The Guided Wave Radar Level Sensor operates on the Time-Domain Reflectometry (TDR) principle. Its core mechanism involves transmitting high-frequency microwave pulses along a guided-wave rod or cable toward the liquid surface. When the pulse encounters the surface of a liquid or solid medium, a portion of the energy is reflected back to the sensor. The liquid level is precisely calculated by measuring the round-trip time.
Guided Wave Radar Level Transmitters are widely used in petroleum and chemical processing facilities. They can measure highly corrosive, flammable, explosive, and high-viscosity media, and are particularly common in large vertical tanks and spherical tanks.
The electronic components of guided wave radar level transmitters rarely fail; problems encountered in the field are almost always caused by mechanical factors. For example: a cable-type probe swinging and striking a ladder; a short pipe installed at a height exceeding 100 millimeters; the probe becoming tangled or piled up at the bottom of the tank; or incorrect model selection (confusion between rod-type and cable-type probes). These situations can all generate interference echoes, causing the transmitter to misinterpret them as liquid levels or masking the true liquid level echoes.
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Guided Wave Radar Level Sensor Installation
Ensure that the cable or rod does not contact internal obstructions throughout the measuring range. Keep it clear of tank internals such as ladders, limit switches, heating coils and brackets. Additionally, ensure that the cable or rod does not intersect the feed material flow.
When installing the meter, additional considerations include:
The highest material level must not enter the measurement blind zone.
The meter must maintain a certain distance from the tank wall.
Install the meter so that the cable or rod is perpendicular to the surface of the measured medium as much as possible. The intrinsically safe version (Ex ia IIC T6 Ga) uses a die-cast aluminum housing sealed with silicone rubber and must be powered through a safety barrier; the flameproof version is Ex d IIC T6 Gb. Follow your local hazardous-area code and earth the instrument.
The following installation guidelines apply to cable and rod probes used on solid powders or liquids.
Installation Location:
- Keep as far away from the discharge and feed ports as possible.
- Make sure the rod or cable cannot touch the tank wall or bottom anywhere in the measuring range, including when the cable swings during filling.
- In silos, mount the probe 1/4 to 1/6 of the diameter in from the wall. Moving solids pull a long cable sideways, so also keep at least 1/10 of the measuring range from the wall, and never less than 300 mm.
- The minimum distance between the cable or rod probe and the tank wall is ≥ 300 mm.
- The bottom of the probe must be ≥ 30 mm from the tank bottom.
- The minimum distance between the probe and any obstructions inside the tank should be ≥ 200 mm.
- If the tank has a conical bottom, the probe can be mounted at the center of the tank top.
The following figure shows the installation diagram of a rod-type radar level sensor. This probe is mainly used for liquids.
Features:
- It can measure any medium with a dielectric constant ≥ 1.8.
- It is generally used to measure media with a viscosity ≤ 500 cSt that do not tend to stick to the probe.
- The maximum length of a rigid rod probe is 6 meters.
- Steam and foam have little effect on the measurement.
- For liquids with high foam content, a single-rod guided wave radar level sensor should be selected.
The following figure shows the installation diagram of a dual-cable radar level sensor. It is primarily used for level measurement of low-dielectric-constant liquids and low-dielectric-constant lightweight solid powders.
Features:
Liquids with relatively low dielectric constants and lightweight solid powders can be measured with a dual-cable probe.
It can measure any medium with a dielectric constant ≥1.6.
It is generally used to measure media with a viscosity ≤ 500 cSt that do not tend to stick to the probe.
The dual-cable radar level sensor has a maximum range of 30 meters.
Installation Method
Proper installation keeps the measurement reliable and accurate over the long term:
Guided wave radar level sensors can be connected with a G1½″ A or 1½″ NPT thread, with the thread length limited to 15 mm. They can also be installed on short pipes. When the nozzle (short pipe) diameter is between 2″ and 6″, the nozzle height should be ≤ 100 mm. The shorter the thread and the nozzle, the more stable the measurement. If the nozzle is longer, shorten it, or anchor the cable probe at the bottom and fit an insulated centering bracket so the cable cannot touch the lower end of the nozzle.
Installation in DN200 or DN250 short pipes:
When a guided wave radar is installed in a short pipe with a diameter greater than 200mm, echoes are generated on the inner wall of the short pipe, which can cause measurement errors in media with low dielectric constants. Therefore, for a short pipe with a diameter of 200mm or 250mm, a special horn-shaped flange is required.
Notes on Installation on Plastic Tanks:
Whether using a cable or rod, for the guided wave radar to function properly, the process connection surface must be metal. If the tank top is plastic or another non-conductive material, mount the instrument on a metal flange or, for a threaded connection, on a metal plate.
Interference Optimization
Interference Echo Suppression: The software can suppress interference echoes to give a stable reading.
Bypass and Waveguide (applicable only to liquids with a viscosity of 500 cSt or less):
For liquids with a viscosity of 500 cSt or less, a bypass or waveguide can be used to avoid interference.
Installation for Low-Dielectric-Constant Liquids
For media with a dielectric constant greater than 1.3, a viscosity ≤500 cSt, and low adhesion, a guided wave radar can be installed in a waveguide. Its advantages are as follows:
- Excellent reliability and high accuracy
- Applicable to any medium with a dielectric constant ≥1.3, independent of the medium’s conductivity
- Measurement is unaffected by obstructions within the tank and the size of the short pipe
Corrosive Media Measurement
For corrosive media, a rod or cable probe with a PTFE or PFA sheath can be used.
Installation on horizontal and vertical tanks
- The rod probe can be up to 6 meters long. For tanks with measurement distances exceeding 6 meters, a 4 mm cable probe can be used.
- The installation and mounting methods are the same as for solid powder silo measurements.
- The distance from the tank wall must be greater than or equal to 300 mm. Avoid contact between the probe and the tank wall.
- When selecting the probe length, ensure that the bottom of the probe is at least 30 mm from the tank bottom.
- If there are numerous obstacles in the tank or if the obstacles are too close to the probe, a waveguide can be installed for measurement.
Special Installation Instructions:
If a cable probe is too long for the tank, cut off the excess so the measurement stays accurate. The cable must not be knotted, tangled, or attached to other objects.
To cut the cable, first disconnect the instrument power, remove the cable, unscrew the weight, and cut the cable from the bottom. After cutting, reinstall the weight. Once the instrument is fully installed, reconnect the power and reset the parameters.
For cable-type guided wave radars with sleeves, if the cable is too long, do not cut it yourself; return it to the manufacturer for cutting.
For guided wave radar level sensors installed in a waveguide, use an insulating bracket to secure the radar probe. Ensure that the probe (rod/cable) is concentric with the waveguide. Otherwise the echo becomes unstable and the reading suffers.
Precautions
Guided wave radars installed in waveguides generally use a rod probe. During installation, an insulating concentric bracket should be installed on the rod probe. Keep the rod concentric with the waveguide; otherwise strong false echoes will appear. If the range exceeds the 6 m rod limit and a cable probe goes into the waveguide (stilling well), the waveguide must be at least 6″ (DN150) in diameter; a narrower one gives strong false echoes.
Correct Installation: Keep the probe out of the fill stream and mount it away from the inlet. Outdoors, fit a sun shade and rain cover.
Moisture-Proof: Tighten the cable gland and bend the cable downward before it enters the housing, so condensate cannot run inside.
Guided Wave Radar Level Sensor Calibration
You do not need to fill the tank to calibrate a guided wave radar. Setup is done on the four-key View Point display, with PC software through a HART modem and a 250 Ω resistor, or with a HART handheld. Enter the empty and full points, choose the medium and probe type, then check the reading once against a manual dip.
1. Parameter Setting
Everything below is on the Basic settings menu of the View Point display, or the same items in the PC software or a HART handheld.
- Min. and Max. adjustment: the distances, measured from the sealing face of the thread or flange, that correspond to 0 % and 100 % (4 mA and 20 mA). Keep the 100 % point below the top blind zone and the 0 % point above the bottom blind zone near the probe end.
- Medium: liquid or solid. This changes how the echo is processed.
- Sensor type: Rod or Rope. It must match the probe actually fitted.
- Damping: slows the output for agitated or turbulent surfaces.
- Near blanking: use it when a fixed obstruction sits close to the process connection and the level never rises that high.
- Gain: three steps; raise it for weak echoes from low-dielectric products.
2. Signal Adjustment and Optimization
In measuring mode, one key toggles the display between the measured value and the echo curve. With the tank as empty as practical, use False echo memory → Create new to learn fixed echoes from the nozzle, ladders or heating coils. If the reading still jumps between a small echo and the real one, adjust the detector settings or First wave under Curve detection.
3. On-site Verification and Fine-Tuning
Compare the reading with a manual dip at one level. If the empty distance is off by a fixed amount, enter the difference in Distance Adj. Lock the settings with a password (Key) once the loop is checked; Simulation can drive the 4–20 mA output to test the control system without moving the level.
Guided Wave Radar Level Sensor Maintenance
Regular maintenance can extend the service life and improve measurement accuracy.
1. Sensor Maintenance
Regular Cleaning
Pull and wipe the probe at each shutdown if the product leaves a film. For sticky products, choose a single rod or cable rather than the coaxial probe, so the coating can be cleaned.
Calibration and Parameter Optimization
There is no fixed recalibration interval. Compare the reading with a manual dip every 6–12 months; if the empty-distance reading is off, enter the difference in Distance Adj. Re-learn the false echoes (False echo memory) after anything inside the tank changes.
Component Inspection
Inspect all components for proper operation. Regularly replace aging seals and cables. On hot vessels, check that cable insulation has not been damaged by heat.
2. Process Connection and Seals
Check the flange or thread seal and its gasket at each shutdown. On hot vessels, bolts can loosen after thermal cycling, so retighten them to the specified torque.
3. Safety and Environmental Management
Operational Safety
Disconnect the power supply before maintenance and wear high-temperature gloves and goggles. Allow high-temperature media to cool to a safe temperature before disassembling the equipment.
Environmental Monitoring
Keep ambient temperature, humidity and electromagnetic interference within the instrument’s rated limits. In hazardous areas, make sure the explosion-protection rating matches the zone.
How Do You Troubleshoot a Guided Wave Radar Level Transmitter?
The table below lists common faults seen in the field, their likely causes and what to check.
| Problems | Causes | Solution |
| Reading jumps or fluctuates | Agitator vortex, fill stream hitting the probe, cable swinging | Move the probe away from the inlet; anchor the cable end or use a rod; increase Damping; switch on Echo tracking |
| Reading stuck near the top | Buildup or condensate in the nozzle, a fixed obstruction close to the process connection, nozzle taller than 100 mm | Clean the nozzle; shorten it; set Near blanking past the obstruction; learn the false echo (False echo memory → Create new) |
| Reading drops to the probe end / 0 % | Weak echo from a low-dielectric product, probe touching the bottom, wrong probe type selected | Check Sensor type (Rod/Rope); raise Gain or lower Threshold; for a dielectric constant below 1.8 use a dual cable (≥1.6) or a waveguide (>1.3); keep the probe end at least 30 mm off the bottom |
| Jumps to a second, lower echo | Multiple reflections in a small or full tank | Adjust First wave; check the false echo curve |
| Echo lost after a few weeks | Heavy coating on a coaxial probe, crystallization | Switch to a single rod or cable; heat-trace the nozzle |
| Noisy signal, unstable 4–20 mA | Cable shielding or earthing | Connect the shield to the earth terminal at both ends; where the current loop is earthed, earth the shield through a 1 nF/1500 V ceramic capacitor; keep signal cable away from power cables |
How Accurate is Guided Wave Radar?
Accuracy is one of the main advantages of guided wave radar. Our 70X series is rated ±10 mm with rod or cable probes and ±5 mm with the coaxial probe (704), with 1 mm display resolution, between the top and bottom blind zones. That makes them a good fit where tight level control matters. For example, in the petrochemical industry, precise level control keeps chemical reactions and product quality on target.
Guided wave radar level sensors can monitor liquid level changes in reactors in real time. Operators can adjust feed and discharge rates in time, which keeps the process stable and safe.
What is the maximum length of a guided-wave radar probe?
The maximum length of our Sino-Inst 70X series guided-wave radar level transmitter rod-type probes is 6 m. For longer measurement ranges, use cable-type probes:
- 701 Single-cable, 703 Dual-cable: Up to 30 m
- 702 Fully PTFE-coated cable: Up to 20 m
- 705 High-temperature, high-pressure model: Up to 15 m (−200 to 400 °C, up to 40 MPa)
- 704 Coaxial probe: Up to 6 m
Does the guided-wave radar have any moving parts?
No. The pulse travels along a fixed rod, cable, or coaxial tube, and the electronic components measure the echo time. There are no parts subject to wear, such as floats, buoys, or bearings. Maintenance primarily involves checking the probe for material buildup or scaling, as well as ensuring the cable entry seal is intact.
What tools are needed for field commissioning?
We recommend choosing one of the following three options:
- A View Point four-button display module plugged into the meter
- PC commissioning software: Connected via a HART converter, with a 250 Ω resistor inserted in series in the loop
- A HART handheld communicator
Additionally, have a tape measure or calibration ruler on hand; a single reading comparison at a specific liquid level is sufficient.
Can guided-wave radar measure liquid levels with foam on the surface?
Generally, yes. Rod-type probes have strong penetration capabilities through steam and foam, so measurements are largely unaffected; for liquids with heavy foam, we recommend selecting a single-rod guided-wave radar. In a firefighting foam storage tank project, we specifically recommended guided-wave radar over surface-mounted ultrasonic sensors precisely because of the foam on the liquid surface.
Can guided-wave radar be installed inside the chamber of a magnetic flip-plate level gauge?
It cannot be installed in a magnetic flip-plate level gauge that already has a float, as the float occupies the space needed for the probe. If you want both local indication and a 4–20 mA signal in the same chamber, our approach is to pair the magnetic flip-plate level gauge with a magnetostrictive transmitter. A standard bypass pipe without a float can accommodate guided wave radar: use a rod-type probe with an insulated centering bracket; this is only suitable for liquids with a viscosity ≤500 cSt.
Most guided wave radar problems on site trace back to installation and setup rather than the electronics. If you’re considering a guided wave radar level sensor but are unsure which one to choose, send Sino-Inst the medium, tank height and process conditions, and we will recommend a suitable model.
