ASTM E879-20

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation:E879 −20
Standard Specification for
Thermistor Sensors for General Purpose and Laboratory
Temperature Measurements
This standard is issued under the fixed designation E879; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope E563Practice for Preparation and Use of an Ice-Point Bath
as a Reference Temperature
1.1 This specification covers the general requirements for
E1502Guide for Use of Fixed-Point Cells for Reference
Negative Temperature Coefficient (NTC) thermistor-type sen-
Temperatures
sors intended to be used for laboratory temperature measure-
E1750Guide for Use of Water Triple Point Cells
ments or control, or both, within the range from−10 °C to
E2488Guide for the Preparation and Evaluation of Liquid
105 °C.
Baths Used for Temperature Calibration by Comparison
1.2 This specification also covers the detailed requirements
F29Specification for Dumet Wire for Glass-to-Metal Seal
for ASTM designated sensors.
Applications
1.3 This specification also covers the requirements for 2.2 NIST Documents:
general purpose, Negative Temperature Coefficient (NTC)
NIST Monograph 126Platinum Resistance Thermometry
thermistor-type sensors intended for use with Digital Contact NIST Special Publication 250-22Platinum Resistance Ther-
Thermometers (also known as Digital Thermometers) within
mometer Calibration
the range from –50 °C to +150 °C. NIST Technical Note 1265Guidelines for Realizing the
International Temperature Scale of 1990
1.4 The values stated in SI units are to be regarded as the
2.3 Other Documents:
standard. The values given in parentheses are for information
JCGM100:2008Evaluationofmeasurementdata–Guideto
only.
the expression of uncertainty in measurement
1.5 This standard does not purport to address all of the
ANSI/NCSL Z540.3-2006 (R2013)Requirements for the
safety concerns, if any, associated with its use. It is the
Calibration of Measuring and Test Equipment
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
3. Terminology
mine the applicability of regulatory limitations prior to use.
3.1 Definitions—The definitions given in Terminology
1.6 This international standard was developed in accor-
E344 shall apply to this specification.
dance with internationally recognized principles on standard-
3.2 Definitions of Terms Specific to This Standard:
ization established in the Decision on Principles for the
3.2.1 dissipation constant, δ,n—the ratio of the change in
Development of International Standards, Guides and Recom-
energy dissipated per unit time (power) in a thermistor,
mendations issued by the World Trade Organization Technical
∆P= P − P , to the resultant temperature change of the
2 1
Barriers to Trade (TBT) Committee.
thermistor, ∆T= T − T .
2 1
2. Referenced Documents
∆P
2 δ 5 (1)
2.1 ASTM Standards: ∆T
E344Terminology Relating to Thermometry and Hydrom-
The dimensions of the dissipation constant are watts per
etry
kelvin (W/K). Note that many NTC thermistors are very
small devices, and as such, the dissipation constant dimen-
This specification is under the jurisdiction of ASTM Committee E20 on
sions are frequently expressed in terms of milliwatts per kel-
Temperature Measurement and is the direct responsibility of Subcommittee E20.03
vin (mW/K).
on Resistance Thermometers.
CurrenteditionapprovedMay1,2020.PublishedJuly2020.Originallyapproved
in 1982. Last previous edition approved in 2012 as E879–12. DOI: 10.1520/
E0879-20. Available from National Institute of Standards and Technology (NIST), 100
For referenced ASTM standards, visit the ASTM website, www.astm.org, or Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http://www.nist.gov.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Available from the BIPM, Sevres, France, http:// www.bipm.org.
Standards volume information, refer to the standard’s Document Summary page on Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
the ASTM website. 4th Floor, New York, NY 10036, http://www.ansi.org.
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959. United States
E879−20
For this specification, T is in the range from 20 °C to 38 °C 4.2.1 Type Designation—Thetypedesignationcodeshallbe
and ∆T=10 °C. a letter symbol to indicate the design and construction of the
thermistor sensor followed by a number to indicate the subset
3.2.2 dumet, n—round,copper-coated42%nickel-ironwire
of specific features as shown on the detailed specification
intended primarily for sealing to soft glass. Also known as
drawingwhenevertherearedesignoptions.(SeeFig.2through
CuNiFe in some communities; see Specification F29 for
Fig. 10).
additional information.
4.2.1.1 Type S—Silicone rubber-coated glass probe with
3.2.3 insulation resistance, dc, n—the resistance at a speci-
tinned Dumet extension leads (see Fig. 2).
fied direct-current voltage between the insulated leads of a
4.2.1.2 Type E—Epoxy-coated glass probe with silver-
thermistor sensor and the metallic enclosure of the sensor, if
plated copper extension leads (see Fig. 3).
such an enclosure is present, or else between the sensor leads
4.2.1.3 Type G—General purpose four-wire sensor in stain-
and a conductive medium in which the sensor is immersed.
less steel housing (see Fig. 4).
3.2.4 qualification test, n—aseriesoftestsconductedbythe
4.2.1.4 Type H—General purpose two-wire sensor in stain-
procuring agency or an agent thereof to determine confor-
less steel housing (see Fig. 5).
mance of thermistor sensors to the requirements of a
4.2.1.5 Type V—Interchangeable sensor enclosed in 1.2 mm
specification, normally for the development of a qualified
vinyl tube (see Fig. 6).
products list under the specification.
4.2.1.6 Type W—Non-interchangeable sensor enclosed in
3.2.5 response time, n—the time required for a sensor to 0.9 mm vinyl tube (see Fig. 7).
change a specified percentage of the total difference between 4.2.1.7 Type P—Interchangeable sensor with flexible cable
its initial and final temperatures as determined from zero- and sealed plastic tip (see Fig. 8).
power resistances when the sensor is subjected to a step 4.2.1.8 Type J—Interchangeablesensorenclosedinstainless
function change in temperature. steel housing (see Fig. 9).
4.2.1.9 Type K—Interchangeable sensor enclosed in stain-
3.2.6 timeconstant,n—the63.2%responsetimeofasensor
less steel housing with threaded pipe fitting (see Fig. 10).
that exhibits a single-exponential response.
4.3 Operating Temperature Range—Theoperatingtempera-
3.2.7 zero-power resistance, n—the dc resistance of a
ture range shall be designated by a letter symbol (see Table 4).
device, at a specified temperature, calculated for zero-power.
3.2.7.1 Discussion—Accurate zero-power resistance is ob-
4.4 Accuracy Class—Theaccuracyclassshallbedesignated
tained by extrapolating to zero-power the resistance values
by a single-digit number (see Table 3).
obtained from measurements at three or more levels of power
4.5 Calibration Type—The type of calibration required for
with the sensor immersed in a constant temperature medium.
each unit shall be designated by a letter symbol. The letter I
For the purpose of this specification, this is obtained from
shall be used to denote units that are interchangeable with
measurements at a single power level that is adjusted or
respect to a single resistance-temperature relationship. The
otherwise determined to be not greater than one-fifth the
letter N shall be used to denote non-interchangeable units for
product of the dissipation constant specified in Table 1 (see
which resistance-temperature information must be furnished
3.2.1 and 7.3) and the appropriate tolerance requirement of
for each unit. For Calibration Type N sensors, serial number
Table 3. Accordingly, the applied power levels required to
identification must be provided.
satisfythezero-powerresistancecriterionasdefinedabovecan
4.6 Zero-power Resistance at 25 °C—Eachoftheindividual
beaslittleas2µW(foraTypeWsensorwithaccuracyclass1)
thermistor sensor types shall have nominal zero-power resis-
to as much as 600 µW (for Types J, K or P sensors with
tance values at 25 °C as specified in Table 1 and as shown on
accuracy class 6). The known excitation current or voltage of
the individual detailed specification drawings. Each nominal
themeasurementsystemalongwiththeresistanceofthesensor
resistance value specified shall also have an associated resis-
at the selected temperature (from the nominal resistance and
tanceratio-versus-temperaturevaluethatischaracteristicofthe
ratiovaluesgiveninTable2)canbeusedtocomputetheactual
thermistor material formulation employed in the sensor. The
applied power to the unit under test (UUT) and to determine if
resistanceratio-versus-temperaturedatafortheselectedtherm-
this power level meets the zero-power criterion.When making
istor material formulations are shown in Table 2. Other
repeat measurements over a specified time period to determine
nominal resistance values at 25 °C, or at another reference
the stability of a sensor, the power level shall be kept constant.
temperature, may be agreed upon by the manufacturer and end
4. Classification
user provided that this information is clearly communicated in
4.1 Thermistorsensorscoveredbythisspecificationshallbe all appropriate documentation; and, that the unique identifica-
classified with a unique identification code that includes the tion code (see Fig. 4.1) is not used under such circumstances.
ASTMdetailedspecificationnumberfollowedbyadescriptive
4.7 Terminations—The detailed specification drawings (see
typedesignationcode,anoperatingtemperaturerangecode,an
Fig. 2 through Fig. 10) show the sensors with the most
accuracy class code, and a calibration type code. (See Fig. 1.)
common type of termination for that type designation. All
4.2 ASTM Specification Number—The ASTM specification sensors,regardlessoftypedesignation,maybeterminatedwith
number specifies uniquely the design and construction of the any suitable electrical connector (as agreed upon by manufac-
sensor including the type designation if more than one type turer and end user) such that it allows the sensor to interface
appears in the same specification. withaspecificthermometersystem.Itisrecommendedthatthe
E879−20
TABLE 1 Specification for ASTM Laboratory Thermistor Sensors
E879 Type S E879 Type E E879 Type G E879 Type H E879 Type V E879 Type W E879 Type P E879 Type J E879 Type K
Non-
4-Wire Non- 2-Wire Non- Interchangeable Interchangeable Interchangeable
Silicone Rubber interchangeable Interchangeable
Epoxy Coated interchangeable interchangeable Sensor Enclosed Sensor with flex- Sensor in S.S.
Description Coated Glass Sensor Enclosedin Sensor in S.S.
Glass Probe Sensor in S.S. Sensor in S.S. in 1.17 mm Plastic ible cable and Housing with
Probe 0.92 mm Plastic Housing
Housing Housing Tube plastic tip 1/8-27 NPT body
Tube
Design and
Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 7 Fig. 8 Fig. 9 Fig. 10
Construction
General Purpose General Purpose General Purpose General Purpose General Purpose General Purpose General Purpose
Major Laboratory Laboratory Laboratory Laboratory Cuvette Cuvette Laboratory Laboratory Laboratory
Applications Temperature Temperature Temperature Temperature Thermometry Thermometry Temperature Temperature Temperature
Measurement Measurement Measurement Measurement Measurement Measurement Measurement
Design Exposure
Temperature
Limits
minimum –50 °C –20 °C –20 °C –20 °C –20 °C –20 °C –20 °C –50 °C –50 °C
maximum 125 °C 105 °C 105 °C 105 °C 70 °C 70 °C 105 °C 105 °C 150 °C
1 (±0.01 °C) 1 (±0.01 °C) 1 (±0.01 °C) 1 (±0.01 °C) . . . . . . . . . . . . . . .
2 (±0.02 °C) 2 (±0.02 °C) 2 (±0.02 °C) 2 (±0.02 °C) . . . . . . . . . . . . . . .
Available
3 (±0.05 °C) 3 (±0.05 °C) 3 (±0.05 °C) 3 (±0.05 °C) . . . . . . . . . . . . . . .
Accuracy
4 (±0.10 °C) 4 (±0.10 °C) 4 (±0.10 °C) 4 (±0.10 °C) 4 (±0.10 °C) 4 (±0.10 °C) 4 (±0.10 °C) 4 (±0.10 °C) 4 (±0.10 °C)
Classes
. . . . . . . . . . . . 5 (±0.20 °C) 5 (±0.20 °C) 5 (±0.20 °C) 5 (±0.20 °C) 5 (±0.20 °C)
... ... ... ... ... ... ... ... 6(±0.50°C)
A A A A A A A
... ...
(–10 °C to 105 °C) (–10 °C to 105 °C) (–10 °C to 105 °C) (–10 °C to 105 °C) (–10 °C to 105 °C) (–10 °C to 105 °C) (-10 °C to 105 °C)
Available B (–10 °C to B (–10 °C to 60 B (–10 °C to 60 B (–10 °C to 60 B (–10 °C to 60
B (–10 °C to 60 °C) B (–10 °C to 60 °C) B (–10 °C to 60 °C) B (–10 °C to 60 °C)
Operating 60 °C) °C) °C) °C) °C)
Temperature C(0°Cto60°C) C(0°Cto60°C) C(0°Cto60°C) C(0°Cto60°C) C(0°Cto60°C) C(0°Cto60°C) C(0°Cto60°C) C(0°Cto60°C) C(0°Cto60°C)
Ranges D(0°Cto70°C) D(0°Cto70°C) D(0°Cto70°C) D(0°Cto70°C) D(0°Cto70°C) D(0°Cto70°C) D(0°Cto70°C) D(0°Cto70°C) D(0°Cto70°C)
E(0°Cto100°C) E(0°Cto100°C) E(0°Cto100°C) E(0°Cto100°C) . . E(0°Cto100°C) E(0°Cto100°C) E(0°Cto100°C)
... ... ... ... ... ... ... F(-50°Cto50°C) F(-50°Cto50°C)
Accuracies for
Other Tempera- Class 3 (±0.05 °C) Class 3 (±0.05 °C)
tures Within n/a n/a n/a n/a Over 24 °C to 45 Over 24 °C to 45 n/a n/a n/a
Specified Tem- °C °C
perature Range
Non- Non-
Non- Non- Non- Non-
Calibration Type Interchangeable Interchangeable Interchangeable
interchangeable interchangeable interchangeable interchangeable interchangeable nterchangeable
all fluids compat- all fluids compat-
all fluids compatible all fluids compatible
Type of Immersion water, air water, oil, air water water water, oil, air ible with Type 304 ible with Type 304
with Type 304 S.S. with Type 304 S.S.
S.S. S.S.
Nominal
Resistance at 2500 (19.86) 2500 (19.86) 5000 (19.86) 5000 (19.86) 11 000 (20.37) 10 000 (19.86) 2252 (29.25) 2252 (29.25) 2252 (29.25)
25 °C in Ohms
with applicable
Curve (Ratio 25/ 10 000 (22.73) 10 000 (22.73) 10 000 (22.06) 10 000 (22.06) 44 000 (20.37) 22 000 (20.37) 10 000 (29.25) 10 000 (29.25) 10 000 (29.25)
125)
Dissipation
3.5 ± 0.9 mW/K 5.0 ± 1.2 mW/K 4.8 ± 1.2 mW/K 4.8 ± 1.2 mW/K 1.1 ± 0.3 mW/K 0.8 ± 0.2 mW/K 6.0 ± 1.5 mW/K 6.0 ± 1.5 mW/K 6.0 ± 1.5 mW/K
Constant
63.2% Response
0.55±0.16s 0.45±0.11 4.5±1.1s 4.5±1.1s 0.5±0.12s 0.26±0.06s 4.5±1.1s 4.5±1.1s 4.5±1.1s
Time
E879−20
TABLE 2 Resistance-temperature Data for ASTM Laboratory Thermistor Sensors
Curve Designation (19.86) (20.37) (22.06) (22.73) (29.25)
11 000
Applicable Nominal Resistance at 4000 5000 10 000 2252
22 000
25 °C (Ohms) 5000 10 000 15 000 10 000
44 000
10 000
Resistance ratio 25 °C to 125 °C 19.86±10% 20.37±10% 22.06±10% 2.73±10% 29.25±10%
Resistance ratio 0 °C to 50 °C 7.04±6% 7.08±6% 7.44±6% 7.58±6% 9.06±6%
Resistance ratio 0 °C to 70 °C 13.33±8% 13.45±8% 14.37±8% 14.75±8% 18.65±8%
Nominal ratio data:
–50 °C 40.15 40.07 44.97 46.74 67.01
–40 °C 22.06 22.07 24.16 24.96 33.65
–30 °C 12.59 12.60 13.53 13.89 17.70
–20 °C 7.433 7.448 7.863 8.025 9.707
–10 °C 4.534 4.543 4.728 4.800 5.532
0°C 2.849 2.853 2.932 2.962 3.265
10 °C 1.840 1.841 1.870 1.881 1.990
20 °C 1.840 1.219 1.224 1.227 1.249
25 °C 1.0000 1.0000 1.0000 1.0000 1.0000
30 °C 0.8262 0.8253 0.8215 0.8197 0.8057
40 °C 0.5725 0.5711 0.5633 0.5600 0.5327
50 °C 0.4048 0.4032 0.3942 0.3906 0.3603
60 °C 0.2917 0.2899 0.2811 0.2776 0.2487
70 °C 0.2138 0.2121 0.2040 0.2008 0.1751
80 °C 0.1593 0.1576 0.1504 0.1477 0.1255
90 °C 0.1206 0.1189 0.1126 0.1102 0.09156
100 °C 0.09245 0.0909 0.08547 0.08346 0.06784
105 °C 0.08138 0.0799 0.07484 0.07298 0.05876
110 °C 0.07186 0.0704 0.06573 0.06402 0.05107
120 °C 0.05654 0.0552 0.05117 0.04971 0.03896
125 °C 0.05036 0.0491 0.04534 0.04400 0.03419
130 °C 0.04487 0.0438 0.04029 0.03905 0.03010
140 °C 0.03619 0.0351 0.03209 0.03100 0.02352
150 °C 0.02953 0.0284 0.02577 0.02485 0.01859
TABLE 3 Equivalent Temperature Tolerances for Different Class
When tested in accordance with 7.2, the zero-power resistance
Sensors (See 4.1 and 4.4)
versus temperature relationship for interchangeable parts shall
Accuracy Temperature
comply to within the tolerance specified in Table 3. The
Class Tolerance, °C
manufacturerofthesensorshall,fornon-interchangeableparts,
1 ±0.02
supply this relationship with each part shipped. This relation-
2 ±0.03
shipmaybesuppliedintheformofdatatables,orbyproviding
3 ±0.05
4 ±0.1
the constants for one or more of the following thermistor
5 ±0.2
equations, or both.
6 ±0.5
Equations representing this relationship use the standard
curve fitting technique of considering the natural logarithm of
the zero-power resistance to be a polynomial in reciprocal
zero-power resistance measurements be performed only after
temperature, or vice versa. Although the polynomial equation
any such modifications have taken place. Examples of such
can be of any higher order, historically it has been shown that
terminations shall include (but are not limited to) phone plugs;
athirdorderpolynomial(Eq2and3)providesexcellentresults
stereo plugs; multiple pin DIN type plugs; multiple pin
over the relatively narrow temperature ranges of thermistor
“Deutsches Institut für Normung” (DIN) circular connectors;
sensor applications. Furthermore, Steinhart and Hart have
or, gold-plated terminals.
proven in oceanographic research studies over the range of
–2 °C to +30 °C that satisfactory results are obtained when the
5. Requirements
squared term is omitted (Eq 4 and 5).
5.1 Specifications—Sensors shall comply with the general
Eq4and5havethreeunknownconstantsthatarederivedby
requirements specified herein as well as with the applicable
the simultaneous solution of three equations based upon three
detailed specifications of Table 1, Table 2, and Fig. 2 through
calibration data points. Eq 2 and 3 have four unknown
Fig. 10. In the event of conflict between this requirement
constants and thus a minimum of four calibration data points
subsection and the detailed specification of Table 1, Table 2,
are required to solve for the constants. Frequently, more than
and Fig. 2 through Fig. 10, the latter shall govern.
four calibration data points are obtained and a polynomial
regression analysis is performed to derive the constants for
5.2 Zero-Power Resistance Versus Temperature
equations Eq 2 and 3. This has the benefit of statistically
Relationship—The zero-power resistance versus temperature
improving the accuracy of the data.
relationship shall be presented in a form such that any
temperature within the specified operating temperature range
can be obtained from that relationship and have an uncertainty
Steinhart, J.S., and Hart, S.R., “Calibration Curves forThermistors,” Deep Sea
no greater than one-tenth the specified tolerance in Table 3. Research, Vol 15, No. 497, 1968.
E879−20
FIG. 1 Thermistor Sensor Type Designation Code
FIG. 2Silicone Rubber Coated Glass Probe (Type S)
2 3
lnR 5 A 1 A ⁄ T 1 A ⁄ T 1 A ⁄ T (2) 5.3 Thermal Requirements:
@ #
T 0 1 2 3
2 3
5.3.1 Dissipation Constant—When tested in accordance
1⁄T 5 a 1a ln R 1a ln R 1a ln R (3)
~ ! ~ ! ~ !
0 1 T 2 T 3 T
with 7.3, the dissipation constant shall be as specified in the
lnR 5 @B 1 B ⁄ T 1 B ⁄ T # (4)
T 0 1 3
detailed specification.
1⁄T 5 b 1b ln R 1b ln R (5)
~ ! ~ !
0 1 T 3 T
5.3.2 Response Time—When tested in accordance with 7.4,
theresponsetimeortimeconstant,orboth,shallbeasspecified
where:
in the detailed specification.
A,a = unique constants derived from calibrations per-
n n
formed at four or more specified data points,
5.4 Environmental Requirements:
B,b = unique constants derived from calibrations per-
n n 5.4.1 Operating Temperature Range—The operating tem-
formed at three specified data points,
peraturerangeshallbeasspecifiedinthetypedesignationcode
T = is the absolute temperature in kelvins, and
(see 4.1 and 4.3).
R = is the zero-power resistance at temperature T.
T
5.4.2 StorageTemperatureRange—Sensorsshallbecapable
5.2.1 Accuracy—The resistance-temperature relationship, of meeting all requirements specified herein as well as those
provided in Table 2, or with the sensor, or both, shall not differ listed in the applicable detailed specification after storage at
from that obtained from measurements made in accordance any temperature (or combination thereof) in the range
with7.2bymorethanthetolerancesspecifiedinTable3forthe from–50 °C minimum (or the design limit for minimum
applicable intervals specified in Table 1. When additional exposure temperature, whichever is higher) up to 60 °C
temperature intervals are specified within the operating tem- maximum (or the design limit for maximum exposure
perature range, the accuracy class for each interval shall be temperature,whicheverislower)foraperiodof1year.Sensors
clearly indicated by the manufacturer. subjected to operation or storage at temperatures that exceed
E879−20
FIG. 3Epoxy Coated Glass Probe (Type E)
FIG. 4General Purpose Four-wire Sensor in Stainless Steel Housing (Type G)
their design limits may experience mechanical damage, de- greater than 10% of the tolerance shown in Table 3 for the
graded stability, or both, as well as unreliable performance. accuracy class specified.
5.4.3 Humidity Requirement—Sensors shall be capable of
5.5.2 Long-term Stability (120 days)—When tested in ac-
being operated or stored at relative humidity from 0 to 95%
cordance with 7.5.2, the equivalent temperature shift shall be
without condensation.
no greater than 25% of the tolerance shown in Table 3 for the
5.5 Stability:
accuracy class specified.
5.5.1 Short-term Stability (10 days)—When tested in accor-
dance with 7.5.1, the equivalent temperature shift shall be no
E879−20
FIG. 5General Purpose Two-wire Sensor in Stainless Steel Housing (Type H)
FIG. 6Interchangeable Sensor Enclosed in 1.2 mm Vinyl Tube (Type V)
5.6 Low-temperature Storage—When tested in accordance 5.8 Insulation Resistance:
with7.6,thereshallbenoevidenceofmechanicaldamageand
5.8.1 Dry Test—Thisrequirementshallapplytosensorsthat
the sensor shall comply with the accuracy requirements of 5.2.
have exposed metallic surfaces, but are not designed for
immersion in conductive fluids. When tested in accordance
5.7 Thermal Shock—When tested in accordance with 7.7,
with 7.8.1, there shall be no evidence of mechanical damage
there shall be no evidence of mechanical damage and the
sensor shall comply with the accuracy requirements of 5.2. and the insulation resistance shall be sufficiently high that its
E879−20
FIG. 7Non-Interchangeable Sensor Enclosed in 0.9 mm Vinyl Tube
FIG. 8Interchangeable Sensor with Flexible Cable and Sealed Plastic Tip (Type P)
shunting effect will not prevent the unit from complying with 6. Quality Assurance Provisions
the accuracy requirement of Table 3. In no case shall the
6.1 General—The methods of examination and tests con-
insulation resistance be less than 10 Ω.
tainedinSection7aretobeusedtodeterminetheconformance
5.8.2 Wet Test—This requirement shall apply to sensors that
of sensors to the requirements of this specification. Each
are designed for use in conductive solutions. When tested in
manufacturer or distributor who represents his products as
accordance with 7.8.2, there shall be no evidence of mechani-
conforming to this specification may, as agreed upon between
cal damage and the insulation resistance shall be sufficiently
the purchaser and seller, use statistically based sampling plans
high that its shunting effect will not prevent the unit from that are appropriate for each inspection lot. Records shall be
complying with the accuracy requirement of Table 3.Inno
kept as necessary to document the claim that all of the
case shall the insulation resistance be less than 10 Ω. requirementsofthisspecificationaremet.Thetestsspecifiedin
E879−20
FIG. 9Interchangeable Sensor In Stainless Steel Housing (Type J)
FIG. 10Interchangeable Sensor In Stainless Steel Housing With Pipe Fitting (Type K)
TABLE 4 Letter Symbol Designation of Operating Temperature
Ranges (See 4.1 and 4.3)
Operating Temperature
Letter Symbol
Range
−10 °C to 105 °C A
−10 °C to 60 °C B
0°Cto60°C C
0°Cto70°C D
0°Cto100°C E
–50 °C to 50 °C F
E879−20
TABLE 6 Manufacturing Screening Tests
this section are intended as minimum requirements.Additional
sampling and testing of the product, as may be agreed upon Examination Requirement Test Method
or Test Section Section
between the purchaser and the seller, are not precluded by this
Visual and mechanical 5.1 7.1
section.
Zero-power resistance versus 5.2 7.2
temperature relationship
6.2 Classification of Inspection:
Insulation resistance 5.8 7.8
6.2.1 Qualification Tests—Qualification tests shall be per-
formed for each basic design manufactured in accordance with
this specification. The sample size required for the tests
conducted shall be in accordance with Table 5. In order for a
Standards and Technology (NIST) using suitable reference
design to qualify, there shall be no failures resulting from any
standards with documentation.
of the tests.
7.2.1.1 Measurement System Uncertainties—Uncertainties
6.2.2 Responsibility for Qualification Testing—The manu-
existinallmeasurementsandthesemustbeproperlyevaluated
facturer shall perform qualification testing, at least once, for
in order to have confidence in the measurement results. An
eachbasicdesignforwhichthisspecificationapplies.Ifabasic
uncertainty budget is an analysis tool that should be used
designincorporatesmorethanoneresistancevalueofaspecific
before the zero-power measurements are taken in order to
materialformulationoraparticularstyleofthermistor,orboth,
determine if the measurement system is capable of achieving
different resistance values may be combined for the qualifica-
the desired results. The uncertainty budget will identify the
tion sample. The highest and lowest resistance values for a
sources of uncertainty and their individual contributions to the
specified thermistor design (type, material formulation, and
overall uncertainty of the measurement system. The result of
geometry) must be included in the qualification sample. Quali-
theanalysisisacombinedexpandeduncertainty,symbolU,for
fication testing, by the manufacturer, must be repeated when-
the measurement system. Typically, U is given at a coverage
ever a design change which may affect the performance of the
factor of 2, approximating to a 95 % confidence level. For the
sensor with regard to Section 5 of this specification is intro-
purpose of performing the zero-power resistance-versus-
duced.
temperature measurements herein, it is recommended that the
6.2.3 Manufacturing Screening Tests—During manufacture,
resulting combined expanded uncertainty for the measurement
all parts produced in accordance with this specification shall
system in use should not exceed 25 % of the allowable
receive 100% testing for compliance with the requirements of
tolerance for the accuracy class of the sensor to be tested.This
Table 6.
provides a desired test uncertainty ratio, TUR, of 4:1 and thus
there is a reasonable degree of confidence in the measurement
7. Methods of Examination and Test
data. Refer to Appendix X2 for a more in-depth discussion of
7.1 Visual and Mechanical Examination—Examine sensors
the concepts and sources of measurement uncertainty, as well
to verify that their design, construction, physical dimensions,
as examples. Also refer to ANSI/NCSL Z540.3 for additional
markings, and workmanship comply with the detailed specifi-
guidance on requirements for calibration of measuring and test
cation.
equipment.
7.2 Zero-power Resistance versus Temperature
7.2.2 Temperature-controlled Medium:
7,8,9
Relationship:
7.2.2.1 Comparison Baths—Make all zero-power resistance
7.2.1 Traceability—All measurements shall be traceable to
versus temperature relationship measurements in a
theInternationalSystemofUnits(SI)throughaNational4,5,6.
temperature-controlled liquid bath (such as a water bath). The
Metrology Institute (NMI) such as the National Institute of
volume of the liquid should be at least 1000 times the volume
ofthesensor(s)undertest,butshallnotbelessthan1L.Baths
having volumes as large as 100 L have been found to be
Mangum,B.W.,“PlatinumResistanceThermometerCalibration,” NBS Special
convenient to use and to be satisfactory with respect to
Publication 250-22, 1987.
temperature control. Ensure that the bath medium is suffi-
Mangum, B. W., and Furukawa, G. T., “Guidelines for Realizing the Interna-
ciently well-stirred so that temperature gradients are small
tional Temperature Scale of 1990 (ITS-90),” NIST Technical Note 1265, 1990.
Riddle, J. L., Furukawa, G. T., and Plumb, H. H., “Platinum Resistance
compared with the temperature accuracy required. Survey the
Thermometry,” NBS Monograph 126, 1973.
bath with a thermometer to ensure that its temperature is
uniform and stable to the extent necessary to perform the tests.
TABLE 5 Qualification Tests Required for Each Basic Design
For further information refer to Guide E2488 which describes
Requirement Method
methods to define the working space of a bath and to evaluate
Examination or Test Sample Size
Section(s) Section(s)
the temperature uniformity and stability within this space.
Visual and mechanical 5.1 7.1 10
Ideally, the working space will be as close as possible to
Zero-power resistance versus 5.2 7.2 10
temperature relationship isothermal.Ifneeded,athermalintegratingblock(equalization
Dissipation constant 5.3.1 7.3 5
block) can be utilized to enhance performance and thus
Response time 5.3.2 7.4 5
minimize the uncertainty contributed by the comparison bath.
Short-term stability 5.5.1 7.5.1 10
Long-term stability 5.5.2 7.5.2 10 7.2.2.2 Fixed-point temperatures—Iftheoperatingtempera-
Low-temperature storage 5.6 7.6 10
ture range of the thermistor sensor includes the ice-point
Thermal shock 5.7 7.7 10
temperature, the water triple-point temperature, or the gallium
Insulation resistance 5.8 7.8 10
melting-point temperature, then an ice-point bath, a water
E879−20
triple-pointcell,oragalliummelting-pointcellmaybeusedas to this type of sensor must not exceed 14.4 µW (one fifth the
the temperature-controlled medium at that respective tempera- product of the dissipation constant and the temperature toler-
ture. Refer to Practice E563 and Guides E1502 and E1750 for ance requirement of Table 3). If the measurement system uses
additional guidance and information on the use of fixed-point an instrument that applies a constant current, then the worst
temperatures. case condition will occur when the thermistor resistance is at
its maximum (29 320 Ω at 0 °C). In this case, the maximum
7.2.3 Temperature Monitoring and Control—While per-
value of the applied current may not exceed 2.2 µA. If the
forming the zero-power resistance versus temperature
measurementsystemusesaninstrumentthatappliesaconstant
measurements,observethetemperaturefluctuationsofthebath
voltage, then the worst case condition will occur when the
withacheckstandardthermometerhavingaresponsetimethat
thermistor resistance is at its minimum value (2811 Ω at
is shorter than or equal to that of the unit under test. The total
60 °C). In this case, the maximum value of the applied voltage
uncertainty resulting from the combined uncertainties of the
may not exceed 200 mV.
check standard thermometer and the bath temperature (due to
temperaturefluctuationsandbathgradientswithintheworking
7.3 Dissipation Constant—Determine the dissipation con-
volume) shall comply with the desired TUR of 4:1.
stant in water unless another fluid is specified. As determined
7.2.4 Resistance Measurement: Evaluate the contributions
here, the dissipation constant is for the specific environment
to overall system uncertainty for all test instruments used to
described in 7.3.1. Measurements made with the sensor in air,
performthezero-powerresistancemeasurementstoensurethat
oil, still water, etc. will yield different values.
the total uncertainty complies with the desired TUR of 4:1 for
7.3.1 Mount the sensor in a fluid bath that is controlled at
the specific accuracy class as specified in Table 3.
some temperature, T, in the range from 24 °C to 38 °C. The
i
7.2.5 Test Procedure: fluid specified for the bath shall have a velocity of no less than
7.2.5.1 Temperature Stabilization—After inserting the sen- 1 m/s and its volume shall be no less than 1000 times the
volume of the sensor. Determine the zero-power resistance, R,
sor into the bath, allow enough time for the sensor and bath to
i
come to equilibrium (see 7.2.3). from measurements made in accordance with 7.2.
7.3.2 Increase the measuring current (or voltage) until the
7.2.5.2 Immersion—Bestresultswillbeobtainedwhenmea-
sensor indicates a resistance R , equivalent to that at a
surements are made with the sensor totally immersed. The i+10
temperature of T , a temperature which is 10 °C higher
manufacturer shall specify the minimum immersion length
i+10
than that of the initial temperature T.
required to obtain the specified tolerance within the tempera- i
7.3.3 Measure the sensor current (or voltage) to within an
ture range permitted. (See Table 3.)
uncertainty of 61% and compute the dissipation constant
7.2.5.3 Zero-power Resistance:
from Eq 6:
(a) Sensors Designed for Operating Temperature Ranges
2 2
With Code Letter Symbols B, C, or D—Determine the zero-
δ 5 ∆P⁄∆T 5 I · R ⁄10 5 E ⁄ 10 · R (6)
~ i 1 10 ! ~ i 1 10 !
~ ! ~ !
power resistance of the sensor at 0 °C 6 0.3 °C, 30 °C 6 0.3
where:
°C, and 60 °C 6 0.5 °C.
δ = dissipation constant,
(b) Sensors Designed or Operating Temperature Ranges
∆ = change in applied power,
With Code Letter Symbols A or E—Determine the zero-power
∆ = resulting change in thermistor temperature,
resistance of the sensor at 0 °C 6 0.3 °C, 30 °C 6 0.3 °C,
I = measured current,
60 °C 6 0.5 °C, and 105 °C 6 1.0 °C.
E = measured voltage, and
(c) Sensors Designed for Operating Temperature Range
R = resistance of thermistor at a temperature 10 °C
(i+ 10)
With Code Letter Symbol F—Determine the zero-power resis-
above the initial temperature, T.
I
tance of the sensor at –20 °C 6 1.0 °C, 0 °C 6 0.3 °C, 30 °C
7.4 Response Time—Determine the response time in water
6 0.3 °C, and 50 °C 6 0.5 °C.
unless another fluid is specified. As determined here, the
7.2.5.3.1 Discussion—While performing the zero-power re-
response time is for the specific environment described in
sistance measurements at any of the specified calibration
7.4.2. Measurements made with the sensor in air, oil, still
temperatures above, verify that the applied power level to the
water, etc. will yield different values.
unit under test (UUT) does not exceed the zero-power resis-
7.4.1 Connect the sensor to an instrument that continuously
tance criterion as described in 3.2.7 (Discussion).
records the sensor output signal. It is desirable that the
Example—A thermistor sensor with ASTM specification
recorded signal be linearly related to temperature. See Appen-
numberE879G2B2Nistobemeasuredpertherequirementsof
dix X3 for information on the design of a thermistor voltage
7.2.5.3(a). This thermistor sensor is defined by type designa-
divider circuit that provides a linear output signal.
tion “G2” (10 000 Ω nominal at 25 °C with a curve ratio value
7.4.2 Mount the sensor in a plunger-type fixture above a
of 22.06); an operating temperature range “B” (–10 °C to 60
°C); an accuracy class “2” (60.02 °C), and a minimum fluid bath having a minimum volume of 1000 times the sensor
volume and a temperature somewhere in the range from
dissipation constant of 3.6 mW/K. Using the nominal resis-
tance as well as the ratio values of Table 2, we can determine 0.01 °C to 5 °C that is constant during the time of measure-
ment. The fluid specified for the bath shall have a velocity of
the UUT resistance will be approximately 29 320, 8215, and
2811 Ωatthespecifiedcalibrationtemperaturesof0°C,30°C, no less than 1 m/s.
and 60 °C respectively. To meet the zero-power resistance 7.4.3 Allowthesensortocometoequilibriuminairatroom
criterion for these measurements the maximum applied power temperature in the range of 20 °C to 25 °C.
E879−20
7.4.4 Plunge the sensor into the bath to the immersion point 7.5.2.4 Compute the fractional change in zero-power
specified in 7.2.5.2. The transit time between the start of the resistance, ∆R /R .
tm tm
plunge and the submerged rest position of the sensor shall be
7.5.2.5 Compute the equivalent temperature shift in accor-
determined to be less than 3% of the 95% thermal response dance with 7.5.3.
time obtained in 7.4.5.
7.5.3 Computation of Equivalent Temperature Shift—
Although it may not always be valid for evaluation purposes,
7.4.5 Observetherecordinganddeterminethetimerequired
for the sensor to change from the initial to the final sensor theassumptionismadethatthestabilityofathermistormaybe
characterized by a fractional change in its zero-power
temperature. Determine the 95% and 63.2% response times
and calculate their ratio. If the ratio lies between 3.0 and 3.7, resistance, which is dependent on time and maximum storage
thenthesensormaybeassumedtoexhibitasingleexponential temperature but independent of the temperature at which the
change is evaluated.
responseandthe63.2%responsetimemaybeconsideredtobe
the time constant of the sensor. If the ratio is greater than 3.7,
7.5.3.1 Sensors That Include 37 °C Within Their Operating
the63.2%responsetimeshallnotbeusedasthetimeconstant Ranges—Compute the equivalent temperature shift at 37 °C
and the total response curve should be considered.
from Eq 7:
∆T 5 @R ~∆ R ⁄ R !#⁄5~R 2 R ! (7)
7.5 Stability: 37 Tm Tm 36.9 37.1
7.5.1 Short-term Stability:
7.5.3.2 Sensors That Do Not Include 37 °C Within Their
7.5.1.1 Class 1 and Class 2 Sensors—Measurements in a
Operating Ranges—Compute the equivalent temperature shift
Triple Point of Water Cell (as described in NBS Monograph from Eq 8 at a temperature, ts, which is the operating
126)oraGalliumMeltingPointStandard(NationalInstituteof
temperature closest to 37 °C.
Standards and Technology SRM 1968 or commercially avail-
∆T 5 R R ⁄ R ⁄5 R 2 R (8)
@ ~ ! ~ !#
Ts Tm Tm Ts20.1 Ts10.1
ableequivalent)arerequiredfortestingtheshort-termstability
7.6 Low-temperature Storage:
of Class 1 and Class 2 sensors. The use of either of these
7.6.1 Determine the zero-power resistance versus tempera-
fixed-point cells is optional for Class 3, 4, 5, and 6 sensors.
ture relationship in accordance with 7.2. If the results of a
ReferenceGuidesE1502andE1750foradditionalinformation
previous set of measurements made within 500 h of the
on the use of these fixed-point cells.
low-temperature exposure exist, then this step may be elimi-
(a)Determine the zero-power resistance, R , in one of the
tm
nated.
above mentioned cells at a measurement temperature, tm.
7.6.2 Place the sensor in a chamber (whose volume and
(b)Store the sensor, with no power applied, at its maxi-
massareatleast1000timesthevolumeandmassofthesensor)
mum rated temperature for a minimum period of ten days.
at room temperature.
(c)Repeat Step (a) at the same temperature.
7.6.3 Reduce the chamber temperature until the chamber is
(d)Compute ∆R /R .
tm tm
controlled at−65 6 5 °C. Allow the sensor to remain at this
(e)Computetheequivalenttemperatureshiftinaccordance
temperature for a period of 6 h 6 15 min.
with 7.5.3.
7.6.4 Remove the sensor from the chamber and allow it to
7.5.1.2 Class3,4,5,and6Sensors—Theuseofeitheranice
stabilize at room temperature for not less than one hour.
bath (see Practice E563 for preparation of ice bath) or a
7.6.5 Determine the zero-power resistance versus tempera-
temperature-controlledbathisoptionalfortestingClass3,4,5,
ture relationship in accordance with 7.2 and verify that it
and 6 sensors.
complies with the accuracy requirement of Table 1.
(a)Determine the zero-power resistance of the sensor in
accordancewith7.2attheicepointorsometemperatureinthe 7.6.6 Examine the sensor for evidence of mechanical dam-
range from 23 °C to 38 °C. age.
(b)Store the sensor, with no power applied, at its maxi-
7.7 Thermal Shock:
mum rated temperature for a minimum period of ten days.
7.7.1 Determine the zero-power resistance versus tempera-
(c)Repeat step (a) at the same temperature.
ture relationship in accordance with 7.2 to ascertain if the
(d)Compute ∆R /R .
tm tm
sensor complies with 5.2.1. This step may be omitted if the
(e)Computetheequivalenttemperatureshiftinaccordance
results of a previous set of measurements were made within
with 7.5.3.
500 h of the thermal shock exposure.
7.5.2 Long-term Stability:
7.7.2 Plungethesensorintoanicebathandallowittocome
7.5.2.1 Determinethezero-powerresistanceofthesensorin
to equilibrium. Leave the sensor in the bath for a period of not
accordance with 7.2 at a measurement temperature, tm, corre-
less than ten times the thermal time constant.
spondingtotheicepoint,triplepointofwater,galliummelting
7.7.3 Remove the sensor from the bath and allow at least
point (see 7.5.1), or some temperature in the range from 23 °C
15 min for it to come to equilibrium at room temperature.
to 38 °C.
7.7.4 Plunge the sensor into a water bath set to control at
7.5.2.2 Store the sensor, with no power applied, at its
55 °C to 60 °C for sensors with operating temperature range
maximum rated temperature for a minimum period of
code letter symbol B, C, D, or F; or set to control at 95 °C to
120 days.
100°Cforsensorswithoperatingtemperaturerangecodeletter
7.5.2.3 Repeat the step outlined in 7.5.2.1 at the same symbol A or E. Allow a period of not less than ten times the
temperature. thermal time constant for the sensor to reach equilibrium.
E879−20
7.7.5 Remove the sensor from the bath and allow at least (c)DeterminethevalueofT ,correspondingtothevalueof
s
15 min for it to come to equilibrium at room temperature. R computedfromEq9,usingthezero-powerresistanceversus
s
temperature relationship for the sensor.
7.7.6 Repeat Steps 7.7.2 – 7.7.5 for a total of five cycles.
(d)Verify that the absolute value of T − T does not
s L
7.7.7 Examine the sensor for evidence of mechanical dam-
exceed the tolerance specified in Table 3 for the accuracy class
age.
specified in Table 1.
7.7.8 Determine the zero-power resistance versus tempera-
7.8.2 Wet Test—Perform this test on sensors that are de-
ture relationship in accordance with 7.2 and verify that it
signed for immersion in a conductive solution.
complies with the accuracy requirement of Table 1.
7.8.2.1 Immerse the sensor in a saturated water solution of
7.8 Insulation Resistance:
sodium chloride for a period of not less than 24 h. The
7.8.1 Dry Test—Perform this test on sensors that have
immersion depth shall be the same as that used in 7.2.
exposed metallic surfaces but are not designed for immersion
7.8.2.2 While the sensor is immersed, connect its leads
in a conductive solution.
together and measure the insulation resistance between the
7.8.1.1 The insulation resistance shall be measured by sensor leads and the solution with 100 V dc applied, unless
applying 100 V dc between the insulated leads connected otherwise specified in the detail specification.
7.8.2.3 Repeat Step 7.8.2.2 with the polarity reversed.
together and the exposed metallic surface of the sensor.
7.8.2.4 Examine the sensors for evidence of mechanical
7.8.1.2 Repeat Step 7.8.1.1 with the polarity reversed.
damage.
7.8.1.3 Examine the sensor for evidence of mechanical
7.8.2.5 Verify that the measured value of insulation resis-
damage.
tance is greater than 10 Ω.
7.8.1.4 Verify that the measured value of insulation resis-
7.8.2.6 Using the zero-power resistance versus temperature
tance is greater than 10 Ω.
relationship specified or provided with the sensor,
7.8.1.5 Using the zero power resistance versus temperature
(a)Determine the zero-power resistance at the lowest
relationship specified or provided with the sensor,
temperature specified in Table 1.
(a)Determine the zero-power resistance at the lowest
(b)Determine the value of zero-power resistance resulting
temperature specified in Table 1.
from the shunting effect of the insulation resistanc
...