A Bin Level You Can’t Trust

A silo level that reads full when the loader shows it half, or drops to zero the moment the pack blower kicks on, will burn your night either way. Operators stop trusting the number, so they climb the silo with a tape or a plumb bob, or they run the discharge dry and cook a bearing. Most of the time the material didn't move the way the number says. The sensor got fooled, the mounting is wrong, or the controls are averaging garbage into something that looks smooth and believable. This guide is about telling those apart on the equipment you actually have, at 2am, without pulling the sensor first thing. Two terms up front so the rest reads clean. FMCW (Frequency-Modulated Continuous Wave) is the radar method most modern non-contact level transmitters use: the antenna sweeps a band of frequency and measures the surface distance from the beat frequency of the returned sweep. It handles dust and vapor far better than the old pulse-time radars. GWR (Guided-Wave Radar) runs the microwave pulse down a physical probe — a rod or cable hanging into the material — so the signal is guided instead of sprayed into open air; it shrugs off dust and low dielectric better, at the cost of a probe you have to keep clean and clear of buildup. I'll define deadband / blocking distance in the near-full section where it bites.

Before anything with a lid on it: this bin can kill you A silo, hopper, bin, or surge bin is a permit-required confined space with an engulfment hazard. People die in these every year, and they die fast. The rules below are not optional and they come before any troubleshooting step that puts you on top of, inside, or opening the vessel. Never enter under a live draw. If discharge can run — screw, rotary valve, gravity gate, pneumatic pack — flowing material pulls a person under in seconds. There is no swimming out. Never trust the top of a bridged or ratholed load. Material that hangs up forms a crust (a bridge) over an open void, or a vertical chimney (a rathole) with caked walls. It looks like solid floor. It collapses without warning when you step on it or when the discharge finally pulls it loose. Assume any hung-up bin is booby-trapped.