...
An
...
Automated
...
Method
...
for
...
Testing
...
Process
...
Parameters
...
Author:
...
Monroe
...
Weber-Shirk
...
...
| Table of Contents |
|---|
...
|
...
|
Abstract
We describe here easily configured process control and data acquisition software and hardware that significantly enhance experimental evaluation of unit processes and that permit fully automated parametric studies. The process control software is a LabVIEW executable and incorporates sensors, states, rules, an external microprocessor for controls, the ability to link to external LabVIEW code to add new features, and data logging. The composite system is flexible and user friendly. First year undergraduates have used the software to control a bench top drinking water treatment plant and both undergraduate and graduate students have used the software to conduct parametric studies of methane generation, the activated sludge process, flocculation, and porous media filtration. The system offers the user the ability to program an entire series of experimental runs including variation of a parameter over a series of values and inclusion of replicate tests to confirm repeatability of the results. The automated parametric testing has greatly increased our ability to study the response of complex systems. Evaluation of colloidal particle flocculation and porous media filtration in bench-scale experiments are presented here as example applications of the process control software.
Keywords: process control, data acquisition, automation, parametric testing, flocculation, filtration
Introduction and Objectives
Process control is commonly used in undergraduate teaching laboratories in electrical and mechanical engineering with an emphasis on the PID (proportional, derivative, integral) control algorithm (Braatz and Johnson, 1998). Process control laboratory experiences typically focus on control of a single parameter such as flow rate, temperature, liquid level, pressure (Rehg et al., 1999), or motor angular velocity (Choi, 2004). Control of real processes generally requires integration of individual process control components into a larger system that includes data acquisition and data logging, as well as the concepts of process state and operating rules. Although researchers have frequently created customized process control code for specific applications we present a highly configurable system that can be used to automate the control of parametric experiments or complex processes.
Experimental work is often characterized by repetitive experiments and the need for an individual to configure each of those experiments and then measure and record the data. In the case of engineered environmental systems we are often interested in optimizing the performance of unit processes and exploring the response of processes to a range of inputs. It is often necessary to cycle a selected process through a sequence of operational stages or states, to change process related variables, and to subject the process to a range of inputs. For example, operation of porous media filtration requires implementation of backwash, optional pretreatment, and particle challenge states. Filtration process variables might include flow velocities or the duration of a state, and inputs might include variation in the type and concentration of colloidal particles or coagulant type and dose. In conventional jar tests an experimenter would evaluate flocculation efficiency based on the turbidity of settled water or measure the critical sedimentation velocity by taking a batch sample of the flocs and measuring the turbidity as the sample settles. The measurement of settled water turbidity requires first loading the sample vial with flocs, then measuring turbidity as the flocs settle, and finally purging the sample vial with clean water. Although the states to control porous media filtration and to measure the effectiveness of flocculation could be implemented by a human operator, they are well suited for automation.
We have taken the automation components that are commonly used to control industrial and municipal processes and adapted them for use in the laboratory. Our objective was to create process control software that was highly configurable and link it to sensors and outputs for control. The process control software began as data acquisition software capable of remote monitoring of experiments with easily configured sensors. The ability to control on/off devices (valves, pumps, mixers, etc) and the ability to control one continuously variable device such as a variable flow peristaltic pump was then added. The process control and data acquisition components were integrated and a user friendly programming environment that is highly configurable was created that incorporates the concepts of states, rules, constants, and variables.
Prior to creating the standalone process control application we developed a first year laboratory focused on drinking water treatment in which the students programmed the states and output settings in LabVIEW. Students spent much of their time focused on programming rather than on experimenting with the water treatment plant and the programming requirements were too advanced for first year students. From that experience it became apparent that a programming environment that was specifically designed for process control could make it easier for students to experiment with the process rather than focusing on the code.
The guiding principle in developing the process controller code was to create an application that was general and easily configured to handle a wide variety of challenges. Thus the code is not designed for a particular unit process. The goal of designing code that was highly adaptable required implementing features that make it possible for users to customize the software for specific tasks. The Process Controller software includes a built in programming environment for defining variables, constants, and sensors and for writing the logic that controls moving from one process state to the next. To extend the capabilities of the software without making the interface overly complex the ability to use external code to define new functions was added. Examples of external code that we have used to extend the capabilities of the Process Controller software include proportional integral derivative control algorithms, acquisition of data from turbidimeters using the serial port, functions that incrementally vary a parameter over a specified range and functions that take a flow rate and tubing size and calculate the peristaltic pump speed.
The Process Control software is available at http://ceeserver.cee.cornell.edu/mw24/Software
...
.
...
The
...
software
...
checks
...
for
...
updates
...
whenever
...
it
...
is
...
started
...
and
...
if
...
a
...
newer
...
version
...
is
...
available
...
at
...
the
...
website
...
it
...
gives
...
the
...
user
...
the
...
option
...
of
...
downloading
...
the
...
latest
...
version.
Procedures
The process control software was written using LabVIEW. The high level predefined functions, the ease of developing graphical user interfaces, and the integration with input and output devices made LabVIEW the preferred programming environment. In addition to the software we designed hardware interfaces to simplify the use of sensors and controls.
Sensor outputs and power supply inputs have been integrated in a single cable to make sensors easy to use in a student laboratory environment. The sensors use a standardized wiring scheme so that a variety of sensors can be used in a connect-calibrate-measure approach. The elimination of power supplies at each experiment location and all of the associated wiring has made sensor use easy for students. The process control software interface for sensors allows adding and configuring sensors while simultaneously collecting data.
The output control module can vary the state of on/off devices as well as control devices that require a 4-20 mA signal. The on/off outputs are 24 V with sufficient current to operate small solenoid valves or to switch relays for controlling the power to any number of devices. The 4-20 mA analog outputs are used to control peristaltic pumps. Control of digital devices has not yet been implemented; however, it is possible to add external code that would send commands to a serial or GPIB port or across the internet to control an instrument.
Data Acquisition
The Process Control software is designed to receive data from two types of digital sources. Sensors or meters that have their own digital communication interface can transmit their data to the process control software through external code that is written specifically for each meter. For example this method is used to acquire data from HF Scientific turbidimeters. Sensors that can be configured to produce an analog voltage such as pressure, pH and dissolved oxygen are monitored with a National Instruments SCXI data acquisition system. A dedicated computer monitors all of the data channels of the SCXI data acquisition system and serves requested data to client computers across the internet using TCP-IP. This data acquisition protocol makes it possible for multiple clients to monitor the same sensor (useful in a teaching laboratory setting) and to remotely monitor experiments. The Data Server software was written using LabVIEW and can transmit data either one scan at a time or continuously at the acquired data acquisition rate. In the single scan mode the client computer must request each scan. This mode is used by the Process Control software. The advantage of the single scan data acquisition mode is that if the Process Control software on the client computer slows down because of a lack of computer resources, the software will continue making decisions using the most current sensor readings. If the continuous data mode had been used and if the Process Control software wasn't able to keep up with the high data rate, then the Process Controller software would begin using old data to control the process. Control issues are a concern for applications where sensor data is used to make decisions about the process.
Sensors are wired using Category 5 or 6 Ethernet cable using our own #analog wiring standard. Two wires are used to carry the sensor output voltage designated as S- and S+. Five wires are used for different voltage power supplies, and one wire is used for the power supply ground. It is convenient if student laboratories are hardwired with data acquisition ports at workstations, but this is not required for use of the Process Control software. When used, each data acquisition port is wired with up to five different power supplies. Sensors are wired to connect to the power supply that they require. Thus, the sensor is powered and monitored through a single port. This scheme is used for a variety of sensors including pressure, strain gage, pH, dissolved oxygen, turbidity, and temperature. For several of the sensors the power supplies are also used to power a signal conditioning circuit to transform the sensor output into a voltage that can easily be monitored with a data acquisition system.
| Wiki Markup |
|---|
h2. Procedures The process control software was written using LabVIEW. The high level predefined functions, the ease of developing graphical user interfaces, and the integration with input and output devices made LabVIEW the preferred programming environment. In addition to the software we designed hardware interfaces to simplify the use of sensors and controls. Sensor outputs and power supply inputs have been integrated in a single cable to make sensors easy to use in a student laboratory environment. The sensors use a standardized wiring scheme so that a variety of sensors can be used in a connect-calibrate-measure approach. The elimination of power supplies at each experiment location and all of the associated wiring has made sensor use easy for students. The process control software interface for sensors allows adding and configuring sensors while simultaneously collecting data. The output control module can vary the state of on/off devices as well as control devices that require a 4-20 mA signal. The on/off outputs are 24 V with sufficient current to operate small solenoid valves or to switch relays for controlling the power to any number of devices. The 4-20 mA analog outputs are used to control peristaltic pumps. Control of digital devices has not yet been implemented; however, it is possible to add external code that would send commands to a serial or GPIB port or across the internet to control an instrument. h3. Data Acquisition The Process Control software is designed to receive data from two types of digital sources. Sensors or meters that have their own digital communication interface can transmit their data to the process control software through external code that is written specifically for each meter. For example this method is used to acquire data from HF Scientific turbidimeters. Sensors that can be configured to produce an analog voltage such as pressure, pH and dissolved oxygen are monitored with a National Instruments SCXI data acquisition system. A dedicated computer monitors all of the data channels of the SCXI data acquisition system and serves requested data to client computers across the internet using TCP-IP. This data acquisition protocol makes it possible for multiple clients to monitor the same sensor (useful in a teaching laboratory setting) and to remotely monitor experiments. The Data Server software was written using LabVIEW and can transmit data either one scan at a time or continuously at the acquired data acquisition rate. In the single scan mode the client computer must request each scan. This mode is used by the Process Control software. The advantage of the single scan data acquisition mode is that if the Process Control software on the client computer slows down because of a lack of computer resources, the software will continue making decisions using the most current sensor readings. If the continuous data mode had been used and if the Process Control software wasn't able to keep up with the high data rate, then the Process Controller software would begin using old data to control the process. Control issues are a concern for applications where sensor data is used to make decisions about the process. Sensors are wired using Category 5 or 6 Ethernet cable using our own [#analog wiring standard]. Two wires are used to carry the sensor output voltage designated as S\- and S+. Five wires are used for different voltage power supplies, and one wire is used for the power supply ground. It is convenient if student laboratories are hardwired with data acquisition ports at workstations, but this is not required for use of the Process Control software. When used, each data acquisition port is wired with up to five different power supplies. Sensors are wired to connect to the power supply that they require. Thus, the sensor is powered and monitored through a single port. This scheme is used for a variety of sensors including pressure, strain gage, pH, dissolved oxygen, turbidity, and temperature. For several of the sensors the power supplies are also used to power a signal conditioning circuit to transform the sensor output into a voltage that can easily be monitored with a data acquisition system. {float:right|border=2px solid black|width=250px} {anchor:analog wiring standard} h5. Wiring standard used for combining power supplies and analog data acquisition in a Category 5 Ethernet cable. || *T-568B standard* || *T-568A standard* || *voltage* || | white/orange | white/green | S\- | | orange | green | S\+ | | white/green | white/orange | ground | | blue | blue | \-5 V | | white/blue | white/blue | \+5 V | | green | orange | \+10V | | white/brown | white/brown | \-15 V | | brown | brown | \+15 V | {float} h3. |
Sensors,
...
Signal
...
Conditioning,
...
and
...
Calibration
...
Monitoring
...
sensors
...
requires
...
conversion
...
of
...
the
...
measured
...
voltage
...
into
...
a
...
physically
...
meaningful
...
unit.
...
The
...
data
...
acquisition
...
module
...
of
...
the
...
Process
...
Controller
...
software
...
uses
...
conversion
...
files
...
to
...
implement
...
a
...
variety
...
of
...
conversion
...
algorithms
...
including
...
polynomials
...
and
...
correspondence
...
tables
...
as
...
well
...
as
...
the
...
calibration
...
algorithms
...
required
...
for
...
pH
...
and
...
dissolved
...
oxygen.
...
The
...
pressure
...
sensor
...
conversion
...
files
...
make
...
it
...
easy
...
to
...
use
...
pressure
...
sensors
...
to
...
measure
...
pressures
...
in
...
various
...
physical
...
units,
...
to
...
measure
...
reactor
...
volumes
...
(of
...
known
...
cross
...
sectional
...
area),
...
and
...
flow
...
rates
...
(through
...
devices
...
with
...
known
...
relationships
...
between
...
flow
...
and
...
pressure
...
drop).
...
In
...
addition
...
to
...
the
...
application
...
of
...
a
...
conversion
...
to
...
a
...
physical
...
unit
...
it
...
is
...
possible
...
to
...
calibrate
...
the
...
pressure
...
sensor
...
output
...
to
...
a
...
specific
...
value
...
by
...
changing
...
an
...
offset.
...
pH
...
Sensors
...
pH
...
sensors
...
produce
...
a
...
voltage
...
output
...
in
...
the
...
range
...
that
...
would
...
normally
...
be
...
easy
...
to
...
measure
...
using
...
standard
...
data
...
acquisition
...
hardware.
...
Unfortunately,
...
the
...
impedance
...
requirement
...
for
...
a
...
pH
...
sensor
...
is
...
orders
...
of
...
magnitude
...
higher
...
than
...
the
...
inputs
...
of
...
standard
...
data
...
acquisition
...
hardware
...
and
...
thus
...
a
...
signal
...
conditioning
...
circuit
...
must
...
be
...
used
...
to
...
amplify
...
the
...
pH
...
sensor
...
output.
...
The
...
circuit
...
consists
...
of
...
unity
...
gain
...
amplifiers
...
that
...
have
...
less
...
than
...
0.1
...
pA
...
input
...
leakage
...
current
...
(anonymous
...
,
...
1993).
...
A
...
circuit
...
diagram
...
is
...
available
...
at
...
http://ceeserver.cee.cornell.edu/mw24/Labdocumentation/pH%20Circuit.pdf
...
.
...
The
...
Process
...
Control
...
software
...
includes
...
automatic
...
pH
...
buffer
...
recognition
...
and
...
piecewise
...
linear
...
calibration
...
between
...
buffers.
...
Pressure sensors
| Wiki Markup |
|---|
sensors {float:right|border=2px solid black|width=200px} {anchor:pressure sensor}[!Process Controller^pressuresensor.jpg|width=200px!|Process Controller^pressuresensor.jpg] h5. Differential pressure sensor. {float} |
We
...
use
...
1
...
psi
...
(7
...
kPa)
...
and
...
30
...
psi
...
(200
...
kPa)
...
pressure
...
sensors
...
(Omega
...
sensor
...
models
...
PX26-001DV,
...
and
...
PX26-030DV)
...
in
...
our
...
laboratory
...
to
...
measure
...
water
...
depth,
...
reactor
...
volumes,
...
flow
...
rates,
...
and
...
head
...
loss.
...
These
...
sensors
...
have
...
maximum
...
output
...
voltages
...
of
...
16.7
...
mV
...
and
...
100
...
mV
...
respectively
...
with
...
a
...
power
...
supply
...
of
...
10
...
V.
...
We
...
use
...
the
...
differential
...
pressure
...
model
...
since
...
the
...
sensors
...
can
...
be
...
used
...
to
...
measure
...
gage
...
pressure
...
or
...
differential
...
pressure.
...
The
...
...
can
...
directly
...
measure
...
water
...
pressure
...
although
...
the
...
electrical
...
connections
...
must
...
be
...
kept
...
dry.
...
The
...
Process
...
Control
...
software
...
converts
...
the
...
voltage
...
output
...
from
...
the
...
pressure
...
sensors
...
into
...
the
...
physical
...
units
...
of
...
water
...
column
...
height
...
or
...
pressure
...
using
...
linear
...
conversion
...
algorithms.
...
The
...
sensors
...
can
...
also
...
be
...
zeroed
...
or
...
set
...
to
...
a
...
measured
...
value
...
using
...
a
...
one
...
point
...
calibration.
...
Dissolved
...
Oxygen
...
Dissolved
...
oxygen
...
probes
...
produce
...
a
...
current
...
in
...
the
...
pA
...
range
...
that
...
is
...
proportional
...
to
...
the
...
oxygen
...
concentration
...
in
...
the
...
bulk
...
solution.
...
The
...
signal
...
conditioning
...
circuit
...
is
...
designed
...
to
...
convert
...
this
...
very
...
small
...
current
...
into
...
a
...
measurable
...
voltage
...
and
...
to
...
isolate
...
the
...
probe
...
from
...
the
...
effects
...
of
...
fluctuations
...
in
...
the
...
voltage
...
level
...
of
...
the
...
solution
...
containing
...
the
...
probe.
...
This
...
isolation
...
is
...
critical
...
if
...
the
...
solution
...
is
...
monitored
...
with
...
additional
...
probes
...
or
...
if
...
the
...
solution
...
is
...
electrically
...
connected
...
to
...
a
...
building
...
plumbing
...
system
...
or
...
to
...
any
...
other
...
voltage
...
source.
...
The
...
circuit
...
design
...
is
...
available
...
at
...
(
...
http://ceeserver.cee.cornell.edu/mw24/Labdocumentation/Dissolved_oxygen/circuit.pdf
...
)
Temperature
We use a linear temperature sensor coupled with a simple voltage dividing circuit such as the Omega sensor model OL703. The voltage output is converted to a temperature using a linear equation.
Controls
| Wiki Markup |
|---|
h4. Temperature We use a linear temperature sensor coupled with a simple voltage dividing circuit such as the Omega sensor model OL703. The voltage output is converted to a temperature using a linear equation. h3. Controls {float:right|border=2px solid black|width=300px} {anchor:output control box}[!Process Controller^stampbox.jpg|width=300px!|Process Controller^stampbox.jpg] h5. Basic Stamp® microprocessor control box with ports for 6 on/off devices and 6 variable speed peristaltic pumps. {float} |
An
...
...
...
...
designed
...
and
...
fabricated
...
around
...
the
...
Basic
...
Stamp®
...
Microprocessors
...
(Parallax
...
16
...
port
...
BS2sx
...
and
...
40
...
port
...
BS2p
...
BASIC
...
Stamp®
...
modules)
...
is
...
used
...
for
...
on/off
...
control
...
of
...
up
...
to
...
six
...
devices
...
and
...
for
...
variable
...
control
...
of
...
up
...
to
...
six
...
peristaltic
...
pumps.
...
The
...
Basic
...
Stamp®
...
microprocessor
...
receives
...
commands
...
through
...
the
...
serial
...
port
...
from
...
the
...
Process
...
Control
...
software
...
and
...
then
...
sets
...
the
...
values
...
of
...
its
...
output
...
ports.
...
We
...
initially
...
used
...
the
...
pulse
...
width
...
modulation
...
capability
...
of
...
the
...
Stamp®
...
microprocessor
...
to
...
create
...
an
...
analog
...
voltage
...
output
...
on
...
one
...
of
...
the
...
ports
...
and
...
then
...
used
...
that
...
voltage
...
to
...
control
...
a
...
4-20
...
mA
...
output
...
that
...
could
...
be
...
used
...
to
...
control
...
MasterFlex
...
Peristaltic
...
pumps.
...
That
...
approach
...
continues
...
to
...
work
...
well
...
when
...
we
...
only
...
need
...
to
...
control
...
one
...
pump,
...
but
...
our
...
filtration
...
experiments
...
require
...
computer
...
control
...
of
...
6
...
variable
...
speed
...
pumps.
...
The
...
pulse
...
width
...
modulation
...
commands
...
take
...
too
...
much
...
time
...
to
...
execute
...
and
...
when
...
we
...
switched
...
to
...
six
...
pumps
...
the
...
slow
...
response
...
of
...
the
...
Stamp®
...
microprocessor
...
caused
...
a
...
series
...
of
...
control
...
and
...
communication
...
problems.
...
We
...
resolved
...
that
...
issue
...
by
...
adding
...
analog
...
output
...
circuitry.
...
The
...
Stamp®
...
microprocessor
...
sets
...
the
...
values
...
of
...
the
...
analog
...
voltages
...
by
...
sending
...
digital
...
commands
...
to
...
three
...
MAXIM
...
MAX518
...
2-wire
...
Serial
...
8-Bit
...
Digital
...
to
...
Analog
...
Converters.
...
The
...
peristaltic
...
pump
...
controls
...
include
...
start/stop
...
and
...
clockwise/counterclockwise
...
rotation
...
in
...
addition
...
to
...
the
...
4-20
...
mA
...
speed
...
control.
...
Software
...
for
...
the
...
Basic
...
Stamp®
...
microprocessor
...
takes
...
the
...
command
...
that
...
it
...
receives
...
across
...
the
...
serial
...
port
...
from
...
the
...
Process
...
Control
...
software
...
to
...
set
...
the
...
output
...
values
...
of
...
the
...
I/O
...
ports.
...
Serial
...
commands
...
are
...
sent
...
one
...
character
...
at
...
a
...
time
...
to
...
the
...
Stamp®
...
microprocessor
...
and
...
each
...
character
...
received
...
is
...
acknowledged.
...
The
...
software
...
controls
...
information
...
flow
...
to
...
overcome
...
the
...
lack
...
of
...
a
...
serial
...
buffer
...
on
...
the
...
Stamp®
...
microprocessor.
...
We
...
currently
...
use
...
both
...
a
...
single
...
pump
...
and
...
a
...
six
...
pump
...
version
...
of
...
the
...
control
...
box
...
and
...
they
...
require
...
different
...
sequences
...
of
...
commands
...
from
...
the
...
Process
...
Control
...
software.
...
The
...
software
...
on
...
the
...
Basic
...
Stamp®
...
sends
...
a
...
version
...
code
...
to
...
the
...
Process
...
Control
...
software
...
as
...
the
...
first
...
response
...
in
...
a
...
communication
...
burst
...
and
...
that
...
version
...
code
...
automatically
...
configures
...
the
...
subsequent
...
communication.
...
The
...
communication
...
interface
...
was
...
designed
...
to
...
handle
...
live
...
connection
...
of
...
the
...
control
...
box
...
to
...
the
...
Process
...
Control
...
software.
...
The
...
Process
...
Control
...
software
...
reports
...
status
...
of
...
the
...
connection
...
with
...
the
...
Basic
...
Stamp®
...
microprocessor
...
and
...
communication
...
begins
...
as
...
soon
...
as
...
the
...
physical
...
connection
...
is
...
made.
...
The
...
Stamp
...
microprocessor
...
control
...
boxes
...
have
...
six
...
24
...
V
...
outputs
...
that
...
can
...
be
...
used
...
to
...
control
...
solenoid
...
valves,
...
pinch
...
valves,
...
relays,
...
or
...
other
...
low
...
current
...
devices.
...
The
...
24
...
V
...
circuits
...
include
...
a
...
pulse
...
width
...
modulation
...
chip
...
that
...
reduces
...
the
...
voltage
...
to
...
the
...
device
...
to
...
reduce
...
power
...
consumption
...
and
...
heating.
...
This
...
feature
...
works
...
well
...
for
...
solenoid
...
valves
...
since
...
they
...
can
...
be
...
held
...
open
...
with
...
a
...
relatively
...
low
...
voltage
...
once
...
open.
...
The
...
circuit
...
design
...
for
...
the
...
Stamp
...
microprocessor
...
controls
...
is
...
available
...
at
...
http://ceeserver.cee.cornell.edu/mw24/Labdocumentation/StampBox.pdf
...
.
...
Process
...
Control
...
Software
...
The
...
Process
...
Control
...
software
...
runs
...
five
...
parallel
...
processes
...
during
...
normal
...
operation.
...
The
...
five
...
processes
...
are
...
- Data
...
- acquisition
...
- from
...
- the
...
- Data
...
- Server
...
- software
...
- using
...
- TCP-IP
...
- Calculation
...
- of
...
- output
...
- values,
...
- processing
...
- of
...
- rules
...
- to
...
- determine
...
- state
...
- changes,
...
- sending
...
- commands
...
- to
...
- the
...
- Stamp
...
- microprocessor,
...
- and
...
- logging
...
- of
...
- state
...
- changes
...
- and
...
- the
...
- rule
...
- that
...
- caused
...
- the
...
- state
...
- to
...
- change
...
- Data
...
- logging
...
- of
...
- sensor
...
- data
...
- as
...
- well
...
- as
...
- all
...
- user
...
- defined
...
- variables
...
- Graphical
...
- display
...
- of
...
- all
...
- sensor
...
- data
...
- as
...
- well
...
- as
...
- all
...
- user
...
- defined
...
- variables
...
- An
...
- event
...
- loop
...
- that
...
- responds
...
- to
...
- 20
...
- user
...
- events
...
- to
...
- initiate
...
- processes
...
- such
...
- as
...
- sensor
...
- configuration,
...
- rule
...
- editing,
...
- pump
...
- calibration,
...
- and
...
- data
...
- server
...
- selection.
...
The
...
parallel
...
processes
...
are
...
asynchronous
...
and
...
share
...
data
...
through
...
the
...
use
...
of
...
code
...
objects
...
(LabVIEW
...
SubVIs)
...
that
...
contain
...
both
...
data
...
and
...
methods.
...
A
...
core
...
feature
...
of
...
the
...
Process
...
Control
...
software
...
is
...
the
...
user
...
programmable
...
feature
...
that
...
facilitates
...
customization
...
of
...
the
...
control
...
logic
...
for
...
specific
...
tasks.
...
The
...
rule
...
editor
...
provides
...
a
...
programming
...
environment
...
for
...
setting
...
up
...
states,
...
control
...
logic,
...
set
...
points,
...
variables
...
defined
...
by
...
links
...
to
...
external
...
code,
...
and
...
selecting
...
which
...
user
...
defined
...
parameter
...
controls
...
each
...
output
...
in
...
each
...
state.
States
| Wiki Markup |
|---|
h3. States {float:right|border=2px solid black|width=300px} {anchor:control settings for each state}[!Process Controller^stateoutput.jpg|width=300px!|Process Controller^stateoutput.jpg] h5. View of the controls used to set all of the Stamp® Microprocessor outputs. These controls can have different values for every state. The "output settings" in the middle column are drop down menus containing a list of all the defined constants and variables. {float} |
States
...
represent
...
different
...
control
...
configurations.
...
For
...
example,
...
rapid
...
sand
...
filters
...
could
...
have
...
several
...
operating
...
states
...
including
...
normal
...
down
...
flow
...
operation,
...
backwash,
...
and
...
filter
...
to
...
waste.
...
Each
...
of
...
these
...
states
...
has
...
different
...
control
...
settings
...
(valves
...
are
...
in
...
different
...
positions)
...
and
...
each
...
of
...
the
...
states
...
has
...
different
...
rules
...
determining
...
when
...
the
...
state
...
ends
...
and
...
which
...
state
...
is
...
next.
...
The
...
Process
...
Control
...
software
...
has
...
independent
...
...
...
...
...
...
.
...
The
...
rule
...
editor
...
is
...
used
...
to
...
set
...
the
...
value
...
of
...
each
...
output
...
control.
...
Outputs
...
can
...
be
...
set
...
either
...
to
...
0
...
or
...
1
...
or
...
they
...
can
...
be
...
set
...
to
...
intermediate
...
values.
...
If
...
a
...
fractional
...
value
...
between
...
0
...
and
...
1
...
is
...
assigned
...
to
...
a
...
Boolean
...
output
...
(such
...
as
...
solenoid
...
valves)
...
the
...
Process
...
Control
...
software
...
will
...
toggle
...
between
...
0
...
and
...
1
...
to
...
attain
...
the
...
target
...
value.
...
If
...
a
...
fractional
...
value
...
is
...
assigned
...
to
...
a
...
pump
...
speed
...
control
...
the
...
pump
...
will
...
operate
...
at
...
the
...
fractional
...
value
...
of
...
its
...
maximum
...
speed.
...
The
...
parameters
...
that
...
are
...
assigned
...
to
...
each
...
output
...
can
...
be
...
either
...
constants
...
or
...
variables.
Rules
| Wiki Markup |
|---|
h3. Rules {float:right|border=2px solid black|width=300px} {anchor:exit rule}[!Process Controller^variabledefinition.jpg|width=300px!|Process Controller^variabledefinition.jpg] h5. Rule that ends the state named "BW filter after challenge" when the time in that state exceeds the set point "backwash (filter) time". The rule also indicates that the next state will be "Acid wash". {float} |
Rules
...
are
...
used
...
to
...
set
...
the
...
exit
...
conditions
...
for
...
states.
...
A
...
common
...
...
...
might
...
be
...
based
...
on
...
elapsed
...
time
...
in
...
the
...
current
...
state,
...
but
...
it
...
could
...
also
...
be
...
based
...
on
...
sensor
...
values
...
or
...
on
...
a
...
parameter
...
that
...
is
...
calculated
...
from
...
a
...
combination
...
of
...
sensors
...
and
...
other
...
parameters.
...
At
...
a
...
water
...
treatment
...
plant,
...
backwash
...
might
...
be
...
automatically
...
initiated
...
after
...
72
...
hours
...
in
...
the
...
down-flow
...
state,
...
when
...
pressure
...
drop
...
across
...
the
...
filter
...
exceeds
...
1
...
m,
...
or
...
when
...
the
...
filtered
...
turbidity
...
exceeds
...
0.05
...
NTU.
...
Each
...
state
...
can
...
have
...
multiple
...
exit
...
rules
...
and
...
the
...
rules
...
can
...
have
...
multiple
...
conditions.
...
The
...
rules
...
are
...
executed
...
and
...
the
...
output
...
settings
...
are
...
updated
...
approximately
...
20
...
times
...
per
...
second
...
with
...
the
...
execution
...
speed
...
controlled
...
by
...
the
...
software
...
running
...
on
...
the
...
Stamp
...
microprocessor.
...
Rules
...
with
...
multiple
...
conditions
...
are
...
used
...
when
...
both
...
conditions
...
must
...
be
...
true
...
simultaneously
...
and
...
thus
...
create
...
a
...
logical
...
"and"
...
condition.
...
Multiple
...
rules
...
are
...
executed
...
sequentially
...
and
...
the
...
first
...
rule
...
that
...
is
...
true
...
will
...
cause
...
the
...
state
...
to
...
change
...
to
...
the
...
state
...
selected
...
by
...
that
...
rule.
...
Thus,
...
multiple
...
rules
...
create
...
the
...
logical
...
"or"
...
condition,
...
but
...
with
...
the
...
added
...
feature
...
that
...
each
...
condition
...
can
...
have
...
a
...
different
...
outcome.
...
This
...
feature
...
is
...
useful
...
for
...
handling
...
emergency
...
conditions
...
that
...
then
...
cause
...
the
...
process
...
to
...
shutdown
...
or
...
for
...
creating
...
programs
...
that
...
cycle
...
through
...
different
...
states
...
depending
...
on
...
measured
...
process
...
values.
...
External logic
| Wiki Markup |
|---|
logic {float:right|border=2px solid black|width=300px} {anchor:math functions} [!Process Controller^addfunctionvi.gif|width=300px!|Process Controller^addfunctionvi.gif] h5. LabVIEW block diagram showing the external code that adds two variables or set points and returns the result. {float} |
LabVIEW
...
executables
...
can
...
be
...
enabled
...
to
...
connect
...
to
...
external
...
code.
...
This
...
capability
...
makes
...
it
...
possible
...
to
...
easily
...
extend
...
the
...
capabilities
...
of
...
the
...
Process
...
Control
...
software.
...
The
...
external
...
code
...
must
...
be
...
designed
...
to
...
meet
...
specific
...
requirements
...
for
...
the
...
data
...
types
...
of
...
inputs
...
and
...
outputs.
...
An
...
external
...
code
...
interface
...
has
...
been
...
created
...
to
...
take
...
a
...
variable
...
number
...
of
...
numeric
...
inputs
...
and
...
produce
...
a
...
single
...
numeric
...
output.
...
The
...
external
...
code
...
can
...
be
...
used
...
for
...
a
...
wide
...
variety
...
of
...
functions
...
including
...
simple
...
...
...
,
...
a
...
specialized
...
function
...
(such
...
as
...
one
...
which
...
sets
...
a
...
...
...
based
...
on
...
raw
...
water
...
turbidity
...
proportional-integral-derivative
...
control
...
that
...
can
...
be
...
used
...
to
...
force
...
a
...
controlled
...
parameter
...
to
...
a
...
desired
...
set
...
point,
...
and
...
data
...
acquisition
...
functions
...
that
...
acquire
...
digital
...
data
...
from
...
instruments.
| Wiki Markup |
|---|
{float:right|border=2px solid black|width=300px} {anchor:coagulant dose} [!Process Controller^variabledefinition.jpg|width=300px!|Process Controller^variabledefinition.jpg] h5. Screen shot from the Process Controller showing how inputs are sent to external code. In this case the external code estimates an alum dose based on measured raw water turbidity and a simple model that relates turbidity and alum dose. {float} |
The
...
programming
...
environment
...
for
...
creating
...
rules
...
that
...
determine
...
exit
...
conditions
...
for
...
states
...
and
...
which
...
state
...
to
...
go
...
to
...
readily
...
facilitates
...
setting
...
up
...
the
...
algorithms
...
for
...
controlling
...
simple
...
repetitive
...
processes
...
such
...
as
...
a
...
sequencing
...
batch
...
reactors
...
or
...
rapid
...
sand
...
filters.
...
For
...
experimental
...
purposes
...
it
...
is
...
desirable
...
to
...
have
...
the
...
capability
...
to
...
systematically
...
vary
...
a
...
parameter
...
to
...
test
...
the
...
performance
...
of
...
the
...
process
...
over
...
a
...
range
...
of
...
input
...
values.
...
This
...
is
...
accomplished
...
via
...
an
...
external
...
code
...
that
...
compares
...
the
...
number
...
of
...
specified
...
replicates
...
to
...
a
...
parameter
...
that
...
increments
...
when
...
the
...
process
...
controller
...
enters
...
a
...
specified
...
state.
...
The
...
output
...
parameter
...
can
...
be
...
used
...
to
...
control
...
pump
...
speeds,
...
times,
...
or
...
can
...
be
...
an
...
input
...
to
...
subsequent
...
calculations.
...
Incrementing
...
functions
...
that
...
increment
...
linearly
...
and
...
that
...
increment
...
following
...
a
...
power
...
law
...
relationship
...
are
...
as
...
follow:
| Include Page | ||||
|---|---|---|---|---|
|
| Include Page | ||||
|---|---|---|---|---|
|
The parameter, x, is an integer that increments from zero to a maximum value set by the user. The output parameters, ylinear and ypower could be used to vary a flow rate, a chemical dose, or any other parameter.
| Wiki Markup |
|---|
{include:linear increment equation}\\ {include:power increment equation} The parameter, x, is an integer that increments from zero to a maximum value set by the user. The output parameters, y{~}linear~ and y{~}power~ could be used to vary a flow rate, a chemical dose, or any other parameter. {float:right|border=2px solid black|width=300px} {anchor:increment functions} [!Process Controller^incrementfunction.gif|width=300px!|Process Controller^incrementfunction.gif] h5. Increment functions showing how the parameter varies as a function of the state. In this example the state cycled between states 1, 2, and 3. The increment state was 2, the number of replicates was 2, the reset state was 0, the y intercept was 200, the slope was 50, and the maximum value of x was 4. The power law relationship used a coefficient of 100 and a base of 1.5. {float} |
The
...
two
...
...
...
are
...
dependent
...
on
...
the
...
state
...
cycles.
...
The
...
state
...
was
...
set
...
to
...
cycle
...
between
...
states
...
1,
...
2,
...
and
...
3
...
with
...
the
...
exception
...
of
...
a
...
manual
...
reset
...
to
...
state
...
0
...
and
...
then
...
to
...
state
...
1
...
to
...
illustrate
...
how
...
the
...
increment
...
function
...
is
...
reset.
...
The
...
power
...
law
...
function
...
is
...
useful
...
when
...
it
...
is
...
desirable
...
to
...
explore
...
a
...
larger
...
parameter
...
space.
...
However,
...
care
...
must
...
be
...
taken
...
to
...
ensure
...
that
...
the
...
controlled
...
processes
...
have
...
the
...
ability
...
to
...
deliver
...
the
...
desired
...
range
...
of
...
the
...
varied
...
parameter.
...
The
...
Process
...
Controller
...
can
...
be
...
configured
...
to
...
stop
...
an
...
experiment
...
after
...
the
...
reaching
...
the
...
maximum
...
value
...
of
...
the
...
parameter.
...
Otherwise
...
it
...
will
...
reset
...
the
...
parameter
...
to
...
its
...
initial
...
value
...
and
...
begin
...
the
...
increment
...
process
...
again.
...
It
...
is
...
also
...
possible
...
to
...
systematically
...
vary
...
more
...
than
...
one
...
parameter.
...
Data
...
and
...
process
...
logging
...
The
...
Process
...
Controller
...
creates
...
two
...
types
...
of
...
data
...
files.
...
The
...
first
...
column
...
in
...
both
...
files
...
is
...
a
...
time
...
stamp
...
and
...
new
...
files
...
are
...
created
...
automatically
...
at
...
midnight.
...
The
...
datalog
...
file
...
contains
...
a
...
column
...
for
...
each
...
sensor
...
and
...
for
...
each
...
variable.
...
The
...
datalog
...
accumulates
...
data
...
at
...
the
...
rate
...
set
...
by
...
the
...
user.
...
Sensor
...
data
...
is
...
averaged
...
over
...
the
...
data
...
interval,
...
but
...
the
...
instantaneous
...
values
...
are
...
recorded
...
for
...
variables.
...
The
...
statelog
...
file
...
contains
...
a
...
row
...
for
...
every
...
time
...
the
...
state
...
changes.
...
The
...
row
...
contains
...
the
...
state
...
ID
...
number
...
and
...
the
...
name
...
of
...
the
...
rule
...
that
...
caused
...
the
...
state
...
to
...
change.
...
If
...
the
...
user
...
caused
...
the
...
state
...
to
...
change
...
that
...
is
...
indicated
...
as
...
well.
...
By
...
using
...
both
...
the
...
data
...
and
...
state
...
logs
...
it
...
is
...
possible
...
to
...
reconstruct
...
the
...
events
...
that
...
occurred
...
during
...
an
...
experiment
...
and
...
correlate
...
sensor
...
and
...
variable
...
values
...
with
...
the
...
state
...
of
...
the
...
Process
...
Controller.
...
The
...
data
...
can
...
be
...
analyzed
...
to
...
troubleshoot
...
and
...
to
...
determine
...
what
...
event
...
caused
...
the
...
Process
...
Controller
...
to
...
perform
...
unexpectedly.
...
The
...
Process
...
Control
...
software
...
is
...
designed
...
to
...
minimize
...
control
...
failures.
...
If
...
a
...
sensor
...
voltage
...
goes
...
out
...
of
...
range
...
for
...
a
...
data
...
acquisition
...
channel
...
or
...
if
...
communication
...
with
...
the
...
Data
...
Server
...
is
...
lost,
...
all
...
control
...
outputs
...
are
...
turned
...
off.
...
The
...
software
...
responds
...
to
...
a
...
power
...
outage
...
or
...
Microsoft
...
Windows
...
restart
...
by
...
automatically
...
opening
...
up
...
Process
...
Control
...
and
...
Data
...
Server
...
software
...
and
...
returning
...
the
...
software
...
to
...
the
...
same
...
state
...
as
...
when
...
it
...
was
...
shut
...
down.
...
Returning
...
to
...
the
...
previous
...
state
...
requires
...
opening
...
up
...
configuration
...
files
...
and
...
then
...
opening
...
up
...
the
...
state
...
log
...
file
...
to
...
determine
...
the
...
state
...
that
...
the
...
software
...
was
...
in
...
when
...
the
...
computer
...
was
...
shut
...
down.
...
Filter
...
Test Apparatus
| Wiki Markup |
|---|
Apparatus {float:right|border=2px solid black|width=300px} {anchor:photo}[!Process Controller^photofiltrationapparatus.jpg|width=300!|Process Controller^photofiltrationapparatus.jpg] h5. Photo of the filter test apparatus. {float} |
Results
...
from
...
operation
...
of
...
an
...
experimental
...
assembly
...
(
...
...
and
...
...
)
...
designed
...
for
...
research
...
on
...
water
...
filtration
...
is
...
provided
...
here
...
as
...
an
...
example
...
of
...
the
...
Process
...
Controller's
...
use.
...
The
...
filter
...
test
...
apparatus
...
(FTA)
...
consists
...
of
...
6
...
variable
...
speed
...
peristaltic
...
pumps
...
(Cole-Parmer,
...
L/S
...
series
...
Masterflex
...
pumps
...
with
...
remote
...
control
...
capabilities),
...
2
...
on-line
...
turbidimeters
...
(HF
...
scientific,
...
MicroTol
...
20053
...
and
...
20055),
...
a
...
15
...
cm
...
long
...
by
...
2.5
...
cm
...
diameter
...
filter
...
cell
...
containing
...
0.4
...
mm
...
to
...
0.5
...
mm
...
sand,
...
4
...
solenoid
...
valves
...
(Farmington
...
Engineering
...
Series
...
6605),
...
the
...
Basic
...
Stamp®
...
microprocessor
...
control
...
box,
...
the
...
data
...
acquisition
...
system,
...
a
...
pH
...
sensor
...
(Oakton
...
*
...
pH
...
Electrode
...
model
...
WD-35801-00),
...
pressure
...
sensors
...
(Omega,
...
model
...
PX26-001DV),
...
and
...
a
...
computer
...
running
...
the
...
Process
...
Control
...
software.
...
A
...
second
...
computer
...
running
...
Process
...
Control
...
software
...
is
...
used
...
to
...
control
...
the
...
temperature
...
of
...
a
...
tap
...
water
...
supply
...
reservoir.
...
The
...
reservoir
...
is
...
instrumented
...
with
...
a
...
temperature
...
sensor
...
and
...
a
...
pressure
...
sensor.
...
The
...
temperature
...
sensor
...
is
...
used
...
to
...
determine
...
whether
...
hot
...
tap
...
water
...
or
...
cold
...
tap
...
water
...
should
...
be
...
added
...
and
...
the
...
pressure
...
sensor
...
is
...
used
...
to
...
determine
...
if
...
water
...
needs
...
to
...
be
...
added
...
to
...
keep
...
the
...
reservoir
...
full.
...
The
...
reservoir
...
contains
...
an
...
aeration
...
stone
...
and
...
is
...
constantly
...
aerated
...
to
...
remove
...
any
...
supersaturated
...
gases
...
that
...
are
...
commonly
...
found
...
in
...
cold
...
surface
...
waters
...
and
...
prevent
...
evolution
...
of
...
gas
...
bubbles
...
in
...
the
...
filter
...
column.
...
The
...
experimental
...
objective
...
of
...
the
...
FTA
...
is
...
to
...
test
...
the
...
effect
...
of
...
various
...
chemical
...
treatments
...
of
...
the
...
filter
...
media
...
on
...
the
...
particle
...
removal
...
efficiency.
...
The
...
Process
...
Controller
...
is
...
used
...
to
...
cycle
...
through
...
the
...
following
...
states
...
for
...
each
...
test.
...
- A
...
- chemical
...
- treatment
...
- (for
...
- example
...
- application
...
- of
...
- alum)
...
- can
...
- be
...
- metered
...
- into
...
- the
...
- filter
...
- using
...
- different
...
- combinations
...
- of
...
- concentration,
...
- filter
...
- approach
...
- velocity,
...
- and
...
- duration.
...
- Clean
...
- water
...
- feed
...
- – A
...
- clean
...
- water
...
- feed
...
- follows
...
- the
...
- pretreatment
...
- step
...
- and
...
- is
...
- used
...
- to
...
- flush
...
- the
...
- residual
...
- pretreatment
...
- chemicals
...
- from
...
- the
...
- column
...
- and
...
- turbidity
...
- sensors.
...
- Particle
...
- Challenge
...
- – The
...
- particle
...
- removal
...
- efficiency
...
- is
...
- measured
...
- by
...
- applying
...
- a
...
- turbid
...
- water
...
- containing
...
- a
...
- clay
...
- suspension
...
- to
...
- the
...
- filter.
- Backwash – The accumulated particles and the chemical from the pretreatment step are removed from the porous media. Additional states can be used to flush the turbidimeter cells with clean water to remove any settled clay or to pump an acidic solution through the filter to ensure complete removal of the surface coatings created by pretreatment of the filter media.
| Wiki Markup |
|---|
# Backwash -- The accumulated particles and the chemical from the pretreatment step are removed from the porous media. Additional states can be used to flush the turbidimeter cells with clean water to remove any settled clay or to pump an acidic solution through the filter to ensure complete removal of the surface coatings created by pretreatment of the filter media. {float:right|border=2px solid black|width=300px} {anchor:schematic}[!Process Controller^schematicfilter.gif|width=300!|Process Controller^schematicfilter.gif] h5. Schematic of the filter test apparatus showing the valve and pump configuration for pretreatment with aluminum sulfate. {float} h2. |
Results and Discussion
| Wiki Markup |
|---|
and Discussion {float:right|border=2px solid black|width=300px} {anchor:data surface}[!Process Controller^filterperformance.gif|width=300px!|Process Controller^filterperformance.gif] h5. Data surface showing the effects of pretreatment with aluminum sulfate. The black data points are measured values and include replicates at each aluminum treatment level. The mass of aluminum applied per filter area increases from left to right on the y axis. The ability of the filter to remove clay is measured as pC\* where C\* is the effluent turbidity normalized by the influent turbidity and "p" is the negative log function. The filter run time is on the x axis. There is a gradual deterioration in filter performance with run time. {float} |
Over
...
the
...
past
...
five
...
years
...
the
...
Process
...
Control
...
software
...
and
...
hardware
...
have
...
been
...
used
...
by
...
students
...
to
...
automate
...
bench
...
scale
...
drinking
...
water
...
treatment
...
plants,
...
activated
...
sludge
...
sequencing
...
batch
...
reactors,
...
temperature
...
controllers,
...
flow
...
controllers,
...
pH
...
controllers,
...
and
...
a
...
large
...
number
...
of
...
other
...
experimental
...
configurations.
...
These
...
experiments
...
were
...
conducted
...
as
...
part
...
of
...
the
...
CornellUniversity
...
undergraduate
...
curriculum
...
in
...
Environmental
...
Engineering.
...
In
...
addition,
...
the
...
ability
...
to
...
automatically
...
vary
...
a
...
parameter
...
over
...
a
...
range
...
of
...
values
...
has
...
significantly
...
increased
...
our
...
ability
...
to
...
characterize
...
performance
...
in
...
research
...
on
...
unit
...
processes
...
for
...
water
...
treatment.
...
As
...
an
...
example
...
of
...
this
...
capability
...
we
...
present
...
data
...
from
...
an
...
experiment
...
that
...
was
...
conducted
...
to
...
determine
...
the
...
effect
...
of
...
an
...
aluminum
...
hydroxide
...
coating
...
on
...
porous
...
media
...
to
...
enhance
...
the
...
removal
...
of
...
kaolin
...
clay.
...
The
...
aluminum
...
concentration
...
in
...
the
...
feed
...
during
...
the
...
pretreatment
...
step
...
was
...
2.5×10^-
...
4^ mole/liter.
...
The
...
amount
...
of
...
aluminum
...
applied
...
to
...
the
...
filter
...
was
...
varied
...
using
...
the
...
power
...
law
...
increment
...
function
...
to
...
adjust
...
the
...
duration
...
of
...
the
...
pretreatment
...
state.
...
Each
...
of
...
the
...
pretreatment
...
conditions
...
was
...
replicated
...
and
...
the
...
results
...
from
...
the
...
two
...
tests
...
were
...
almost
...
identical.
...
The
...
...
...
is
...
from
...
the
...
particle
...
challenge
...
state
...
from
...
the
...
6
...
treatment
...
levels
...
and
...
a
...
replicate
...
for
...
a
...
total
...
of
...
12
...
tests.
...
The
...
filter
...
performance
...
is
...
measured
...
as
...
pC
...
*
...
where
...
C
...
*
...
is
...
the
...
turbidity
...
of
...
the
...
effluent
...
water
...
normalized
...
by
...
the
...
turbidity
...
of
...
the
...
influent
...
water
...
and
...
p
...
is
...
the
...
--log
...
function.
...
Thus
...
a
...
value
...
of
...
zero
...
for
...
pC
...
*
...
would
...
indicate
...
no
...
particle
...
removal
...
and
...
a
...
value
...
of
...
1
...
indicates
...
90%
...
particle
...
removal.
...
The
...
x
...
axis
...
is
...
time
...
and
...
data
...
is
...
shown
...
between
...
600
...
and
...
1000
...
s.
...
The
...
data
...
from
...
the
...
first
...
residence
...
time
...
for
...
the
...
experimental
...
apparatus
...
are
...
not
...
shown
...
since
...
it
...
takes
...
several
...
residence
...
times
...
to
...
purge
...
the
...
filter
...
column
...
of
...
the
...
water
...
from
...
the
...
previous
...
state.
...
The
...
aluminum
...
pretreatment
...
is
...
reported
...
on
...
the
...
y
...
axis
...
as
...
moles
...
of
...
aluminum
...
per
...
square
...
meter
...
of
...
filter
...
top
...
surface
...
area.
...
The
...
data
...
clearly
...
show
...
that
...
the
...
aluminum
...
pretreatment
...
enhances
...
particle
...
capture
...
and
...
that
...
at
...
low
...
doses
...
the
...
filter
...
performance
...
improves
...
as
...
the
...
amount
...
of
...
aluminum
...
applied
...
to
...
the
...
filter
...
increase.
...
However,
...
at
...
the
...
very
...
highest
...
dose
...
the
...
filter
...
performance
...
begins
...
to
...
deteriorate.
...
We
...
will
...
compare
...
aluminum
...
sulfate
...
with
...
other
...
filter
...
aids
...
and
...
discuss
...
the
...
significance
...
of
...
these
...
experimental
...
results
...
in
...
a
...
future
...
paper.
...
Conclusions
The automation of unit processes and the integration of process control and data acquisition greatly facilitate characterization of unit process performance. The Process Control software makes it easy for students in laboratory courses and in research laboratories to configure and automate a wide variety of unit processes. The ability to generate reproducible data including information on the process control states greatly facilitates data analysis. The ability to collect data at higher sampling rates than possible with manual sample also increases confidence in the significance of the data. Automation of a sequence of experimental conditions and of data collection also permits researchers to conduct many more experiments than would otherwise be possible if they were performed manually.
Acknowledgments
This work was funded by the National Science Foundation and Cornell University. The author would like to thank Leonard Lion for his thoughtful review of this paper, Po-Hsun Lin for the rapid sand filtration data, and Cameron Willkens for design and fabrication of the microprocessor control box and the sensor signal conditioning circuits.
References
anonymous (1993) MAXIM 1.2 mA Max, Single/Dual/Quad, Single-Supply Op Amps. Accessed 4/16 2007. http://www.ortodoxism.ro/datasheets/maxim/MAX406-MAX419.pdf
...
Braatz,
...
R.
...
D.
...
and
...
Johnson,
...
M.
...
R.
...
(1998)
...
Process
...
control
...
laboratory
...
education
...
using
...
a
...
graphical
...
operator
...
interface.
...
Computer
...
Applications
...
in
...
Engineering
...
Education
...
6
...
(3),
...
151.
...
Choi,
...
C.
...
H.
...
(2004)
...
Undergraduate
...
controls
...
laboratory
...
experience.
...
In:
...
ASEE
...
Annual
...
Conference
...
Proceedings,
...
14425.
...
Rehg,
...
J.
...
A.,
...
Swain,
...
W.
...
H.,
...
Yangula,
...
B.
...
P.,
...
Wheatman,
...
S.
...
(1999)
...
Fieldbus
...
in
...
the
...
process
...
control
...
laboratory
...
-
...
its
...
time
...
has
...
come.
...
In:
...
Proceedings
...
-
...
Frontiers
...
in
...
Education
...
Conference,
...
13b4-12.
...