An Automated Ferranti-Shirley Viscometer - ACS Symposium Series

13 An Automated Ferranti-Shirley Viscometer

Downloaded by FUDAN UNIV on March 14, 2017 | http://pubs.acs.org Publication Date: September 24, 1982 | doi: 10.1021/bk-1982-0197.ch013

A. F. KAH, M. E. KOEHLER, T. F. NIEMANN, T. PROVDER, and R. R. ELEY SCM Corporation, Glidden Coatings and Resins Division, Dwight P. Joyce Research Center, Strongsville, OH 44136

A Ferranti-Shirley cone-plate viscometer was interfaced to a minicomputer system by means of a microcomputer. The microcomputer collects data from the instrument corresponding to shear rate, shear stress and temperature. Data are transmitted to the minicomputer for storage, analysis and the generation of reports and plots. Four types of analyses are performed: 1)

2)

3) 4)

Casson analysis of shear stress vs. shear rate for a linear ramp of shear rate with time yields viscosity vs. shear rate and the Casson "infinite shear rate" viscosity. Analysis of shear stress at constant shear rate yields an average viscosity and changes in viscosity with time due to effects such as shear thinning, viscous heating and thermoset curing. Analysis of spring relaxation data yields viscosity vs. shear rate information at low shear rates. A step shear rate experiment which studies the build-up of structure at low shear rate after the sample has been "sheared out" at a high shear rate.

Benefits derived from automation include time savings, improved record keeping and reporting, and a better understanding of the instrument operating characteristics and performance.

0097-6156/82/0197-0223$06.00/0 © 1982 American Chemical Society

Provder; Computer Applications in Applied Polymer Science ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

224

COMPUTER APPLICATIONS IN APPLIED POLYMER SCIENCE

The F e r r a n t i - S h i r l e y Viscometer i s a cone-plate type instrument which can be used in a v a r i e t y of o p e r a t i n g modes. Its d u r a b i l i t y and the wide temperature range a c c e s s i b l e with t h i s instrument have made i t a v a l u a b l e tool in the c h a r a c t e r i z a t i o n of polymers and c o a t i n g s . The main drawback i n using t h i s instrument for large numbers of samples has been that the time required t o manually c a l c u l a t e , t a b u l a t e and p l o t the data obtained from the graphical output frequently exceeds the time required to make the experimental runs themselves.


Data A q u i s i t i o n System Automation of the viscometer was achieved by i n t e r f a c i n g the instrument to a microcomputer for data a c q u i s i t i o n . Data are then t r a n s f e r r e d v i a a s e r i a l l i n e t o a minicomputer system f o r storage, a n a l y s i s , report generation and p l o t t i n g . D e t a i l s of the mini-microcomputer system and i t s o r g a n i z a t i o n and operation have been reported elsewhere (V). The microcomputer system chosen i s based on the Pro-Log 8821 processor card which uses the I n t e l 8080A m i c r o p r o c e s s o r . In a d d i t i o n , t h i s card contains l k bytes of RAM memory and sockets for up t o 4k bytes of EPROM memory c o n t a i n i n g the programs used i n data c o l l e c t i o n and communication. The system a l s o contains 32k b y t e s o f RAM memory f o r d a t a s t o r a g e . Analog to d i g i t a l conversion i s accomplished using an Analog Devices RTI 1220-12 card which contains an 8 channel d i f f e r e n t i a l input m u l t i p l e x e d 1 2 - b i t A/D c o n v e r t e r . The f o l l o w i n g functions are implemented on two c i r c u i t cards designed in our l a b o r a t o r y . S e r i a l I/O f o r communication with the minicomputer i s implemented using a UART. P a r a l l e l I/O i s used for status l i g h t s and communication w i t h TTL compatible i n s t r u m e n t a t i o n and i s implemented u s i n g a M o t o r o l a 6821 p e r i p h e r a l i n t e r f a c e adapter. The I n t e l 8214 p r i o r i t y i n t e r r u p t c o n t r o l chip i s used to provide eight p r i o r i t y l e v e l s of vectored interrupts. A r e a l - t i m e programmable clock i s implemented using the I n t e l 8253 chip c o n t r o l l e d by a c r y s t a l time base. The clock is used to control the data a c q u i s i t i o n r a t e . The m i c r o c o m p u t e r i s i n t e r f a c e d t o a D i g i t a l Equipment Corporation PDP 11/34 minicomputer system with 68 Mbytes of d i s k s t o r a g e , two s e r i a l p r i n t e r s , a Gould 5005 e l e c t r o s t a t i c p r i n t e r / p l o t t e r , m a g n e t i c t a p e s t o r a g e and s e v e r a l hard and softcopy t e r m i n a l s l o c a t e d throughout the f a c i l i t y . The minicomputer operates in a general t i m e - s h a r i n g mode using the RSX11-M operating system. The f u n c t i o n of the minicomputer i s to provide bulk s t o r a g e , computational power i n a high l e v e l language (FORTRAN), and graphic and alphanumeric hard-copy output in the form of reports and p l o t s . Also a v a i l a b l e on the minicomputer are program packages f o r s t a t i s t i c a l a n a l y s i s and d a t a base management.


13.

KAHETAL.

Automated Ferranti-Shirley Viscometer

225


Automated Instrument A n a l y s i s Process There are four stages i n an automated instrument a n a l y s i s . These are shown s c h e m a t i c a l l y i n Figure 1. In the f i r s t s t a g e , the instrument operator i n i t i a t e s the experiment by means of a d i a l o g program on the minicomputer. An example of the d i a l o g f o r the F e r r a n t i - S h i r l e y operation i s shown in Figure 2. The program asks a s e r i e s of questions regarding the sample i d e n t i f i c a t i o n and the experimental parameters required f o r data c o l l e c t i o n and analysis. This includes instrument s e t t i n g s and data c o l l e c t i o n rates f o r s p r i n g and rpm data and f o r the temperature. A maximum run time f o r the s e l e c t e d data c o l l e c t i o n rates i s c a l c u l a t e d based on memory c a p a c i t y . Values are checked f o r e r r o r s by comparing the entered values to allowed values or ranges f o r each parameter. Default values are d i s p l a y e d based on the parameters entered f o r the previous run and may be changed i f d e s i r e d . This s i m p l i f i e s the entry when several runs are made under the same or s i m i l a r c o n d i t i o n s . When the d i a l o g i s complete the minicomputer sends a l l of t h e i n p u t d a t a t o t h e m i c r o c o m p u t e r . The microcomputer acknowledges that i t has received the data and turns on a s t a t u s l i g h t at the instrument i n d i c a t i n g that i t i s ready. The second s t a g e i s d a t a a c q u i s i t i o n . This stage i s i n i t i a t e d when the operator s t a r t s the instrument. For the F e r r a n t i - S h i r l e y o p e r a t i o n d a t a i s c o l l e c t e d on two a n a l o g channels corresponding to the motor speed (tachometer output) and to the torque ( s p r i n g displacement). The analog s i g n a l s from the instrument are conditioned and scaled before passing them to the A/D c o n v e r t e r . This i s accomplished by means of instrumentation a m p l i f i e r s f o l l o w e d by low pass a c t i v e f i l t e r s which a r e implemented on p r i n t e d c i r c u i t boards designed in our l a b o r a t o r y . The voltage l e v e l s of the s i g n a l s output from the instrument are h i g h l y dependent on the r e s i s t i v e loading designed t o be a p p l i e d by the recorder s u p p l i e d with the instrument. To avoid d i f f i c u l t i e s caused by d i f f e r e n c e s in loading when the data c o l l e c t i o n unit or the recorder are connected or disconnected from the c i r c u i t , the s i g n a l s are loaded at a constant l e v e l at the inputs of the instrumentation a m p l i f i e r s and the output of the a c t i v e f i l t e r , which i s capable of d r i v i n g as low as a Ik ohm l o a d , then feeds the s i g n a l to both the microcomputer and to the reactor. The temperature i s input as a BCD number from a d i g i t a l thermometer which converts the thermocouple voltage to temperature (degrees C) to the nearest 0.1 degree. The d i g i t a l thermometer i s c o n t r o l l e d by the microcomputer to convert at the d e s i r e d rate at up to one conversion per second. During the t h i r d stage the microcomputer t r a n s m i t s the data i t has c o l l e c t e d and stored i n i t s memory to the minicomputer. The minicomputer stores t h i s data in data f i l e s on one of the d i s k s .


226


1. Dialog Operator«—> Mini —•Micro 2. Data Aquisition Micro«—> Instrument 3. Data Transmission Downloaded by FUDAN UNIV on March 14, 2017 | http://pubs.acs.org Publication Date: September 24, 1982 | doi: 10.1021/bk-1982-0197.ch013

Micro—•Mini 4. Data Reduction Mini*—^Operator Figure 1.

Steps in an A utomated Instrument Operation.

DIA 35 INSTRUMENT

NO* 31 -

FERRANTI-SHIRLEY

5462

JOB

Initials*.•MEK S a n p l e ID*•••LATEX A Analysis t v r e * * * l Cone*•*LT-100 S p r i n g * • • 1275 Thermocouple p o s i t i o n * * *A Motor speed* * *A Gear* * *L Scale M u l t i p l i e r * * * 1 Sweep

tifte*•*

20

S p r i n g I RPM d a t a r a t e s ( p t s / s e c ) * * * 2*00 Temperature d a t a r a t e < p t s / « i n ) * * * 60*00 Mexiauft run t i e e based on Temperature r a t e * * * Use

default

values

?

16*7 e i n

Y

OK

> Figure 2.

Dialog for Ferranti-Shirley

Operation.


13.

KAHETAL.

Automated Ferranti-Shirley

227

Viscometer

The f o u r t h stage i s the f i n a l data a n a l y s i s and takes place in the minicomputer. This data reduction i s done by FORTRAN programs. Reports and p l o t s are generated at t h i s t i m e . Data A n a l y s i s Methods


Voltages corresponding to the tachometer output and s p r i n g displacement are converted t o angular v e l o c i t y , u , and angular displacement, 6 in units of r a d i a n s / s e c o n d and radians respectively. Shear s t r e s s , T , i s c a l c u l a t e d from the equation x - U j

(1)

2TT R

where R i s the radius of the c a l c u l a t e d from the r e l a t i o n

cone

in

cm and T

is

the

torque

T = K0 where < i s the s p r i n g constant in dyne-cm/radian. For analyses where the motor i s used to d r i v e shear r a t e , y, i s c a l c u l a t e d from the equation

(2) the cone the

• u>r Y = —

/

M

(3)

where c i s the cone-plate gap at radius r and the term wr represents the l i n e a r v e l o c i t y at that r a d i u s . Since u> and c are both l i n e a r l y dependent on r, the r a t i o w/c i s not a f u n c t i o n of the r a d i u s . Furthermore, s i n c e £ = tan a ~ a

(4)

where a i s the cone a n g l e , f o r a small angle a expressed r a d i a n s , equation (3) can be s i m p l i f i e d f u r t h e r t o y i e l d * - 5

in

5

which enables us to c a l c u l a t e the shear rate from the angular v e l o c i t y and the cone angle. Three types of analyses are c u r r e n t l y incorporated i n the a n a l y s i s program. A fourth type of a n a l y s i s i s being developed and w i l l be included a l s o . These are as f o l l o w s : 1.

Casson a n a l y s i s (2): For t h i s c a s e , shear s t r e s s and shear rate begin at z e r o . The shear rate ramps l i n e a r l y to a maximum and returns t o zero. The upward and downward s l o p i n g p o r t i o n s of the c u r v e are a n a l y z e d s e p a r a t e l y . Those



228

portions of the data at the beginning, turnaround and end of the curve may be edited out at the operators d i s c r e t i o n by e n t e r i n g the l i m i t s i n rpm. A form of the Casson Equation T

l/2

=

n

1/2

;i/2

+

T

1/2

( ) 6

i s used to c a l c u l a t e the y i e l d s t r e s s , T and the Casson " i n f i n i t e shear rate v i s c o s i t y " , n , by means of a l i n e a r l e a s t squares f i t of the square root of shear s t r e s s _vs. the square root of shear rate which gives n ^ as the slope and T as the intercept. A report detailing the i d e n t i f i c a t i o n i n f o r m a t i o n , experimental c o n d i t i o n s and the r e s u l t s of the a n a l y s i s i s produced, as shown in Figure 3. P l o t s of shear rate _vs. shear s t r e s s shown in Figure 4 ; square root of shear rate _vs. square root of shear s t r e s s shown in Figure 5; v i s c o s i t y _vs. shear rate shown i n Figure 6; and temperature jvs. time can be generated. Results from several experiments can be c o p l o t t e d as i s shown in Figure 6. to


1 7 2

1

/

2

2.

V i s c o s i t y at constant RPM: In t h i s c a s e , shear s t r e s s i s recorded as a f u n c t i o n of time at constant shear r a t e . Shear s t r e s s may be nearly constant or may drop ( e . g . , shear t h i n n i n g or viscous heating) or r i s e ( e . g . thermoset c u r i n g ) . An average shear rate i s determined and the v i s c o s i t y i s c a l c u l a t e d using t h i s average. V i s c o s i t y minima and maxima are reported. The operator may e d i t the data by e n t e r i n g the l i m i t s in minutes. For edited d a t a , a l e a s t squares f i t of the logarithm of the v i s c o s i t y ^ s . time i s found. P l o t s of v i s c o s i t y _vs. time shown in Figure 7; log v i s c o s i t y _vs. time shown in Figure 8; and temperature vs. time shown in Figure 9 can be generated and r e s u l t s from several experiments c o p l o t t e d . This type of a n a l y s i s i s a l s o used t o c a l i b r a t e the e f f e c t i v e cone a n g l e by making measurements on standard Newtonian fluids and b a c k - c a l c u l a t i n g the value of e f f e c t i v e cone angle.

3.

Spring r e l a x a t i o n : In t h i s case, the torque s p r i n g i s compressed and held in place by means of a ratchet and l e v e r . The cone i s then released and allowed to turn i n the f l u i d as the spring unwinds. Shear s t r e s s data are c o l l e c t e d as a f u n c t i o n of time. The data are analyzed from the point of maximum shear r a t e , which occurs s h o r t l y a f t e r the s p r i n g i s r e l e a s e d , up to a time s e l e c t e d by the o p e r a t o r . Values at l e s s than 5% of spring compression are a u t o m a t i c a l l y r e j e c t e d due to torque n o n l i n e a r i t i e s . The object of t h i s experiment i s to obtain v i s c o s i t y as a f u n c t i o n of shear r a t e , n ( y ) , at low shear r a t e s . The shear r a t e , y i s defined in equation (5) as a f u n c t i o n of


13.

KAHETAL.

Automated

Ferranti-Shirley

Viscometer

FERRANTI SHI RLE Y V1SCOMETER SHEAR STRESS VS.SHEAR RATE


AC 64-633-10

HOOD & TROUGH

JOB NUMBER 3498 RUN NUMBER 1 OPERATOR RAZ DATE 09--APR-81 TIME 09:11:31 -

CASSON ANALYSIS UP DOWN VISCOSITY 0.3731 0.3864 ARITHMETIC AVERAGE 0.3798 POISE SLOPE INTERCEPT CORRELATION POINTS USED

~ TEMPERATURE HIGH LOW AVERAGE -

0.6109 13.4218 0.9999 139

0.6216 12.1505 0.9999 162

(C) ON THERMOCOUPLE A 25.1 25.1 24.9 24.9 24.97 25.07

EXPERIMENTAL CONDITIONS LT--100 CONE 3.50 CONE RADIUS (CM) 1275 SPRING 60 SWEEP TIME (SECONDS) 534.3 MAXIMUM RPM 7134.1 MAXIMUM SHEAR RATE (1/SEC) 224.34 RATE DERIVATIVE (RPM/SEC) 200 DATA INTERVAL (MILLISEC)

-

CALIBRATION VALUES 223872.8 SPRING FACTOR (DYNE-CM/RAD) 0.785000E-02 EFFECTIVE CONE ANGLE (RAD) Figure 3.

Sample report from Program FRANT I.


229



230


KAHETAL.

Automated

Ferranti-Shirley

Viscometer


13.


231



232

Figure 6. Plot of viscosity vs. shear rate for Casson analysis. Key: Q], 3498 Run 1, U; 0,3498 Run 1, D; &,3499 Run 1, U; +, 3499 Run 1, D; X , 3503 Run 2, U; 0, 3503 Run 2, D; t , 3505 Run 1, U; X , 3505 Run 1, D.


KAHETAL.


Viscometer


13.

Figure 7.

Plot of viscosity vs. time for a curing system. Job # 3330.


233

234



Figure 8.

Plot of log

10

viscosity vs. time for curing systems. Key: 3330; A , 3327; +, 3328.

3407; O ,


KAHETAL.

Automated

Ferranti-Shirley

Viscometer


13.


235


236

angular v e l o c i t y , w, which can be expressed as

w

=

de dt

(7)

where 6 i s the angular displacement measured by the torque transducer potentiometer. The time dependent shear rate y (t) i s then defined as


The time dependence of the shear r e w r i t i n g equation (1) in the form (t)

stress

can

be

shown

= 3T_eitl

by

(9)

2irlT

The r e s u l t i s that the v i s c o s i t y as a f u n c t i o n of shear can be w r i t t e n as (T)

rate

(10)

where i ( t ) i s determined from the angular displacement at time t , y ( t ) i s determined from the rate of change of the angular displacement with t i m e , and k i s a combination of constants i n c l u d i n g cone angle, cone r a d i u s , s p r i n g constant etc. To avoid problems with n o i s e , which i s a m p l i f i e d by f a c t t h a t y i s p r o p o r t i o n a l t o the d e r i r a t i v e of t h e displacement d i v i d e d by the displacement, an a n a l y t i c a l l y smooth data curve i s obtained by a polynomial f i t to the s h e a r s t r e s s - t i m e d a t a and t h e c a l c u l a t e d c u r v e is d i f f e r e n t i a t e d by means of the Savitsky-Golay method t o obtain the shear rate and v i s c o s i t y (.3,4-). P l o t s of l o g shear s t r e s s ^ , time shown in Figure 10; v i s c o s i t y _vs. shear rate f o r the polynomial f i t curve shown i n Figure 1 1 a ; and v i s c o s i t y ys_. shear rate experimental curve shown in Figure l i b can be generated. 4.

Shear Rate Step: This method i s under development and w i l l be included in the a n a l y s i s program. The experiment c o n s i s t s of shearing out a t h i x o t r o p i c material at a r e l a t i v e l y high shear rate and then stepping the rate of r o t a t i o n back to a v e r y low l e v e l and m e a s u r i n g t h e r a t e of i n c r e a s e i n v i s c o s i t y corresponding to the recovery of s t r u c t u r e . The F e r r a n t i - S h i r l e y motor speed c o n t r o l was modified by the


Automated

Ferranti-Shirley

Viscometer

237


KAH ET AL.

Figure 10.

Plot oj log

10

shear stress vs. time for spring relaxation experiment. Job # 5374.




238

Figure 11.

Plot oj viscosity vs. shear rate jor spring relaxation experiment. Job # 5374. Key: fit curve; O , actual data.


13.

KAH ET AL.


Viscometer

239

a d d i t i o n of a second t e n - t u r n potentiometer with counting d i a l and a s e l e c t o r switch to r a p i d l y change between the speeds s e l e c t e d on the two d i a l s . The data i s analyzed by f i t t i n g an exponential f u n c t i o n to the recovery curve and c a l c u l a t i n g a time-constant parameter which c h a r a c t e r i z e s the rate of recovery. A report and a p l o t of the experimental and f i t t e d v i s c o s i t y _vs. time curves as shown in Figure 12 are generated.


Conclusions B e n e f i t s have been r e a l i z e d from the automation of the F e r r a n t i - S h i r l e y in several areas. F i r s t , a s i g n i f i c a n t amount of time has been saved in performing the experiment and in analyzing the d a t a . This has a l s o allowed time f o r more extensive or v a r i e d approaches to the c h a r a c t e r i z a t i o n of the samples. Secondly, record-keeping i s more complete and a c c u r a t e . This has s i m p l i f i e d accurate reproduction of experimental c o n d i t i o n s and has aided in surveying and r e p o r t i n g r e s u l t s . L a s t l y , automation has made i t p r a c t i c a l to i n v e s t i g a t e some problematic areas of viscometer p e r f o r m a n c e and has h e l p e d t o d i s c e r n s u b t l e or l o n g term v a r i a b i l i t y in the operating c h a r a c t e r i s t i c s of the instrument.




240


13.

KAHETAL.


241

Viscometer

Acknowledgement The a u t h o r s adknowledge the a s s i s t a n c e of Stansbrey with the numerical methods used in the data.

Dr. John treatment

J. of

Literature Cited


1.

2. 3. 4.

Niemann, T. F.; Koehler M. E.; Provder, T. "Microcomputers Used as Laboratory Instrument Controllers and Intelligent Interfaces to a Minicomputer Timesharing System"; in "Personal Computers in Chemistry", Lykos P. Ed.; John Wiley and Sons: New York, 1981. Casson, N. "Rheology of Disperse Systems"; Mill, C. C., Ed.; Pergamon Press: New York, 1959; Chapter 5. Savitsky, A.; Golay, M. J. E. Anal. Chem. 1964, 36, 1627. Stienier, J.; Termonia, Y.; Deltour, J. Anal. Chem. 1972, 44, 1906.

RECEIVED May 4, 1982.


An Automated Ferranti-Shirley Viscometer - ACS Symposium Series

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