The Fischer Mess DS21010A21BK0W00U0700 is a heavy-duty industrial safety differential pressure switch belonging to the specialized DS21 Series engineered and manufactured by FISCHER Mess- und Regeltechnik GmbH (Germany) – a world-renowned leader in instrumentation for high-temperature and safety-critical process installations. The DS21 series is purpose-engineered to provide fail-safe differential pressure monitoring and limit switching across severe liquid thermal loops, notably high-pressure hot water systems and organic heat transfer fluid circuits (thermal oil).

The instrument features a heavy-duty metallic measuring chamber built to withstand high static operating pressures (PN16 / PN25) and severe thermal conditions, coupled with a high-endurance measuring diaphragm calibrated for a 0..0.6 bar (0..60 kPa / 0..600 mbar) differential pressure span. Diaphragm deflection is mechanically coupled to two independent microswitches (2 x SPDT potential-free changeover contacts), allowing two individually adjustable setpoints across the measuring range (e.g., Switch 1 for early warning on reduced flow or filter loading, and Switch 2 for safety shutdown of burners and circulation pumps to prevent pipeline overheating). Configured with a dedicated wall-mounting assembly, model DS21010A21BK0W00U0700 holds TÜV Component Type-Test certification conforming to DIN 4754, DIN EN 12952, DIN EN 12953, and satisfies functional safety requirements up to SIL 2 (IEC 61508 / EN 50156). Enclosed in an IP65-rated housing, it serves as the ultimate safety device for thermal oil boiler rooms, district heating substations, and industrial heat exchangers.

• Manufacturer: FISCHER Mess- und Regeltechnik GmbH
• Brand Origin: Germany
• Full Order Code: DS21010A21BK0W00U0700
• Product Classification: Industrial Safety Differential Pressure Switch for Hot Water & Thermal Oil (DS21 Series)
• Safety Function: Differential pressure monitoring, minimum circulation flow protection, and burner/pump safety interlock
• Standards & Safety Approvals:
  - Functional Safety Certification: SIL 2 capable (Safety Integrity Level conforming to IEC 61508 / EN 50156)
  - TÜV Component Type-Tested according to DIN 4754 (Heat transfer installations operating with organic heat transfer fluids)
  - Compliant with industrial boiler safety standards DIN EN 12952 / DIN EN 12953 / DIN EN 12828
• Compatible Media: High-temperature hot water, boiler feedwater, thermal oil (organic heat transfer fluids, synthetic/mineral thermal oils), glycol solutions, and compatible high-temperature industrial fluids
• Measuring & Switching Range: 0 to 0.6 bar (0 to 60 kPa / 0 to 600 mbar)
• Switching Outputs: 2 independent microswitches (2 x SPDT potential-free changeover contacts)
• Switching Operation: Individually adjustable setpoints across the span for dual-stage control (Pre-alarm / Safety trip)
• Contact Electrical Rating: 250V AC, 5A / 24V DC, 3A
• Switching Reproducibility / Accuracy: ≤ ±1.5% to ±2.0% of full scale (F.S.)
• Nominal Static Operating Pressure: Up to 16 bar / 25 bar (PN16 / PN25 rating)
• Overpressure Safety Limit: Unilateral overpressure protected up to nominal static chamber pressure without damaging the diaphragm
• Process Pressure Connections: Female thread G 1/4 (standard industrial port spacing)
• Diaphragm Material: Stainless steel or high-temperature engineered elastomer
• Measuring Chamber Material: High-strength ductile iron, heat-resistant steel, or coated die-cast alloy
• Mechanical Mounting: Wall-mounting configuration (integrated mounting bracket)
• Electrical Connection: Internal terminal strip with watertight industrial cable gland (PG / M20)
• Enclosure Protection Rating: IP65 conforming to EN 60529 (Total dust ingress prevention and resistance against water jets)
• Permissible Medium Temperature: Up to 200°C – 350°C (when utilized with appropriate cooling coils/siphon loops)
• Operating Ambient Temperature: -10°C to +70°C
• Industrial Applications: Minimum circulation flow surveillance in thermal fluid boilers, dry-run protection in industrial steam systems, district heating heat exchanger differential monitoring, dual-stage hot oil filter clogging detection, and burner management safety interlocks