The Towa Seiden PRL-S7 Compact Paddle Type Level Switch, manufactured by Towa Seiden Industrial Co., Ltd. (Japan), is a next-generation point level detection instrument specifically engineered for space-constrained bulk handling applications. Built upon the precision electromechanical engineering of the acclaimed PRL product ecosystem, the PRL-S7 model features a significantly downscaled enclosure footprint while delivering uncompromising industrial robustness. It is widely specified on plastic injection molding machine hoppers, vacuum dehumidifying resin dryers, mini powder blenders, packaging funnels, and automated dosing chutes.

The operational mechanism of the Towa Seiden PRL-S7 utilizes an electromechanical torque-reaction principle with integrated motor overload protection:
- Under unconstrained conditions (when bulk material has not reached the sensing paddle): A low-speed internal synchronous motor drives the paddle continuously at approximately 1 revolution per minute (RPM).
- When bulk material rises and restricts paddle rotation: The mechanical drag exerted by surrounding granules or powder arrests paddle rotation. The resulting reactive torque causes the suspended motor assembly to rotate slightly around its axis, tripping an integrated SPDT microswitch (rated 250V AC, 3A / 5A) to actuate high-level alarms or stop upstream feeding conveyors; concurrently, a secondary contact automatically de-energizes the drive motor. By eliminating electrical power while the paddle remains stalled in material, motor coil burnout is entirely avoided.
- When the material level falls (releasing the paddle): A precision return spring pulls the motor assembly back to its starting position, resetting the SPDT microswitch contacts and restoring electrical power to resume paddle rotation.

A distinct technical feature of the PRL-S7 is its internal adjustable return spring mechanism with multiple tension settings, allowing technicians on-site to calibrate sensing sensitivity to match varying apparent material densities (from lightweight fluffy powders to dense plastic pellets). The drive shaft and sensing paddle are fabricated from high-grade SUS304 (AISI 304) stainless steel, ensuring high abrasion resistance and zero media contamination. The upper enclosure is cast from high-pressure aluminum alloy (ADC12) finished with electrostatic powder coating, providing IP65 dust and water ingress protection. Featuring an industry-standard R 3/4" (PT 3/4") process mounting thread, the Towa Seiden PRL-S7 represents a benchmark solution for automated machinery and packaging lines.

• Manufacturer: Towa Seiden Industrial Co., Ltd.
• Country of Origin: Japan
• Complete Part Number: Towa Seiden PRL-S7
• Product Category: Compact Rotary Paddle Level Switch
• Operating Principle: Electromechanical torque-reaction with automatic motor cut-off
• Supply Voltage Ratings: 100V AC, 110V AC, 200V AC, 220V AC (50/60 Hz) or optional 24V DC
• Power Consumption: Approximately 1.5 W to 2.5 W
• Paddle Rotational Speed: Approximately 1.0 RPM (at 50 Hz) / 1.2 RPM (at 60 Hz)
• Electrical Output Contact: 1 SPDT microswitch (Single-Pole Double-Throw)
• Contact Current Rating: 250V AC, 3A / 5A (Resistive load)
• Detectable Bulk Density: From 0.2 g/cm³ or greater (Adjustable sensitivity via internal spring settings)
• Mechanical Process Connection: Male thread R 3/4" (PT 3/4") (Optional NPT or G threads upon request)
• Standard Immersion Length (L): 85 mm (Measured from thread hex shoulder to paddle tip) or custom extended
• Paddle Configuration: Standard single-vane or folding paddle in SUS304 stainless steel
• Wetted Materials:
  - Shaft and Paddle: Stainless Steel SUS304 (AISI 304)
  - Shaft Seal: Abrasion-resistant Nitrile rubber (NBR) seal or specialized packing
• Housing Enclosure Material: Heavy-duty aluminum diecast (ADC12)
• Process Vessel Operating Temperature: -10°C to +70°C (High-temperature options up to 120°C)
• Ambient Enclosure Operating Temperature: -10°C to +50°C
• Maximum Process Operating Pressure: Up to 196 kPa (approx. 2.0 bar / atmospheric pressure)
• Ingress Protection Rating: IP65 (per IEC/EN 60529 standard)
• Net Product Weight: Approximately 1.1 kg