The Model 21512 Pneumatic Sensor is a fixed gap nozzle, designed primarily for use with non-polarizing films such as polyethylene. This sensor detects the edge position pneumatically and transmits this information to a pneumatic-hydraulic controller.
The unique and new sensor design incorporates a sturdy, but light weight, plastic construction material streamlined to prevent snagging of the web on sharp edges.
This non-contact sensor directs a stream of very low pressure air across the edge of the web as illustrated below. The recovery pressure is proportional to the web position.
A small air bleed through the purge orifice (patented) puts a positive pressure at both sensing orifices and prevents foreign material from entering the sensor and clogging the orifices. This preventative measure does not affect the control at the recovery orifice.
The proportional pressure signal is generally transmitted to a diaphragm on a hydraulic controller. The very low pressure at which this sensor operates will not offset even the lightest film, and requires only a pressure reducing valve to operate from normal plant air supply.