API OICSGuided Wave Radar

Probe types and applicationsBy

Kevin MartynMagnetrolApril 14/08

Types

TwinCoaxial Single rod

Dual element probes, no beam spread, high sensitivity. Single element probes, lesssensitivity. High build upresistance. In a matched chamberperforms like a coaxial probe

Selecting the right probe is key to the application, in both electrical and mechanical aspects.It their simplest form they are just a rod in a process, made with compatible metal, that can be cut,bent, or coated to suit the application. Over 20 types to choose from, that fall into two simplecategories, single or dual element. Twin and Single Rod Probe can be rigid or flexible.

Anatomy and function of GWR Probes

End of Probe Pulse

To better understand their application, lets look at what they do.

Fiducial Pulse Level Pulse

Anatomy and function of GWR Probes

End of Probe Pulse

Fiducial Pulse Level Pulse

Let’s break our look at this into 3 sections.

Starting at the top of the probe

• Engineered impedance change (Fiducial) causes a reference reflection in the probegland rather that in the vessel where it can cause error (transition zone) or completeloss of signal (blind zone). This allows a true overfill rated device, as opposed to “holdlast value” approaches and their associated risk. This contributes to their suitability asSIL 2 devices. Deadzones, null areas, transition zones etc. can now be avoided inalmost all applications

• Delay line which connects the electronics to the probe is a predetermined length (9”Typical) . The fiducial is continuously measured to verify calibration and accuracy. Canbe extended to 15 feet for convenient remote electronics.be extended to 15 feet for convenient remote electronics.

• The process seal is also contained in this section. Certified to ISA 12.27.01, confirmingreliability of both hard bonded, and soft (o-ring) type seals. Our seals are tested up to16,000 psi by accredited 3rd party agencies. Seals can be bonded borosilicate glass(hermetic) or a variety of o-rings materials combined with other materials like Teflon,Peek , or alumina, depending on application requirements.

• A reference target is added to the probe a few inches below the gland, in those caseswhere the dielectric of the upper gas vapor is variable and high enough to startimpacting accuracy (steam). It measures and provides correction of error. With thiscompensation algorithm, boiler drum level, feed water heaters and flash tanksbecome excellent applications.

Seal types and related applications

Hard Seals• Contain borosilicate glass• Rated to 800F or 6250 PSI• Hermetic seal useful for full-vacuum applications• Rated to -320F for cryogenic applications• Must be used for ALL anhydrous ammonia and chlorine applications• Not a good choice for saturated steam

Hard bonded seals, and soft o-ring seals

Soft Seals• O-ring material selected for application• Faced with TFE, Peek, or Alumina, to suit application• 650F or 2400 PSI• Suitable for vacuum, but not true hermetic

Spacers (coax probes)• TFE, Peek, or alumina

The level reflection

• Correct probe / chamber / electronicsconfiguration will yield a suitable levelreflection in even the lowest dielectric media

• There will be one reflection in overall levelapplication or two reflections in interfaceapplications.

• The second (interface) reflection can be• The second (interface) reflection can begenerated with any probe type.

• The standard electronics looks at the distancebetween the two reflections and corrects forthe time of flight delay through thehydrocarbon layer.

• Probe reflections can easily be observed andoptimized with free industry standard FDTsoftware.

Interface Measurement

Interface Specifications:Interface Specifications:

• Top Layer r = 1.4 to 5

• Bottom Layer r > 15

• Probes to 40 feet

• Tracks upper edge of emulsion

• Emulsion can be several feet

• Resolves 1-2 inch of hydrocarbon even in high temperature apps

• Coaxial probe, 500cP

• Enlarged Coaxial probe or Twin Flexible probe, 2000cP

• SRP in matched chamber

Interface Level measurement & Emulsion Layers

Air

Oil

Air

Oil

Rag Layer

Air

Oil

Air

Oil

Rag Layer

Does overall level vary,as well as interface?

Clean interface oremulsion?

GWR will track here

Clean Interface

Water

Rag Layer

Water

Rag LayerClean Interface

Water

Rag Layer

Water

Rag Layer

Do you have one variable (interface) or two (overall level and interface). Many technologies can handleonly one variable. A second will introduce substantial error.

End of Probe reflection

• In low E applications, or when there is no level on probe, thissignal can be seen a verified to be in the correct location. Ahelpful diagnostic.

• This EOP signal does move with level on the probe, but shouldnot be used to infer level (EOP following) as it is affected bydielectric changes in the media, and offers poor resolution andaccuracy.

Probe Choice Is Critical!

Must Consider….. Temperature

Pressure

Steam

Mounting fitting

Viscosity

Material compatibility

Seal / O-rings

Turbulence Mounting fitting

Length

Head room

Dielectric sensitivity

Coating/bridging/buildup

Obstructions/proximity effects

Overfill considerations

Probe typesProbe types

Probe Configurations

Coaxial Probe

Coaxial Probe

• 0.375” (10mm) rod inside of a 0.875” (22 mm tube (standard)• 0.6” (16mm) rod inside a 1.75” (45 mm) tube (enlarged)• Most efficient waveguide, Er > 1.4• No proximity effects.

Electromagnetic Propagation

Bottom View

• No proximity effects.•Reads level accurately to the very top (no transition zone)•Suitable for very high RF fields•Viscosity < 500 cp (standard)/ <2000 cP (enlarged)• High Temperature, High pressure versions (800F or 6250 PSI)• Probe lengths to 20 Feet rigid• 316 ss standard. Hastelloy and Monel optional

•Single bottom spacer for viscous applications

•Optional flushing connection allows CIP without processinterruption

Probe ConfigurationsTwin Rod Probe

•Two 0.5” (12 mm) parallel rods

• General purpose probe, Er > 1.9

• 3” or larger chamber

Bottom ViewElectromagnetic Propagation

• Viscosity < 1500 cp

• Rigid Probe lengths to 20 feet (6 meters)

• FEP Coated Flexible Probes to 75 feet (22 meters)

• 316ss (std.) Hastelloy and Monel optional

Probe ConfigurationsSingle Rod Probe

Single Rod Probe• Solid 0.5” (12mm) rod

• Er > 1.9 when used in chambers, 1.4 if impedance matched.

• Er > 10 when used in open vessels

• High viscosity applications (<10,000 cP)

• Immune to high dielectric buildup

• Rigid probes to 20 feet, flexible cable to 75 feet

• Exotic metals and PFA coating optional

The larger the launch plate (flange, top of tank), the better the performance.

The least sensitive probe also has a large impedance change as the signal enters the vesselwhich can cause a small blind area at the top. Mounting in a matched chamber turns it into alarge coax probe, making it very sensitive and overfill suitable.

Yes you can really bend it!

Probe mountingProbe mountingChambers and nozzles

Invasive or bridle mounts – present different issues

Single rod probe in amatched chamber givesconstant impedance andcoax performance.

Typical approach in refineries, & chemical plants

• Isolation allows maintenance withoutinterrupting the process.

• Chamber is sized and matched toinstrument characteristics.

• Option for redundant indicator (MLI).

• B31.3 piping code typical

• NACE, insulation, heat trace optional

• Available as a complete package.

Temperature effect

Cooler product becomes more dense, and indicates a lowerlevel for same weight. Insulation & heat tracing can help.

Why “Overfill Safe”?

•Overfill probes can measure to within specification all the way upto the process seal

•Important in cage applicationsLLSD - 1208

•Don’t go blind! ?

Piping Configurations

C

B

A

Single Rod Probe

nozzles

= Diameter ______

= Length ______

A

B

B

AB

C

Note: divided

2"x6" (50x150mm) nozzles (typ.) will force increasedBLOCKING DISTANCE and possible decreased SENSITIVITY

Note: divided by should be >or= 1 for optimum performance

= Length ______

= Mounting ______

Bent Probe with built in chamberPopular displacer level transmitter replacer

Before After

Coaxial vs. SRP invasive vs SRP

FiducialNo unwantedchanges inimpedance

Coaxial Probe Single Rod Probe

Fiducial

Mismatch depending onmounting

Level Level

Coaxial vs. Single Rod Probe

FiducialNo unwantedchanges impedance

Fiducial

Smaller mismatchdepending on chamber

Coaxial Probe Single Rod Probe in Stillwell/Cage

Level Level

depending on chamberdimensions

Frequently Asked Questions

Q: Is the probe matched to the electronics, such that I need to select a certain combination for myapplication?A: No, the electronics quick connect to, and work with any probe. It is the probe and optional chamber youselect for the application, not the electronics. Electronics are typically selected to meet area classifications.

Q: I am replacing displacer transmitters that came with chambers, can I do the same with GWR?A: Yes this matching chambers are becoming increasingly popular, However you may be able to use theexisting chamber with a new GWR probe as well.

Q: Do GWR probes work if the application is producing steam?A: Yes, but only if a steam probe with compensating reference target is selected.

Q: I have a vacuum tower application, any special concerns?A: Yes, you should select a probe that accurately reads to the face of the probe, and you may also want a truehermetic seal.

Q: Can I cut the probe if it is too long.A: Yes, please request the appropriate procedure from the manufacturer.

Q: What about liquid /liquid interface applications?A: Fine for a standard unit, but if non invasive (in a bridle), make sure you have sufficient equalizationconnections, if it is not flooded service.

Q: What about critical overfill applications?A: Select a probe that has no transition zone for accuracy and reliability to the very top of the probe.

Questions?

E-mail kmartyn@magnetrol.com for additional info, or a copy of this presentation.

For the internal use of API OICS

This presentation contains Magnetrol proprietary and confidential information. Do not reproduce or distribute without written permission