Ultrasonic liquid level measurement system

An ultrasonic level measuring system includes a transducer mounted on the bottom of a pipe which launches acoustic pulses up through the pipe wall into the water. The pulses are reflected from the water surface and received by the transducer along with pulses reflected by the pipe wall and reverberations within the pipe wall. The system has a monitor mode in which a variable threshold for the reflected pulses is set by dividing the time after a trigger pulse into time bins and automatically establishing a threshold level for each time bin. In a signal search mode, the time bin containing the liquid level is identified from a histogram recording reflected pulses which exceed the threshold levels for the various time bins. In a normal operating mode, foreground calculations precisely calculating the liquid level in the identified bin alternate with background calculations which reassess the identification of the time bin containing the liquid level. If the bin identified by the background calculation does not agree with the time bin being used by the foreground calculation, the system restarts by returning to the signal search mode. Various system parameters can be easily changed without the need to rewrite code.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an ultrasonic system for measuring the level of a 
liquid in a container, such as for instance, the level of reactor coolant 
in the pipes of a nuclear reactor. 
2. Background Information 
There are many applications where it is desirable to measure the level of 
liquid in a container, such as a pipe, without penetrating the liquid 
barrier. One such application is a nuclear power plant where there is a 
need to accurately know the water level in the main coolant pipes during 
maintenance operations when water is being circulated for residual heat 
removal (RHR). The normal water level under these conditions is above the 
center of the horizontal pipes, but below the full-pipe level. If the 
level drops too low, vortexing can occur causing air entrainment with the 
potential for air binding of the pump. High water levels during 
maintenance activities on steam generators or reactor pump seals, on the 
other hand, have resulted in reactor coolant spills and personnel 
contamination. 
A commonly used method of measuring water level in the coolant pipes is to 
observe the level on a flexible plastic tube connected to the coolant 
pipe. This requires penetration of the pipe which has the potential for 
leaks and loss-of-residual-heat-removal events. 
Assignee of the subject invention has developed a non-intrusive ultrasonic 
level measurement system which does not require penetration of the pipe. 
While other ultrasonic liquid level measurement systems exist, there are 
particular problems in their application to nuclear power plants. First, 
it is desired that the transducers remain in place during plant operation 
in order to eliminate the cost AND personnel radiation exposure of 
repeated installations. However, this exposes the transducers to 
temperatures up to 650.degree. F. and high radiation levels for long 
periods of time. Another difficulty in this application is that most 
plants have centrifugally cast stainless steel pipe, which strongly 
attenuates ultrasonic waves. Also typical pipe dimensions are 29 inch to 
50 inch inside diameter and about 21/2 inches in wall thickness. 
In the existing ultrasonic level measurement system, a transducer placed on 
the bottom of the horizontal pipe launches an acoustic wave which passes 
upward through the pipe into the water where it is reflected by the water 
surface and returns back through the wall to the transducer. The total 
travel time of the pulse reflected by the water surface is used to 
calculate water level. An echo is also produced at the pipe's inner 
surface because of the acoustic impedance mismatch between stainless steel 
and water. This echo reverberates within the pipe wall with the 
reverberation decaying with time. A threshold is established to 
distinguish the surface reflection signal from the reverberations. This 
threshold must be set low enough to detect high water level signals which 
are attenuated by their longer travel through the water, resulting in the 
reverberation signals being greater than the threshold for low level 
signals. The threshold is set by assuming a high threshold and then 
successively lowering the threshold until a selected number of reflected 
pulses out of a given number of trigger pulses exceed the threshold. If a 
prescribed number of these reflected pulses are within a predetermined 
time range, the last value of the threshold is reduced by a given percent 
with the result used as the threshold for determining water level. This 
system could not monitor the required lower water levels because of 
reverberation. 
There is a need for an improved ultrasonic level measuring system which is 
more reliable and can accurately measure low liquid levels. 
SUMMARY OF THE INVENTION 
In accordance with the invention, an ultrasonic level measurement system 
establishes a variable threshold for detecting pulses reflected from the 
surface of the liquid in a container such as a pipe. This variable 
threshold essentially tracks the reverberation profile, and preferably 
establishes individual threshold levels for time bins calculated from the 
trigger pulse generated when the transducer launches the acoustic wave 
through the pipe wall into the contained liquid. This variable threshold 
can be manually set, but is preferably automatically set by iteratively 
raising or lowering the threshold to achieve a selected low percentage of 
reverberations which exceed the threshold and then increasing the 
threshold by a percentage and a fixed offset above that level. 
The system also includes an improved signal search mode in which a 
histogram is generated from rounds of data to record the number of pulses 
during each time bin which exceed the threshold level for that bin. The 
lowest bin number for which the recorded number of reflection pulses 
exceeds a programmable percentage of trigger pulses is selected as the 
initial bin in which the present water level is located. 
The system is then switched to a normal operating mode which repetitively, 
alternately performs a foreground calculation which calculates the precise 
water level from reflected pulses received in the initial bin identified 
in the signal search mode, and a background calculation which in a manner 
similar to that of the signal search mode, generates a histogram of 
reflected pulses exceeding the variable thresholds for each of the bins. 
This background calculation is used to verify that the foreground 
calculation is being performed on the proper signal in the proper bin. If 
the bin identified by the background calculation does not agree with the 
result of the foreground calculation, and this occurs a programmable 
number of times, the system transfers back to the signal search mode to 
reestablish the location of the water level. The system also reverts to 
the signal search mode if a programmable percentage of pulses are not 
detected in the foreground calculation. 
In accordance with the invention, the various parameters, such as for 
instance the percentage of reflected pulses that must be seen for a valid 
calculation of liquid level, can be easily programmed by the operator 
without the need for modifying code. This provides a great deal of 
flexibility for fine tuning the system, and for adapting the system for 
different applications. 
More particularly, the invention comprises a system for measuring a liquid 
level in a liquid carrying container including a transducer acoustically 
coupled to the container wall, pulse generating means applying a pulse to 
the transducer to launch an acoustic pulse through the container wall into 
the liquid which generates reflected pulses from the container wall and 
liquid surface and reverberations which decay with time following the 
trigger pulse to produce a reverberation profile, threshold setting means, 
setting a variable threshold which is reduced in magnitude with time 
following the trigger pulse and which exceeds the reverberation profile in 
magnitude, and means comparing reflective pulses with the variable 
threshold at the time the reflected pulses are received, and generating a 
liquid level signal when the magnitude of reflected pulses exceeds the 
variable threshold.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The invention will be described as applied to determining the water level 
in the pipes of a pressurized water reactor; however, it will be 
appreciated by those skilled in the art that the invention has application 
to determining liquid levels in other containers. 
FIG. 1 illustrates the lower section of a hot leg pipe 1 of a nuclear 
reactor which is located inside of containment 3. Water 5 contained in the 
pipe 1 has an upper surface 7 to which the height, H, of the water is 
measured. A transducer 9 is acoustically coupled to the bottom of the 
horizontal pipe 1. A pulser/preamplifier 11 located inside containment 3, 
but separated from the pipe 1 by a shield wall 13 is connected to the 
transducer 9 by cabling 15. A transmit pulse generator and timing circuit 
17 in the pulser/preamp 11 repetitively generates with a period T a 
voltage transient which shock-excites the transducer 9. The transducer 9 
in turn launches a transient ultrasonic wavefront through the wall of the 
pipe 1 and into the water 5. Echoes, in the form of short wave packets 
return to the transducer 9 and produce electrical signals in the form of 
short bursts at the transducer resonant frequency. 
The pulser/preamp 11 also includes a transmit/receive (T/R) network 19 and 
a high pass (HP) filter 21 which, respectively protect the receiver 
circuits from the transmit pulse and eliminate low frequency energy caused 
by vibration and other sources. A preamp 23 provides linear gain with low 
noise, while blanking the transducer output for nominally 20 .mu.Sec and 
injecting a trigger signal into a triaxial cable 25 connecting the 
pulser/preamp 11 with a signal processing unit 27 outside of containment 
3. The trigger pulse is sent to the signal processing unit 27 to 
synchronize its operations. 
Some of the acoustic signal generated by the transducer 9 reflects off the 
inner wall of the pipe 1 and is detected by the transducer 9, and 
significant acoustic signals reverberate in the pipe 1 and may be observed 
by the transducer 9 for a relatively long period time. However, a 
sufficient portion of the signal propagates through the pipe 1 and is 
coupled into the water 5. This desired signal propagates through the water 
5, reflects off the surface 7 of the water, travels back toward the 
transducer 9, is coupled into the pipe 1, propagates through the pipe, and 
is finally presented to the transducer. 
Immediately after the transmit pulse is generated, the T/R network 19 
switches to the receive mode and the reflected signal detected by the 
transducer 9 is filtered in the HP filter 21, amplified in the preamp 23 
and sent to the signal processing unit 27 over the cable 25. The function 
of the signal processing unit 27 is to determine which signal received is 
the true indication of the signal reflected off the surface of the water, 
measure the time between the trigger signal and the water reflection 
signal, and produce an analog signal proportional to the detected water 
level. 
FIG. 2 is a diagram showing a response of the transducer 9. The trigger 
pulse 29 is a very large signal. The reflection from the interior wall of 
the pipe is shown at 31 and the reverberation profile which decays with 
time is shown by the trace 33 with the reflection from the water surface 
indicated by the spike 35. The variable threshold 37 is set above the 
reverberation profile 33, but below the level of the water surface 
reflection 35. The variable threshold 37 is set, as discussed in more 
detail below, by dividing the time following the trigger pulse into time 
bins 39. In the exemplary system, these time bins are each 50 .mu.s in 
duration and 79 such time bins are provided to accommodate pipes with an 
ID up to 50 inches and a wall thickness of about 21/2 inches, filled with 
water at high temperature. The first bin representing the water level 
inside the pipe is the second bin which begins at 50 .mu.s and extends to 
100 .mu.s. The threshold 37 remains above the noise 40 for all bins. 
Returning to FIG. 1, the signal from the pulser/preamp 11 is sent directly 
over channel 1 to a first peak detector 41 which detects and shapes the 
envelope of the pulse received and applies it to a first comparator 43. 
The threshold for the comparator 43, identified as the trigger threshold, 
is generated by a quad digital to analog (D/A) converter 45 under control 
of a microprocessor circuit 47. This trigger threshold is set so that the 
trigger signal is reliably detected, but the signals detected by the 
transducer 9 are not seen at the output of the comparator 43. 
A separate channel 2 includes an amplifier 49 which detects signals 
received by the transducer 9. A second peak detector 51 is enabled by a 
reset signal from the microprocessor circuit 47 a predetermined time after 
the trigger signal is detected. The peak detector 2 shapes the received 
pulses and applies them to a second comparator 53. The microprocessor 
circuit 47 sets the reflection threshold of the comparator 53 to the 
variable threshold shown in FIG. 2, in a manner to be discussed. The 
microprocessor 47 determines the time between its receipt of the trigger 
signal as detected by the comparator 43 and the water reflection signal as 
output by the comparator 53 corrects this time for the selected 
temperature and produces a signal proportional to water level which is 
converted by the quad A/D converter 45 into either a zero to ten volt 
voltage signal or four to twenty milliamp current signal which is sent to 
a display unit 55 in the plant control room over a twisted shielded pair 
cable 57. 
The ultrasonic level measurement system 59 of the invention has multiple 
operating modes including: a monitor mode, a signal search mode, and a 
normal operating mode. In the monitor mode, the operator may program 
system parameters through commands entered by an RS232 interface 61. These 
parameters are stored in an electrically erasable programmable read only 
memory (EEPROM) 63. Table 1 lists the parameters A-P available in the 
exemplary system and indicates sample values. Some of these parameters are 
self explanatory and others will be understood from the following 
discussion. Each of these parameters is programmable. 
TABLE 1 
______________________________________ 
A: Pipe inside diameter (in mils) = 
29000 
B: Pipe wall thickness (in mils) = 
02760 
C: Calibration temperature (in degrees Fahrenheit) = 
110 
D: Number of background data collection = 
010 
periods before calculation 
E: Number of rounds in each background data = 
020 
collection period 
F: Number of pulses monitored for each foreground = 
100 
calculation 
G: Percent of pulses needed in correct bin for = 
020 
Signal Search Mode 
H: Percent of pules needed to allow a = 
010 
foreground calculation 
I: Number of consecutive insufficient foreground = 
010 
ops for restart 
J: Number of consecutive differing fore and = 
002 
background for restart 
K: Auto-threshold percent of margin for each bin = 
025 
L: Auto-threshold offset margin (.times. 20 mVolts) = 
002 
M: Disable restart based on fore & = 
NO 
background differences 
N: Disable signal search mode marker = 
NO 
O: Parameter measured (Water level or Temperature) = 
Level 
P: Analog output format for level measurement = 
Format 
(Range of level) 1 
______________________________________ 
An important function of the monitor mode is setting of the variable 
reflection threshold. This water reflection threshold must be greater than 
the reverberation and electrical noise. The thresholds may be manually set 
through the parameter Q in Table 1 or by invoking an auto-adjust threshold 
routine. 
A flow chart for a routine for automatically adjusting the variable 
threshold is shown in FIG. 3. This routine automatically sets the 
threshold level individually for each of the time bins from bin 2 up to 
the highest numbered bin. Upon being called at 65, the routine sets a test 
threshold to 21/2 volts and sets a variable BIN# to bin 2 at 67. The 
number of pulses observed as exceeding this present threshold are then 
counted at 69. The microprocessor 47 controls the reset of the peak 
detector 53 so that only signals in the time bin for which the threshold 
is being set are counted. If more than 2% of the pulses result in detected 
reflections as determined at 71, the threshold is increased by 50% of the 
last voltage step at 73. On the other hand, if reflections are detected 
for less than 2% of the pulses, the threshold is decreased by 50% of the 
last voltage step at 75. This process is repeated for 7 iterations as 
determined at 77 in order to refine the threshold. The resultant threshold 
level is then stored in the EEPROM 63 at 79. The thresholds for the 
additional bins are then set in a similar manner by incrementing the bin 
number at 81 and determining when the threshold for all bins have been set 
at 83. The bin threshold is then made monotonically decreasing at 85. That 
is, the thresholds are set so that the thresholds for time bins 
successively later in time decrease or stay the same, but never increase 
over a threshold for an earlier time bin. Gains and offsets are applied to 
the thresholds with the results saved in the EEPROM 63 at 87. 
The monitor mode is selected manually by the operator when any of the 
parameters are to be changed. This includes setting of the variable 
reflection threshold which may be done manually but which is preferably 
done automatically by the routine just discussed. 
On startup of the system, the signal search mode is entered which locates 
the time bin of the reflection signal representing the water surface. The 
normal operation mode then entered. The normal operation mode performs 
foreground calculations and background calculations. The first foreground 
calculation looks in the bin identified in the signal search mode for the 
surface reflection signal. The background calculation performs a search 
like the search performed in the signal search mode to provide an extra 
level of assurance that the correct signal is being used to obtain the 
water level. 
An overall flow chart for the signal search and normal operating modes is 
shown in FIG. 4. The signal search mode 88 is entered upon power-up at 89 
or after abnormal conditions have resulted in the system calling for a 
restart. The signal search mode 88 initializes the system at 91. This 
initialization includes determining the threshold for the trigger signal. 
Initially, this threshold is set at a high level and reduced in 40 mVolts 
increments until the trigger signal is first detected. If a lower limit is 
reached without detecting the trigger, the system is not allowed to 
continue until the trigger has been detected. When the trigger signal is 
detected, the trigger threshold is set to be 2/3 of the level where it was 
first detected. This trigger threshold is used for the detection of the 
trigger signal in all subsequent operations. The trigger is the timing 
reference for all data collected for an individual ultrasonic pulse. 
Initialization also includes determination of the wall reflection 
threshold. This wall reflection signal is used to provide a certain level 
of validity of the sensor 9 and the pulser/preamplifier 11. The wall 
reflection signal must be found in a window of between approximately 20 to 
50 .mu.Sec from the trigger signal. The wall reflection signal is also 
detected by setting an initial high value for the threshold and then 
decreasing this value for successive ultrasonic pulses until the wall 
reflection signal is detected or a lower limit is reached. The system is 
not allowed to continue in the signal search mode until the wall 
reflection signal is reached. This wall reflection threshold information 
is saved for use during the detection of the wall reflection signal and 
all further data acquisition operations. The wall reflection threshold is 
displayed on the terminal 55 after completion of the process. 
Following initialization, if the signal search marker is not disabled as 
determined at 93 in FIG. 3, it is output at 95. The signal search marker 
consists of alternatively setting the analog output between full-scale and 
the minimum value for three cycles, staying on each level for 
approximately one second. After the third cycle, the analog output remains 
at the minimum value for the remainder of the signal search mode. This 
marker may be disabled through the parameter N. 
The signal search mode then determines the initial bin for the water level 
at 97. The flow chart of a routine for accomplishes this is shown in FIG. 
5 which is discussed below. 
The system then enters the normal operation mode which is the most 
frequently used mode while the system is successfully sensing the water 
level within the pipe. This mode alternates between a foreground 
calculation and background calculation. Upon entering the normal operation 
mode, the RS232 display is formatted at 99. A loop is then entered which 
performs the foreground and background calculations. The foreground 
calculation is responsible for the termination of the precise water level 
and its output to the water level indication analog output as well as the 
status display on the RS 232 port. This is accomplished by acquiring the 
timing information from parameter F consecutive ultrasonic pulses and 
averaging the water reflection times which normally occur within a timing 
window centered around the last water level indication was observed. In 
the exemplary system, the timing window is plus or minus 125 .mu.Sec. In 
order to remove the approximately 10 .mu.Sec uncertainty in the individual 
data acquisition operations, any water level indication in the lower 20 
.mu.Sec of each 50 .mu.Sec time bin will call for the data acquisition to 
begin in the previous bin. All water times in the timing window are 
averaged together to determine the water level. The analog output and the 
RS232 status message will then be updated to indicate the water level. The 
analog output will either correspondence to 0 inch to full pipe or 4 inch 
to full pipe, depending on the setting of parameter P. 
As seen in FIG. 4, the foreground calculation is performed at 101 and is 
followed at 103 by the background calculation. 
The background calculation part of the normal operation mode is needed to 
provide an extra level of assurance that the correct signal is being used 
to obtained the water level. It may be thought of as redoing of the signal 
search mode in the middle of normal operation for the purpose of 
restarting the system if a different signal is determined to be the proper 
water reflection signal. From the starting of the system with the water 
level below four inches. As the system will not detect such low water 
levels, the system may interpret a signal from a multiple reflection as 
the proper signal. The water level is then raised above four inches, the 
background calculation will detect the difference between the true level 
and the incorrectly determined level. The system will then be reset, 
allowing the correct level to be detected in the signal search mode. 
The first background calculation begins with the clearing of the 
Calibration Histogram. Statistics are then collected in this array for 
parameter E rounds of ultrasonic pulses. A foreground calculation 
operation then takes place. This alternating operation sequence is 
repeated parameter D number of times. This results in the background 
calculation observing the same number of ultrasonic pulses as was done in 
the signal search mode. 
As shown at 105, a number of these background calculations equal to the 
parameter D in Table 1 are performed. When this background data has been 
gathered, the background results are sent to the RS232 port at 107. The 
parameters stored in EEPROM are then checked at 109. If they are not 
valid, the system restarts by returning to the signal search mode. 
If the stored parameters remain valid, a determination of the initial bin 
from the background calculations is performed at 111. This routine is 
shown in FIG. 5. If the initial bin determined from the background 
calculations agrees with the time bin being used by the foreground 
calculation as determined at 113, the program loops back and repeats the 
foreground and background calculation innerloop. If the initial bin 
determined by the background calculation differs from the bin used in the 
foreground calculation at 113, and the parameter M which can be selected 
to disable restart is equal to NO and the number of times that the initial 
bin selected by the background calculation differs from that used by the 
foreground calculation is equal to the parameter J at 115, the system 
restarts by returning to the signal search mode. Otherwise, the routine 
loops back and repeats the foreground and background calculations. 
FIG. 5 illustrates a flow chart for determining the initial bin in the 
signal search mode which was identified at 97 in FIG. 4. This is 
accomplished by first acquiring the statistics from a number of rounds of 
trigger pulses. A round refers to the sequential collection of data from 
bin 2 to the maximum bin number. The number of rounds used in determining 
the initial bin is equal to the parameter D times the parameter E from 
Table 1. The statistics from these rounds are saved in an array referred 
to as the Calibration Histogram. Table 2 illustrates the Calibration 
Histogram for a 29 inch ID pipe for which 22 time bins are required. 
Individual bins are located in this histogram by adding the row number 
down the left side to the column number across the top. Thus, bin 21 is in 
the row labeled 20 and the column labeled 1 and records 200 reflected 
pulses. An element of the array is incremented when a signal is detected 
in the associated bin. The water level is then approximated through the 
selection of the bin represented by the lowest array element which has a 
value greater than or equal to a specified percentage of the number of 
rounds for which data was collected. Later entries in the array may be 
greater than this value, but may represent the detection of multiple 
reflections between the water surface and the pipe wall. 
TABLE 2 
______________________________________ 
CALIBRATION HISTOGRAM 
Bin Numbers 
0 1 2 3 4 5 6 7 8 9 
______________________________________ 
0 0 0 0 0 0 0 0 0 
10 0 0 0 0 0 0 0 0 0 0 
20 0 200 
______________________________________ 
If a different sized pipe is selected, or operation at another temperature 
is selected, the number of bins monitored will change accordingly. 
Turning to FIG. 5, when the Determine Initial Bin routine is called at 117, 
a variable BIN# is set to 2 at 119 to begin a round. The timing 
information for that bin is then acquired at 121. The routine for this is 
shown in FIG. 6. If a pulse is seen in this bin as determined at 122, the 
entry for the bin in the Calibration Histogram is incremented at 123. In 
either event, if the round is not completed as determined at 125, BIN# is 
incremented at 127 and collection of the round continues. Successive 
rounds are completed until the total number of rounds completed equals the 
parameter D* parameter E as determined at 129. The initial bin is selected 
at 131 by selecting from the histogram the lowest time bin with counts 
greater than the parameter G % of parameter D* parameter E. The program 
then returns to the calling program at 133. 
A flow chart for the routine 121 for acquiring single pulse timing 
information is illustrated in FIG. 6. When called at 135, the routine 
calculates the delay between the trigger pulse and opening of the second 
peak detector 51 (see FIG. 1) to look for the water reflection as 
indicated at 137. The trigger signal is then obtained from the first 
comparator 43 at 139. Following this, the wall reflection signal is 
obtained at 141 from the second comparator 53 and the second peak detector 
51 is then reset to block the input of reflection pulses until the 
selected time bin. The threshold for this time bin is then set at 143. The 
system then delays at 145 until about 20 .mu.s before the bin time and 
then opens the second peak 2 detector at 147 in order to record the time 
of signals having a magnitude greater than the threshold at 149. The 
system then returns to the calling routine at 151. 
FIG. 7 illustrates a flow chart for the foreground calculation 101 (in FIG. 
4). When called at 153, the foreground calculation acquires the timing bin 
number for the water level determined by the last water level calculated. 
This time bin number is used to set the threshold and to open the second 
peak detector at the correct time. To Acquire Single Pulse Timing 
Information routine 121 is then used to gather the number of reflected 
pulses seen for a number of trigger pulses set by the parameter F as 
indicated at 157. If the number of pulses seen within the timing window is 
not parameter H % of the number of pulses (parameter F) as determined at 
159, another set of data is gathered. If the parameter H % of the pulses 
is not seen for the parameter J consecutive number of times as determined 
at 161, the system is restarted by returning to the signal search mode. 
This would be an indication that the water level has been lowered below 
the time bin being examined. 
When the selected percentage of pulses is seen as determined at 159, the 
average time for the pulses within the timing window is calculated at 163 
and output to the analog and RS232 at 165 as the water level. The routine 
then exits at 167 to the background calculation 103 in FIG. 4. 
A flow chart for the background calculation 103 (FIG. 4) is shown in FIG. 
8. This routine which is called at 169 is similar to the Determine Initial 
Bin routine 97 (FIG. 5) used in the signal search mode. The parameter BIN# 
is initialized to 2 at 171, rounds of data are collected by utilizing the 
Acquire Single Pulse Timing Information routing 121 with the results 
recorded in a histogram as indicated at 173 and 175. Rounds of data are 
collected by cycling through the bins as indicated at 177 and 179. When 
the parameter E number of rounds have been collected as indicated at 181, 
the background calculation is exited at 183. 
While specific embodiments of the invention have been described in detail, 
it will be appreciated by those skilled in the art that various 
modifications and alternatives to those details could be developed in 
light of the overall teachings of the disclosure. Accordingly, the 
particular arrangements disclosed are meant to be illustrative only and 
not limiting as to the scope of the invention which is to be given the 
full breadth of the appended claims and any and all equivalents thereof.