Pig Detectors are devices with some type of indicator to detect the passage of a pig in the pipeline during a pig run. They can easily be classified into two groups: intrusive and non-intrusive.
The intrusive type is permanently mounted to pipe via fitting (thread-o-let or flange mounting), and can be used with any type of pig with no special accessories needed to be used with the pig. It usually consists of some sort of probe that protrudes into the pipe and is mechanically triggered when the pig passes.
The non-intrusive type does not require a permanent mounting. It is usually attached to the pipe via a fiberglass saddle, strap, or other banding method. For this type of detector, the pig must be equipped with a magnet (or other accessory) for sensor detection.
Pig detectors are usually located near the launcher and receiver to confirm successful launch and receipt of the pigs or any trouble area of the pipeline, such as at a tee, elbow, wye, etc. They can be equipped with electrical switches and connected to a PLC to be used to operate piping equipment, such as pumps, compressors, valves, mixing tanks, etc., when strategically located along the pipeline or plant.