Verified = checked against an official document listed in References · Concept = general measurement principle · Verify in manual = model-specific, confirm in the current manual before use.
A · How the 5300 guided wave radar works
Verified The 5300 data sheet describes low-power, nanosecond microwave pulses guided down a probe in the process. Concept Where the pulse meets a change in dielectric constant, part of its energy reflects. The electronics time the echo (a form of time-domain reflectometry) and turn time into distance, then distance into level.
Level = Reference height − Measured distance → 10.00 − 4.00 = 6.00 m
- The transmitter launches a low-energy pulse along the probe.
- At the product surface the dielectric changes and part of the energy reflects.
- The echo travels back up the probe.
- The electronics time the echo and evaluate it.
- Distance is converted to level using the configured reference height.
Conceptual: real signal processing, reference point and offsets depend on the model and its configuration Verify in manual. The animation is slowed enormously: a real pulse covers 10 m in roughly 33 ns each way.
Time-domain reflectometry in three sentences
Along the probe the pulse travels at a known speed, close to the speed of light in vapour and slower inside a liquid layer. Any change in the material around the probe changes its impedance and sends part of the pulse back. Timing that echo gives distance: D = v · t / 2.
Conceptual echo plot (simulated), not transmitter or manufacturer software output.
B · GWR liquid-liquid interface measurement
Verified The 5300 data sheet covers level-and-interface measurement and lists interface measurement with a fully submerged probe, noting that some diagnostics are not compatible with the submerged-probe interface mode. Concept With a light, low-dielectric liquid floating on a heavier, high-dielectric liquid, the pulse reflects partly at the top surface, continues through the upper liquid, and reflects again at the liquid-liquid boundary.
Vessel reference height 4.00 m (simulated). Levels are heights above the tank datum; distances are from the probe reference point.
Echo visualization: two peaks
Illustrative dielectric values and a simplified reflection model (reflection grows with dielectric contrast). These are not acceptance limits: whether a given pair of liquids is measurable depends on the application, probe, liquids, signal strength and configuration Verify in manual.
Why the upper-layer dielectric setting matters
Inside the upper liquid the pulse travels slower, by a factor of roughly √εr. The transmitter therefore needs the upper product's dielectric constant to convert the extra echo time into a real thickness. A wrong setting gives a wrong interface level even when the echoes are perfect (try it in the fault lab).
| Operating approach | What is measured | When it fits | Watch out |
|---|---|---|---|
| Level only | Top surface | Single liquid or when the interface is not needed | An emulsion or second liquid is ignored |
| Level and interface | Top surface + liquid-liquid boundary | Separators, tanks with a water bottom | Needs a usable upper-layer echo path and a correct upper-layer dielectric setting |
| Interface with submerged probe | Interface only (probe fully covered) | Vessels that are always full, e.g. some separators and flooded chambers | No product-level reading; some diagnostics not compatible (per data sheet) Verify in manual |
B2 · How specific gravity affects interface level
Concept Two very different things decide an interface reading, depending on the technology:
- DP (and displacer) interface measures weight. The reading is calculated from the specific gravities (SG) of both liquids, so if the real SG differs from the configured SG, the interface reading is wrong.
- Radar (GWR) interface measures echo time. It does not use SG at all; it needs the upper liquid's dielectric constant instead (module B). A change in density alone does not move a radar interface reading, but a change in dielectric can.
DP interface between two taps
With both taps covered by liquid, the transmitter sees the weight of the column between the taps. With the interface I metres above the lower tap and tap spacing h:
DP = ρw·g·[ I·SGlower + (h − I)·SGupper ] → I = h · (DP/(ρw·g·h) − SGupper) / (SGlower − SGupper)
What to take away
- The DP span depends on the SG difference: span = ρw·g·h·(SGlower − SGupper). A small difference gives a small span, so any SG error causes a large interface error.
- If the upper liquid gets heavier than configured, a DP interface reads high; if the lower liquid gets heavier, it also reads high. Try both buttons above.
- DP interface also assumes both taps are covered; if the top liquid drops below the upper tap, the reading is meaningless.
- Radar interface is immune to SG changes but needs dielectric contrast and the correct upper-layer dielectric setting. Each technology has its own "hidden" process property.
Range a DP interface or density transmitter with the app's Interface & Density calculator. Illustrative simulation; use your process data and approved calculations for real ranging.
C · Rosemount 5408 non-contacting radar (FMCW)
Verified The official 5408 product page describes it as a non-contacting radar using frequency-modulated continuous-wave (FMCW) technology. Concept The antenna sends a continuous signal whose frequency sweeps up over time. The echo from the surface comes back slightly later, so at any instant it has a slightly different frequency from what is being transmitted. That frequency difference (the beat frequency) is proportional to distance. Nothing touches the liquid.
FMCW: frequency vs time
Illustrative sweep (bandwidth 1 GHz over 1 ms, chosen only to make the numbers readable), not the 5408's actual parameters or algorithm. Relationship: f_beat = 2 · D · B / (c · T).
Not an interface instrument. The 5408 is designed for non-contacting level measurement. Its official page makes no claim of measuring the boundary between two submerged liquids, so it is not a direct substitute for a GWR interface application.
D · GWR versus non-contacting radar
| Aspect | Guided wave radar (5300 class) | Non-contacting radar (5408 class) | Why it matters in a plant |
|---|---|---|---|
| Principle | Time of flight of pulses guided along a probe | FMCW: beat frequency between sent and received sweep | Explains what can disturb each measurement |
| Contact | Probe in the product | No contact; antenna above the surface | Wetted materials, coating and mechanical loads only matter for GWR |
| Primary quantity | Distance to surface (and interface) | Distance to surface | Both derive level from a configured reference |
| Interface | Yes, in suitable applications | Not its application | Separators and water-bottom tanks usually point to GWR (or another interface technology) |
| Installation | Probe length, clearance to walls and internals, anchoring | Nozzle, clear beam path, antenna placement | Headroom to insert a probe vs. a free path for the beam |
| Dielectric effects | Energy concentrated on the probe helps with weak reflectors | Relies on enough reflected energy from the surface | Low-εr products need careful selection either way |
| Turbulence, obstructions | Largely unaffected by internals away from the probe | Internals, agitators, foam and turbulence can create false or weak echoes | Mapping false echoes and placement are critical for NCR |
| Maintenance | Probe coating, mechanical damage | Antenna coating, condensation | Different inspection items |
| Commissioning | Probe type/length, mode, upper-layer εr for interface | Tank geometry, false-echo handling | Most errors are configuration, not hardware |
Guided application selector
E · Commissioning simulator
F · Calibration and verification
| Activity | What it changes or checks |
|---|---|
| Configuration | Units, reference height/geometry, mode, range (LRV/URV), damping: settings, not a calibration |
| Level / distance correction | An offset or reference adjustment so the reading matches a trusted independent value. Only per the approved procedure |
| 4–20 mA output trim | Corrects the analog output stage only; the measured level does not change |
| Loop verification | Confirms the control system receives and scales the current correctly |
| Independent verification | Compares the indicated level with a reference (dip, gauge glass, other instrument) |
| Safety proof test | For SIS use: follow the approved safety-lifecycle procedure and the device's proof-test documentation |
For both the 5300 and the 5408, output trim and changes to the level reference or range are different things: never "fix" a level error with an output trim. Verify in manual for the exact procedures.
4–20 mA calculator
Current (mA) = 4 + 16 × (PV − LRV) / (URV − LRV)
Check the actual transmitter configuration, scaling, alarm behaviour, output mode and control-system scaling before using these numbers operationally.
Guided verification exercise
| Point | Reference (m) | Indicated (m) | Error (m) |
|---|
Assess errors against your approved acceptance criteria; this lab does not supply tolerances. Do not adjust factory settings arbitrarily. Safety applications: follow the approved safety lifecycle procedure and device-specific proof-test documentation.
G · Troubleshooting decision tree
Never open a pressurised vessel, remove an energised transmitter, bypass a safety system or do hazardous work without the required isolation, permits and approved procedures.
H · Animated fault laboratory
Pick a fault, look at the healthy instrument, inject the fault, then work out what happened. All values are simulated and are not real alarm codes or device responses.
I · Engineering tools
Level ⇄ distance
Interface layer thickness
Maintenance & inspection checklist
Other tools in this lab: configurable tank (A), echo analyser (B), FMCW demo (C), decision tree (G), commissioning checklist (E), verification worksheet (F). These are conceptual tools, not a substitute for the transmitter's configuration software.
J · Glossary and knowledge check
Quiz
References
- Verified Rosemount 5300 Level Transmitter, Guided Wave Radar: Product Data Sheet, document 00813-0100-4530, Rev KJ, October 2025. PDF on emerson.com ↗. Used for: pulse principle, level and interface measurement, submerged-probe interface and its diagnostic restriction, SIL 2 (IEC 61508) certification. Note: this link is the data sheet, not the reference manual.
- Verify Rosemount 5300 Reference Manual: referred to by the data sheet for installation and configuration details. Obtain the current revision from Emerson's documentation pages; this lab does not quote it.
- Verified Rosemount 5408 Non-Contacting Radar Level Transmitter: product page. emerson.com ↗. Used for: FMCW principle, non-contacting level measurement.
- Verify Rosemount 5408 Reference Manual, document number 00809-0100-4408 as listed on the product page; check the current revision there.
Everything not marked "Verified" is either a general measurement principle or is explicitly flagged for verification. Commissioning steps, troubleshooting trees, the fault lab and all numbers are original educational content and simulations.
Related: Radar vs Guided-Wave Radar · Level Measurement · 4–20 mA Signal Scaler · HART Communication