Cotton Production and Processing LaboratoryLubbock, TX

& Cotton Incorporated

Researcher Mathew G. Pelletier

Research Goal

• Development of accurate bale moisture sensing.

• Focus on issues relevant to wet bales

•Adding moisture reduces bale packing forces. This effect minimizes the number of repair cycles required to maintain the bale press.

•Adding moisture also adds weight back to bale, so there’s also an economic incentive for moisture restoration.

Moisture Restoration before the Bale Press

Excess Bale Moisture in storageCauses Change in Color Grade

Color Change in Storage due to Excess Moisture

-8

-7

-6

-5

-4

-3

-2

-1

0

1

2

3

%Moisture

Co

lor

cha

ng

e

Rd (reflectance)

+b (Yellowness)

New CC Loan rules dictate all bales must be certified by the gin to contain less than 7.5% M.C. at

ANY point in the bale.

Moisture Sensing Technologies

• Resistance sensors (bale probes, bale-press)

• Capacitance roller conveyor

• Infrared (top 1mm of surface only)

• Microwave through transmission (2 types)– Signal absorbance (Vomax, Malcalm)– Signal propagation time (USDA-ARS;

Pelletier)

Current industry standard for testing bale moisture is

By hand-held resistance sensors.

How accurate are they really for use with wet cotton bales?

To test the accuracy of the hand-held sensors;

A nation-wide test was conducted by all 3 of USDA-ARS cotton gin labs

Hand-held Resistance Sensorsfor Bale Moisture Measurement

AQB-SC versus Oven Moisture:Uncertainty (95%) +/-2.31% (as read by meter)

After correction for slope-offset; Uncertainty (95%) = +/-1.83%M.C.

y = 0.578x + 1.6066

R2 = 0.5314

0.00

2.00

4.00

6.00

8.00

10.00

12.00

4.0 6.0 8.0 10.0 12.0 14.0

AQB-SC Meter Readings (%M.C.)

Ove

n %

M.C

.

AQB-BS versus Oven Moisture:Uncertainty (95%) +/-3.34% (as read by meter)

After correction for slope-offset; Uncertainty (95%) = +/-2.33%M.C.

y = 0.4267x + 3.1301

R2 = 0.3707

0.00

2.00

4.00

6.00

8.00

10.00

12.00

2.0 4.0 6.0 8.0 10.0 12.0 14.0

AQB-BS Meter Readings (%M.C.)

Ove

n %

M.C

.

DHT-EC versus Oven Moisture:Uncertainty (95%) +/-1.95% (as read by meter)

y = 0.7309x + 3.0362

R2 = 0.4665

3.50

4.50

5.50

6.50

7.50

8.50

9.50

3.5 4.5 5.5 6.5 7.5 8.5 9.5DHT-EC Meter Readings (%M.C.)

Ove

n %

M.C

.

How well do the meters agree to each other?

Comparison between commercial hand-held bale moisture meters (low freq. resistance)

0

2

4

6

8

10

0 2 4 6 8 10

Oven Tested %M.C.

Ave

rage

Met

er

Rea

ding

%M

.C.

DHT-EC

SDB-LP

AQB-BS

AQB-SC

What are the error sources?

Within-Bale Moisture Variationfor very wet bale

Low MHz Frequency Roller Conveyor Capacitance Sensor

-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5

-1.5

-1

-0.5

0

0.5

1

1.5

Surface Sensors can’t detect interior moisture

How to detect interior wet spots per FSA/CC mandate?

Disadvantages of current microwave moisture sensors

• Modern Microwave systems average moisture over large sensing areas.

• The large sampling volume dilutes or misses localized high moisture areas

Experimental USDA-ARS Microwave Sensor for bale moisture

Sensing of local moisture variability critical for wet bale

moisture determination

• Experimental Lubbock Gin Lab Microwave Imaging system in development to sense internal wettest spot in bale.

Impulse response of microwave imager

-0.3

0.0

0.3

0.6

1.0

1.3

-60 -40 -20 0 20 40 60

Distance to Imaging Axis (cm)

Pro

pa

ga

tion

De

lay

(ps)

Microwave Pencil Beam Imaging Can Resolve Interior Moisture

Advantages to Pencil Beam Microwave Imaging

• Ability to measure wettest spot in bale per new 2006 FSA CC Regulations

• Local moisture as well as large sample estimation of moisture available through full bale scanning

• With what accuracy can the new microwave imaging technique perform quantitative analysis?

• To test accuracy; the microwave imager was tested on a set of known permittivitty standards (traceable to NIST labs).

Chemical Concentration versus Measured Propagation Delay

(Propagation delay range chosen to match typical range for U.D. cotton bales ranging from 5.5 - 8.5% M.C.)

R2 = 0.9988

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Chemical Concentration (by mass)

Me

as

ure

d P

rop

ag

ati

on

D

ela

y (

ns

).

NIST Propagation Delay versus Measured Propagation Delay

(Propagation delay range chosen to match typical range for U.D. cotton bales ranging from 5.5 - 8.5%M.C.)

R2 = 0.9974

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.15 0.2 0.25 0.3 0.35 0.4 0.45

NISTPropagation Delay (ns)

Me

asu

red

Pro

pa

ga

tion

De

lay

(ns)

.

Equivalent Cotton Moisture versus Predicted Cotton Moisture

Accuracy (95% confidence) = 0.097%M.C.

R2 = 0.9978

5.5

6

6.5

7

7.5

8

8.5

5.5 6 6.5 7 7.5 8 8.5

% Moisture Content

Pre

dict

ed %

Moi

st.

Controlled Testing of Microwave Imager on Mini-Cotton bales

Goals:

• Verify new Imaging System has comparable accuracy to standard microwave sensors.

• Establish cotton bale’s true permittivity for creation of a standard linkage by which all future sensors and cotton bale-moisture can be traced to NIST Laboratory measurements.

Microwave Imager test on mini-bales

R2 = 0.9628

4

6

8

10

12

14

4 6 8 10 12 14

%M.C.

Pre

dict

ed %

M.C

.

Conclusion

• Wet bales exhibit extreme amounts of local variability.

• A suitable sensing system for moisture restoration systems must be able to sense local variability and control to the wettest spot in the bale; not the average.

• New USDA-ARS Microwave Imager shows promise for detection of local moisture variability in addition to average bale moisture

Bale Moisture Sensors must be able to

Resolve Interior Spot Moisture, Not just Surface or Average Moisture