Guided wave radar gauge
Guided wave radar (GWR) is also called time domain reflectometry (TDR) or micro-impulse radar (MIR). In a guided wave radar installation, the GWR is mounted on the top of the tank or chamber, and the probe usually extends to the full depth of the vessel. A low energy pulse of microwaves, travelling at the speed of light, is sent down the probe. At the point of the product level on the probe, a significant proportion of the microwave energy is reflected back up the probe to the transmitter. The transmitter measures the time delay between the transmitted and received echo signal, and the on-board microprocessor calculates the distance to the liquid surface using the formula:
Distance = (Speed of light x time delay) / 2
Once the transmitter is programmed with the reference gauge height of the application – usually the bottom of the tank or chamber – the liquid level is calculated by the microprocessor.
Because a proportion of the pulse will continue down the probe through low dielectric fluids, a second echo can be detected from an interface between two liquids at a point below the initial liquid level.
This characteristic makes guided wave radar a good technique for measuring liquid/liquid interfaces such as oil and water and measuring through some foams. Guided wave radar can be used in vessels with tight geometry, in chambers, and in tanks of all sizes. Advanced GWR also works well in low dielectric and turbulent applications. Because it is not dependent on reflecting off a “flat” surface, it works well with many powders and grains as well as liquids with slanted surfaces caused by vortices.
Applications:- Liquids and solids with dielectric greater than 1.4 (lower with special techniques) Supply Voltage Line (24 to 240 VAC) or loop (24 VDC, two-wire) Design Pressure Full vacuum to 5000 PSIG (–1 to 345 bar)
Design Temperature:- − 230 to + 750 ° F ( − 150 to + 400 ° C)
Range :- 2 to 200 ft (0.67 to 60 m)
Dielectric range:- 1.4 to 100 Sensor Pull Strength 11,000 lb (4330 kg)
Cost :- $750 to $3500
Radar level sensor advantages and disadvantages
- Guided wave radar (GWR) provides an accurate and reliable.
- Continuous level measurement.
- GWR is easy to install and enables simple replacement of older technologies
- GWR can be used with liquids, sludges, slurries, and some solids.
- Changes in pressure, temperature Gravity and vapor pressure have no impact on the accuracy of radar measurements.
- radar devices have no moving parts so maintenance is minimal.
- No calibration required GMR required only simple configuration.
Disadvantage / Limitations
- High cost as compared with other instruments.
- While guided wave radar works in many conditions, some precautions need to be taken with respect to probe choice. Several probe styles are available and the application, length, and mounting restrictions influence the choice. Unless a coax-style probe is used, probes should not be in direct contact with a metallic object, as that will impact the signal. If the application tends to be sticky or coat, then only single lead probes should be used. Some advanced GWRs on the market have advanced diagnostics, with the ability to detect build-up on the probe. Chambers with a diameter less than 3 in. (75 mm) may cause problems with build-up and may make it difficult to avoid contact between chamber wall and probe.
Radar gauge technical specification :-
|Sl. No.||Parameters||Minimum Requirements|
|1.||Instrument factory accuracy||+/ – 1 mm|
|2.||Field/ Installed Accuracy||Within +/- 4mm as per OIML|
|3.||Measuring Range||0.5 m to 30 m|
|4.||Measuring resolution||1 mm|
|5.||Product temperature range||-5 to 55 deg C|
|7.||Antenna type||Parabolic/Horn/Planar/Array/Lens as per OEM’s standards|
|8.||Antenna size||As per site condition|
|9.||Measuring principle||Frequency Modulation|
|10.||Signal processing||Digital signal processing (DSP)|
|11.||Operating frequency||X-band (9.15 to 10.85 GHz) / (70 to 80 GHz) / 6 GHz/ 10GHz/26 GHz or as per OEM’s standards|
|12.||Ambient temperature range||Refer Site Data|
|14.||Protection Class||IP 65 (NEMA 4)or better|
|15.||Relay output||SIL2 certified relay for Hi Hi level required|
|16 (a)||Hazardous Area Classification||Zone 1, Group II A & IIB, T3|
|16 (b)||Safety Approval/ Certification||Explosion proof / Intrinsic safe & PESO, SIL2 certified by|
|17.||Certification||ATEX, CENELEC, FM, BASEEFA|
|18.||Other Approvals||Department of legal metrology, custody transfer approval, OIML certificate etc|
|20.||Finishing||Chromatised /hard anodized/polyurethane paint|
|21.||Antenna material||AISI 316 (acid resistant SS) and PTFE / SS 316 and FEP or equivalent as per OEM’s standard and shall be compatible with the process fluid and weather condition.|
|22.||Process connection||On the Roof Top of the tank either on Still well pipe or Manhole cover as per site condition|
|23.||Power Supply||230 V ±10% AC 50Hz +/- 5% / 24 V DC|
|24.||Rating||Vendor to specify|
|25.||Lightning protection||Full galvanic separation|
|26.||Field communication||Vendor to specify|
|27.||Protocol||Vendor to specify|
|28.||Common mode rejection||> 150 dB|
Maximum 8 tanks shall be multi dropped in a loop connected from field to control room subject to meeting the Functional Requirement and min 25% Spare capacity of Loop
Radar Gauge Tank side Indicator
|1.||Display||Back Lit LCD /LED display|
|2.||Ambient temperature range||Refer Site Data|
|3.||Protection||IP 65 or better|
|4.||Safety||Explosion proof / Intrinsic safe|
|5.||Power Supply||Loop powered / Bus powered|
|8.||Finish||Powder coated/hard anodized/polyurethane paint/ Chrome free coated Aluminum|
|9.||Cable entry||Vendor to specify|
|10.||Parameters to be displayed||Product Level, Temperature, water interface level and alarm / other diagnostics information etc (as applicable).|
Radar Level gauge Transmitter Manufacturer
|Radar Type Level Transmitter Manufacturers / Vendors||Country||Website||Phone No.|
|ENDRESS & HAUSER||GERMANY||www.endress.com||+49 71562090|
|ENRAF BV||NETHERLANDS||www.enraf.com||+31 152701100|
|FUJI ELECTRIC CO LTD.||JAPAN||+81 425856201|
|KROHNE MESSTECHNIK GMBH & Co. KG||GERMANY||www.krohne.de||+49 2033010|
|SAAB TANK CONTROL (UK) LTD.||UK||www.saabtankcontrol.co.uk||+44 1189736670|
|SAKURA ENDRESS CO., LTD.||JAPAN||www.jp.endress.com||+81 422542311|