Knowledge / Ex protection
What intrinsic safety means, how to read an ATEX marking, and which isolation stage you need.
Wherever flammable gases, vapours or dusts can occur — biogas plants, solvent processes in pharma, mills, paint shops — the operator classifies the plant into zones. The zone definitions are laid down in Directive 1999/92/EC, Annex I; the assignment of equipment categories to zones is governed by Annex II B of the same directive. The more frequently the explosive atmosphere is present, the higher the requirement placed on the equipment.
Inside fermenters, tanks, vessels
Around filling nozzles, pump rooms
Areas around tight flange connections
The IEC/EN 60079 series defines several types of protection. The three most relevant for instrumentation differ fundamentally in approach:
An internal ignition is permitted — the enclosure withstands the explosion and prevents it from propagating outwards. Robust, but heavy and maintenance-intensive: the circuit must be isolated before every opening.
Typical for motors and high-power switchgear.
Ignition sources such as sparks and hot surfaces are avoided by design — increased clearance and creepage distances, special terminals, over-temperature protection. Applies only to equipment without normal sparking.
Typical for terminal boxes and luminaires.
The electrical energy in the circuit is limited so far that neither sparks nor thermal effects can become ignition-capable — at level of protection “ia” even with up to two countable faults applied (IEC 60079-11:2023, Clause 5.2.2). Work on intrinsically safe circuits is permitted during operation.
Zone 0 requires Category 1 equipment — within intrinsic safety, only level of protection “ia” meets this requirement. The standard in process instrumentation.
Every Ex device carries a standardised marking (Directive 2014/34/EU, Annex II No. 1.0.5, in conjunction with EN IEC 60079-0). Using the RW65_EX_II as an example:
Category 1 with IIC/IIIC is the widest approval a gauge can have: it may be used in any ATEX zone — including where hydrogen or conductive dusts occur.
The identical marking is also carried by the intrinsically safe LED beacon DKL01 — the breakdown applies regardless of device type, from differential pressure gauge to signal beacon.
View DKL01A common misconception: “The device is intrinsically safe, so I can connect it directly.” In fact, the circuit only becomes intrinsically safe through the combination of the field device and the associated apparatus (isolation stage) on the safe side; the formal proof of intrinsic safety is carried out per EN 60079-14, Clause 16. The isolation stage limits voltage and current before the line enters the zone. Three designs are common:
Never connect directly to the power supply — without an isolation stage, ATEX protection is not effective.
When a reliable IS earth exists and cost matters.
The standard route in most new plants — straightforward and robust.
When a supply for the 4–20 mA loop is needed anyway.
Selection is governed by the entity parameters (EN 60079-14, Clause 16; cable parameters per Annex J): Ui ≥ Uo, Ii ≥ Io, Pi ≥ Po; in addition, Ci plus cable capacitance must stay below Co, and Li plus cable inductance below Lo. For the RW65_EX_II: Ui ≤ 30 V DC, Ii ≤ 100 mA, Pi ≤ 620 mW; Ci and Li are negligible — virtually the entire cable allowance of the isolation stage remains available for the line.
In hazardous areas, the mechanical ring-balance principle offers three advantages that electronic sensors cannot provide by design:
The measuring element works purely mechanically — pressure difference against gravity. The element itself cannot generate ignition-capable energy. The built-in loop-powered 2-wire transmitter (4–20 mA) carries only the energy limited by the isolation stage; optionally, the device can be fitted with up to two intrinsically safe NAMUR contacts.
The 150 mm scale works even during a power failure or with the isolation stage disconnected. For visual checks in the Ex zone this means: no transmitter display that needs powering first.
Every recalibration in the Ex zone means a permit process, downtime and documentation. The drift-free mechanical principle extends the intervals considerably — in practice the biggest cost lever.
For context: electronic transmitters for such minimum ranges generally contain sensors designed for much larger ranges (typically 750 to 2,500 Pa upper range limit), whose signal is electronically amplified onto the small measuring range — referred to in data sheets as “turndown”, e.g. 100:1. Accuracy, temperature and stability figures, however, refer to the sensor's upper range limit, not to the configured range: the greater the amplification, the larger these errors become relative to the measuring range.
Based on our market research (as of July 2026), the RW65_EX_II is the only locally readable differential pressure gauge that combines an ATEX Category 1 approval (Zones 0/20, Ex ia) with a native measuring range from 40 Pa. Ex ia transmitters reach comparable spans only via the stretching described above — with long-term stability specified at ±0.1–0.2 % of the cell's upper range limit per year for these minimum ranges; relative to a 40 Pa span, that corresponds to several percent of drift per year and a corresponding recalibration burden.
Intrinsically safe ATEX differential pressure gauge — II 1 GD, Zones 0/1/2 and 20/21/22, ranges from 40 Pa, 4–20 mA passive, up to 2 NAMUR contacts.
The legal and normative basis of this article at a glance:
Liability note: This article is provided for general guidance and replaces neither the operator's risk assessment nor case-by-case verification by qualified personnel. Responsibility for zone classification, equipment selection, installation and operation lies solely with the operator. Despite careful research, we accept no liability for accuracy or completeness; solely the currently valid edition of the directives and standards prevails. As of July 2026.
Zone, measuring range, isolation stage, entity parameters — for applications using our devices we answer sizing questions directly. We do not offer general ATEX consultancy.