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Radar level resolution describes the smallest distinguishable or reported change at a specified point in the measurement chain. A display that shows millimetres does not prove millimetre accuracy in a tank. The sensing method, internal processing, output conversion and receiving instrument can each impose different limits.
Specify where radar level resolution is required
For an operator, the relevant question may be whether the displayed level changes in 1 mm steps. For a dosing controller, it may be the smallest repeatable process change that can be detected without confusing noise with real movement. These are different requirements and should not share one unexplained number on an enquiry.
| Stage | Check | Limit |
|---|---|---|
| Sensor | Distance result and repeatability under the actual surface conditions | More output digits cannot recover an unreliable echo |
| Display | Decimal places, units and rounding | A small displayed step is not an accuracy statement |
| Loop | Configured span and usable analogue input performance | Scaling and electrical noise can hide small changes |
| PLC | Data type, rounding and calculation order | Software can discard information received from the instrument |
Calculate the loop-current change before specifying small level steps
If a 4-20 mA signal represents 0-10 m, a 1 mm level change corresponds mathematically to 0.0016 mA. That calculation describes scaling only. It does not demonstrate that the transmitter, wiring and analogue input can reliably distinguish such a change in service.
Similarly, a PLC value stored in whole centimetres cannot show every millimetre even if the upstream instrument reports them. Check engineering units before replacing a transmitter. A digital connection can avoid an analogue conversion, but it does not remove the instrument's own uncertainty or guarantee a particular update rate.
Read the model accuracy in context
METRAVON MV-RD12 lists a nominal accuracy of +/-2 mm and a liquid measuring interval of 0.1-30 m. These figures do not establish a complete installed uncertainty budget or a guaranteed smallest detectable change in a moving, foaming surface. Ask for the relevant test conditions and output details for the offered configuration. For echo separation rather than displayed increments, see the FMCW bandwidth and target-separation explanation.
During acceptance, compare the local value, transmitted value and PLC result at the same stable level. Then make controlled changes that are meaningful to the process and large enough to verify with the available reference. Record both repeated readings and the reference method; do not judge precision from the number of decimal places alone.
Questions about fine level changes
Q1. Will adding decimal places improve control?
Only if useful information exists upstream and the control strategy can use it. Extra decimals can otherwise expose noise or create false confidence without improving the actual measurement.
Q2. What should a resolution requirement say?
State the required detectable level change, tank conditions, output point and acceptable repeatability. Include the process response time separately so a heavily filtered value is not mistaken for a fast measurement.
Summary
Follow the smallest useful change through the complete signal chain. Request a radar and interface review with the tank span, PLC input details and the process change you need to observe, rather than specifying display digits alone.
