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Rechner Sensors

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Rechner Sensors / applications / plastics /
Plastic Pellets

Level Control of Plastic Pellets

Download this application note as a PDF with connection diagrams: PDF


KAS Series sensors are used as level detectors in the plastics industry for many operations. Plastic pellets, which form the raw materials for the injection and blow molding industries, can be detected in bins, hoppers, and transfer systems. The signal from the sensors can be used to control bin levels, shut off pneumatic conveyors or operate alarm systems.


The level of plastic pellets in the hopper of an injection molding machine must be kept above a minimum level at all times to prevent voids in the end product. The machine hopper is filled by a pneumatic conveyor system from a large storage silo.

For detection of plastic pellets, it is recommended that the sensor be immersed in the material. A non-flush style sensor is installed through the wall of the hopper to obtain accurate results. Flush mount style sensors can also be used to detect the level through the wall when the hopper is made out of plastic or glass.

One KA0417 sensor is mounted through the machine hopper wall. The sensor is mounted near the bottom of the feeding hopper and sends a signal to refill the hopper when the plastic pellet level falls below where the sensor is mounted. This ensures that the machine never runs out of material.

When choosing a mounting point for the sensor it is necessary to select a point high enough above the first heater element to keep the sensor temperature below 70 degrees C (158 Degrees F). This ensures proper operation of the sensor at all times.

After installation, a 'full adjustment' of the sensor is done in this order:

  1. Locate the sensitivity adjustment potentiometer on the sensor. The adjustment potentiometer is recessed and located under a plastic flap that is there to keep dust out.
  2. Fully immerse the sensor into the bulk material.
  3. Reset the sensor's sensitivity by turning the potentiometer counter-clockwise 20 full turns, or until the sensor no longer sees the product (whichever comes first).
  4. Adjust the sensor to the product to be detected by turning the potentiometer clockwise until the sensor detects the product.
  5. Add 1/4 turn for safety by turning the potentiometer a further 90 degrees clockwise.

Parts Required:

  1. Sensor: KA0417
  2. Relay Power Supply: NA7001
  3. 5 Meter Cable: 0.25SQX4C