Hydraulic reservoirs and diesel day-tanks need a level alarm that works during a power failure, which is exactly what a passive float switch does. The HBE NS series switches a reed contact through a magnet-coupled nylon float on a brass stem, with no supply voltage in the level circuit.

When does a float switch beat a transmitter?

A transmitter tells a PLC how full the tank is; a float switch only answers the question that matters on most reservoirs, whether the level has crossed the alarm line. The NS answers it with a dry contact rated 250 VAC at 1 A and 80 W/VA, hysteresis held to 2-3 mm so the contact does not chatter on waves. Standard lengths run 100 to 700 mm, a two-contact NS 2 version covers separate min and max points on one stem, and turning the float reverses the contact logic from level-max-opens to level-max-closes. Compared with a conductive probe, the float works on non-conductive mineral oils, diesel and petrol where electrode sensors cannot see the fluid at all.

What do the variants add?

The NS 1-TE adds a bimetal temperature switch fixed at 70 deg C to the same stem, covering the oil-temperature alarm without a second instrument. The NS 1-VR uses a stainless stem with an NBR float whose length is set by cutting the tube between 200 and 500 mm, aimed at non-standard tank heights. Compared with the combined level-and-temperature instruments on the market, the HBE GmbH NS keeps the electronics out entirely, which is why it survives the wash-down and vibration reality of machine reservoirs at IP65.