4
012208
Failure Alarm:
Integral:
Included
Remote:
Included
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 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 R e m o t e P r o b e :
T h e
R o n a n
Remote Probe (located on vessel) with the X90-301
switch electronics may be located in a general
purpose or Division II location. This is the most
widely used configuration.
3.1.2 Integral Switch:
The Ronan Model Integral
Switch in an explosion-proof housing is usually
specified when the 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.
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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 detector receives full radiation and
produces an output. This output will fail, producing
an alarm when either the radiation is interrupted by
the process level rising to above the set limit or the
detector or its power supply fails. However, if the
detector or power supply fails, a failure alarm will
be actuated, indicating the problem is in the unit.
If the detector output does not indicate a minimum
background value (due to a malfunction in the
detector or its power supply) the process (and
failure, if used) relay automatically changes over,
indicating an alarm condition.
The failure alarm will occur anytime the output from