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2026-09-09
In chemical, pharmaceutical, food processing, and mining applications, level monitoring in powder silos often presents a difficult selection problem: the device must simultaneously satisfy explosion protection certification for hazardous areas and functional safety integration into Safety Instrumented Systems (SIS) for overfill prevention or dry-run protection.
Explosion protection addresses “not igniting the atmosphere”; SIL certification addresses “acting reliably when required.” Both are essential, but when combined in a single device, selection complexity increases significantly.
Taking dust explosion risk as an example, IEC 60079 classifies hazardous areas into zones (Zone 20/21/22 for dust, Zone 0/1/2 for gas). Different zones require different protection types (e.g., Ex d flameproof, Ex ia intrinsic safety, Ex t enclosure protection). Concurrently, IEC 61508 functional safety requires the device to reliably execute safety actions (e.g., triggering alarms or shutting off feed) upon demand, where the SIL level directly determines the device’s probability of failure on demand (PFD).
Soliphant M FTM50 provides a path to satisfy both certification frameworks.
Not all Ex-certified versions of FTM50 support SIL2 functional safety. Achieving both requires locking down a specific configuration combination.
According to Endress+Hauser’s Functional Safety Data Sheet, SIL2 capability for FTM50 is only valid under the following conditions:
Electronic insert: FEM58 (NAMUR output per IEC 60947-5-6)
Order code: Specific variants (FTM50-xxxxx8xxxRx / xxxxx8xxxSx)
Safety mode: MAX (overfill prevention) or MIN (dry-run protection)
Architecture: 1oo1D (single channel with internal diagnostics and failure output)
In SIL2 configuration, key reliability metrics for FTM50 include:
Probability of Failure on Demand (PFD_av): 2.09 × 10⁻⁴ (T₁ = 1 year)
Safe Failure Fraction (SFF): 91%
Mean Time Between Failures (MTBF_tot): 184 years
This indicates that under low-demand mode requiring annual proof testing, the probability of safety function failure is controlled at an extremely low level, meeting the quantitative requirements for most SIL2 applications.
FTM50 supports multiple explosion protection types, but different types have different process boundaries:
| Protection Type | Applicable Zone | Process Temperature Range | Ambient Temperature Range (FEM58) |
|---|---|---|---|
| Ex d IIC T6...T2 Ga/Gb | Gas Zone 0/1 | -50°C ~ +280°C | -50°C ~ +70°C |
| Ex de IIC T6...T2 Ga/Gb | Gas Zone 0/1 | -50°C ~ +280°C | -50°C ~ +60°C |
| Ex ta IIIC T**°C Da | Dust Zone 20 | -50°C ~ +150°C | Model dependent |
A noteworthy limitation: When selecting FEM58 (mandatory for SIL2) with Ex de flameproof enclosure, the ambient temperature upper limit is +60°C, rather than the standard +70°C. For high-ambient sites (e.g., Middle East summer or near heat sources), this temperature derating must be factored into selection calculations.
Additionally, certain Ex versions support only a 150°C process temperature upper limit. For applications requiring both 280°C medium temperature and specific Ex protection, the relevant Safety Instructions (XA document) must be consulted for verification.
The FEM58 electronic insert includes a test button that simulates fork coverage to verify communication and signal integrity between the sensor and the isolating amplifier without changing actual level. This is particularly valuable for periodic proof testing in SIL2 safety loops.
From a process safety perspective, this self-test function reduces testing costs and improves test frequency feasibility, thereby lowering the cumulative PFD value.
When selecting FTM50 under dual Ex+SIL2 constraints, the following items should be verified:
Hazardous area classification: Confirm dust zone (Zone 20/21/22) vs. gas zone (Zone 0/1/2), or mixed classification
Process temperature vs. Ex version compatibility: Verify whether high-temperature version (280°C) is compatible with selected Ex protection type
Ambient temperature vs. housing type: With FEM58, Ex de version upper limit is 60°C
Order code accuracy: SIL2 capability is code-specific; confirm via Product Configurator
Safety Manual (SD206F) acquisition and adherence: Installation, commissioning, and proof testing must follow the Safety Manual
Soliphant M FTM50 addresses both Ex protection (gas/dust multi-zone) and SIL2 functional safety in a single device, reducing interface count and system complexity. However, precise matching of process parameters, Ex protection type, electronic insert version (FEM58), and order code is essential during selection to achieve the dual objective of “non-igniting protection and reliable safety action” at the installation site.
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