The Towa Seiden PRL-100 Series Heavy-Duty Rotary Paddle Level Switches, manufactured by Towa Seiden Industrial Co., Ltd. (Japan), represent the pinnacle of point level detection instrumentation for granular and powdered bulk solids. Built upon and superseding the classic HL Series, the PRL-100 Series incorporates modern advancements in mechanical clutch durability, enclosure sealing integrity, and specialized mechanical adaptations to resolve demanding bulk-handling challenges across heavy industries.

The series is structured into dedicated, task-specific models:
1. PRL-100: The standard industrial flange-mounted model (JIS 5K65A) featuring a compact immersion shaft (standard L = 85 mm or customized), ideal for side-wall mounting on surge bins, weighing hoppers, and processing vessels handling plastic pellets, grains, and dry powders.
2. PRL-100EB: Gas explosion-proof (flameproof) version rated for Ex d IIB T4 (or equivalent Japanese d2G4 standards). Encased in a heavy-duty enclosure with precision flame-arresting joints, it delivers total operational safety in petrochemical plants, solvent storage facilities, and hazardous volatile gas environments.
3. PRL-100ED: Dust ignition-proof version engineered specifically for combustible dust hazards encountered in coal pulverizers, wood chip silos, flour mills, starch processors, and grain handling facilities where airborne dust layers present severe ignition risks.
4. PRL-100F: Flexible wire rope type. The rigid metal shaft is replaced with a high-tensile SUS304 stainless steel wire cable assembly with a bottom weighting element and paddle. This enables the sensor to absorb intense lateral deflection forces generated by avalanching bulk materials when suspended vertically from silo roofs at depths from 1 to over 4 meters.
5. PRL-101: Protective tube type. The central rotating shaft is housed within a rigid, heavy-gauge protective sleeve that absorbs destructive lateral bending stresses and impacts from tons of freely falling bulk material.
6. PRL-170: Rigid shaft extension type, offering customizable rigid stem lengths (L = 250 mm to 1500 mm) for vertical top-mounting where specific lower switching thresholds are required.

The operating principle utilizes an electromechanical torque-reaction mechanism with integrated motor shut-off: an internal low-speed synchronous motor (~1 RPM) continuously turns the SUS304 stainless steel paddle. When rising material impedes paddle rotation, the reactive torque shifts the suspended motor assembly, actuating a microswitch to trip the SPDT output contacts (250V AC, 5A) for process interlocking while immediately disconnecting electrical power to the drive motor. This eliminates motor coil burnout even during extended periods of complete paddle burial. Housed in a rugged ADC12 diecast aluminum enclosure sealed to IP65/IP66, the PRL-100 Series guarantees over a decade of continuous service.

• Manufacturer: Towa Seiden Industrial Co., Ltd.
• Country of Origin: Japan
• Product Models Covered:
  - PRL-100 (Standard industrial flange-mounted model JIS 5K65A)
  - PRL-100EB (Gas explosion-proof / Flameproof model Ex d IIB T4)
  - PRL-100ED (Dust ignition-proof model for combustible dust zones)
  - PRL-100F (Flexible wire rope suspension model for deep vertical mounting)
  - PRL-101 (Protective tube model for heavy falling material impact resistance)
  - PRL-170 (Rigid shaft extended model for customized vertical reach)
• 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 / wide-range 120-250V AC
• Power Consumption: Approximately 2.5 W to 3.5 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 Rating: 250V AC, 5A (Resistive load)
• Detectable Bulk Density: Approx. 0.2 g/cm³ or greater (High-sensitivity paddle options available for lighter media)
• Process Mounting Connection: Standard Flange JIS 5K65A (ANSI / DIN compatible flanges available upon request)
• Immersion Lengths:
  - Model PRL-100: Standard 85 mm (or customized)
  - Model PRL-100F: Flexible cable from 500 mm to 4000 mm
  - Model PRL-101: Protective tube sleeve from 250 mm to 1000 mm
  - Model PRL-170: Rigid shaft from 250 mm to 1500 mm
• Wetted Materials:
  - Shaft, Paddles, and Protective Tube: Stainless Steel SUS304 (AISI 304) or optional SUS316
  - Flexible Cable (PRL-100F): High-tensile SUS304 stainless steel rope
  - Shaft Sealing: High-grade abrasion-resistant mechanical packing seal
• Housing Enclosure Material: Heavy-duty aluminum diecast (ADC12) with industrial coating
• Explosion Protection Ratings (Models PRL-100EB / ED): Ex d IIB T4 / Dust ignition-proof
• Process Operating Temperature Range: -10°C to +70°C (High-temperature options up to 150°C - 200°C)
• Ambient Enclosure Operating Temperature: -10°C to +55°C
• Operating Pressure Range: Up to 196 kPa (approx. 2.0 bar / atmospheric pressure)
• Ingress Protection Rating: IP65 / IP66 (per IEC/EN 60529 standard)
• Net Product Weight: Approximately 3.5 kg to 8.0 kg (depending on model and stem length)