ML20012B352

Median Signal Selector for Foxboro Series Process Instrumentation.

ML20012B352
Person / Time
Site:	Sequoyah
Issue date:	10/31/1989
From:	Mermigos J WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:
Shared Package
ML19293A213	List: ML20012B345 ML20012B348 ML20012B352
References
WCAP-12418, NUDOCS 9003140243
Download: ML20012B352 (24)

Text

__

t ,

p _ a a

• ; WESTINGHOUSE CLASS-3

.MCAP-12418- -

MEDIAN SIGNAL SELECTOR FOR FOXBORO SERIES PROCESS INSTRUMENTATION

- APPLICATION TO DELETION'0F LOW FEEDWATER FLOM REACTOR TRIP J. F. Hermigos October 1989 ,

i i

i Westinghouse Electric Corporation ')

Energy Systems '

P. O. Box 355 -

Pittsburgh, PA 15230 00590:10/011090

'9oo31'40243 900301 7 1 R .ADOCK 0500

- . . . , , c.

s , ,

ABSTRACT To maintain the current level of functional performance of.the Reactor

- Protection System' subsequent to deletion of the Low Feedwater Flow Reactor '

Trip, the existing Feedwater Control System may be modified by installation of a Median Signal Selector. The signal selector. will prevent a potential control and protection interaction mechanism involving the steam generator low-low water protective functions by providing C 4

'3*'C between the Reactor Protection System and the feedwater Control System, in accordance with the requirements of IEEE Standard 279-1971, .

Section'4.7.

Various aspects of signal selector use are addressed by this report; these l aspects include a demonstration of the functional adequacy of the signal selection process in preventing the interaction mechanism and requirements regarding device reliability such as signal ' selector test, failure detection capabilities, and the Median Signal Selector's [

]"'C Additionally, t

. recommendations regarding actions on the part of the operator necessary to-

' ~

support signal selector use are presented, e 4

4 c

t 0069D:1D/011090

ye *.

- *s TABLE OF CONTENTS e

TABLE OF CONTENTS i

, LIST OF FIGURES ii ACRONYHS iii-1.0 -INTRODUCTION 1 1.1 Background 1

'1.2 - Application to Low Feedwater-Flow Reactor Trip Deletion 2

2.0 SIGNAL SELECTOR IMPLEMENTATION 4

-2.1 Signal Selector Operation & Configuration 4 2.2- Signal Selector Reliability 6 2.3 Failure' Detection -10 2 .~ 4 Fault Conditions From Eagle 21 Failure 12 4 2.5 Recommended Operator Actions 14 i.

3.0 CONCLUSION

S 16 I

)

i t

00690:1D/011090 i

9 ,. . . 4

,7 ,

-]

g:

• LIST OF FIGLIRES  !

s Figure.1: Existing Steam Generator Protection Scheme Figu're ~ 2: Low Level Protection with a Signal Selector

- J l

Figure 3: Signal: Selection Logic Matrix--

1

.g Y

.i I

f s? ,

t E

i 1

i. {

.-,; s

> j

, 00690:1D/011090- 11

.:. .L *, .-

p N. : > ,

' ' l .-

ACRONYMS tV r f

. CIE- . Class'iE j EXNOR- - Exclusive NOR 3

MSS- . Median' Signal Selector i,

MTBF - Mean Time Before Failure i.

RCS' - Reactor Coolant System f t

i i

) .'

1 l

4

+

i i

i 00690:1D/011090 111

~ l'.0_ INTRODUCTION In order to implement the' Low Feedwater Flow Reactor Trip deletion, certain-configurational changes must be made to the existing plant instrumentation and control complex to assure that the functional capability and inherent reliability provided in the original Reactor Protection System design are not compromised. Consequently, to preserve these characteristics, a Median Signal s Selector is implemented in the Reactor Control System for receiving steam generator level-information. The function of the signal selector is to eliminate'the potential for a control and protection system interaction mechanism involving the Feedwater Control System and the low-low steam l generator water level protective functions in accordance with the requirements

.of The Institute of Electrical and Electronics Engineers Standard, IEEE Standard 279-1971, " Criteria for Protection Systems for Nuclear Powered l Generating Stations", Section 4.7. .

'The following report constitutes the technical basis upon which the application of a signal' selection device to the Low Feedwater Flow Reactor {

Deletion is justified. Various aspects of signal selector use are addressed by this report; these aspects include a demonstration of the sufficiency of the signal selection process in eliminating the interaction mechanism, and requirements regarding device reliability such as signal selector test and failure detection capabilities. Additionally, recommendations regarding 1 actions on the part of the utility necessary to support signal selector use are provided. i i

l 1.1 Backaround j i

The fundamental purpose of plant instrumentation and control systems is to .. !

' permit control of nuclear plant operations, and to initiate automatic protective action in response to unsafe operating conditions. The infrastructure of instrumentation and control systems constitutes an interactive network of electrical ~:rcuits through which protection and control functions are carried out. This network can be best described in terms of two functionally defined systems called the Reactor Protection System, and the Reactor Control System. The Reactor Protection System is defined as n

1 00690:1D/011090

y. . . . f l

• lthat part'of_the sense and command features involved in generating those signals.used primarily for reactor trip functions and the actuation of

' engineered safety features. The Reactor Control Systems are defined as those  !

electrical instrumentation and control systems that provide the operator with  ;

the necessary information and controls to effect proper primary plant control.

IEEE Standard 279-1971 is the governing criteria to which the Reactor Protection System design must conform, as a minimum, in order to meet the degree of operational reliability and functional adequacy considered ]

acceptable for nuclear plant service. One of the specific provisions of this j '

standard is the issue of. control and protection system interaction as presented in Section 4.7.

l l

Control and protection system. interaction addresses any mechanism whereby the ability of the protection system to accomplish its safety related function is adversely affected by nonsafety related plant control systems. The mechanism may be a physical interaction such as electrical faults originating from within the control system and propagating to the Re:ctor Protection System (thereby bringing about an attendant failure within the protection system), or a functional interaction whereby the action of a control system degrades the ability of the protection-system to provide adequate core protection consistent with the requirements of IEEE Standard 279-1971. To prevent  !

control and protection system' interactions, protection systems'are, in general, designed with due regard for the requirements of physical, electrical '

and functional independence relative.to non-protection (control) systems.

a 1.2 Anol'ication to the Low Feedwater Flow Reactor Trio Deletion Protective functions associated with the Steam Generator Protection System

• include two reactor trip channels (the low-low steam generator water level trip channel, and the low feedwater flow trip channel) to provide core

, protection against a loss of heat sink; and feedwater isolation and turbine 1 trip on high' steam generator water level to protect the main turbine from moisture carryover during the high level condition.

+

-00690:1D/011090 2

C. .

i l

The level protective functions are configured with two out of three (2/3)  ;

actuation logic derived directly from level measurements for each steam l

generator. The low feedwater flow trip channel is configured to initiate a i reactor trip during a condition of steam and feedwater flow mismatch in )

coincidence with low steam generator water level, in one out of two (1/2) j channels. This trip provides a diverse trip to the low-low steam generator j water level trip. The logic scheme is depicted in Figure 1. Existing Steam  !

Generator Protection Scheme.

1 i

From this diagram it is evident that Channel 1 of the three water level  ;

~

measurement channels is also utilized for control purposes. Thus, proper operation of the Feedwater Control System is dependent on the integrity of this channel. This characteristic permits certain failures which may occur in  ;

the Reactor Protection System to negate a particular channel of a protective ,

function, and simultaneously cause undesirable control system action that requires subsequent protective action, from the failed safety function, in l order to prevent the transient from exceeding any design safety limits. For I I

example, failure in the high direction of the steam generator water level protection channel I will generate control system action that results in  :

decreasing steam generabr water level. Consequently Iow steam generator ,

water level prot s tion may be subsequently required; however, this protective  ;

I action is also derived from the steam generator water level measurement l channels. For such a scenario, IEEE-279, Section 4.7.3 imposes the .

consideration of an additional random failure in the Reactor Protection [

System. The underlying logic is that the initial protection system failure is  ;

considered the initiating event for the transient, and, therefore, does not constitute the " single failure" IEEE-279 imposes on the protection system. As such, an additional protection system failure must continue to be capable of  ;

initiating the appropriate protective action.

~

ll The limiting-single failure in this instance would be a failure of one of the remaining steam generator level inannels. This leaves only one operating channel which is insufficient to satisfy the 2/3 logic implemented in the low-L low steam generator water level reactor trip function. Nevertheless, the diverse low feedwater flow trip will remain functional, despite the previously 1

postulated failures, to provide the necessary protective action.

I l

00690:1D/011090 3

.= __J

- The Low Feedwater Flow Reactor Trip was used to satisfy this IEEE-279 j requirement in conjunction with the Low-Low Steam Generator Water Level Trip.

l The Low Feedwater Flow Reactor Trip is not required for IEEE-279 if you do not need to consider a second random failure by functionally isolating the  !

Feedwater Control System from the Reactor Protection System. This is l accomplished by implementing a Median Signal Selector in the Feedwater Control System. Thus, since IEEE Std 279-1971, control and protection interaction r criteria is satisfied with implementation of the MSS and the accident analyses f I

for steam generator low lesel protection is satisfied through the steam generator low-low level reactor trip, there is no requirement to maintain the ,

low feedwater flow reactor trip. -

2.0 SIGNAL SELECTOR IMPLEMENTATION The objective of this report is to address engineering issues relative to the use of a Median Signal Selector in eliminating control and protecticn system interaction involving the Reactor Control System. In meeting this objective, the characteristics of signal selector operation and signal selector reliability will be developed. The discussion regarding signal selector operation describes the units hardware configuration and the operating principal of the signal selector. This demonstrates how the device provides

[ 3"'C as detailed in Section 1. The discussion regarding signal selector reliability demonstrates that the signal selector possesses the requisite degree of operational readiness acceptable for nuclear  :

plant service. This discussion will address quality of signal selector l hardware, and the capability for and adequacy of signal selector testing as .

j well as possible fault conditions affecting the Median Signal Selector. ,

2.1 Sianal Selector coeration and Confiauration ,

l

- - a,c The material in this section has been deleted from the nonproprietary version -

due to its proprietary nature. The material in this section discussed Signal ,

Selector Operation and Configuration.

L i

00690:10/011590 4 -

t i

- ,_ a,c f

l The material in this section has been deleted from the nonproprietary version i due to its proprietary nature. The material in this saction discussed Signal  ;

Selector Operation and Configuration.

The Median Signal Selector for Foxboro series process instrumentation consists of a power supply / voltage regulator, an input stage which performs the signal selection function, a level shift stage which tailors the output j

characteristic to the desired value, and an output stage. The device basically functions as follows. Input signals are first filtered, then routed via buffer amplifiers to a logic circuit which performs the median selection l algorithm. This portion of the input stage is the heart of the signal selector. The selection function is performed by a series of operational amplifiers and exclusive NOR (EXNOR) gates which provide appropriate signals to a bilateral switch package. Switch action is based on these signals such as to establish a direct signal path from the input buffer amplifier which is j processing the median signal, past the logic gates, directly to another buffer )

4 amplifier which represents the input to the level shift circuitry. )

i The level shift circuitry controls the current delivered from a +24 VDC i

reference voltage (established by the units power supply / voltage regulator) to the output stage as dettrained by the magnitude of the signal which is >

presented to the level shift circuit, i.e., the median signal. As such the level shift circuitry, consisting of two operational amplifiers and a power ,

transistor, regulates the character of the signal delivered from the power supply to the output stage (another operational amplifier and power transistor) and, therefore, the output signal itself. '

After input signals are processed by the buffer amplifiers, they are routed to

an array of three operational amplifiers which are configured as comparators.

l l

l 00690:10/011090 5

l The comparators generate an output voltage level (logic value 0 or 1) based on the relative magnitudes of the paired inputs. Comparator 1, which received channels A and B as input will generate an output voltage, logic value  :

asserted at 1, when signal B is greater than signal A, and a zero output value j when signal A is greater than signal B. Similarly, comparator 2 compares l signals A and C. generating a logic value 1 when signal A is greater than j signal C, and comparator 3 compares signals B and C generating a logic value  !

I asserted at I when signal B exceeds signal C. The outputs from these amplifiers are then delivered to the arrangement of exclusive NOR gates.

These logic gates have been suitably configured to provide output signals t' hat l establish the state of three bilateral switches based on the output level of l operational amplifiers 1, 2, and 3. The switch which is " turned on" directly j routes the median signal to the input of the level shift circuitry (bypassing j the logic circuitry), which, in turn, determines the magnitude of the output j signal as a function of the median signal. (n.b., switch 4 establishes the  !

input to one pin of its associated EXNOR gate at either +12 VDC (logic state '

1) or zero volts (logic state 0) depending on the output of comparator 1; it therefore works in conjunction with comparator 1, acting as an inverter.)

As an example, consider the following assignments of hypothetical signal i values to the three instrument channels feeding the signal selector: ,

channel A . 4.0 milliamps  ;

channel B = 5.0 milliamps ,

channel C 6.0 milliamps Hith these assignments, channel B would be selected as the median signal.

Comparator 1 will generate a logic output of I since signal B exceeds signal A. Similarly, comparators 2 and 3 will generate logic outputs of zero since signal C exceeds both signals A and B. With these level assertions, EXNOR i

0069D:10/011090 6

i i .

gate 1 will have its output asserted low which maintains switch 1 in the open  ;

position preventing signal A'from being transmitted to the level shift j circuitry. EXNOR gate 2 will have its output asserted high causing EXNOR gate l 3 to have its output asserted low. This maintains switch 2 in the open  !

position blocking signal C. A logic state 1 input to switch 4 causes one f input to EXNOR gate 4 to be asserted low (grounded) such that the output of gate 4 is asserted high. This results in switch 3 changing state to permit ,

signal B to be directly passed to the level shift circuitry.

l 2.2 Sinnal Selector Reliability  ;

~

a,c l

l The material in this section has been deleted from the nonproprietary version i due to its proprietary nature. The material in this section discussed Signal ; j

, Selector Reliability.  ;

_J  ;

i >

t 3"'C Therefore, steps f have been taken to ensure the reliability of the signal selection process. (

34,C The key to ensuring proper signal selector operation lie with the unit's reliability. . The signal selector is designed to possess those reliability i characteristics necessary to preserve the total integrity of the protection 1 system.

C [

3a ,c ,

i L

00690:10/011090 7 l

...*... J

• a,c i

= -

l

. l The material in this section has been deleted from the nonproprietary version due to its proprietary nature. The material in this section discussed Signal l Selector Reliability.  !

=

~

, [

IEEE Standard 279-1971 delineates certain functional performance requirements j regarding aspects of system reliability for protection systems. Because the I signal selector will be implemented to support the protection system, it has been evaluated against those criteria considered applicable to its design as  ;

presented below.

Capability for Unit Test:

The signal selector has been provided with the capability for on line j testing. Signal selector testing consists of monitoring the three input ,

signals and the one output signal via test points. Comparison of the output .

. signal to the input signals permits determination of whether or not the median  !

signal is being passed, and, consequently, whether the signal selector is functioning properly. Any output signal at a value other than that corresponding to the median signal is indicative of a unit failure, j The signal selector can be tested concurrently with the protection instrument [

channels feeding the unit. Test signals are received from the protection system, as would a normal process signal, when the individual instrument channels are placed in the test mode.

[  !

3"'C As the test signal magnitude ^

is varied, that instrument channel which represents the median signal will also be altered allowing the technician to determine the presence of proper signal selector action.  ;

00690:1D/011090 8

. c. .- ,

. o a*..

signal selector testitg consists'of measuring input and cutput signals which j allow the operator to infer proper unit operation. We may examine, in

> principal, a typical test sequence for the signal selector. With the previous signal assignments in force, channel B would be selected as the median signal. This may be verified by noting the signal selector output voltage at the appropriate test point. Now, let channel A be taken to test. As the ,

signal strength of channel A is adjusted to any value less than 5.0 milliamps,  !

channel 2 will continue to be selected as the median signal. However, as the j

~

test signal strength is adjusted to a value between 5.0 and 6.0 milliamps, l channel A (the test channel) should be selected as the median signal, and -

finally as the test signal is raised to a value in excess of 6.0 milliamps,  ;

channels C will be selected. l In this manner, testing with a single input channel permits an assessment of a spectrum of signal selector operational modes. Furthermore, it should be emphasized that although each operational amplifier in the circuit is not specifically exercised during testing of an individual channel, all

! operational amplifiers will have been exercised once each of the three protection sets has been tested. [ ,

l j a.c h

It should also be noted that in practice, during normal operation, instru-mentation channel signal strengths may be sufficiently close that their degree of proximity to one another makes it difficult (if not impossible) to determine when the test channel signal falls between the remaining two channels. Nevertheless, it is still possible to determine proper signal selector operation by verifying that the test channel is indeed rejected when it is taken to the high or low position.

+

L L

-00690:1D/011090 9 t

l

..a.,.

l Quality of Components:

i Components utilized in the signal selector are of a quality consistent with  !

low failure rates. The minimum predicted mean time before failure (MTBF) l considered acceptable for the signal selector in its present application has been established as [

3"'C represents a reasonable time in which component failures brought about by age induced effects are not expected to surface. A reliability evaluation has been conducted on the signal selector employing the methodology of [

]"'C Based on this study, the signal selector is predicted [

3a .c ,

Furthermore, maximum use is made of existing hardware and cabling to minimize ,

design complexity, and minimize the number of added components. Consequently, the signal selector design _is consistent with a low failure probability.

Equipment Qualification:

Equipment qualification is aimed at improving the operational reliability of safety related quipment by reducing the potential for common mode failures brought about by adverse environmental influences [

3a .c The remaining attributes of IEEE Standard 279-1971 Section 4 are not considered applicable to the signal selector design.

00690:10/011000- 10

s. o*,o j

..- i

• t

' :. - 2.3 Failure Detection j e

At this point it is instruct've i to illustrate how system failures will }

manifest themselves at the signal selector output in doing so, we further {

justify the test capabilities of the signal selector as being adequate for j failure detection.  ;

I The signal selector principally consists of an arrangement of linear and nonlinear semiconductor devices configured to perform the median selection  ;

function, and process the chosen signal to obtain the desired output j characteristic. As such, the signal selector can be thought of as a coupled l analog / digital system. The digital portion consists of nonlinear devices {

(logic gates, switches and comparators) that produce a specific output i depending on the particular input configuration presented to the device. The [

~

digital logic network functions to select the appropriate (median) input signal to be processed by the analog portion of the unit. Once this is i accomplished, the action of switches then bypasses this network, and it plays j no further role in the signal processing. The analog portion of the circuit, consisting principally of operational amplifiers, power transistors, filters,  ;

cnd a power supply / voltage regulator unit processes the selected input signal  ;

to generate the appropriate output, i

In examining unit failures, we will investigate failures occurring within each ,

portion (analog or digital) of the overall signal selector circuit to-  ;

determine the impact on the unit's functional capabilities. Consider first the digital portion.

The three comparators, including switch 4, act as an analog to digital i conversion stage whereby an appropriate output level is selected depending on l the-relative magnitudes of the signals at the input to these units. Failure of a comparator (including switch 4) will result in an incorrect combination of. logic values being presented to the EXNOR gates. Such circumstances will result in actuation of any or all of the output switches such that a signal other than the median is passed to the level shift circuitry, or multiple .

. signals are presented to this circuit such that the output circuitry will be L

r 0069D:10/011090 11

, g o. , ,

-- saturated.-Sucha.conditionisread11fdetectablebymeasurementsofthe input and output signals in conjunction with a unit test sequence. ]

Failure of an EXNOR gate will either result in saturating the output from multiple signals, or prevent any signal from being presented to the level shift circuitry. Failure of an output switch will also bring about similar ,

results. As above, all possibilities are detectable during a test sequence I I

when all active components are exercised. -

Failures within the analog portion are slightly more complex to discuss; however, they are nonetheless as easily detectable as their digital }

counterparts. The analog portions of the circuit consist of buffer amplifiers j upstream of the logic section, and the level shift circuitry and output circuitry existing downstream of the selection logic. Any failure in an j upstream component will result in an anomalous signal being presented to the  ;

logic circuitry. This has the same effect as a failure in an instrument channel feeding the signal selector. The action of the logic gates will j prevent this signal from being passed to the balance of the control system,  ;

and simple measurements of the input and output signals in conjunction with a l' test sequence will reveal that the true median signal is not being selected, and, therefore, a unit failure exists. -

As discussed above, once the appropriate signal has been selected, the digital ,

portion of the circuit is effectively bypassed resulting in a purely analog signal processor. Due to the continuous nature of analog circuitry, the l l

functional relationship established between the input and output is a 1:1 mapping as determined by the operating characteristics, and circuit

[ i L arrangement of the various subcomponents comprising the circuit. A failure of a component within the balance of the analog circuitry will therefore result l in a shift of the output signal. Thus, by knowing the functional relationship between the input and output, and the measured values of the input and output signals, one can readily determine a malfunction of the analog portion of the circuit.

1 00690:1D/011090 12 ,

,osss i

In as much as all amplifiers will be exercised during a complete test sequence, even "as is" failures, in which an amplifier fails at an output ,

voltage which corresponds to its output under normal operating conditions, )

will be readily detected as the test procedure is conducted. Multiple i failures in the signal selector will simply compound the effects of any single )

failure. Of course, in practice it is not necessary to determine exactly l which component the failure has affected; rather, simple unit replacement ]

followed by a repeat test sequence will reveal correction of any problems that j have been identified. Thus, we find that not only is the signal selector design consistent with low failure probability, but that circuit. failures are clearly manifested during signal selector testing.

2.4 Fault Conditions from EAGLE 21 Failures j Another topic that must be addressed is the occurrence of a random failure in ]

the protection channel negating the protective action and propagating to the ]

Median Signal Selector and limiting the ability of the Median Signal Selector to perform its function.  ;

- a.c The material in this section has been deleted from the nonproprietary version ~"  ;

due to its proprietary nature. The material in this section discussed Fault' i Conditions from EAGLE 21 failures.

~

The following assumptions were made in evaluating the EA0 fault outputs:

(1) A failure on the non-C1E side was considered the same as a control failure. [

l 3"*C It was assumed that the isolation device does not prevent the failure from propagating-to the non-CIE side.

l l

+

1 0069D:1D/011090 13 l

j F+ +.; o I

(D The analysis was limited to a :. ingle failure. Multiple failures on the  !

same board / channel were not considered. f o

(3) Failures that cause the output to remain "as-is" were considered  ;

acceptable. p I

tasults i

[- .

i j

I 4

3C ,

2.5 Recc-- nded Onorator Actions i 1

I The objective of this' report is to present information which supports the j implementation of a signal selection device as part of the Low Feedwater flow l Reactor Trip deletion. A properly designed selection unit, that possesses the l requisite reliability characteristics as presented earlier, is paramount to l

preserving the total integrity of the Reactor Protection System. (

Notwithstanding, signakselector implementation must be fully integrated into j the overall plant operating scheme. Consequently, certain actions and policies need to be adapted by the utility in order to preserve the integrity of the Reactor Protection System. These actions include: j 1.- Conducting a review of all pertinent operating procedures to ensure they are consistent with, and support operation with a signal selector, including administrative controls for operations with the signal selector disabled, or in a test mode. Attendant procedural modification should be 1 l

effected.. l 0069D:lD/011090 14

hidi ct, o; 47 -  ;

45 '

2. - ' Implementing necessary administra'tive controls to ensure that signal selector testing is carried out at the appropriate frequency, and that .

consistent requirements for control room surveillance of the Steam  !

Generator water level during the shift are established.

3. Developing procedures for signal selector testing including test acceptance criteria.

,' 1 i

1

)

i I

I l

i

'i l-

! i l-L l

0069D:10/011090 15  :

g -y - . . .

, yy-. . , - . . - _ , . -

.,m- , -- - - - - --w

oO d,0

3.0 CONCLUSION

l Based on the information presented in this document, a Median Signal Selector '

is deemed an acceptable means of addressing control and protection system I interaction following the implementation of the Low Feedwater Flow Reactor  !

Trip deletion. Whereas the signal selector is being utilized to address an i aspect of protection system functional performance relative to IEEE Standard 279-1971, [ ,

3"'C Additionally, high quality components commensurate i with those used in the protection system are also used to improve the overall [

unit reliability. Due consideration of the " Recommended Operator Actions" '

presented in Section 2.5 is essential to the application of the signal selector in preserving the total protection system integrity. P e

I r

t s

l l

l l

1 l

l' 0069D:1D/011590 16

J m-I 1

F .

g

)

g

~&

-p '

s t t

l g.O~ '

+- l t i 1'O i l

l8 s  !

--e_

+ t+_  :

i .

3 I .

8,B f Figure 1 Existing Steam Generator Protection Scheme 6

mmSDS.ih1999AC9 ii

• amp, .sn g___, _ _ , , , , _ _ _ _ ._%.

",~~*m-

'l ,

-...-..-.s ...._-...M-a**4***--44_

1 b

\

\

{1 -

N .

1\

1.

\

i ss N k N

S xN' NN \

s N g  :

t t@ - -

4 t p -

e +T - 4Q i & i 9

~ A

\  % -\\

Figure t g ye) Prot *Cti'" With & ISI ""

..... ,n . n s, non 18

. _ - - . - . - . . . . - - - . - . . . . . . - . ~ . _ - _ . . . . - - . - . - . . _ . - _ _ . _ _ - _ _ - .

~ i d

'*Qs4 . .

i a

tli lll .

jL _ '==. jL ji _ - .

]

h h hb D fi 4

l [ w

= M l ;

p'% Wu% W'A ,

I m  ;.

N l

,L e,  !

h h

~

I 1

6 6 6  ;

l 19

'0028D:10/100989

.. .. . -. . _ - . . _ - . . . _ _ - . - - . . . . . _ _ . - - - . - - . .