Level as a pressure
Wells, reservoirs and pumping-station wet wells are most often measured with a submersible transmitter that senses the pressure of the water above it. Ten metres of water at 20 °C is 0.979 bar, so a 0 to 1 bar transmitter covers a little over ten metres, and a 0 to 10 m level range is not exactly 0 to 1 bar. The level to pressure calculator gives the range to calibrate, and the reading at any level.
Two details decide whether the reading is right. The transmitter measures from its own diaphragm, so the height at which it hangs above the bottom is an offset. And it must be vented to atmosphere through its cable, or it will follow the weather: a change of 10 mbar in barometric pressure is 10 cm of water.
Sludge and brine are denser than water, and the level read by pressure scales with density. A transmitter calibrated for water reads high in a denser liquid by the same percentage.
Units of pressure
Network pressure is given in bar, in metres of water column or in psi depending on the country and the age of the drawing: 1 bar is 10.197 m of water column. The pressure converter shows all units together. Its water-column units are the conventional ones, defined with a density of exactly 1000 kg/m³, which differ from real water at 20 °C by about 0.2 %.
Long loops to remote sites
Boreholes and outstations put hundreds of metres of cable between the transmitter and the controller. The cable resistance takes voltage away from the transmitter at exactly the moment it needs the most, at the upscale alarm current. With a 24 V supply, a 250 Ω input and 800 m of 0.75 mm² cable, the cable adds 36.7 Ω and a transmitter needing 12 V keeps a margin of 5.7 V. The loop power calculator checks any combination and gives the longest cable that still works.
At the controller, the current is scaled back to level: on a 0 to 10 m range, 14.4 mA is 6.5 m. The 4–20 mA converter does this and marks currents below 3.6 mA or above 21 mA as a failure signal, which separates a broken cable from an empty well.
Immersion and gas
Sensors and junction boxes in chambers that flood need a rating for continuous immersion, IP68, with the depth and duration stated by the manufacturer; IP67 covers only temporary immersion. Neither includes protection against water jets unless it is marked as well. The IP rating decoder explains what each code does and does not cover.
Digesters and sewers can contain methane and hydrogen sulphide, and equipment installed there needs the appropriate Ex certification. The Ex marking decoder reads a marking and compares it with a zone; the area classification itself is a matter for the plant’s own documentation.
Machines
Aeration blowers, pumps and mixers are monitored by vibration velocity. A reading of 2.8 mm/s RMS sits on the boundary between zones B and C of ISO 10816-3 for a medium-sized machine on a rigid foundation. The vibration converter shows the zone and converts between velocity and the acceleration an accelerometer reports.
Outside the scope of this site
Flow measurement with electromagnetic and ultrasonic meters, open-channel flow, and water-quality analysis such as pH, dissolved oxygen, turbidity and chlorine are not covered here.
Updated October 11, 2026