Choosing between radar and ultrasonic is one decision; writing down what you actually need is another. This guide explains every parameter that appears on a level transmitter datasheet — what it means, why it matters, and the mistake engineers make with it — and gives you a specification template you can send to a supplier and compare quotes against.
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A usable specification is not a list of features — it is the set of facts a supplier needs to quote the right model. Nine questions cover almost every project:
Water, chemical, slurry, grain, powder or oil. Its dielectric constant and behaviour decide radar vs ultrasonic before any other number.
Diameter, height, and whether the beam will see a wall or structure before it sees the surface.
Temperature, pressure, vacuum, vapour, foam, condensation and build-up on the antenna.
Flange size and rating, threaded connection, or a bracket on a standpipe.
4–20 mA, HART, Modbus RTU over RS485, or a wireless 4G report to a cloud platform.
Level control tolerates ±10 mm; custody transfer and billing do not.
IP rating, sun exposure, salt, washdown, vibration, hazardous area.
CE, ATEX/IECEx, or none for a water tank in a field.
A trained instrument tech on site, or a self-install solar unit read from an app.
If the technology choice itself is still open, start with our selection guide and come back here to write it down.
These three lines decide more than anything else on the datasheet:
Radar reflects off conductive or high-εr media. Water (εr ≈ 80) is easy; oil, solvents and plastic pellets (εr < 3) are hard and need 80 GHz rather than 26 GHz.
Foam absorbs ultrasonic energy and can reflect radar. Specify stilling wells, or choose guided-wave radar which follows the surface regardless.
Both the medium temperature and the electronics/ambient limit. Standard units handle −40 to +80 °C; beyond that you need high-temperature options or a standpipe.
Flange rating must match the process, and vacuum can deform thin antenna cones — specify the design pressure, not just the working pressure.
Sticky media coat the antenna. Specify a PTFE or horn antenna, or plan a purged connection, rather than accepting a drifting reading later.
Every non-contact sensor has a near zone it simply cannot measure. The specification has to leave room for it:
| Parameter | What it means | Specification mistake to avoid |
|---|---|---|
| Measuring range | Minimum to maximum distance from the sensor face to the surface. | Specifying range to the tank floor when the real span is only the top 2 m. |
| Dead zone / blind zone | The near distance where the sensor is still ringing and cannot measure. | Placing max level inside it — the top of the tank then reads erratically or not at all. |
| Beam angle | Cone the energy spreads into; wider beams hit tank walls sooner. | Ignoring it in narrow tanks and stilling wells — the beam must clear the wall. |
| Output span | Which distance maps to 4 mA and which to 20 mA. | Mapping 20 mA to the sensor’s maximum range instead of the tank’s working range. |
Best for Setting the 20 mA point 100–200 mm below the highest level the tank will ever reach, so a filling surge never over-ranges the loop.
Watch out Small tanks and standpipes: the dead zone plus the beam angle can consume more room than the measurement itself. Confirm the geometry before ordering.
This is the mechanical interface — get it wrong and the instrument will not physically fit the tank you already have:
State the standard (DIN, ANSI, JIS), nominal size and pressure rating. “DN50 PN16” is quotable; “a flange” is not.
316L stainless for most waters and chemicals; Hastelloy or PTFE-lined for aggressive media. Probe or antenna material matters if the medium coats.
Food and pharma need tri-clamp connections, Ra finishes and no dead legs — a standard thread will not pass an audit.
Gland size and thread (M20, NPT½) plus whether the cable runs inside or outside a conduit.
Specify internal diameter and length; the beam must fit the pipe and the pipe must not fill with the medium.
Three output families cover almost every site, and the choice drives wiring, power and cost:
Powered from the loop, so no separate supply. Simple and PLC-friendly; keep loop resistance under the limit or 20 mA is never reached.
Same two wires carry configuration and diagnostics — valuable when the transmitter is mounted where nobody can reach it.
Many sensors on one bus with level, temperature and status registers. Needs a unique address and termination at both ends.
No cable run at all: solar panel, battery and an IoT SIM reporting to a cloud platform. Ideal for remote tanks — see our 4G setup guide.
For a local high/low alarm or pump control without a PLC. Specify contact rating and whether it is fail-safe.
Accuracy on a level datasheet is a percentage of the measured span, not of the tank height — a ±0.5 % unit over a 2 m span is ±10 mm, and over a 10 m span it is ±50 mm:
Quoted as % of span. Always ask “% of what span?” and recompute it against your tank.
Usually better than accuracy and the number that matters for pump control and alarm thresholds.
How far the reading moves over the ambient range; matters on outdoor tanks that swing 40 °C between seasons.
IP65 is rain-proof; IP67/68 is washdown and temporary submersion. Outdoor units should be at least IP66.
If the tank sits in an Ex zone, the instrument certification is not optional and must match the zone and gas group.
Send that to our team and you will get a comparable quote instead of a guess. For the models behind the parameters, see the 80 GHz radar, ultrasonic and 4G solar product pages.
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