Non contact radar level transmitter principle




non-contacting radar level measurement there are two main modulation techniques, pulse radar and FMCW (Frequency Modulated Continuous Wave) radar techniques. Non-contacting pulse radar sends out a microwave signal that bounces off the product surface and returns to the gauge. 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.

The FMCW radar also transmits microwaves towards the product surface, but the transmitted signal is of continuously varying frequency. When the signal has travelled down to the liquid surface and back to the antenna, it is mixed with the signal that is being transmitted at that time. The difference in frequency between the received and transmitted signal is directly proportional to the distance to the liquid with high precision

Installation position of the radar Gauge

  • Installation on a nozzle with diameter Less than 100mm and longer than 300 mm height.
  • Avoid contact of the sensor with the wall of the tank. In case of an installation in a stilling pipe diameter less than 100mm,an  in-situ calibration will be required to respect accuracy specification. For a coaxial version, there is no problem you can install it without precautions.
  • Avoid an installation too close to an agitator. The cables/ rods may become entangled.

Non-contacting radar level transmitter advantages and disadvantages

Advantage of radar level Gauge :-

  • Non-contacting radar provides a top-down, direct measurement as it measures the distance to the surface.
  • It can be used with liquids, sludges, slurries and solid.
  • No impact on accuracy if change pressure, Temperature, dielectric, conductivity and density.
  • Radar devices have no moving parts so maintenance is minimal.
  • No calibration required GMR required only simple configuration.
  • It is a top-down, direct measurement as it measures the distance to the surface.

 

Disadvantage of radar Level Gauge

For non-contacting radar, good installation is the key to success. The gauge needs a clear view of the surface with a smooth, unobstructed, unrestricted mounting nozzle. Obstructions in the tank, such as pipes, strengthening bars, and agitators can cause false echoes, but most transmitters have sophisticated software algorithms to allow masking or ignoring of these echoes.

Non-contacting radar gauges can handle agitation, but their success will depend on a combination of the fluid properties and the amount of turbulence. Dielectric constant (DK) of the medium and the surface conditions will impact the measurement. The measurement may be influenced by the presence of foam. Energy tends to not be reflected by light and airy foam while a dense and heavy foam typically reflects the energy.




Radar gauge technical specification :-

Sl. No.ParametersMinimum Requirements
1.Instrument factory accuracy+/ – 1 mm
2.Field/ Installed AccuracyWithin +/- 4mm as per OIML
3.Measuring Range0.5 m to 30 m
4.Measuring resolution1 mm
5.Product temperature range-5 to 55 deg C
6.Repeatability+/-1 mm
7.Antenna typeParabolic/Horn/Planar/Array/Lens     as     per     OEM’s standards
8.Antenna sizeAs per site condition
9.Measuring principleFrequency Modulation
10.Signal processingDigital signal processing (DSP)
11.Operating frequencyX-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 rangeRefer Site Data
14.Protection ClassIP 65 (NEMA 4)or better
15.Relay outputSIL2 certified relay for Hi Hi level required
16 (a)Hazardous Area ClassificationZone 1, Group II A & IIB, T3
16 (b)Safety Approval/ CertificationExplosion proof / Intrinsic safe & PESO, SIL2 certified by
17.CertificationATEX, CENELEC, FM, BASEEFA
18.Other ApprovalsDepartment   of    legal   metrology,   custody   transfer approval, OIML certificate etc
19.HousingsCast aluminum
20.FinishingChromatised /hard anodized/polyurethane paint
21.Antenna materialAISI 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 connectionOn the Roof Top of the tank either on Still well pipe or Manhole cover as per site condition




23.Power Supply230 V ±10% AC 50Hz +/- 5% / 24 V DC
24.RatingVendor to specify
25.Lightning protectionFull galvanic separation
 Transmission 
26.Field communicationVendor to specify
27.ProtocolVendor to specify
28.Common mode rejection> 150 dB
29.Communication distance

4-Km min

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

Sl. No.ParametersDescription
1.DisplayBack Lit LCD /LED display
2.Ambient temperature rangeRefer Site Data
3.ProtectionIP 65 or better
4.SafetyExplosion proof / Intrinsic safe
5.Power SupplyLoop powered / Bus powered
6.CommunicationDigital
7.MaterialCast aluminum
8.FinishPowder coated/hard anodized/polyurethane paint/ Chrome free coated Aluminum
9.Cable entryVendor to specify
10.Parameters to be displayedProduct Level, Temperature, water interface level and alarm / other diagnostics information etc (as applicable).




Radar  Level Transmitter Manufacturer



Radar  Level Transmitter Manufacturer

Radar Type Level Transmitter Manufacturers / VendorsCountryWebsitePhone No.
EMERSONUKwww.frco.com+44 1162822822
ENDRESS & HAUSERGERMANYwww.endress.com+49 71562090
ENRAF BVNETHERLANDSwww.enraf.com+31 152701100
FUJI ELECTRIC CO LTD.JAPAN +81 425856201
KROHNE MESSTECHNIK GMBH & Co. KGGERMANYwww.krohne.de+49 2033010
SAAB TANK CONTROL (UK) LTD.UKwww.saabtankcontrol.co.uk+44 1189736670
SAKURA ENDRESS CO., LTD.JAPANwww.jp.endress.com+81 422542311
VEGAGERMANYwww.vega.com+49 7836500
WHESSOEUKwww.whessoe.co.uk+44 1325390000