Note: Descriptions are shown in the official language in which they were submitted.
Case 2316
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This invention relates to the detection of a "trip"
or emergency shutdown of a process.
In certain processes it is desirable, and in fact
in some instances safety regulations may require, that one or
more protective systems or arrangements be provided for
emergency shutdown of the process. For example, regulations
pertaining to the operation of a nuclear reactor may require
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one or more protective systems to chutdown the process of the
reactor under certain conditions. Thus, in such a process there
may be one or two protective systems as well as the control
system which provides the normal control and regulation of
the process. It may also be desirable that in the event of an
emergency shutdown, each protective system and control system
be automatically switched to its appropriate shutdown mode
as soon as the emergency shutdown occurs~to avoid the
possibility of continuing operation or restarting of the process.
At the present time the conventional practice is to initiate
the automatic switching to the shutdown mode of the protective
systems and the control systems by means of a signal which
originates in the one system which carried out the shutdown.
This involves a certain degree of interconnection between the
various protective and control systems and the emergency
shutdown system. This interconnection is undesirable from a
safety standpoint.
The present invention may be used to detect an
emergency shutdown by direct measurement of the process state
and provide a signal suitable for switching one or more systems
to the shutdown mode. It does not require interconnection
with other systems for detlermining that an emergency shutdown
has been carried out by another system. The present invention
therefore reduces interconnection between the various
protective and control sysltems.
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It is therefore a feature of this invention to
provide a method for detection of the trip or emergency
shutdown of a process.
It is also a feature of the invention to provide a
novel apparatus for detecting directly a trip condition of a
process.
In accordance with the invention there is provided
a method for detecting a process trip, comprising the steps
of determining the rate of change of at least one parameter
representative of the state of the process, and providing a
signal representing said rate of change, determining from
said signal that (a? said parameter has changed by a pre-
determin0d amount and (b) said rate of change has exceeded
a predetermined level continuously for a predetermined period
of time consistent with a process trip, and then providing
an output indicative of a process trip.
In accordance with the invention in another form
there is provided apparatus for the detection of a process
trip, comprising means ror determining the rate of change of
2Q at least one parameter representative of the process and
for providing a signal representing the rate of change,
comparator means for comparing said first signal with a
predetermined reference level and providing a second signal
only when said first signal exceeds said predetermined
reference level, and timing means for establishing a predeter-
mined period of time, said timing means providing an output
signal when said second signal is received continuously for
said predetermired period of time and is consistent with a
process trip, said output signal being indicative of a process
trip.
The invention will be described with reference to
the accompanying drawings, in which
10'31~9B Case 2316
Figure 1 is a schematic block diagram of apparatus
according to one form of the invention, and
Figure 2 is a schematic block diagram of apparatus
in a simplified form.
Referring now to Figure 1, a process is represented
by block 10, and the process has at least one measurable
parameter which is representative of the state of the
process and which reflects the nature of the process. For
~ example, block 10 might represent a nuclear reactorJ and the
process therefore a nuclear reaction)with a suitable parameter
being neutron flux. Neutron flux is a parameter which
reflects the essence of a nuclear reaction.
The particular parameter of process 10 must be
measured and the measurement device 11 is arranged to measure
the parameter (or parameters if more than one is used) and
provide a signal which repres nts the parameter. In the example
where process 10 is a nuclear reaction, because it is best
c~aracterized as a logarithmic process, the signal provided
by measurement device 11 is conveniently the logarithm of the
sum of one or more measurements of the neutron flux level.
The parameter measurement device 11 is connected to
a differentiator 14 by conductor 12. The conductor 12 carries
the signal representing the parameter as measured by device
llJand the differentiator 14 differentiates the signal with
respect to time. The differentiator 14 is connected to a
smoothing filter 16 by a conductor 15. The differentiator 14
provides an output signal on conductor 15 which corresponds
to the time rate of change of the signal on conductor 12.
The signal on conductor 15 is passed by smoothing filter 16
to conductor 17. The smoo1:hing filter 16 attenuates high
frequency components of the signal it passes~as these are not
b~
meaningful to trip detection e~ this invention. Filter 16
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may be omitted Eor simplicity where hiyh Erequency components
are not excessive. Conduc-tor 17 is connected to comparator 18
and applies the filtered signal to comparator 18. Comparator
18 compares the smoothed signal with a preset reference value.
Whenever the signal has a magnitude greater than the reference
value and has a first polarity consistent with the shutting down
of process 10, an output signal is generated on conductor 20.
The output signal on conductor 20 has a magnitude proportional
to the smoothed rate signal on conductor 17 and a polarity
lQ corresponding to the first polarity consistent with shutting
down process 10 whenever the smoothed rate signal exceeds the
reference. Otherwise the signal on conductor 20 is zero or
possibly it may have a second pola~ity opposite that consistent
with shut down and may be considered to be zero as far as it
affects the circuitry.
Conductor 20 is connected to a timer 21 (or integrator
21) which performs an integrating function. Timer 21 generates
a signal on conductor 22 corresponding to the time integral
of the signal on conductor 20 whenever the signal on conductor
20 has a polarity corresponding to the aforementioned first
polarity. When the signal on conductor 20 is zero, or if i-t
assumes the second polarity, the signal on conductor 22 is
rapidly returned towards zero (i.e. to a reference level we
can consider as zero.)
From the description given thus far, it will be
understood that the signal on conductor 22 corresponds to an
amount by which the signal representing the measured parameter
(the signal on conductor 12) has changed at a rate which is
continuously in excess of a preset reference value set into
comparator 18. It will be further understood that if this
amount exceeds a prescribed minimum amount, a process trip
can be deemed to have occurred.
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~ ccordingly, the presen-t invention identifies a
process trip as the fulfillment of two requirements, namely:
(a) that the parameter as represented by the signal
on conductor 12 must have changed by some minimum amount in
the direction consistent with shutting down the process 10, and
(b) that the change in the parameter must have occurred
at a continuous fast rate as preset into comparator 1~,
consistent with a process trip.
Ordinary transients in a process might fulfill one or
other of the two requirements above, but not both, and so ordinary
transients will not be identified as a process trip.
Conductor 22 is connected to a switching circuit 23
and supplies the integral signal thereto. Switching circuit
23 performs two functions, namely:
(a) it compares the integral signal on conductor 22
with a predetermined reference value, and
(b) if the comparison shows that the magnitude of
the integral signal on conductor 22 exceeds the predetermined
reference value, the switching circuit 23 operates one or
more sets of contacts 24 to change their state (the contacts
24 may be solid state devices).
While the schematic diagram of Figure 1 was described
with respect to electric or electronic equipment, it will be
apparent to those skilled in the art that combinations of
pneumatic, electronic or hydraulic means might be used.
~arious alternatives may be used as required or as
convenient for the particular process. For example, comparator
18 has been described as providing a signal on conductor 20
when the rate signal on conductor 17 is greater than the
preset reference value, and of the proper polarity, and the
signal on conductor 20 is proportional to the signal on
conductor 17. However, other alternatives may be used when
circumstances favour them, for example:
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Case 2316
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when the rate signal on conductor 17 is greater than
the preset reference value in comparator 18 and is of the
proper polarity, the comparator may generate a signal on
conductor 20 that is proportional to the excess of the rate
signal on conductor 17 over the preset reference value, or
when the rate signal on conductor 17 is greater than
ue
~J the preset reference ~e in comparator 18 and is of the proper
polarity, the comparator may generate a signal on conductor
23 that is of a fixed magnitude.
lQ Also, the timer 21 has been described as receiving
the signal on conductor 20 and when the signal has a proper
polarity generating a signal which appears on conductor 22, the
generated signal corresponding to a time integral of the
signal on conductor 20. However, other alternatives may be
used when circumstances favour them, for example:
the timer 21 may generate a signal corresponding to
a time integral of only a limited portion of the signal
on conductor 20, or
the timer 21 may generate a signal on conductor 22
2Q which corresponds to a fixed function of time (e.g. a fixed
integration rate) and is triggered by the signal on conductor
20 but is otherwise not responsive to the signal on conductor
20.
The aorementioned alternatives may be used above
or in appropriate combination as circumstances require.
Referring now to figure 2, there is shown a specific
example of a simplified trip detection arrangement according
to the invention. In Figure 2 the process 10, parameter
mea~urement device 11, conductor 12, differentiator 14,
3Q conductor 15, filter 16 and conductor 17 are similar to those
in Figure 1. The comparator 18, timer 21 and switching circuit
23 of Figure 1 are replaced by a time delay relay 26 in Figure 2.
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The time delay relay 26 receives a filtered rate signal
from conductor 17 and it provides an output which operates one
or more sets of contacts 2~a to change their state.
The time delay relay 26 has the following characteristics:
(a) It has a predetermined trigger level such that
timing will be initiated only when the signal on conductor 17
exceeds the trigger level.
(b) It has a predetermined reset level such that
timing will reset to zero when the signal on conductor 17 drops
lQ below the reset level.
(c) It has a suitable time delay incorporated to
delay actuation ~so that an actual process trip can be
distinguished from lesser disturbances~.
When the necessary criteria are met, the time delay
relay will cause contacts 24a to operate or change their state.
The form of the invention as described with reference
to Figure 2, identifies a process trip as a fulfillment of
the same two requirements as the form of the invention described
with reference to Figure 1, namely:
2Q (a) the parameter as represented by the signal on
conductor 12 must have changed by some minimum amount in
the direction consistent with shutdown, and
(b) the change in the parameter must have occurred
at a continuous fast rate in accordance with the trigger
level in relay 26 (the time delay and the reset level ensure
that the change is fast and continuous~.
It is helieved the invention in its various forms
and alternatives will be clear from the preceding description.
