The first question with a level switch is never "which model" but "what is actually in the tank, and does anyone need a number or just an alarm". A point switch tells you full or empty at one elevation, and it will do that for twenty years without maintenance if the principle suits the medium. A continuous transmitter tells you how much is left, and costs accordingly. Buying a radar to detect a high-level alarm is a common and expensive way to solve a simple problem; buying a paddle switch for a foaming detergent tank is the reverse mistake, and one that generates callouts every month.

For powders, granules and pellets in silos and bins, the rotary paddle switch is still the most forgiving device on the market. A small synchronous motor turns a paddle at about one revolution per minute, and when material buries the paddle the motor stalls and trips a microswitch. FineTek's SE series follows that pattern with a screw-mounted version, a flange version, a shaft-protected version for side mounting, an adjustable-shaft version and high-temperature variants that run up to 200 °C. Standard units tolerate roughly 0.3 g/cm³ minimum bulk density, switch 3 A at 250 VAC, and are IP65 protected — which is adequate for a cement silo and not adequate for a washdown room. Its weakness is anything that bridges: wet sand, sticky meal or a material that packs between the blades will hold the paddle and hold the contact with it.

Where a paddle struggles, the tuning fork usually wins. FineTek's SC series vibrates a fork at its resonant frequency and detects the change in frequency when the fork is covered, so there are no moving parts to stall and nothing to calibrate. The standard liquid versions sense down to about 0.7 g/cm³ and the solid versions down to 0.07 g/cm³, which reaches fine powders and light flakes that a paddle cannot feel. Fork switches are also the better choice for liquids with some viscosity, and the sanitary SIS variant with a PEEK probe and a surface finish under Ra 0.8 is what food and pharmaceutical tanks tend to specify. Watch the fork length against the nozzle: a fork that sits inside a long standpipe will sense the standpipe, not the tank.

Optical switches are the quiet specialists. An SD series prism detects the presence of liquid by the change in light reflection at the tip, which makes it fast, repeatable and cheap for clean transparent or translucent liquids in small tanks and pipework — leak detection, low-level alarms on reagent bottles, coolant reservoirs. What it will not tolerate is coating: an oily film or a crystallising product on the prism will fool it permanently. If the medium leaves a deposit, do not use optics, however convenient the price looks.

Floats cover the applications where the medium is simple and the budget is tight. The FA and FB cable float switches are the classic sump and pump-control device, hanging on their own cable with no mounting boss needed, and the FC and FD magnetic float switches give several switching points from a single top entry — useful on a tank where you need pump start, pump stop and a high alarm without drilling three holes. Float devices remain the most predictable option for clean water and light oils, and the least suitable for anything with suspended solids that can jam the float travel.

When a continuous reading is genuinely required, the choice comes down to contact and non-contact. FineTek's JFR FMCW radar works at 10 or 26 GHz with a range up to about 70 m, accuracy around ±3 mm and 4–20 mA with HART, and being non-contact it does not care about the product being abrasive or hot. Guided-wave radar (JTR) is the better fit in narrow tanks, standpipes and stilling wells where free-space radar would bounce off the walls, and ultrasonic (EAX) is the economical non-contact choice for water and simple liquids in open tanks. For bulk inventory in tall silos where an actual tonnage figure is needed at the end of the month, the electromechanical weight-and-cable system in the EE300 range is still doing that job in plants where radar was tried and abandoned.

Whatever the principle, mounting decides whether it works. Keep the probe clear of the filling stream, of agitator sweep and of the tank wall, and set a delay of a few seconds so that splashing or a falling product stream does not produce a one-second alarm. On foaming media, choose a device that measures density change rather than one that looks for a surface. And when a switch starts giving false high alarms after two years of clean service, suspect build-up on the probe before suspecting the electronics — a five-minute clean solves more of these than any configuration change.