This dust filter must be large and is installed external to the silo for easy maintenance. Sample is then circulated into another filter and then pumped back to the silo. A small amount of sample is extracted for measurement through a fine particle filter. This pass-through filter bowl is a standard filter used in an air compressor. The line size is one-half inch ID flexible tubing.
Parts are standard and readily available.
A 3-way solenoid valve is used to switch the stream between air and sample. Both air and sample are filtered through a hydrophobic filter and metered using a needle valve to adjust the flow rate. B. A 3-way solenoid valve is controlled by timers in the circuit card, which control the amount of time the sensor is exposed to sample, or alternately air. A small internal pump is on constantly to flow either sample or clean air to the sensor. Control Circuit Three timers are used to control the proper functioning of the system.