions (e.g. HS-150IS). In the product specifications, check the “Hazardous-area version” and “Approvals and certificates” entries, and in the “Documentation” section, the datasheet with the explosion protection marking.

Choosing a sensor for the zone, step by step

1. Establish the zone (0, 1, 2 for gases; 20, 21, 22 for dusts) on the basis of the plant documentation.

2. Determine the required equipment category or equipment protection level (EPL), the gas or dust group and the temperature class.

3. Check the ambient temperature at the mounting point — including heat from the machine — and compare it with the Ta range in the sensor marking.

4. Choose the signal type: AC (IEPE) for vibration analysis or 4–20 mA for the control system.

5. Select a Zener barrier or galvanic isolator with parameters that match the sensor certificate — with a separate channel for each measurement chain.

6. Check the cable parameters and length, as well as the requirements for cable glands and connections.

7. Gather the documentation: certificates, declarations of conformity, datasheets and manuals.

Signal selection in an Ex zone follows the same rules as outside it: intrinsically safe 4–20 mA transmitters send the overall vibration value to the DCS or PLC, while intrinsically safe AC accelerometers send the full signal for analysis. If you need both, the HS-421I combines a 4–20 mA output with an AC signal in one sensor; how both signals are connected through barriers is specified in the certificate and the manufacturer’s instructions.

We explain zones, categories, intrinsic safety and the matching of circuit parameters in the guide Vibration sensors in hazardous areas.

Barriers and cabling

An intrinsically safe sensor operates in a circuit with associated apparatus — a Zener barrier or a galvanic isolator — located outside the hazardous area or in a suitable enclosure. The barrier’s output parameters must be compatible with the sensor’s input parameters, and the capacitance and inductance of the cable limit its permissible length. The barrier must also suit the signal type — powering an IEPE accelerometer has different requirements from a 4–20 mA loop.

The manufacturer provides guides on safety barriers and on the maximum cable length for intrinsically safe versions. You will find them with the products, in the “Documentation” section, and in the document library.

Documentation

The “Documentation” section of each product page contains datasheets (in metric and imperial units) and, for Ex versions, usually also manuals, system diagrams and the manufacturer’s guides. Certificates and other manufacturer documents are collected in the document library. Most documents are in English. If you need a document for a specific model that is not available with the product, write to us using the contact form.