23FALL 20 03• h o t l i n k s

A E R O D Y N A M I C R E S E A R C H

THE ANSWER IS BLOWIN’IN THE WIND

InTouch HMI MonitorsWind Tunnel Use at NASA Ames ResearchCenter.

T H E N AT I O N A L A E R O N A U T I C S & S PA C E A D M I N I S T R AT I O N

(NASA) I S O N E O F T H E WO R L D’S L E A D I N G R E S E A RC H I N S T I-T U T I O N S S T U D Y I N G A E R O D Y N A M I C P H E N O M E N A . Much of the

advanced work conducted in this subject area is performed in the Fluid

Mechanics Laboratory (FML) at NASA Ames Research Center in Mountain

View, Calif., using in-draft wind tunnel systems controlled by a network of com-

puters and a single programmable logic controller (PLC).

The system is designed to allow multiple researchers to conduct simul-

taneous experiments in multiple wind tunnels, using wind flow generated by

a single large compressor — a 9,000,000-horsepower, 240,000,000-cubic-

foot-per-minute vacuum compressor. The system must be able to generate

air speeds of Mach 1 or greater in the experiment test section of these wind

tunnels, but also be tightly controlled so that the start-up or shutdown of

any one wind tunnel doesn’t affect the operation of any others.

Despite the sophistication of the PLC-based system that controls all the

wind tunnel interaction, its primitive operator interface (OI) provided little vis-

ibility into the compressor system’s online operation. Information about oper-

ating conditions was insufficient to allow less experienced operators — such as

doctoral candidates from around the country who use the lab for aerodynamic

research for their dissertations — to operate it as well as the best NASA operator

could.

It also was insufficient for use by FML facility engineers to analyze effi-

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25FALL 20 03• h o t l i n k s

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tem verified the state of the vanes, monitored the

surge control valve that admits atmospheric air

from outside the building, started and tested the

main and backup oil pumps, started the main drive

motor and then brought the compressor up to

speed under a low-load condition.

Once the compressor was at speed, the PLC

released the valve and the vanes under propor-

tional, integral derivative (PID) loop control and

modulated the volume of atmospheric air versus

manifold flow. The object was to maintain a fixed

pressure of 8.3 pounds per square inch absolute

(PSIA), which was ideal for providing Mach 1 air

flow, regardless of the control valve settings at the

individual test cells.

The new system was set up so that the com-

pressor always stays on-line and manifold pressure

is always available for experiments in the wind

tunnels. A General Electric 90-70 PLC MO handles

all input/output (I/O) and control functions using

a mix of I/O cards and GE Fanuc Genius blocks.

Data is passed from the PLC to the HMI computer

via a PC interface module that communicates at

153 kilobauds. Separate PID loops control the

valves and the vanes, updating data every 30 milli-

seconds.

No matter how fast the users can open or close

the valves, the compressor manifold pressure

always stays at 8.3 PSIA (+0.05) from zero to

175,000 cubic feet per minute air flow, at which

point some drift is noticeable because the compres-

sor begins to fall behind.

“The problem was that the control system was

highly reactive, so it tended to get a bit unstable,

particularly early in its development,” explains

Dave Yaste, NASA senior aerospace engineering

technician.

“We had some problems keeping the compres-

sor on set points and sometimes the IGVs and SCV

would go into oscillations and feed off each other

until the machine detected surge and shut itself

down.

“It took a lot of trial-and-error manipulation

to get it under control because we couldn’t track all

this activity other than by reading through reams of

ladder logic and trying to correlate it to columns of

historical figures. We were doing detective work,

not monitoring the process as it ran. In addition, it

was a very difficult system to learn to run simply

because we had no visibility into it.”

In 1991, a project team was created to investi-

gate the development of an advanced human-

machine interface to solve the problem. The team

included Yaste, controls engineer Peter Graube and

facility manager James Laub.

After researching more than 20 HMI possi-

bilities, the team arrived at six key features that

would be the base requirements for a successful

installation:

• Personal computer compatibility

• Statistical capability

• User-friendly interface

• Dynamic data

• Full animation

• Multi-tasking capabilities.

NASA Ames selected Wonderware’s InTouch

HMI software and NetDDE for real-time data

exchange between the InTouch HMI and the lab’s

Excel spreadsheet program via networks. This real-

time data exchange facilitates long-term trending

and statistical analysis.

The InTouch software runs on a Pentium

90 microcomputer made by EPS Technologies. The

system uses an ATI Mach 64 video accelerator,

which is configured for 1,024 x 768 resolution and

65,000 colors. The monitor is a ViewSonic 20.

Intuitive, Powerful Interface

TH E I N TO U C H S O F T WA R E H A S P R OV E N

T O B E A N I N T U I T I V E A N D P O W E R F U L

U S E R I N T E R F A C E T O T H E C O M P R E S S O R

CONTROL SYSTEM. The software displays a replica

of the compressor equipment configuration, with

appropriate operating data displayed in on-screen

windows so that operation is visible at all times,

regardless of operator familiarity with the system.

ciently any automated compressor shut-

down and determine its cause and effects.

They had to dig through extensive PLC

ladder logic to diagnose faults because

the simple OI controls that existed — dis-

crete lamps indicating on and off condi-

tions and a Panalarm light box —were

inadequate.

The problem was solved with

the addition of a PC-based, human-

machine interface (HMI) developed

using Windows-based InTouch® HMI

application development software from

Wonderware, a business unit of Invensys’

Production Management Division.

The resulting compressor and control

system now provides a sophisticated plat-

form on which NASA Ames engineers are

planning to build even more capable sys-

tems for future experiments.

The New System

TH E FML C O M P R E S S O R S Y S T E M

C O N S I S T S O F A C E N T R I F U G A L

FLOW COMPRESSOR BUILT BY ALLIS-CH A L M E R S , A 9,000-H O R S E P OW E R

S Y N C H R O N O U S M O T O R A N D A

S PE E D-I N C R E A S I N G G E A R B OX BU I LT

BY HITACHI ELECTRIC. The compres-

sor is housed in its own building adjacent

to the wind tunnel laboratory. It is con-

nected to a vacuum manifold that pro-

vides vacuum to four in-draft wind tunnel

test cells.

Variable-incidence inlet guide vanes

(IGV) open and close like venetian blinds

to provide greater or lesser air flow to each

tunnel. A 30-inch surge control valve

(SCV) opens to admit outside air, acting as

a buffer to prevent compressor damage

when the wind tunnels are turned on or

off.

The original PLC-based control sys-

The decision to move to the InTouchHMI has been an extremely profitablemove. — D A V E YA S T E , S E N I O R E N G I N E E R I N G T E C H N I C I A N

HLS0311_23_26_NASA.qxd 12/17/03 2:38 PM Page 24

One new screen is used to automate

the compressor start-up sequence, with

each step in the process causing on-screen

graphics/text blocks to change color from

yellow to green as the step is passed. In the

past, start-up was an extremely difficult

procedure because of the defense mecha-

nisms that were built in to protect the com-

pressor. Now, it starts without incident

more than 95 percent of the time. On those

occasions when any steps fail, and, there-

fore, cause a failed start sequence, problems

are instantly obvious to operators.

In addition, the Excel spreadsheet

program running in the background is

used for collecting data from about 400

system control points to build a database

for statistical analysis of trends. The lab

now allows researchers to sample any of 71

analog channels and 155 discrete points,

simultaneously animating the compressor

train and several zoom screens and storing

sample values for later analysis.

The use of InTouch HMI has allowed

the FML staff to replace a strip-chart

recorder with a four-channel, high-speed,

real-time trend program that provides an

on-screen chart view of transient data at

sample rates of up to four samples per sec-

ond. Staff can now easily compare live data

to historical data and download results to

Excel for future analysis and hard-copy

output.

As a problem-detection tool, InTouch

software allows the FML team to pop up a

screen, zoom in on any alarmed point and

show the temperatures, vibrations, pres-

sures or other variables of the components

directly related to the alarm condition.

If there is a question at any time

about operating conditions or alarm sta-

tus, the operator simply ‘walks’ through

the progressive screens to single out the

failed start step or the status of each com-

ponent. This is a far easier process than

with the old system, under which the lab

team would have to search through ladder

logic data to find the offending rung (a

sometimes cryptic troubleshooting path).

Now, the operator merely points and clicks

his way to the answer.

Adding ControlFunctionality

“T HE DECISION TO MOVE TO A

W I N D OW S - B A S E D G R A P H I -C A L HMI H A S B E E N A N E XT R E M E LY

P R O F I TA B L E M O V E , E V E N I F O N LY

MEASURED IN TERMS OF THE TROU-B L E S H O O T I N G A N D T R A I N I N G A N D

MAN-HOURS SAVED,” YASTE SAYS.“The added capabilities our new test

facility has gained, from advanced controls

and user-friendly tools, however, is

immeasurable. Even though InTouch soft-

ware is technically an HMI program, we’re

already implementing some control activi-

ties with it on one of our test stations.

“We’ve built our own stepper motor

and actuator for two tunnels, and we’re

now doing comparison studies to see

whether we should write our own DDE

using Wonderware’s DDE Server Toolkit

or use NetDDE and dynamic link libraries

to incorporate an off-the-shelf controller,”

he adds.

“Linking the screen graphics and out-

put displays to the Genius blocks and

using the logic capabilities of the InTouch

HMI will allow us to provide some very

flexible yet sophisticated control tech-

niques for customizing experiments.

“This could be very useful to candi-

dates because it would let them simply

specify the Mach number they want in the

test section of the wind tunnel, and the

InTouch HMI can calculate how far open

the choke throat should be,” he says.

“There’s a specific ratio between the

supersonic, sonic and subsonic sections by

which area ratio alone will generate a

Mach number. So merely by creating a

graphic slider on the screen, we can let the

user enter the air speed desired, and

InTouch logic will calculate and set the

tunnel parameters.”

“The success of the HMI program

and the new vistas it has opened for us has

inspired us to upgrade our PLC systems,”

Yaste notes. THE END

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