Text

Calculation 98-ENG-02405D2, Revision 2 Attachment 1, Page 1 of 13
	ML12227A514
Person / Time
Site:	Millstone
Issue date:	08/09/2012
From:	Wynn P; Dominion Nuclear Connecticut
To:	; Office of Nuclear Reactor Regulation
References
	12-474A 98-ENG-02405D2, Rev 2
	Download: ML12227A514 (15)
	v • d • e

Calculation 98-ENG-02405D2, Revision 2 Attachment I .

i~i~DominA7 /j ., /1 Item Equivalency Evaluation Signature Page wi' M , , i ..-

Iltem Equivalency Evaluation Tiitle/Stalion/Unit lEE Number Version MINCO S7927 RTD, BURNS MODEL WSP/Milfstone /100600098752 VOO Unit 2'

.... O.................. . "............

Preparer Procurement Engineer (Print) Signatur4*, //1//)/ "- Date P. Wynn/' 9/28/09 Independent Procurement Engineer (Print) Signatbre Date R. Malinowsky ._____., ________,_______

Peer ReviewlDesign Authority (Print) S, t Date

/C~~L ODi~'ae.ol0 60 Other/ReviewerfAffiliation (Print) Signature Da e--

OtherdReviewer/Affiliation (Print) Signature Date Other/Reviewer/Affiliation (Print) Signature Date Other/Reviewer/Affiliation (Print) Signature Date

.Notes:

Backlog Item Form No 730920(May 2009)

Packing Slip Report 12/14/2009 12:20:28PM From: Packing Slip: 34182 Burns Engineering, Inc, Order No.: S000425772 10201 Bren Road East 111111111111111 Oil 111111111111111111 1 Minnetonka MN 55343 Page:

United States Toll Free: 1-800-328-3871 Tel: 952-935-4400 Fax: 952-935-8782 Bill To: C000834 Ship To: (1)

Attn:

Dominion Nuclear Connecticut, Ina Dominion Nuclear Connecticut, Inc Accounts Payable Rope Ferry Road (Route 156).

PO Box 25459 Waterford CT 06385 Richmond VA 23260-5459 Ref PO:

Order

Contact:

Bonnie Cuelbart Proj No:

8000425772 45711234 UPS N/C LinelRelease: Item U'M Qty Ordered Qty To Pack 1 WSP2C2-4-5A/C125 1.00 1,00, RTD MO Type C OAL=8.5 200 Ohm 4-Wire 42142388 Model: WSP2C2-4-5A/C025 MAT[UIAL RECLPT VERI PICATION CARFRlER R0. NO._________

STKHDL INIT.__ _ _

Returned merclhandise must have a return material authiorizationc(RW). Non-stocked, made-to-order items are not returnable Stocked parts returned are subject to a restocking fee and must be returned within one year of purchase shipping Page 1 ofl1

NEW noun BUR: NSReport EHGINE E R ING of Calibration ivLAg

r. d spa or~A-rdha a 10201 BranRoad East Mlnnetonka, tnnnoola 65343 V*ad WYVLAPL6 Cod2(x706-Model: WSP2C2-4-5A1C125 Serial Number: 838621 PO Number: 45711234

Description:

Platinum Resistance Thermometer, Secondary Standard Calibration Procedure Numbers: SOPC3 Rev D Calibration Method: Cornparison to SPRT Calibration Range: -381C to 100'C Customer: Dominion Nuclear Connecticut, Inc. Calibration Date: 12/1U/2009 Rope Ferry Road (Route 156) As-Found Condition: New Waterford, CT 06385 As-Left Condition: Calibrated This platinum resistance thermometer (PRT) was calibrated using an AC bridge at a current of imA, at the temperatures reported below by comparison to Standard Platinum Resistance Thermometers (SPRTs). These SPRTs are calibrated to the International Temperature Scale of 1990 (ITS-90) and their calibration is traceable to the National Institute of Standards and Technology.

The combined standard uncertainty of this calibration includes all known sources present at the time of calibration. The uncertainties are reported at the calibration temperatures only, the uncertainties at intermediate temperatures can be computed from these values and the 1TS-90 propagation of error curves. The combined standard uncertainty is multiplied by a coverage factor of 2 to give an expanded uncertainty, which defines the interval having a level of confidence of approximately 95 percent. The expanded uncertainty presented in this report is consistent with the 1993 ISO Guide to the Expressionh of Uncertainty in Measurement. The expanded uncertainty is not to be confused with a tolerance limit for the user during application. -

Calibration Results .

Temperature (deg C) Resistance (ohms) Uncertainty (inK)

-38.000 169.7716 +/- 25 mk 0.000 199.9705 +/-25 mik 50.000 239.1699 -25 mk 100.000 277.7691 .25 rk Callendar-Van Dusen Calibration Coefficients R0= 199.9705 T Al ha = 0.0038905 Delta= 1.5430 Beta 0.0997 I A = 3.950536e-03 B = -6.003035e-07 C = -3.877400e-12 Comments and Limitations: None The temperature calibration system used by Burns Engineering complies with the requirements of ANSI/NCSL Z540-1-1994, Part 1, and ISO/IEC 17025:2005. This calibration report applies only to the item calibrated. This report shall not be used to claim certification, approval, or endorsement by NVLAP, NIST, or any agency of the federal government.

Environmental conditions:

The ambient conditions of the laboratory are controlled to 21 +/- 4 degrees C and 80% maximum relative humidity.

The following measuring and test equipment were used in this calibration:

Item Model Serial Number Recall Date SPRT 8163QB 1873681 5/25/2010 SPRT 8163Q S96S4772 7/2/2012 Bridge F700 1337-006-446 4/14/2010 Standard Resistor 5685A-100 8738/14 1/9/2010 The attached resistance vs temperature table was generated for this sensbr using the Callendar-Van Dusen interpolation equations and the results of this calibration.

Calibration performed and Approved by:

r...W 4h44 Date of Issue: 12-11-2009 Metrology Technician: Terry Walsh This report may not be reproduced, except in full, without the written permission of Buums Bengineering, Burns Engineering Calibration Report Number: 101525 Page I of 3

Resistance vs. Temperature table using Callendar-Van Dusen coefficients for RTD Serial Number: 838621 Coefficlents used: Ro: 199.9705 Alpha: 0.0038905 Delta: 1.5430 Beta: 0,0997 Temperatures are In deg Celclus

-0 -1 -2 -3 -4 -5 -6 -7 -8 -9

-40 -40

-30 176.1600 175.3623 174.5645 173.7663 172.9679 172,1692 171.3703 170.5711 169.7716 -30

-20 184.1219 183.3268 182.5315 181.7360 180.9402 180.1441 179.3478 178.5513 177.7544 176.9573 -20

-10 192.0585 191.2659 190.4731 189.6801 188.8868 188.0933 187.2995 186.5055 185.7112 184.9167 -10 0 199.9705 199.1804 198.3900 197.5994 196.8086 196.0175 195.2262 194.4346 193.6428 192.8508 0 0 -1 -2 -3 .4 -5 -6 -7 -8 -9 (cdCca'tv? !/ d? 4O Burns Engineering Calibration Report Number: 101525 Page 2 of 3

Resistance vs. Temperature table using Callendar-Van Dusen coefficients for RTD Serial Number: 838621 cgoefficlents used: RH: 199.9705 . Alpha: 0.0038905 Della: 1.6430. Beta; 0.0997 Temperatures are In deg Celclus 0 1 2 3 4 5 6 7 a 9 0 199.9705 200.7603 201.5500 202.3394 203.1285 203.9174 204.7061 205.4945 206.2827 207.07'07 0 10 207.8584 208.6459 209.4331 210.2201 211.0068 211.7933 212.5796 213.3656 214.1514 214.93370 10 20 215.7223 216.5074 217.2922 218.0768 218.8611 219.6452 220.4291 221.2127 221.9861 222.77'93 20 30 223.5622 224.3448 225.1273 225.9095 226.6914 227.4731 228.2546 229.0358 229.8168 230.59P76 30 40 231.3781 232.1583 232.9384 233.7181 234.4977 235.2770 236.0561 236.8349 237.6135 238.39)18 40 50 239.1699 239.9478 240.7254 241.5028 242.2800 243.0569 243.8335 244.6100 245.3861 246.16 21 50 60 246.9378 247.7133 248.4885 249.2635 250.0382 250.8127, 251.5870 252.8610 253.1348 253.90p84 60 70 254.6817 255.4547 256.2275 257,0001 257.7725 288.5446 259.3164 260.0881 260.8595 261.63 06 70 80 262.4015 263.1722 263.9426 264.7128 265,4827 266,2524 267.0219 267.7911 268.5601 269.32 88 80 90 270.0973 270.8656 271,6336 272.4014 273.1690 273.9363 274,7033 275.4702 276.2367 277.0C131 90 100 277.7692 100 0 1 2 3 4 5 8 7 8 9 Bums Engineering Calibration Report Number: 101525 Page 3 of 3

A+/-~i A*I Item Equivalency Evaluation WDominianw ; i'3 rd5 lý -0*ýA a"M''--2*.-" 4 6f7, Item Equivalency Evaluation Title/Station/Unit lEE Number Version MINCO S7927 RTD, BURNS MODEL WSP / Millstone / Unit 2 10000008752 00 Attachments (Each page of the lEE shall have lEE#, Revision, & pagination including attachments):

Drawing 25203-31147 Sheet R Drawing 25203-28408 SH. 312, MP2 HUD Piping Thermowell MINCO Drawing S7927 Fax from MINCO dated May 10, 2000 Comparison Table from DCN DM2-04-0524-98 Page from Calculation No. 98-ENG-02405D2, Rev 01 BURNS Engineering Quote WQ13270 Dated 9/9/2009 Pages from BURNS Engineering catalog for Model WSP Resistance Thermometers (Bulletin 973A)

BURNS Engineering Curve 2 BURNS Engineering Technical Paper on Stability

_ .. * - --. .7i:E Material Master Number M365721R 42142388 Item Description Precision Platinum Resistance Precision Platinum Resistance Thermometer (Resistance Thermometer (Resistance Temperature Temperature Detector (RTD)) Detector (RTD))

Manufacturer MINCO BURNS Engineering Part Number XS7927PK1 L76S WSP2C2-4-5A/CI25 Model Number S7927 WSP Specifications 200 0 Platinum wire 200 Q Platinum wire Accuracy +/- 0.025 degrees C Accuracy +1- 0.025 degrees C Stainless steel case Stainless steel case 4-wire 4-wire 14 in diameter / in diameter 1 inch temp sensitive zone Maximum 1 inch temp sensitive zone 7.6 in case length 7.0 in probe length Vendor Manuals N/A BURNS Bulletin 973A Other The 'X' in the original item part number means 200 ohm platinum, no 2.25 inch spring, and variable case length. For the MINCO design, the spring is used for strain relief. (See MINCO fax attached to this lEE)

Form No 73091 8(May 2009)

f\A* i.W,.L,,*, I Item Equivalency Evaluation

~Domii niono P C'.--- 7 V V

& £ -

rio- '-

Item Equivalency Evaluation Title/Station/Unit -lEE Number Version MINCO S7927 RTD, BURNS MODEL WSP I Millstone I Unit 2 10000008752 00 Par ut~juui ju, f ecnlci urn

-!*efl:i--lyfA*e.ri.a.u~s~e loc~ation~s-h~ave form-fnt'.ftunc`tioriaj ahfieatln.cr design req~uir~ements mole restrictve.thlan those re oft-mt cristaucthosioe Characteristic Original Replacement SamelDifferent !Acceptable Form Precision Platinum Resistance Precilsion Platinum Resistance Same Yes Thermometer Thermometer Fits in 4 '1/4 inch bore depth Fits in 4 % inch bore depth thermowell, thermowell, contains nipple and contains nipple and connection head connection head 2 inch NPT threads 1/2 inch NPT threads

% in diameter 1A in diameter Fit 7.6 inch case length 7 inch probe length (length below Different Yes spring). 8 1/2 inch overall length.

Cable and sensor leads terminated at connection head Cable and sensor leads terminated at connection head No spring Spring Loaded Function Provide a resistance value that changes Provide a resistance value that with Swith service water temperature changes temperaturewith service water Same Yes 200 Q Platinum 200 Q Platinum Yes 4-wire lead construction 4-wire lead construction Temperature 0.00392 (Q/D/°C min.) 0.003902 (0/0J0C min.), BURNS Different Coefficient Engineering Curve No. 2 Yes Temperature -180 to 260 Degrees C -38 to 100 Degrees C (Range Different Yes Range calibrated by vendor) Different Case Material Stainless steel with copper alloy tip Stainless steel case and tip Different Yes Pressure Yes Rating (psi) 100 3000 Different Accuracy +/- 0.025 degrees C +/- 0.025 degrees C Same Yes StabilityYe (degrees C /yr) - 0.05 at 0 degrees C Unspecified Different Yes Self-Heating 0.015 degrees C/mW 0.02 degrees C/mW Different Yes

-i/- 0.01 ato0degrees C Yes Repeatability Maximum +/- 0.047 at 0 degrees C Different (degrees C)

Form No 730918(May 2009)

A.A,'c.' " k Item Equivalency Evaluation Dominion "

Al~~ I6 ,,. !

Item Equivalency Evaluation Title/Station/Unit lEE Number Version MINCO S7927 RTD, BURNS MODEL WSP/ Millstone / 10000008752 00 Unit 2 lEE Basis -- Engineering justification for the acceptability of the differences in the critical characteristics:

Fit: The original item has a 7.6 inch case length and fits In a 4 4 inch bore depth thermowell. Walkdown of the original item showed that a nipple is used in the installation to accommodate the difference between RTD case length and bore depth.

The replacement item will also be provided with a nipple to allow installing it, with its 7.0 inch probe length, into the existing 4 / inch bore depth. The replacement item installation configuration will be similar to that of the original Item. The replacement item Is spring loaded so that the element and thermowell are kept in contact firm contact. This item is acceptable.

Temperature Coefficient: The replacement item has a slightly different temperature coefficient than the original. However, the replacement item is still a 200 ohm platinum precision RTD and will be provided with full calibration data. Procedure MP-PROC-MP-IC 2429B will need to be updated with the replacement item's calibration data. This item is acceptable.

Temperature Range: The replacement item will be calibrated by the vendor over the range of-38 to 100 degrees C. This Is acceptable since the system fluid is service water and in-service calibration of service water system temperature sensors is performed over a range of 0 to 100 degrees F.

Case Material: Both items have a stainless steel case. The original item has a copper alloy tip to improve sensor time response. The material for the replacement item tip is stainless steel. This may slow the replacement item's response time slightly, Burns Bulletin states a 5 Y2 second time constant for the replacement Item, but the critical performance characteristic of the replacement item is accuracy. Accuracy of the replacement item is the same as that of the original item. This is acceptable.

Pressure rating: The RTD is inserted into a dry thermowell. Additionally, the system fluid is low pressure service water.

Pressure ratings for the original and replacement items are of no concern for the component locations evaluated. This is acceptable.

Stability: The stability of the replacement item is not specified. A review of Burns Engineering Technical Paper on stability, attached to this lEE, shows that the stability of a platinum resistance thermometer (PRT) at the service water system temperatures can be ignored as a potential error source. This item is acceptable.

Self-Heating: The self-heating effect for the original item is stated as negligible in calculation No. 98-ENG-02405D2. The replacement Item's self-heating Is approximately the same as that of the original item and would also be negligible in the calculation. This is acceptable.

Repeatability: The repeatability of the replacement item is conservatively high since it is specified over a temperature range that cycles up to 900 degrees F. The actual temperature conditions of the service water system where the replacement items will be installed provide a small range of temperature cycling so the replacement item repeatability will be much better than 0.047 and should be close to that stated on the MINCO drawing for the original item. Additionally, repeatability Is not a source of error considered In calculation No. 98-ENG-02405D2. This Is acceptable.

The replacement item will be provided with a full vendor calibration with calibration report and temperature verses resistance tables from -38 degrees C to 100 degrees C resulting in an accuracy of +/- 0.025 degrees C.

The replacement item has different wire lead colors, red and black, than the original item's colors which are red and white.

This will require drawing updates upon installation of the replacement item.

[] The Design Effects Table (DET) was revie' ved and no programs were impacted.

El The DET is attached to this lEE.

Form No 730918(May 2009)

-bij P401/ý fLv (7 LA-r- e ft 1ýzdv X,2 /j -_Aq*e i -U itQ Burns Eng. 800-328-3871 01 7 SPECIFICATIONS C.0-mm" -

For Standard Length 1/4/4" OD Type A, B, C, D, & G Elements IVA W ELEMENT RESISTANCE SELF HEATING 0

Resistance at 32'F Resistance Change at 32 F

Self heating is caused by @I ric . d t 100 ohm platinum .22 ohms per F mine element esistanc e error is typically 50 milli-200 ohm platinum .44 ohms per 0 F watt-*sperthgreer m e d for 1/4 inch diameterre-byers 500 ohm platinum 1.10 ohms perOF ance termometers in water moving at tthree feet per second.

The 100 ohm platinum element is most standard and 0.021 ~c/~W least expensive. When the total resistance change for the Example:

100 ohm element for a narrow temperature span does Water moving at 3 feet per second.

not meet the minimum resistance change for the instru- Current of 2 milliamps.

ment it is to be connected to, then a 200 ohm or a 500 Element resistance 2

of 110 ohms ohm element should be selected. Example: if the tem- Power - 1 R perature span is 50F .a 100 ohm element will have a = (2 x 10,3 Amps) 2 (110 ohms) = 0.44 milliwatts total resistance change of 50 x .22 = 11.0 ohms. If the instrument requires a 20 ohm minimum span, then a Self heating error = Power 20G ohm element should be used, which has a resistance Self-heating coefficient change of 50 x .44 = 22.0 ohms.

0.44 miiliwatts ACCURACY 50 milliwattsf'C 0088oC "0158sF All elements will follow the Resistance vs Temperature Example:

Tables shown on pages 8 and 9 within the interchange- Same conditions except current is 5 miilliamps 2

ability limits shown. Note that there are two classes of Power= (5 x 10-3 AMPS) (110 ohms)'

Precision Accuracy Elements as well as one class of Standard Accuracy Elements. These classes are identified Self heating error " 2.75 milliwatts 0

by the resistance tolerance at the ice point (0 C). 50 milliwatts/'C

= .055ec = .099°F PRECISION ACCURACY PLATINUM ELEMENTS

+/-0.02% of Resistance at 0°C. For stock sensors only. Factors that affect self heating error are thermal con-.

0

-s0.05% of Resistance at WC for all dual element and ductivity and velocity of the process medium being mea-most non-standard sensors. sured. These are the same factors that affect time re-sponse.

STANDARD ACCURACY PLATINUM ELEMENTS For most applications self-heating error is negligible and 0

+/-0.10% of Resistance at 0 C. can be Ignored.

For all sensors.

INSULATION RESISTANCE The available accuracies are listed in the ordering information tables on the following pages. With dry external surfaces the insulation resistance be-tween any lead wire and the metal sheath will be as REPEATABILITY follows:

t0.1OF over range 320 F to 9000oF. 0oa 0 4-4+ Sheath Temperature 1 Insulation Resistance, (tC) Minimum MATCHED PAIRS 20 200 Megohms at 100 VDC When two unmatched elements are used to measure temperature difference, one of the elements could be off 225 J 100 Megohms at 100 VDC 500 10 Megohms at 100 VDC by +1/22F and the other, off by -1/2'F. This would re- 650 5 Megohms at 100 VDC suit in a 1'F error in temperature difference. Matched pairs are selected to assure that the two elements are matched to each other to minimize errors. Thus, the 0 TEMPERATURE LIMITS error is not greater than !/2 F at 32ZF, (For the standard accuracy platinum elementsj PLATINUM ELEMENTS PRESSURE RATING Standard Limits -3250 F to 900 F (element enclosed in 3000 psi at 7000F standard for all stainless steel sheath type 316 stainless steel sheath).

elements. Extended Limits -3250 F to 12000 F (element enclosed in TIME CONSTANT inconel sheath).

2Y1/2 seconds for 63.2% reponse in water moving at three END SEAL AND LEAD WIRES Sfeet per second for the type "D" sheath (1/8" dia-meter fast response tip). This portion of the element assembly is rated from

-50°F to 2000F for the waterproof construction and 51/2 seconds for the type "A" sheath (1/4" diameter).

-50WF to 4000F for the nonwaterproof construction

'? I[ 1 0 0 75ooZ VO Q (911Lý LO~ 1)j '_tI with the No. I head (higher ratings available).

NNW E N 6.I H E E R I H 0 Error Sources That Effect Platinum Resistance Thermometer Accuracy Part 3 - Stability Introduction There are many sources of error that affect the performance of Platinum Resistance Thermometers (PRTs). These error sources are inherent in the design and manufacture of all PRTs, but the magnitude of the resulting error can vary greatly depending on the specific PRT design and environment that it is used in. It is important for users of PRTs to know and understand what these error sources are so they can make intelligent decisions related to PRT selection and use. The most common error sources fall within the following categories: Interchangeability, Insulation Resistance, Stability, Repeatability, Stem Conduction, Hysteresis, Calibration and Interpolation, Lead Wire Resistance, Self-Heating, Time Response, and Thermal EMF. This paper will discuss the topic of Stability.

Stability Stability refers to the ability of a PRT to maintain its' Resistance vs. Temperature (R vs.

T) relationship over time as a result of thermal exposure. Both ASTM El 137 and IEC 60751 address resistance change due to thermal exposure, however the criteria are somewhat different. ASTM El 137 essentially states that the PRT must meet the resistance tolerance for a Grade A or Grade B sensor as applicable, after 4 weeks (672 hours0.00778 days 0.187 hours 0.00111 weeks 2.55696e-4 months ) of exposure to the maximum rated temperature. While this is a well defined criteria, it essentially does not permit any change in the resistance unless the manufacturer held a tighter tolerance to account for the change. IEC 60751 states that the PRT can change at 0°C by the equivalent of 0. 15'C for a Class A sensor and 0.30'C for a Class B sensor after 250 hours0.00289 days 0.0694 hours 4.133598e-4 weeks 9.5125e-5 months at maximum rated temperature. While this standard allows for an R vs. T shift outside of the original tolerance, the 250 hour0.00289 days 0.0694 hours 4.133598e-4 weeks 9.5125e-5 months duration may be quite short for estimating longer term effects. Both of these standards leave something to be desired with respect to stability. Many manufacturers state stability specifications more like the IEC 60751 standard, stating a maximum change at 00 C as a result of exposure to maximum rated temperature for a given period of time. These specifications typically do not require the PRT to remain within the original R vs. T tolerance after the exposure.

Given the information contained above, it may be possible to perform a comparison between PRTs, but it is likely insufficient for determining how a PRT will perform in actual use. In the case where the PRT is used continuously for one year (-9000 hours) at 350'C, what estimation of performance can be made if stability information of .15'C per

e~wA/

/a4(,/A'7K 250 hours0.00289 days 0.0694 hours 4.133598e-4 weeks 9.5125e-5 months at 500'C is the only detail provided? Additional information regarding stability would certainly be beneficial.

The additional information that would be valuable for estimating stability en'or would be a set of specifications that state the change due to exposure to varying temperatures over varying intervals of time. Typically three or four temperatures including the maximum rated temperature, would be adequate to estimate stability. The graph in Figure 3-1 below gives a realistic representation of the stability of a typical industrial PRT at 5 different exposure temperatures.

Figure 3-1 Industrial PRT Stability Example 0.6 g 0.5 50000 p

0 0.4 -4000C Cu 0.3

.4-

- 3000 C

0) 0.2 - 200'C C

Cu -- 230C 0.1 0

0 0 500 1000 1500 2000 2500 Hours at Temperature By examining Figure 3-1, a few generalizations can be made about the stability of this industrial PRT. These generalizations hold true for the behavior of most industrial PRTs, however the numbers, maximum temperatures, etc., will all be unique based on the specific PRT design. If a better understanding is needed regarding a specific PRT, the manu acturer of that PRT should he cnnsnlted.

)lThe stance change due to exposure to room temperature and below can be considered negligible. Test results on several industrial PRTs have shown that the ice point resistance shift following 25,000+ hours at 23°C is less than 73- 1 C2 C. This is a very small change in comparison to other potential error

2) The magnitude of the change increases with increasing exposure temperature and is a maximum at maximum rated temperature. For example, the change after 1000 hours0.0116 days 0.278 hours 0.00165 weeks 3.805e-4 months will be larger for an exposure temperature of 500'C than an exposure temperature of 400'C.

(,j4F

%\4A zcOe, /to

3) The magnitude of the change is not linear with temperature and cannot be extrapolated beyond the upper temperature limit. For example, the change caused by exposure to 550 0C cannot be reliably predicted based on the changes observed due to 500'C or 400'C exposure.

4) The rate of change over time is fairly linear and remains fairly constant. For example, the change after 2000 hours0.0231 days 0.556 hours 0.00331 weeks 7.61e-4 months can be approximated as twice the amount of change as was present after 1000 hours0.0116 days 0.278 hours 0.00165 weeks 3.805e-4 months for the same exposure temperature.

Given the generalizations above along with the information illustrated in Figure 3-1, a reasonably accurate estimation of stability can be made for the hypothetical example of a PRT at 350'C for one year. The stability can be estimated by looking at the graph and estimating a change after 1000 hours0.0116 days 0.278 hours 0.00165 weeks 3.805e-4 months for a 350'C exposure. According to the graph, this would be approximately 0.1°C. Multiplying this number by 9 to determine the cumulative effect over 9000 hours0.104 days 2.5 hours 0.0149 weeks 0.00342 months gives a result of .90 C maximum change at 00 C after one year of exposure to 350'C. This is likely to be a more accurate estimate than extrapolating the IEC 60751 requirement of .15°C (or .30'C) per 250 hours0.00289 days 0.0694 hours 4.133598e-4 weeks 9.5125e-5 months out to 9000 hours0.104 days 2.5 hours 0.0149 weeks 0.00342 months which would result in an estimated value of 5.4'C (or 10.8'C)

Causes of Stability Error Many factors can contribute to the instability of a PRT, but the most prominent source of instability is contamination of the platinum in the sensing element. Contamination can come from a variety of sources, such as metals that alloy with platinum at elevated temperatures, and very small amounts of these contaminants can have large effects on resistance. The materials and processes used to manufacture the sensor must be carefully selected and/or developed such that they have minimal affect on the platinum at temperatures up to the maximum rated temperature of the PRT. Cleanliness during manufacture is also critical as any foreign substance may become a source of contamination. In general, the materials, processes, and cleanliness become more critical as the maximum rated temperature of the PRT increases.

How to Reduce Stability Error Since stability is controlled almost exclusively by the design and manufacture of the PRT, the best way to reduce stability error is to select a high quality PRT that has a low specified stability. When selecting a PRT, the stability must be considered for the maximum temperature of use, not necessarily the maximum rated temperature of the PRT itself since many PRTs are not used to maximum rated temperatures. Never expose PRTs to temperatures in excess of their maximum rated temperature without consulting the manufacturer first to determine the effect on stability. Also, avoid unnecessary exposure to elevated temperature, the less time the sensor is exposed to elevated temperature the smaller the cumulative effect.

As mentioned in Part 1 on Interchangeability, using a transmitter with "matching" capabilities can nearly eliminate interchangeability error and the same is true with stability error. Periodic calibration of the PRT and transmitter system can allow a transmitter to be matched to the newly characterized R vs. T relationship of the PRT.

This can "calibrate out" the change of the PRT due to stability, and significantly reduce the cumulative effect of this error source.

Summary There are many sources of error that affect the performance of a PRT. One of these sources is Stability, the ability of a PRT to maintain its R vs. T relationship over time as a result of thermal exposure. The most prominent source of instability is contamination of the platinum sensing element which can come from the materials, build processes, and foreign substances introduced during manufacture. The best way to reduce stability error is to select a high quality PRT that has a low specified stability and to minimize the PRTs exposure to elevated temperatures. Matching a transmitter to a PRT and periodically calibrating the system to adjust for changes can significantly reduce the cumulative effect of this error source.

John Zwak www.bumsengineering.com Metrology Engineer www.burnsengineering.com/BEblog/

jzwak@burnsengineering.com

Calculation 98-ENG-02405D2, Revision 2 Attachment 2 Attachment 2 71i;

ML12227A514

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