High Dust Levels, high moisture levels from dust suppression water sprays, ore varies from lump to fines, high build-up on instruments.
Level Technology Choice:
In the past, the backup level high, high switch was normally a tilt switch. They are inexpensive to purchase. The problems with the tilt switch are:
- They suffer from build-up problems and will not tilt when required.
- They are not failsafe when they fail.
- They cannot be remotely tested and are very difficult to get at for routine maintenance.
- They must be installed in a passive part of the surge bin, out of the way of incoming ore flow and flying rocks.
A better choice would be a non-contact, self-cleaning, remote testing, and low-frequency Acoustic switch. See the attached application sheet that shows the 15 kHz transducer mounted under the mantle. The 15 kHz transducer will not interfere with the continuous-level transmitters. It has two relay outputs that can be programmed for two heights, or one can be a failsafe relay. It can also be operated on a two-wire Comms network (Foundation FieldBus, ProfiBus PA, etc.). It can be remotely tested by a PLC to test for continuity, which is of paramount importance. In mining and minerals operations where the ore body has sticky residues and clay deposits, etc. this is the best option for high, high switch backup. Use a polyurethane rubber focalizer cone to reduce breakage from flying rock.