The Towa Seiden HL-400S Paddle Type Level Switch is a specialized, compact point level detection instrument manufactured by Towa Seiden Industrial Co., Ltd. (Japan). The paramount engineering highlight of the HL-400S variant is its streamlined small blade paddle geometry (S-Paddle / Small Blade Type): the entire paddle profile fits comfortably within the clearance envelope of a standard R 3/4" (PT 3/4" / G 3/4") half-coupling or tapped hole. This enables maintenance technicians to insert or withdraw the sensor directly through the hopper wall mounting port without detaching the paddle from the drive shaft. This design eliminates cumbersome assembly steps, drastically shortens installation downtime, and prevents accidental drops of mounting pins or hardware into sensitive bulk material bins.

The operational mechanism of the Towa Seiden HL-400S 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 resistance exerted by the surrounding pellets or powder stops the paddle. The resulting reactive torque causes the suspended motor assembly to rotate around its internal axis, tripping an integrated microswitch. This instantly changes the electrical state of the SPDT output contact to trigger alarms, halt feeding conveyors, or shut down supply valves. Concurrently, a secondary internal contact automatically de-energizes the drive motor. By removing electrical power while the paddle remains stalled in material, motor coil burnout is entirely prevented, ensuring outstanding longevity.
- 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.

The wetted measuring paddle and drive shaft are fabricated from high-grade SUS304 (AISI 304) stainless steel, offering high resistance to mechanical abrasion while ensuring zero contamination of sensitive process media. The upper housing is precision-cast from heavy-duty industrial aluminum alloy (ADC12) finished with electrostatic powder coating, providing IP65 dust and water ingress protection. Featuring an industry-standard R 3/4" process mounting thread, the Towa Seiden HL-400S enables quick horizontal side-wall or vertical top-cover installation, providing dependable, maintenance-free performance across automated material handling lines.

• Manufacturer: Towa Seiden Industrial Co., Ltd.
• Country of Origin: Japan
• Complete Part Number: Towa Seiden HL-400S
• Product Category: Compact Paddle Type Level Switch with Small Blade
• Operating Principle: Electromechanical torque-reaction with automatic motor cut-off
• Paddle Execution: Slim small-blade profile (S-Paddle) passing directly through R 3/4" ports without detachment
• 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 RPM (at 50 Hz) / 1.2 RPM (at 60 Hz)
• Electrical Output Contact: 1 SPDT microswitch (Single-Pole Double-Throw)
• Contact Rating: 250V AC, 3A / 5A (Resistive load)
• Detectable Apparent Density: Approx. 0.2 g/cm³ or greater (Suitable for plastic pellets, grains, and industrial powders)
• Mechanical Process Mounting: Male thread R 3/4" (Optional G 3/4", NPT 3/4", or mounting flanges upon request)
• Standard Immersion Length (L): 85 mm (Measured from thread hex shoulder to paddle tip) or custom extended
• Wetted Materials:
  - Shaft and Paddle: Stainless Steel SUS304 (AISI 304)
  - Shaft Seal: Abrasion-resistant Nitrile rubber (NBR) or high-temperature packing seal
• Housing Enclosure Material: Heavy-duty aluminum diecast (ADC12)
• Maximum Process Operating Pressure: Up to 196 kPa (approx. 2.0 bar / atmospheric pressure)
• Process Operating Temperature Range: -10°C to +70°C (High-temp versions extendable up to 120°C)
• Ambient Operating Temperature Range: -10°C to +50°C
• Ingress Protection Rating: IP65 (per IEC/EN 60529 standard)
• Net Product Weight: Approximately 1.2 kg