Pump station flowmeter

A pump station flowmeter is disclosed including a pump status comparator for creating level status without being connected to any level sensors by comparing pump status to a list of association between expected pump status and levels. The wet well dimension, pump status signals, clock signals, level status are recorded in memory before being used as input to a flow calculator which calculates inflow and outflow. A flow rectifier readjusts the inflow and outflow according to a variable proportion of the difference between an average of many outflows and one outflow, and using this difference to readjust a variable tolerance and the variable proportion. This optimizes accuracy according to each specific installation. Abnormal pump operations are confirmed when a predetermined number of possible abnormal pump operations occur in a row are detected by comparing the outflow to the average of many outflows plus or minus the variable tolerance. A maintenance status is declared when an outflow calculated is physically impossible so the inflow calculated is the time of operation of the pumps divided by the time of the maintenance status. Alarms are generated when the outflow or the inflow is over or under predetermined values. Outflow can be replaced by a coefficient if the wet well dimension is unknown so the flowmeter can still be used to generate alarms.

BACKGROUND 
1. Field of Invention 
A pump station flowmeter is disclosed which includes a volumetric flowmeter 
for determining an accurate measurement of the flow of liquid through a 
liquid system like a sewage system, a pump status converter for 
eliminating the usual heavy modification of the control panel required by 
the installation of volumetric flowmeters, a flow rectifier to calculate 
flow with maximum accuracy according to each specific installation, an 
abnormal pump operation processor to differentiate pump flow error 
calculation from real abnormal pump operation, and a pump flow variation 
alarm gate for generating alarms when abnormal pump flow is calculated 
based only on pump-on and pump-off inputs. 
2. Description of Prior Art 
Most Prior Art is related to volumetric flowmeters specially designed for 
pump stations. They require level inputs to work. None calculates flow 
without being connected to level sensors, none individually optimizes its 
calculus for each specific installation, and none is able to generate pump 
flow variation alarms without any inputs other than pump-on and pump-off. 
Pump station flowmeters, or the like, are well known in the patented prior 
art, such as the U.S. Pat. Nos.: Martig, Jr. 4,127,030, Jorritsma 
4,455,870, 4,669,308 and 4,821,580; Olsson 4,467,657, Free et al. 
4,897,797, Hon 4,856,343, Adney 4,962,666, and Marsh et al. 5,313,842 and 
5,385,056 
(a) All the instruments using these patents must be physically connected to 
level sensors and/or pressure devices in order to be used. This makes the 
installation of these instruments laborious and expensive. 
Pump stations are composed of a wet well which accepts liquid inflow and 
temporarily stores such inflow, and a pump, or combination of pumps, which 
discharge the accumulated liquid from the wet well. The rate of change of 
level in the wet well with respect to time (dl/dt) is a function of the 
shape and size of the wet well, the flow entering the wet well is the 
inflow, and the flow leaving the wet well is the outflow. 
The shape and size of the wet well are usually known, and therefore if 
dl/dt is measured, it can be converted to the rate of change of volume 
with respect to time (dV/dt). The rate of change of volume depends on the 
inflow and outflow. 
While the pump (or pumps) is off, the inflow can be measured by timing how 
long it takes for the liquid to fill a known volume. This is done by using 
existing upper and lower limit switches which are already present to turn 
the pumps on and off. This method provides an average inflow (Inflow) over 
the time that it takes to fill the known wet well volume. 
If the Inflow is also known during the pump on time, the total volume 
passed through the wet well in one wet well pump cycle can be calculated 
by the equation: Outflow=Vp/tp+Inflow.Outflow is the average outflow of 
the pump in operation for that cycle, Vp is the volume of the wet well 
between the pump on and pump-off switches, and tp is the length of time 
the pumps were on. It is important to note that the inflow is a function 
of time and is not a constant. If an Inflow for the pump-on time is known, 
then a numerical version of equation Outflow=Vp/tp+Inflow would be used: 
EQU Volume/cycle=Vp+Inflow.times.tp. 
(b) Unfortunately, timing the wet well as it fills will give an Inflow 
which is not an accurate estimate of inflow during the pump on time if the 
inflow significantly increases or decreases between the pump off time and 
pump on time. One way to reduce this error is to add another level switch 
at an intermediate level to define another, smaller volume. The fill time 
of this intermediate volume can be used to measure an Inflow over a 
shorter period of time which is closer to the onset of the pump-on time, 
and, hence, is a better estimate of the Inflow during the pump on time. 
Variations on this idea include measuring the Inflow before and after the 
pump on time and calculating their average which is Inflow, or adding more 
intermediate level switches to measure several Inflows and then performing 
a best fit of the Inflow versus time for interpolation and averaging. 
Although these techniques improve the system's performance, a sudden flow 
change will still lead to large errors, and the installation process 
becomes impractical. 
(c) Inflow changing at a high frequency can cause large errors in the flow 
calculus. High frequency inflows are flows which change a significant 
amount over a short period of time, making it difficult for a system which 
samples the flow periodically to obtain an accurate estimate of the inflow 
during the pump-on time. High frequency flows are likely to occur at pump 
stations downstream of another pump station or at industrial pump 
stations. Small domestic pump stations may have high frequency phenomena 
as well. 
A method disclosed in the Jorritsma U.S. Pat. No. 4,455,870 samples the 
inflow once per pump cycle, and a second method samples the inflow twice 
per pump cycle, and therefore, it was thought to be twice as accurate as 
the first method. Adding more intermediate switches allows a system to 
measure the volume through the wet well accurately at even higher inflow 
frequencies. However, it is not practical to measure high frequency 
inflows in this manner because too many switches are required, and the 
errors related to the sensors themselves add-up. 
(d) One important phenomenon of periodic flow entering a pump station can 
be termed "lock-on". Lock-on occurs when the pump-on time and the inflow 
synchronize and remain that way which means the liquid is going in at 
about the same speed it is going out. Lock-on maximizes the errors in flow 
measurement systems which use fill times to estimate the inflow during the 
pump on time. The occurrence of lock on is affected by the size of the wet 
well, the inflow frequency, the inflow magnitude, and the pump 
characteristics. It occurs very easily over a relatively wide range of 
frequencies. Such frequency conditions often exist downstream of another 
pump station or at relatively small pump stations. 
Once a pump station is locked on, it will remain so until the inflow 
frequency changes enough to disturb it. The tendency of the pump-on time 
and the maximum inflow to remain locked in phase can be explained as 
follows. At low inflows, the pump is less likely to come on because the 
level is less likely to reach the top level switch. Conversely, the pump 
is more likely to come on when the inflow is high. This tendency forces 
the pump to turn on during the increasing part of the inflow cycle. The 
pump-on time lengthens because of the increasing inflow. Ultimately, the 
pump-on time straddles and then passes the inflow peak. Once the pump on 
time occurs during the period of decreasing inflow, the pump flow is large 
enough to empty the wet well before the inflow reaches its minimum. At 
this point, the two cycles are locked in phase and the pump-on time will 
not advance across the inflow minimum. Under these conditions, inflow 
estimates based on prior fill time data will be highly inaccurate. 
(e) These problems are partially overcome by using a different approach. If 
the outflow of the pump (or pumps) and the time of operation of the pumps 
are known, the volume passing through the wet well in one pump cycle can 
be calculated by: Volume per cycle =pump outflow.times.time of operation. 
The filling time of the well being known, the Inflow of a cycle can be 
calculated by: Inflow=volume per cycle/(time of operation+filling time). 
In most cases, wet well pumps discharge into an open channel pipe which 
carries the liquid downstream by gravity: the pumps simply lift the water 
a constant distance from the pump outlet to the elevation of the open 
channel pipe. The pump outlet is under a constant pressure due to the 
column of water between the pump outlet and the beginning of the open 
channel flow line where the liquid discharges to a gravity feed line. The 
pressure on the inlet side of the pump is directly related to the level of 
the liquid in the wet well. The liquid level changes from the pump stop 
level to the start level to the stop level at each cycle. Each level being 
reached at each cycle, we can conclude that a constant average pressure 
generates a constant average pump outflow. If the inflow is accurately 
calculated, the outflow calculated will be fairly constant. If the 
calculated outflow is not constant, we can assume two possibilities: the 
inflow was not properly calculated or the pump outflow had really changed. 
Marsh U.S. Pat. No. 5,385,056 assume only the first possibility by 
comparing the last calculated Outflow of a pump to the average of all the 
Outflow for that pump which is Outflow. If the Outflow is within a 
specified range of Outflow, then Outflow is updated with Outflow. If the 
Outflow calculated is outside the specified range, then Outflow is used 
instead of the last Outflow. The possibility that an outflow can change 
drastically, like when a pump is damaged or blocked was not considered. It 
is more accurate to say that the exact Outflow is somewhere between the 
last calculated Outflow and Outflow. 
Furthermore, they assume that by adding intermediate levels, they would 
gain accuracy. Level sensors operating in pump stations wetwell are rarely 
highly accurate due to turbulent liquid surface, grease build-up, solids, 
etc. Adding levels means less distance between levels. Reducing the 
distance between levels by two is like doubling the resulting sensor 
related error. For example, let's say a station using float switches has 
an accuracy of 1/2 inch each. Two sensors are necessary to calculate a 
volume. If 20 inches separates the 2 switches, then the error is 5% 
(1/2.times.2/20"). If an intermediate switch is installed 8 inches from 
the top switch, the error becomes 12.5% (1/2.times.2/8"). 
(f) Each pump station being different with its own filling and emptying 
characteristics, a specific range, common to all stations can not generate 
the most accurate values for all stations. The station's characteristics 
change over time, ruling out the possibility of using a specific range 
even within a station as specified in Marsh U.S. Pat. No. 5,385,056. 
(g) The stability of the outflow calculated for each pump, which is 
calculated using the inflow, is a proof of the accuracy of the inflow. Two 
reasons can create rapid outflow changes that could let us believe the 
inflow causes the errors in the calculation. One is natural, meaning 
inhuman factors cause it, and one is human, meaning the level sensors or 
the pumps are manually activated because the pump station is in a period 
of maintenance. Usually in a period of maintenance, the wet well is 
cleaned using high pressure water. This makes the level detector, 
specially if floats are used, send false signals to the control panel 
which starts and stops the pumps at any level at any time. This induces 
errors in the volumetric flowmeter which understands that the start and 
stop levels were reached in a matter of seconds generating gigantic inflow 
and outflow. The maintenance people might turn the pump off or on to 
determine if they are working properly, which gives the impression that 
the starting or stopping levels were reached. None of the above patents 
have any way to detect that a pump station is in a maintenance period. 
(h) All the above volumetric methods calculate flow using functions that 
assume a constant Inflow or average outflow. The real inflow entering the 
pump station is always changing. This fact invalidates the uses of a 
constant inflow calculation as an acceptable representation of reality. 
(i) Most of the instruments using the above volumetric methods generate 
alarms based on low or high pump outflow which indicate a pump problem. To 
do this, the minimum information supplied by the user to the instrument is 
the geometry of the well, and the instrument must be connected to the 
level sensors. They can not generate abnormal pump flow alarms without 
them. It is not practical for a pump manufacturer to integrate in its 
pumps an outflow alarm system without knowing if the end user will be able 
to provide the wet well geometry and the level sensors. 
(j) No Prior Art shows how to calculate inflow and outflow when a pump is 
continuously running and when more than one pump is running. 
(k) This device can be used in any installation that has a mechanism that 
changes its state at set levels. This apparatus can facilitate the 
installation of instruments that need to know the level to operate. 
Volumetric flowmeters are good examples of these instruments. This 
apparatus reduces installation time of such instrument from hours to 
minutes by reducing or eliminating the necessary modification of the 
control panel of the pump station. 
The present invention was developed to avoid the above and other drawbacks 
of the prior systems. 
OBJECTS AND ADVANTAGES 
Accordingly, several objects and advantages of my invention are: 
(a) to provide a pump station flowmeter that can be installed without being 
connected to any level sensor, reducing the cost of installation; 
(b) to provide a pump station flowmeter that reduces the pump on time 
inflow and outflow errors without the use of additional or existing level 
sensors; 
(c) to provide a pump station flowmeter that accurately calculates flows, 
even when inflow changes rapidly without the use of additional or existing 
level sensors; 
(d) to provide a pump station flowmeter that calculates accurately when the 
"lock-on" phenomenon occurs; 
(e) to provide a pump station flowmeter that discerns outflow calculation 
errors from abnormal pump operation; 
(f) to provide a pump station flowmeter that continuously self adjusts its 
parameters to optimize the accuracy for each individual station; 
(g) To provide a flowmeter which can identify when a pump station is in 
maintenance period. 
(h) to provide a pump station flowmeter that calculates inflow using a 
function representing the time changing reality; 
(i) to provide a pump station flowmeter that can generate abnormal pump 
flow alarms, even without supplying the wet well geometry or being 
connected to the level sensors; 
(j) to provide a pump station flowmeter that calculates inflow and outflow 
when a pump is continuously running and when more than one pump is 
running. 
(k) to provide to other instruments the level data they need without being 
connected to any level sensor. 
Further objects and advantages of my invention will become apparent from a 
consideration of the drawings and ensuing description.

DESCRIPTION OF INVENTION 
FIG. 1 illustrates by a diagram a wet well pumping system, commonly called 
a pump station, in which a liquid 20 from inflow source 22 fills a wet 
well 24 until a level sensor 26 starts a pump or combination of pumps 28 
to pump out the liquid through an outlet 30 until a level sensor 32 stops 
the pump or combination of pumps. Throughout the following text, a pump 
equals one or more pumps. The source 22 fills the wet well 24 at a 
variable filling rate, or inflow. A pumping rate, or outflow, is usually 
constant for a pump, but not always, so it can not be assumed to be a 
constant value. An electric control panel 34 receives a signal from a 
level sensor system (26 & 32) when the start and stop levels are reached, 
then starts or stops the pump 28 according to an operating configuration 
specifying an operating sequence related to the pump operation when 
different levels are reached. 
The level sensor system can be a float switch system, an ultrasonic system, 
a pressure system, a resistive system, a capacitive system or any other 
type of system supplying a level signal to the control panel 34 when 
specific levels are reached. A control panel 34 is usually designed to 
control two or more pumps and supply the user with information such as 
pump status, current, cumulative operation time, level of the liquid, etc. 
The operating sequence can be altered by human factors, like a user 
manually starting or stopping the pumps, and abnormal factors, like a 
defective pump. 
FIG. 2 illustrates the basic operation of the pump station described in 
FIG. 1 in relation to time. A pump cycle 36 is a repetition of the steps 
describe in FIG. 1. A pump cycle 36 begins when the pump stops when stop 
level 32 is reached. A liquid level 38 rises from the stop level 32 to a 
start level 26. A volume of liquid 40 between the start level 26 and the 
stop level 32 is known. The volume between levels 40 is constant and used 
in the following equations to calculate an inflow. A fill up time between 
pump operation D1 is calculated by subtracting t2 from t1. An average 
inflow D1 for the period t1 to t2 is calculated by: 
##EQU1## 
The same applies to period 
##EQU2## 
This is true only if no pump runs while D1, D2, D3 or D4 are calculated. 
But sometimes, pump stations operate in a condition where a pump p is 
almost always running and a second pump operates from a higher level. In 
this case, the outflow generated by the pump p is added to the value of 
the inflow. The pump p is usually running between lower levels at which an 
average outflow of p (Outflow(p)) was calculated when the pump was 
stopping from time to time. The average level at which the Outflow(p) is 
calculated directly influences its value: The higher the level, the higher 
the value. When a pump is almost always running, the average level of 
operation between the starts and stops of the second pump is higher, 
meaning the Outflow of the pump that is always running is higher. A 
coefficient Kp adjusts the value of Outflow(p) according to the difference 
of performance of the pump p due to an operation at a different average 
level. To calculate Inflows for D1, D2, D3 or D4 while a pump p is 
running, the following equations 1, 2, 3 and 4 apply: 
##EQU3## 
The volume between levels 40 and the time are the only accurate basic 
information used by the present invention to calculate accurate inflow and 
outflow. When the pump is not in operation, an accurate Inflow is 
calculated. 
FIG. 3 to FIG. 8 shows why an equation calculating a curve represents more 
accurately the reality continually changing rate of an inflow. FIG. 3 to 
FIG. 5 and FIG. 6 to FIG. 8 represent 2 examples of continually changing 
rate of an inflow over a period of 4 cycles. 
FIG. 3 is a graph showing inflow calculated using an average method. It 
represents 4 cycles of a pump station in which the inflow rate had changed 
over time. An accurate Inflow 42 is calculated for each period t1-t2, 
t3-t4, t5-t6 and t7-t8 in which the pump are not in operation. D1=Inflow 
of period t1-t2, D2=Inflow of period t3-t4, D3=Inflow of period t5-t6, and 
D=Inflow of period t7-t8. Knowing the accurate volume between levels 40 
and the accurate time at which the levels are reached, the Inflow is 
therefore accurate. 
A method of calculating inflow while the pump is running is to extrapolate 
the last calculated inflow in the pump running period t2-t3, t4-t5 and 
t6-t7. Extrapolating assumes a non changing rate of inflow over time which 
is a highly unfair representation of reality, so it was not included with 
the drawings. FIG. 3 shows a more accurate, but not perfect method of 
calculating inflow while the pump is running. It calculates an average 44 
of the inflow (Inflow) for the period before and after the pump operation 
period which is 
##EQU4## 
and so on for the other cycles. Averaging assumes a fixed changing rate of 
inflow over time which is not a fair representation of reality either. It 
appears accurate that the inflow at one time is somewhere between the 
inflow before and after that time, but if the time was a peak and inflow 
before and after were calculated on each side of it, then assuming the 
average of the inflow before and after represents the flow at this time is 
wrong. 
FIG. 4 is a graph of 4 pump cycles showing an inflow calculated using a 
function which generates a curve of the inflow and time f(t). It 
represents the same cycles as FIG. 3 using a function Inflow(t) of the 
inflow in relation to time that uses the trend on the inflow over 4 
cycles, which is over 4 Inflow calculations. The curve 46 represents 
Inflow(t) created using the Inflow of the period D1, D2, D3 and D4. 
Averages 48 are extracted from Inflow(t). 
FIG. 5 is a graph of 4 pump cycles comparing the results of the average 
method, explained in FIG. 3, and the function Inflow(t), explained in FIG. 
4. It compares the averages 44 calculated with the average method and the 
averages 48 calculated with Inflow(t). The difference, between the 
averages 44 and 48 for each period of pump running, is related to the 
variation of the inflow during these period. 
FIG. 6 is a graph of 4 pump cycles showing inflow calculated using the 
average method in which a peak inflow is reached. 
FIG. 7 is a graph of 4 pump cycles showing an inflow calculated using a 
function which generates a curve of the inflow and time f(t). It 
represents the same cycles as FIG. 6 using a function Inflow(t) of the 
inflow in relation to time that uses the trend on the inflow over 4 
cycles, which is over 4 Inflow calculations. 
The curve 46 represents Inflow(t) created using the Inflow of the period 
D1, D2, D3 and D4. Averages 48 are extracted from Inflow(t). 
FIG. 8 is a graph of 4 pump cycles comparing the results of the average 
method and the function Inflow(t) in which a peak inflow is reached. It 
compares the averages 44 calculated with the average method and the 
averages 48 calculated from Inflow(t) for the same cycles as FIG. 6 and 
FIG. 7. The difference between the averages 44 and 48 for each period of 
pump operation, becomes large when a peak is present. To increase the 
accuracy of the curve, only the middle on the curve, between t4 and t5, is 
used. Every time a new Inflow can be calculated, a new Inflow(t) is 
calculated and only the middle portion is used because it is the most 
accurate portion of Inflow(t). 
The result of the following equation 5 is Inflow(t). 
EQU Inflow(t)=at.sup.3 +bt.sup.2 +ct+d 
The function Inflow(t) is a curve with two possible changes of direction. 
This formula gives a function in which the average of each interval is 
equal to the Inflow used to calculate it. 
This means: 
##EQU5## 
Inflow(t) is extracted by following these steps: 
##EQU6## 
It is the same for the 3 other intervals: 
##EQU7## 
It gives 4 equations with 4 unknowns that can be resolved to find the 
values of a, b, c and d of the function Inflow(t)=at.sup.3 +bt.sup.2 
+ct+d. 
If a flow calculator is not powerful enough to use this sophisticated 
function, the following less accurate, but still usable functions can be 
used where 
##EQU8## 
An Outflow represents the average of a plurality of Outflows. 
The liquid level in the wet well directly affects the performance, or 
outflow, of the pump. The higher the level, the better the performance. 
The lower the level, the lower the performance. If the liquid level stays 
higher for more than half the pumping time, then it is expected to 
calculate an Outflow higher than the Outflow. If the liquid level stays 
lower for more than half the pumping time, then it is expected to 
calculate an Outflow lower than the Outflow. Outflow is accurate only if 
the period in which the liquid level is high is as long as the period in 
which the liquid level is low in the pumping time. Inflow(t) is also used 
to figure out the liquid level while the pump is running. 
FIG. 9 is a block diagram of a basic embodiment of the present invention 
using a pump status converter, a flow rectifier, a maintenance gate, an 
abnormal event gate, and flow variation alarm gates. The block diagram of 
FIG. 9 discloses a system, according to the present invention, for 
obtaining accurate outflow and inflow by using solely the pump 28 status 
from the basic apparatus described in FIG. 1 operating according to FIG. 
2, and time. The user supplies the volume between levels 40 and the 
operating configuration 50 to a pump status convertor 52, if the pump 
station operates differently than the one described in FIG. 2. If the user 
does not supply the volume 40, the present invention can still generate 
alarms based on variation of the pump outflow. 
A clock 54 generates the time at which the pump status 28 is changing. The 
pump status is also used to identify the pump for which an outflow is 
calculated and its associated time. The time and the pump status can 
optionally be recorded in a data storage memory 60 for later processing. 
The pump status and its related time of occurrence is transmitted to a 
pump status converter 52. The pump status converter 52 generates the start 
levels status and stop levels status from the pump status 28 and the 
operating configuration 50. This information is recorded in a raw data 
memory 56. A flow calculator 58 calculates Inflow(t), and Outflow of the 
pump in operation between the time t4 and t5 as described in FIG. 2. 
Equation 6 extracts from Inflow(t) the Inflow for the period t4 to t5. 
Outflow is calculated using equation 7. 
##EQU9## 
To achieve the maximum accuracy for each individual pump station 
installation, the following hypotheses are assumed: 
a) An outflow for a pump varies slowly over time, unless an abnormal 
condition occurs; 
b) An inflow varies rapidly; therefore the difference between reality and 
the calculated inflow can be high; 
c) An average of Outflow calculated over many cycles, Outflow, is usually 
accurate, unless an abnormal condition occurs; 
d) The real outflow for a pump is somewhere between Outflow and Outflow, 
unless an abnormal condition occurs. 
e) An Outflow is influenced by the average liquid level for the period at 
which Outflow is calculated. 
A flow rectifier 62 is used to cross check the accuracy of the Outflow and 
Inflow according to the preceding hypotheses in which an average of 
Outflow is calculated using many Outflow, an acceptable difference between 
Outflow and Outflow is considered, adjusted and applied, and an adjustment 
is made to Outflow to reflect the average liquid level for the period at 
which Outflow is calculated. 
A variable tolerance refers to an acceptable percentage of difference 
between the Outflow and the Outflow. The variable tolerance is increased 
if Outflow is too close to the limit of Outflow.+-.the variable tolerance 
or if it exceeds it. The variable tolerance is reduced if Outflow is 
closer to Outflow than the limit of Outflow.+-.the variable tolerance. The 
Outflow is used to update Outflow. A proportion of accuracy factor is used 
to specify where the real outflow is between Outflow and Outflow. The 
function Inflow(t) is used to calculate at which average liquid level 
Outflow was calculated and affect the proportion of accuracy factor 
accordingly. If the Outflow calculated is within the range of 
Outflow.+-.the variable tolerance, then the proportion of accuracy factor 
will be different than if Outflow was outside the variable tolerance. The 
proportion of accuracy is always applied to readjust the values of Inflow 
and Outflow according to the following equations 8 and 9: 
EQU Accurate Inflow=Inflow+(Outflow-Outflow).times.proportion (8) 
EQU Accurate Outflow=Outflow+(Outflow-Outflow).times.proportion (9) 
The flow rectifier 62 gives accurate results if the station is operating 
normally, but can not discern errors in calculation from abnormal pump 
operation. A combination of counters and gates determine if the results, 
calculated when the pump is in operation, are right or wrong. An event is 
composed of the pump status, the start and stop time of the pump, the 
Inflow, the Outflow and the Outflow for the period included between the 
start and stop time. Variation determining means illustrated as under and 
over counters 64, 66 is provided responsive to the flow rectifier 62 for 
determining the occurrence of a variation between the average emptying 
characteristic and a predetermined tolerance, and tagging the level status 
signal, the timing signal, and the volume signal used to calculate the 
emptying characteristic as being a possible abnormal event. 
An under counter 64 is increasing each time Outflow is lower than Outflow 
minus the variable tolerance. When this occurs, the under counter 64 tags 
the events used to calculate Outflow as being possibly abnormal events. 
An over counter 66 is increasing each time Outflow is higher than Outflow 
added to the variable tolerance. When this occurs, the over counter 66 
tags the events used to calculate Outflow as being possibly abnormal 
events. 
A reset means 68 resets the under counter 64 when the over counter 66 
increases, and resets the over counter 66 when the under counter 64 
increases. It untags the possible abnormal events tagged by the under 
counter 64 when the over counter 66 increases, and untags the possible 
abnormal events tagged by the over counter 66 when the under counter 64 
increases. It resets both counters and untags all possible abnormal events 
tagged by both counters when the Outflow is within Outflow .+-.the 
variable tolerance. 
A maintenance gate 70 operates when Outflow is higher than a predetermined 
maximum outflow representing an outflow that could not be achieved under 
the best conditions. When the Outflow is higher than the predetermined 
maximum outflow, it resets both counters (64 and 66) and untags the 
possible abnormal events tagged by both counters (64 and 66). It 
calculates the time of operation of the maintenance gate 70 and the 
cumulative time of operation of the pump during the operation of the 
maintenance gate 70. It calculates the total flow through wet well using 
the Outflow multiplied by the time of operation of pump. It calculates the 
average inflow for the time in which the maintenance gate 70 is in 
operation by dividing the total flow through wet well by the time of 
operation of the maintenance gate 70. Then it generates a maintenance 
status signal. 
An abnormal event gate 72 is used when one of the counters (64 or 66) 
increases. It operates when one of the counters (64 or 66) is higher than 
a predetermined value representing the number of possible abnormal events 
necessary to become confirmed abnormal events. It recalculates the Outflow 
from the time of the first tagged possible abnormal event then reprocesses 
the information recorded in the raw data memory 56 from the time of the 
first tagged possible abnormal event using the newly calculated Outflow 
when necessary. When the abnormal event gate 72 is not in operation, it 
records the time of the first tagged possible abnormal event in its 
memory, then tells the flow calculator 58 to read a new event from the raw 
data memory 56. 
The data can be used to calculate other valuable information like volume 
through the wet well, pump's outflow and combination of pump's outflow. 
Most pump stations are designed to accept a certain inflow, and a specific 
outflow is expected for each pump and combination of pumps. An inflow 
alarm gate 7,4 can be set to generate an alarm when the Inflow is outside 
a preset maximum and minimum inflow or a maximum flow variation. An 
outflow alarm gate 7,6 can be set to generate an alarm when the Outflow is 
outside a preset maximum and minimum outflow or a maximum variation flow 
for each possible combination of pumps. 
It is sometimes difficult or impossible for a user to know the volume 
between levels in the wet well, but the user might want to know if the 
pump is performing as expected. Most pump stations are designed to have 
the same pump operating between the same level. This means a pump always 
operates within a constant volume. The volume is the most important 
ingredient to calculate flow. If it can not be supplied, the inflow or 
outflow can not be calculated, but it is still possible to generate alarms 
based on a variation of their outflow. In this case, the present invention 
supplies a constant to replace the volume which means the inflow and 
outflow can not be called as such, but the outflow alarm gate 76 and 
inflow alarm gate 74 still can be used to generate alarms based on flow 
variation. 
This method could use level status received from the pump station level 
sensors (26 and 32) when the pump status converter is not used. 
The inflow or outflow calculation could come from an external flowmeter 96. 
This is useful when such external flowmeter 96 is known to be more 
accurate, already installed, or when the volume between level can not be 
determined with accuracy. In these conditions, the Inflow could be 
calculated if the external flowmeter 96 supplys the Outflow, or the 
Outflow could be calculated if the external flowmeter 96 supplys the 
Inflow. It could also be used to readjust the Outflow of a pump based on 
the difference between the Outflow calculated with the external flowmeter 
96 and the Outflow calculated using the present invention, then applying 
this difference to the other pumps calculated solely with the present 
invention. 
FIG. 11 is a block diagram of a pump status conveyer. It describes in 
detail how the pump status conveyer 52 generates level status from pump 
status for a pump station having 3 pumps. This model can be used for any 
number of pumps. Level sensors like float switches, ultrasonic or pressure 
sensors, just to name a few, are installed to start and stop the pumps in 
a preset and known sequence when preset levels are reached. Then, if the 
preset sequence and the pump status is known, it is possible to know the 
level at which a pump status is changing without being connected to any 
sensor. The level status generated represents which level is reached and 
the time at which it is reached. These pieces of information are the basic 
elements used by volumetric flowmeters. They are known to be accurate if 
the pump station is not in a maintenance period. 
Pump station control panels are built to start and stop the pumps in a 
predetermined sequence when the liquid level rises and falls. The 
operational sequence can be affected by two external factors: the level 
reached and an optional time delay that suspends momentarily the beginning 
or the end of an event, which can be a pump start or stop. 
The pump status comparator 52 converts pump status signals into level 
status to determine the level of the liquid in the wet well system and the 
time at which the level is reached. An operation sequence memory 80 is 
used for storing an association sequence 82 (expected pump status--level 
reached) representing, for each level, the pump status expected to be 
received when the level is reached. A comparator 84 compares the pump 
status signal to the expected pump status in the association sequence 82, 
which returns an associated level reached. A level memory 86 records the 
level reached and time of occurrence. A level gate operates when the level 
reached is different than the last level in level memory 86 to replace it 
with the last level reached which indicates the level of the liquid in the 
wet well when the pump status changed. 
Two things can happen to the liquid level in a pump station: it can rise or 
fall. For each level, two types of pump status can happen: pumps can start 
or stop. In the operation sequence memory 80, the lowest level, the one 
under which no other events occur, is level 1. The highest, the one over 
which no other events occur, have the highest number. When the liquid 
level is rising from level 1 and up, a specific pump status that 
represents the operation of the pumps is selected for each level. When the 
liquid level is falling, a specific pump action that represents the 
operation of the pumps when the level is falling is selected for each 
level. Pump action, like Pump #1 starts or Pump #1 stops, can only be 
chosen once for all the levels because of their specificities. When a pump 
action is not related to a specific pump, like a pump starts or stops, it 
means it can apply to any of the pumps. This is mostly used for pump 
stations with alternating pumps. 
A list of predetermined possible pump status 94 can be used to help the 
selection. 
A predetermined association sequence 82 can be recorded in the operation 
sequence memory 80 to eliminate the intervention of the user. 
A self adjusting operating sequence 92 could read the sequence of the pump 
status recorded in the data storage memory 60, analyze it, then record the 
right sequence in the operation sequence memory 80. 
FIG. 11 is a schematic of pump operation and level activation with 
reference to time for a pump station having 3 pumps operating according to 
the association sequence 82 configured in the pump status converter 52 of 
FIG. 10. In most pump stations, pumps alternate to wear them equally. 
Usually, the inflow is lower than the outflow of a pump, but not all the 
time. The outflow of a pump is higher than the inflow when only one pump 
starts, then stops. If the inflow is higher than the outflow of the pump 
in operation, the liquid level continues to rise until a higher level is 
reached which starts a second pump. The pumps will stop at level 1 if the 
outflow of the pumps combined is higher than the inflow. If the inflow is 
still higher than the outflow of the two pumps in operation, the liquid 
level continues to rise until a higher level is reached which starts a 
third pump. Pump stations are designed to have a higher outflow than 
inflow. 
Events number 1 to 6 show pumps having individually a higher outflow than 
the inflow, and they alternate. Event 7 to 8 shows an inflow higher than 
the outflow of the pump, this is why the liquid level 38 is rising. A 
second pump starts at event 8 and the outflow of the combination of pumps 
is higher than the inflow so the level falls between events 8 and 9 until 
level 1 is reached again. Event 10 to 11 shows an inflow higher than the 
outflow of the pump, this is why the liquid level 38 is rising. A second 
pump starts at event 11, but the outflow of the combination of pumps is 
still lower than the inflow, so the level continues to rise until a third 
pump starts at event 12 when level 4 is reached. The outflow of the 
combination of pumps is higher than the inflow so the level falls between 
events 12 and 13 to reach level 1 again. Events 14 to 16 are the same as 7 
to 9. Events 17 to 34 are the same as 1 to 6. 
By associating the pump status of FIG. 11 with the settings of the 
association sequence selection 82, we can see that the first pump starts 
at event 1, level 2 was reached and recorded with its time of occurrence. 
The next pump status is a pump stop at event 2, which translates to a 
level 1 in the association sequence selection 82. So a level 1 is recorded 
with its time of occurrence. The same occurs until event 8 when a second 
pump starts. This translate to level 3 in the association sequence 
selection 82. When all pumps stop at event 9, the association sequence 
selection 82 associates this pump sequence with level 1. All the other 
events use the same procedure. 
SUMMARY, RAMIFICATIONS, AND SCOPE 
Accordingly, the reader will see that the pump station flowmeter of this 
invention can be installed without being connected to any level sensors, 
therefore reducing the cost of installation. Furthermore, the pump station 
flowmeter has the advantages of: 
reducing the inflow and outflow errors without the use of additional or 
existing level sensors; 
accurately calculating flows, even when inflow changes rapidly without the 
use of additional or existing level sensors; 
discerning outflow calculation errors from abnormal pump operation; 
continuously self adjusting the equation parameters to optimize the 
accuracy for each individual station; 
identifying when a pump station is in maintenance period; 
calculating inflow using a function representing the time changing reality; 
generating abnormal pump flow alarms, even without supplying the wet well 
geometry or being connected to the level sensors; 
calculating inflow and outflow when a pump is continuously running and when 
more than one pump is running. 
The pump status converter 52, which is part of this invention can be used 
to supply to other instruments the level data they need without being 
connected to any level sensor. This device can be used in any installation 
that has a mechanism that changes its state at set levels. This device 
facilitates the installation of instruments that need to know the level to 
operate. Volumetric flowmeters are good examples of these instruments. 
This apparatus reduces installation time of such instrument from hours to 
minutes by reducing or eliminating the necessary modification of the 
control panel of the pump station. 
Although the description above contains many specificities, these should 
not be construed as limiting the scope of the invention but as merely 
providing illustrations of some of the presently preferred embodiments of 
this invention. For example, the flowmeter could be used to calculate the 
flow of a solid (like powder) filling a silo at a rate, and a mechanical 
device emptying it at a constant rate when set levels are reached. Another 
example, the invention could be integrated to a pump to generate flow 
variation alarms when the pump is having problems. 
Thus, the scope of the invention should be determined by the appended 
claims and their legal equivalents, rather than by the examples given.