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Journal of Engineering Science and Technology Special Issue on
Applied Engineering and Sciences, October (2014) 66 - 75 School of
Engineering, Taylors University
66
LABVIEW BASED FLOW RATE MONITORING AND MEASUREMENT ALGORITHM FOR
ROTARY ENCODER
R. GARMABDARI1,*, S. SHAFIE
1,3, A. GARMABDARI
2,
H. JAAFAR1, A. K. ARAM
1
1Faculty of Engineering, Universiti Putra Malaysia, 43400 UPM
Serdang, Selangor, Malaysia 2Faculty of Engineering, Islamic Azad
University of Qazvin, 1655, Barajin, Qazvin, Iran
3Institute of Advanced Technology, Universiti Putra Malaysia,
43300 Serdang, Selangor, Malaysia
*Corresponding Author: [email protected]
Abstract
The water usage is increasing twice of the rate of global
population growth
within the last century. According to the statistical studies,
the global
population is growing by roughly 80 million people annually,
representing
increased freshwater demand of around 64 billion cubic meters in
the same
period of time. This amount of water is being consumed in three
fields
comprising irrigation 70%, industry 20% and domestic usage
10%.Therefore,
monitoring and controlling of natural water resources are
counted as two most
vital issues in water crisis. For the purpose of control and
supervision on natural
water sources, the water consumption parameters such as
instantaneous
consumption, flow rate, and accumulated consumption should be
measured and
monitored. This paper presents a new monitoring algorithm
implemented in
Labview to monitor, calculate and plot the mentioned parameters
based on the
rotary encoders such as electromagnetic, ultrasonic, capacitive,
or even hall-
effect sensors based. The results show that, the algorithm is
capable to measure
and display flow rate, instantaneous and cumulative consumption.
It is also able
to recognise and present the fluid flow direction and the system
fault.
Keywords: Water measurement, Rotary encoder, Flow rate,
Monitoring algorithm.
1. Introduction
Although there are various techniques to monitor and measure
water flow rate,
instantaneous and cumulative water consumption parameters, but
they require
different equipment to measure and register each one of them.
For instance, a water
meter and flow meter are needed to measure consumption and flow
rate respectively.
Furthermore, the peripheral software may be required to extract
the statistical
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Nomenclatures
Vx Output voltage of hall sensor x, V
Vy Output voltage of hall sensor y, V
Abbreviations
C.P Counted Pulses
CC Cumulative Consumption
CET Constant Elapsed Time Technique
F.R Flow Rate
MFR Mean of Flow Rate
MR Magneto Resistive Sensor
RPM Round per Minute
information [1]. The difficulty and cost of implementation of
such these
measurement systems motivated to design and develop a new
display algorithm
based on Labview which is able to plot flow rate, the mean of
flow rate,
instantaneous and cumulative consumption graphs. The mean of
flow rate has a
statistical concept and generally is calculated every hour
during a day. All these
values can be recorded in a database according to their date and
time. The stored
information can be utilised to achieve more statistical
information such as
periodical consumption which needs to be accomplished in a long
period of time.
Furthermore, the errors of the system and flow direction of
fluid are presented on
the display of the developed Labview based algorithm.
2. Hall Effect Sensor Based Encoder
Generally, rotary encoders recognise the position of rotary
shaft connected to the
rotary part of encoder. Basically, rotary encoders comprise
revolving part to
install sensors actuators, fixed part wherein the sensors are
placed on it, readout circuit and processor to analyze the coded
data [2]. Although rotary encoders are
classified based on principle of operation such as
electromagnetic, capacitive,
optical, ultrasonic based encoders, they may also be categorised
to magnetic and
optical encoders in terms of small dimension, high performance
and dependency
to the environment conditions [3]. Since, the structure of
optical encoders are
more complicated than electromagnetic types and also the
electromagnetic
encoders have less dependency to the environment condition such
as mist, mud,
dirt, water, dust and vibration [4], in this paper, it is
focused on electromagnetic
rotary encoders and especially hall-effect based due to their
low power
consumption. However, the optical encoders are capable to
recognise the angular
position of the revolving shaft in high resolution, but in this
scheme, it is
supposed to count the number of rotation of the shaft, detect
the direction [5] of
rotation, and recognise the source of error occurred in the
system as the main
functions of measurement.
Basically, magnetic encoders are used as non-contacting encoders
in restricted
applications like the speed of rotation [6]. Many different
types of magnetic
encoders have been reported based on the applied technique to
sense the motion
of revolving shaft such as magneto resistive sensor (MR) based,
differential
transformer with a rotary core, induction based using inductor,
and hall-effect
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sensor based. Although, the proposed Labview based measurement
system can be
applied for all types of encoders and the functionality of
different blocks of
algorithm are similar, but the approach and method of
acquisition data and
calculation blocks must be changed according to the data
encrypting procedure.
The hall-effect sensor based angular position encoders are
normally utilised in
automotive and industrial applications due to their long life,
low power
consumption, and also low cost implementation [7]. The operation
principle of
hall-effect sensors is based on the induced voltage in two sides
of a hall material
when it is located in a magnetic field according to the angle
between materials surface axis and the magnetic flux.
The hall-effect encoders can be classified to different types in
aspect of
configuration and application. Some encoders are assigned to
only detect and
count the number of complete rotations of rotary shaft [8,
9]whereas another
group is developed to calculate the angular position of rotating
shaft with respect
to either a reference point or the last position of rotary
shaft. The proposed
algorithm can be applied to both groups of encoders but the only
blocks that
should be modified is the calculation and acquisition blocks
according to the
output of sensors and utilised measurement technique. For
instance, the encoder
which is shown in Fig. 1(a) computes the angular position of
rotary shaft utilising
two hall-effect sensors which are separated by 90 degree angular
distance. In this
encoder, the angular position of rotary shaft is formulated as
follows [10]
{ =
= = 1
(1)
On the other hand, rotary encoders may also be designed to only
recognise
and count the number of complete rotations, in order to
calculate rotational speed
and detect the direction of rotation. In this case, the number
of applied sensors
and actuators can be reduced according to the required accuracy.
Since digital
sensors are generally used in this type of rotary encoders, one
or more digital
signals are provided at the output of readout circuit. The
calculation block of
display algorithm is designed based on inspection of the
sequential codes which
are generated by the affected sensors. The structure of a three
sensor rotary
encoder implemented on a water meter is presented in Fig. 1(b)
[9].
(a) Angular Position
Rotary Encoder.
(b) Three Hall-Effect Sensor
Rotary Encoder.
Fig. 1. Structure of Hall-Effect Sensor Based Rotary
Encoder.
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In this apparatus, since three digital hall-effect sensors have
been sequentially
located on the dial plate, the generated code at the output of
interface circuit will
also be sequential according to the direction of rotation and
arrangement of
sensors position.
3. Flow Rate and Consumption Measurement and Monitoring
Technique
For the purposes of analysis of the obtained data from readout
circuit to calculate
and display the water flow rate and consumption, a processing
and monitoring
algorithm is required to develop on a standalone system.
Basically, the angular speed is considered as one of the most
important types
of measurement in rotary based machines in order to monitor and
control the
effective factors on rotation. Basically, there are several
techniques to measure the
speed of a rotating shaft. The applied speed measurement
approach depends on
the sensory system and interface circuit architecture [11].
Although, the angular velocity can be measured by different
methods which are
classified into two main categories; timer /counter based and
analog-to-digital based
techniques. These two techniques can also be divided to variety
types based on the
predetermined parameters of measurement technique and the data
acquisition
approach [11, 12]. The most appropriate technique is selected
according to the
required range of measurement such as maximum and minimum value
of speed, the
required accuracy, and the output signal of interface circuit.
In this paper the constant
elapsed time technique (CET) is applied due to increase the
accuracy of measurement
at low speed [13]. The principle of this technique is a
combination of two simple and
basic methods including pulse counting and period measurement
[14]. As illustrated
in Fig. 2, the input velocity pulse is counted within a
predetermined time by a pulse
counter, and also a timer simultaneously is assigned to start
and stop timing
between two consecutive velocity pulses, therefore, in spite of
termination the
predetermined time, the pulse counter still is running until the
next velocity pulse
starts. Therefore, pulse counter continues the counting of speed
pulses as long as the
velocity pulse is high[11].
Fig. 2. Principle of CET Method to Measure the Angular
Velocity.
In this paper, a monitoring and velocity measurement algorithm
is developed
based on Labview due to its capability to implement the
mathematical and logical
functions. Furthermore, it supports different communication
protocols of
peripheral devices such as RS232 and USB [15]. The flow chart of
the developed
algorithm is shown in Fig. 3. The proposed algorithm is able to
measure the flow
rate, the mean of flow rate, instantaneous and accumulative
consumption.
Besides, the source of occurred fault and flow direction can be
recognised
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utilising this algorithm. The input of the algorithm is an
encrypted data string
comprising the number of complete rotations and the BCD code of
current state.
This data is transmitted from the interface circuit to the
computer (P.C) using
RS232 serial protocol. At the first step of algorithm, the
encrypted string is
received via a serial port based on predetermined settings.
Fig. 3. Applied Flow Chart of into Labview Program.
Clearly, the algorithm should be infinitely repeated to plot
continuous graphs.
Since the Labview is capable to concurrently execute two
different infinite loops
without any interactions on operation of the other blocks. Thus,
the receiver block
is separated from the main block of algorithm in order to avoid
of missing data at
input while the main loop is being processed as depicted in Fig
4.
In the data receiver block a shift register is employed to store
consecutively
each character of data and consequently, the data string is
reconstructed
automatically when transmission is completed. Since the main
loop was separated
from the received loop, each complete string must be stored in
an interface
Check validity and Frame of Data
Yes
No
Read Input Data
Current consumption, the BCD code of current state
START
Data separation
Store the current state BCD code
Store the consumption
Data is valid?
Yes
No
Recognise the source of fault
Fault occurred?
Detect flow direction
Extract Instantaneous consumption
Compute flow rate using CET method
END
Compute cumulative consumption
Display graphs of results, indicate the flow direction
Display the source of the occurred fault
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register to compensate the none-synchronization between the main
and receiver
loops. It should be considered that the interface register
should be cleared after
every reading by the main block.
In the next step of the proposed algorithm as shown in Fig. 5,
the validity of
data is checked according to the predefined format of data
string. The data format
includes the starting, separating, stopping and the length
characters. The length
indicates the number of characters in a data string whereas
separating character
presents the start of BCD code for current situation [16].
Fig. 4. Implemented Received Data Stage in Labview.
Fig. 5. Implemented Validity Check, Data
Separation and Fault Recognition Stages.
If the received data is recognised as valid information, then
the start and
stop characters are removed and subsequently, the consumption
value will be
detached from the BCD code of current state; otherwise, the
algorithm starts
again from the beginning to receive new data string. After that,
the extracted
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information is stored in two registers. Now, the current state
of sensors is
compared to the predetermined sequential BCD codes and the last
stored state
code in order to recognise the source of fault if any happened.
Afterward, the
current codes are substituted with the last codes in a register.
In case of fault
occurred in the system, the algorithm is transferred directly to
the display fault
source stage and then the iteration will be stopped until the
fault is resolved and
system is restarted. If no error is detected in the fault
inspecting step, the flow
direction is determined by comparison between the extracted
current and last
stored consumption values. Obviously, the flow direction is
forward if the
current consumption is greater than its last value and it is
reverse if the current
consumption is smaller than the last consumption.
The flow rate is calculated based on CET method as the next task
of this stage.
For this purpose, two timers are applied which first one
measures the constant
predetermined time while another one measures the actual time.
Once, the first
valid data string is received, both timers and the pulse counter
are run. The
number of pulses is counted within the constant time period of
the first timer and
when the predetermined time period elapsed, the current state of
sensors is
compared with the reference state wherein the encoder had
started to rotate. So,
whenever the last rotation is completed another timer also is
stopped and the
measured time by the second timer is stored as the actual time.
Then, the flow rate
can be computed by dividing the number of counted pulses (. )
overthe actual time () converted to minute. The unit of calculated
flow rate (. ) is round per minute (RPM).
. =.
[]
[]= [] (2)
Next, the cumulative consumption (. ) which is defined as the
sum of consumption from the start time till the current moment is
computed to display as
below equation.
. = .=0
(3)
The mean of flow rate ()during a certain period of time which
normally is considered every one hour, can be computed to determine
the peak usage hours.
The mean of flow rate can be extracted using an independent
timer to measure the
intervals and it also can be calculated as below.
= (.)
=1
=
.
=1
(4)
where the index refers to the number of calculated flow
speeds.The . and represent the counted pulse and measured actual
time in each speed calculation
respectively, and denotes the total number of calculated speed
within the time period of independent time like one hour. The
implemented computation stage of
the algorithm base on Labview program is shown in Fig. 6.
As it can be seen timers A and B are utilised to calculate the
flow rate as
explained above and timer C is applied to calculate the mean of
flow rate during
every hour. In order to make a pulse counter, the current
consumption is
compared with the previous stored value, and if it was not
repetitive, the pulse
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counter is incremented by one, Otherwise; the value of pulse
counter will remain
unchanged. The computed results should be plotted on graphs
versus absolute
time as the penultimate stage of algorithm. For this purpose
three waveform chart
are utilised as shown in Fig. 6.
Fig. 6. Implemented Computing and Plotting Stages in
Labview.
4. The Outputs
The proposed algorithm to measure flow rate, instantaneous
consumption, the mean
of flow rate and accumulated consumption was implemented in a
hall sensor based
rotary encoder [8]. The rotary encoder detects the number of
rotations according to
the sequence of happen states during rotation as explained
above. The graphs are
plotted versus absolute time as shown below. As it can be seen
from Fig. 7(a), the
flow rate is calculated as a positive value even while the
direction of flow is
reversed. Figure 7(b) represents the instantaneous consumption
which its gradient
slope is proportional to the flow rate whether in forward or
reverse direction.
Therefore, the flow rate and direction of flow can be calculated
from the
instantaneous consumption.
(a) Flow Rate. (b) Instantaneous Consumption.
Fig. 7. Experimental Result of Flow Rate and Instantaneous
Consumption.
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The fault in the measurement system can be recognised based on
the
comparison between the sequences of predetermined codes and
occur codes.
Therefore if any error in the sensory system or interface
circuit happens, the
corresponding code and error message are presented in the front
panel of Labview
program as shown in Fig. 8. The flow direction is illustrated
via a Boolean
indicator in Labview so that it is switched on once the
direction of flow is forward
and vice versa. The mean of flow rate is plotted within a period
of one minute to
test the performance of system and it is computed every one
hour. This curve
shows how the rate of consumption is changed and determines the
maximum
demand of water every hour. The accumulated consumption shows he
total water
consumption measured by the proposed system.
Fig. 8. The Mean of Flow Rate, Accumulated, Consumption,
Fault Recognition and Flow Direction Indicators.
5. Conclusion
The implemented algorithm was tested using Labview program and
its operation
was verified to plot the flow speed, instantaneous consumption.
The functionality
to diagnose the fault and direction has also been confirmed. As
a result the
employed algorithm can accurately collect the necessary data
utilising minimum
number of measurement equipment. Moreover, all data of the
system are saved
into separate files in the database to be used for statistical
analysis. The
implemented monitoring algorithm can be utilised by water
distributor
organisations in order to monitoring and control the consumption
based on water
demand and more importantly to conserve water resources.
Acknowledgment
The authors would like to thank to University Putra of Malaysia
and Ministry of
Education, Malaysia for supporting this work under the
Fundamental Research
Grant Scheme.
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