8AA2A1006 datasheet(2/20 Pages) MAGNETROL

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P R O C E S S

M E D I A

G U I D E L I N E S

Bare metal

probe

Air

Metal vessel wall

(ground reference)

Non-conductive

(insulating medium)

Insulated

probe

Metal

rod probe

Probe

insulation

Metal vessel wall

Conductive medium

(ground reference)

Conductive

media

Non-conductive (dielectric less than 10 or conductivity

less than 10 µsiemens/cm)

Hydrocarbons, solvents, and bulk solids typically fall into

the category of non-conductive media. Initially, when the

vessel is empty, the dielectric constant is 1 (air). As the

media level rises, the dielectric of the media replaces the

air,

thus

causing

the

capacitance

increase.

This

increase is linear with the level increase. A bare probe is

usually the best choice for this application.

Conductive (dielectric greater than 10 or conductivity

greater than 10 µsiemens/cm)

Conductive media in conjunction with a bare probe will

result in an electrical “short”, causing a transmitter to

indicate a high level or a switch to change state. The

solution is to use an insulated probe constructed of

Teflon®, Kynar®, or Halar®. The conductive media creates an

electrical connection between a metal vessel wall and the

probe insulation. Like the non-conductive application,

the distance between the probe and ground, and the

probe diameter is fixed. Instead of measuring the dielec-

tric of the media, we are measuring the dielectric of the

probe insulation which is covered by the media.

M A G N E S E A L

P R O B E S

Probes are an essential component of the RF Capacitance

measurement system. They are critical in development of

the proper “capacitor” for reliable level measurement. As

importantly, the probe becomes part of the process seal

of the vessel; its reliability is crucial. With the develop-

ment of the Magneseal probe, Magnetrol has taken strides

to further ensure this reliability.

The Magneseal probe offers the following advantages:

1. A sophisticated compression seal exerts radial pressure

between the center rod and the mounting nut yielding

bulletproof sealing up to 3000 psig (205 bar).

2. Spring washers maintain the seal particularly during

varying temperature and pressure that can degrade

other process seals.

3. The Teflon® (TFE) probe insulation is

heat-treated which forms the material

tight to the probe rod. This process

yields better linearity and eliminates

“stress-relieving”

(elongation)

the

material at elevated temperatures.

4. Stability of the outer jacket is main-

tained by the end of the probe barb

which further secures the insulating

jacket.

The Magneseal design ensures reliability

long after initial installation.

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