Ronan X90 Series Manuel d'utilisateur télécharger pdf (Page 4)

Time Delay Range:

Integral: 0.5 to 20 seconds (10 or

20 seconds normal); jumper-selectable Remote: .05 to

20 seconds (10 or 20 seconds normal); jumper-

selectable

Display: Integral: LED status indicator Remote: LED

status indicator

Accuracy: Integral ± 1/8” Remote: ± 1/8”

All equipment approved by CSA.

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3.0 THEORY OF OPERATION

The Ronan Series X90 gamma switches provide an

alarm signal whenever the radiation field intensity at the

detector (G-M tube) changes by more than its

predetermined value. The variation in the field intensity

may be due to either a change in the level (at the limit),

or a change in the density of the process material in the

radiation beam path. In a typical arrangement, the X90

detects the level of liquid in a vessel when it has

exceeded a predetermined limit. The level limit is

defined by an imaginary straight line drawn from the

source to the detector.

Figure 1: Source and Detector

When the feed valve is open, liquid is fed into the vessel

and the liquid level rises. The liquid level will rise until it

interrupts the gamma ray beam. There is then a change

in the field intensity at the detector due to absorption by

the process of some of the energy present in the beam,

and the instrument puts out an alarm signal in the form

of a relay contact changeover. This signal may be used

to close the feed valve and/or activate an annunciator.

As the liquid is used from the vessel, the level will fall,

thus again exposing the detector to the gamma radiation

and the feed valve will be opened when the contacts

revert to normal.

This is an example of a high limit switch, i.e., the process

level is not allowed to rise above a certain limit.

Conversely, the source and the detector may be lowered

to below the liquid level and the system functions as a

low limit switch, in which case the system will produce an

alarm when the liquid level falls below this low limit. The

liquid itself may be under pressure at high temperature

or even corrosive, but its characteristics will not affect

the switch, since the system components are outside of

the vessel.

A time delay based on the measurement controls the

interval between radiation level change and alarm. A

hysteresis band about the required level prevents

fluttering and spurious alarm situations.

3.1 Optional Gaging Configurations

3.1.1 Model X90-1004 Remote Probe: The Ronan

Model X90-1004 Remote Probe (located on vessel)

with the X90-301(V) switch electronics may be

located in a general purpose or Division II location.

This is the most widely used configuration. The

X90-1004X is a high-sensitivity tube, which may be

specified for very weak fields (0.1 mR/hr. or less).

3.1.2 Model X90-1005 Integral Switch: The

Ronan Model X90-1005 Integral Switch in a Model

X90-1001XP housing is usually specified when the

X90-301(V) switch electronics cannot be located in

a general purpose or Division II area. It may be

used when the vessel is easily accessible for

calibration and maintenance.

The Model X90-1005 contains the G-M tube sensor

and switch electronics on a single chassis and is

mounted on or just off the vessel wall.

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4.0 FUNCTIONAL OPTIONS

4.1 High-Limit Process Alarm

The Process alarm relay will change over when the

level of process material rises above the set limit.

4.2 Low-Limit Process Alarm

The process alarm relay will change over when the

process level falls below the set limit.

4.3 Failure Alarm

In the case of the high-limit switch, under normal

conditions the G-M tube receives full radiation and

produces an output. This output will fall, producing

an alarm when either the radiation is interrupted by

the process level rising to above the set limit or the

G-M tube or its power supply fails. However, if the

tube or power supply fails, a failure alarm will be

actuated, indicating the problem is in the unit. If

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Ronan X90 Series Manuel d'utilisateur Page 4

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