The R. STAHL 8146/5 series comprises safety temperature monitors (STW) and limiters (STB) for deployment in explosion-hazardous areas of Zones 1, 2, 21, and 22. Unlike electronic temperature controllers, the 8146/5 operates on a purely mechanical fluid-filled capillary measuring system: a temperature-induced volume change of the filling fluid drives a change-over contact directly, without any embedded processor or software. This principle eliminates systematic software-related failure modes and provides an inherently safe shut-down function for critical process protection.

Working Principle

• Fluid-Filled Measuring System: A fluid-filled capillary sensor detects temperature changes. Volume expansion or contraction of the fluid mechanically actuates a change-over contact.
• Limiter (STB) vs. Monitor (STW): When the preset limit is exceeded, the limiter disconnects and remains latched; manual unlocking is required. The monitor disconnects on exceedance but automatically resets when the temperature returns within the permissible range.
• Self-Monitoring on Leakage: If the fluid-filled measuring system develops a leak, the device permanently disconnects the circuit and prevents reconnection until the fault is physically rectified.
• Setpoint Visibility: The limit value is adjustable via a setpoint adjuster on the device and can be read externally through a sight glass.

Certifications & Hazardous Zones

• ATEX Gas: II 2 G Ex db eb IIC T6 Gb (Zones 1 & 2)
• ATEX Dust: II 2 D Ex tb IIIC T80 °C Db (Zones 21 & 22)
• IECEx Gas: Ex db eb IIC T6 Gb (IECEx PTB 06.0090)
• IECEx Dust: Ex tb IIIC T80 °C Db
• Certification Bodies: PTB (ATEX/IECEx), NEPSI (China), PESO (India)

Technical Data

• Switching Capacity: Up to 25 A at AC 24 V rated operational voltage
• Measurable Temperature Range: -60 °C to +345 °C (sensor-dependent)
• Ambient Operating Temperature: -20 °C to +50 °C
• Enclosure: Ex e increased safety, Series 8146
• Ingress Protection: IP54 / IP55 / IP56 / IP64 / IP65 / IP66 (depending on configuration)