Plug Chute DiagramSensors that can be used to detect a plug chute condition

If properly implemented, a level sensor / switch or solids flow monitor can indicate a condition consistent with a flow stoppage within a chute, hopper or conveying line. Depicted here are some of the more common methods of determining a plugged chute condition.

A.
Microwave Solids Flow Detector
, model SFD-2 or SFI employed to monitor the flow or no flow state of the process material.

Benefit:
Non-intrusive monitoring of flow condition.

Caution:
The SFD-2 or SFI cannot differentiate between a plugged no flow condition and an empty no flow condition.

A logic function must be employed to definitively determine a flow anomaly. The material flow state is generally compared, either manually or via computer, against the operating state of the process. If no flow is detected and the process is in operation, then a problem can be concluded. If no flow is detected and the process is shut down, it can then be concluded there is no problem.

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B & C.
Point Level Sensor, like the SafePoint® and Model KA/KAX Rotary Paddles or TrueCap® RF Capacitance Probe, employed to detect the presence of material that would be exposed to the monitor/sensor only during a plug condition.

Benefit:
Low cost detection of material backed up in the chute or line; condition indicative of a flow obstruction.

Caution:
It is problematic to mount a sensing probe directly into a flow stream to monitor for a plug condition. The level monitor cannot differentiate between a highly saturated dynamic condition (e.g. dense flow stream) and a highly saturated static condition (e.g. line plugged). It is often necessary to make some modification to the process line so as to isolate the level sensor from the material flow stream.

If the process involves a round pipe it is common to make use of a pipe Y with the level monitor installed in one leg of the Y. It is important that the level sensor be installed in such a fashion so as to ensure that the material clears away from the sensing element when the plug condition passes.

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D.
Diaphragm-Style Switch
, like the Model G/GX, is a surface mounted, minimally intrusive pressure switch that makes it ideal for chutes or vessels limited in size or internal clearance.

A diaphragm switch provides indication by detecting pressure applied by the backed-up bulk material to the sensing diaphragm. The unit should be installed to a chute, line or vessel wall so that the diaphragm is exposed to the material to be sensed during a back-up or plugged condition. As material contacts the diaphragm, a force is exerted through the diaphragm to a pressure plate within the bin monitor. Physical deflection of the pressure plate activates an internal switch which is user accessible for signaling alarms, lights or PLC inputs. When material recedes from the diaphragm, a light duty spring returns the pressure plate and internal switch back to their original positions.

Benefit:
Low cost; Minimally intrusive; Fits into area with limited space.

Caution:
Since it is a pressure switch, situations with a lot of air pressure could cause false alarms. Also, the switch should be placed in a location where there will only be minimal contact with material, mainly during a back-up alarm condition. Constant, direct contact with material flow could cause diaphragm to wear out faster.


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Last Rev.: March 07, 2016