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Transcript of Therm is Tor Design Guide
8/2/2019 Therm is Tor Design Guide
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Ntc thermistor DesiGN GUiDeF O R D I S C R E T E C O M P O N E N T S & P R O B E S
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OUR MISSION: Troug tamwork, to aciv industr’s confidnc as t
igst quait producr of tmpratur snsors in t word.
i NDUstrY ’ s PArtNer iN QUAL i tY AND PerFormANce ™
Ntc thermistor DesiGN GUiDe For DiscretecomPoNeNts & Probes
What is a thermistor? ..........................................................................................3
How to use a thermistor .....................................................................................5
Wh use a thermistor? ........................................................................................6
How do I use a Thermistor? ...............................................................................7How much resistance do I need? .....................................................................8
What’s a curve and which curve do I choose? .............................................9
What is Therma Time Constant? (Mi-PRF 23648) ..................................10
What is Therma Dissipation Constant? .......................................................11
What is Se Heating? ........................................................................................11
How do I design a probe? .................................................................................12
Insuation Properties ..........................................................................................13
Conversion Tabes ................................................................................................14
Frequent Asked Questions .............................................................................15
New Products .......................................................................................................16
How sma can ou make a part? ...................................................................17
sPeciAL serVices .........................................................18
Since 1977, Quait Thermistor, Inc. has designed and manuactured PTC and NTC thermistors
o superior quait. Miions o QTI TM Brand thermistor temperature probes have been used or
mission critica appications rom deep beow the oceans’ surace to the outer reaches o space.
Our state-o-the-art manuacturing aciit ocated in Boise, Idaho combined with our high-voume
assemb pant in Mexico ensure no project is to sma or arge or us to accommodate.
This NTC thermistor design guide has been thoughtu prepared to address some o the most common
temperature reated questions acing design engineers. I ou have additiona questions, pease ee ree
to contact us. We woud be happ to work with ou on our appication.
CONTENTS
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An NTC thermistor is a semiconductor made rom metaic
oxides, pressed into a sma bead, disk, waer, or other shape,
sintered at high temperatures, and then coated with epox or
gass. The resuting device exhibits an eectrica resistance that
has a ver predictabe change with temperature.
Thermistors are wide used or temperature monitoring, contro
and compensation. The are extreme sensitive to temperature
change, ver accurate and interchangeabe. The have a wide
temperature enveope and can be hermetica seaed or use in
humid environments.
The term “thermistor” originated rom the descriptor therma
sensitive Resistor. The two basic tpes o thermistors are the
Negative Temperature Coeicient (NTC) and Positive TemperatureCoeicient (PTC).
Thermistors are avaiabe as surace mount or radia and axia
eaded packages. The eaded parts can then be either over
moded or housed in a variet o shapes and materias.
Athough this design guide ocuses on NTC (Negative
Temperature Coeicient), thermistors are aso avaiabe in
Positive Temperature Coeicients.
··
Pronunciation: ther--ter, thur-u-sterOrigin: 1935–40Function: nounEtmoog: a res
An electrical resistor whose resistance varies
rapidly and predictably with temperature and
as a result can be used to measure temperature.
TheRMISTOR STyleS
Aia ladd (PTC)
RTh42
RTh22 PTC
QTG12 PTC
OTG10 PTC
Surfac Mount
1206
0805 NTC & PTC0603
0402
NTC Radia ladd
QTMC
QTlC
Bar Di
QTC11 NTC
QTC11 PTC
WHAT IS A THERMISTOR?
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Thermistor From Wikipedia, the ree enccopedia
A thermistor is a tpe o resistor used to measure temperature
changes, reing on the change in its resistance with chang-
ing temperature. The Thermistor was irst invented b Samue
Ruben in 1930, and has U.S. Patent #2,021,491.
I we assume that the reationship between resistance and
temperature is inear (i.e. we make a irst-order approximation),
then we can sa that:
∆R = k∆T
Where
∆R = change in resistance t
∆T = change in temperature
k = irst-order temperature coeicient o resistance
Thermistors can be cassiied into two tpes depending on the
sign o k. I k is positive, the resistance increases with increas-
ing temperature, and the device is caed a positive temperature
coeicient (PTC) thermistor. I k is negative, the resistance
decreases with increasing temperature, and the device is caed a
negative temperature coeicient (NTC) thermistor. Resistors that
are not thermistors are designed to have the smaest possibe
k, so that their resistance remains amost constant over a wide
temperature range.
sna ha quanIn practice, the inear approximation (above) works on over a
sma temperature range. For accurate temperature measure-
ments, the resistance/temperature curve o the device must be
described in more detai. The Steinhart-Hart equation is a wide
used third-order approximation:
where a, b and c are caed the Steinhart-Hart parameters, and
must be speciied or each device. T is the temperature in Kevin
and R is the resistance in ohms. To give resistance as a unction
o temperature, the above can be rearranged into:
where and
The error in the Steinhart-Hart equation is genera ess than
0.02°C in the measurement o temperature. As an exampe, tpi-
ca vaues or a thermistor with a resistance o 3000Ω
at roomtemperature (25°C = 298.15 K) are:
a =1.40 x 10-3
b =2.37 x 10-4
c =9.90 x 10-8
cndun dlMan NTC thermistors are made rom a pressed disc or cast chip
o a semiconductor such as a sintered meta oxide. The work
because raising the temperature o a semiconductor increases
the number o eectrons abe to move about and carr charge
- it promotes them into the conducting band. The more charge
carriers that are avaiabe, the more current a materia can con-
duct. This is described in the ormua:
I = n • A • v • e
I = eectric current (ampere)
n = densit o charge carriers (count/m3)
A = cross-sectiona area o the materia (m2)
v = veocit o charge carriers (m/s)
e = charge o an eectron
The current is measured using an ammeter. Over arge changes
in temperature, caibration is necessar. Over sma changes in
temperature, i the right semiconductor is used, the resistance
o the materia is inear proportiona to the temperature. There
are man dierent semiconducting thermistors and their rangegoes rom about 0.01 Kevin to 2,000 Kevins (-273.14°C to
1,700°C). QTI range -55 to 300ºC.
Most PTC thermistors are o the "switching" tpe, which means
that their resistance rises sudden at a certain critica tempera-
ture. The devices are made o a doped pocrstaine ceramic
containing barium titanate (BaTiO3) and other compounds. QTI
manuactures siicon based PTC thermistors that are .7%/ºC.
Thermistor Symbol
WHAT IS A THERMISTOR?
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HOW TO USE A THERMISTOR
The NTC thermistor is best suited or precision temperature mea-surement. The PTC is best suited or temperature compensation.
The NTC thermistor is used in three dierent modes o operation,
which services a variet o appications.
ran-Vu-tpau md - B ar the
most prevaent. These circuits perorm precision temperature
measurement, contro and compensation. Unike the other appi-
cations this method depends on the thermistor being operated in
a “zero-power” condition. This condition impies that there is no
se-heating.
The resistance across the sensor is reative high in comparison
to an RTD eement, which is usua in the hundreds o ohmsrange. Tpica, the 25°C rating or thermistors is rom 10Ω up
to 10,000,000Ω. The housing o the thermistor varies as the
requirements or a hermetic sea and ruggedness, but in most
cases, there are on two wires going to the eement. This is pos-
sibe because o the resistance o the wire over temperature is
considerab ower than the thermistor eement. And tpica
does not require compensation because o the overa resistance.
cun-ov-t md – This depends on the dissipa-
tion constant o the thermistor package as we as eement’s
heat capacit. As current is appied to a thermistor, the package
wi begin to se-heat. I the current is continuous, the resis-
tance o the thermistor wi start to essen. The thermistor cur-rent-time characteristics can be used to sow down the aects
o a high votage spike, which coud be or a short duration. In
this manner, a time dea rom the thermistor is used to prevent
ase triggering o reas.
This tpe o time response is reative ast as compared to
diodes or siicon based temperature sensors. In contrast, ther-
mocoupes and RTD’s are equa as ast as the thermistor, but
the don’t have the equivaent high eve outputs.
Vlag-Vu-cun md - Votage-versus-current
appications use one or more thermistors that are operated in a
se-heated condition. An exampe o this woud be a ow meter.The thermistor woud be in an ambient se-heated condition.
The thermistor’s resistance is changed b the amount o heat
generated b the power dissipated b the eement. An change
in the media (gas/iquid) across the device changes the power
dissipation actor o the thermistor. The sma size o the therm-
istor aows or this tpe o appication to be impemented with
minima intererence to the sstem.
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rlun - larg cang in rsistanc for a sma
cang in tmpratur
Another advantage o the thermistor is its reative high resis-
tance. Thermistors are avaiabe with base resistances (at 25°
C) ranging rom tens to miions o ohms. This high resistance
reduces the eect o resistance in the ead wires, which can
cause signiicant errors with ow resistance devices such as
RTD’s. An exampe o this is the traditiona RTD, which tpica
requires 3-wire or 4-wire connections to reduce errors, caused
b ead wire resistance; 2-wire connections to thermistors are
usua adequate.
The thermistor has been used primari or high-resoution mea-surements over imited temperature ranges (-55° to 150°C). The
cassic exampe o this woud be a medica appication where
the user is on concerned with bod temperature. However,
widespread improvements in thermistor stabiit, accurac, and
interchangeabiit have prompted increased usage o thermistors
in a tpes o industries.
cThermistors are b ar the most economica choice when it
comes to temperature sensors. Not on are the ess expensive
to purchase, but aso there are no caibration costs during insta-
ation or during the service ie o the sensor. In addition, i
there is a aiure in the ied, interchangeabe thermistors can beswapped out without caibration.
spdDue to their sma size, thermistors can respond ver quick to
sight changes in temperature. Caution must be taken when
designing probes because materias and mass pa an important
roe in the reaction time o the sensor. See section on “Therma
Time Constant” and “How do I design a probe?” or urther
detais.
N calan rqudProper manuactured thermistors are aged to reduce drit
beore eaving the actor. Thereore, thermistors can provide astabe resistance output over ong periods o time.
WHy USE A THERMISTOR?
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HOW DO I USE A THERMISTOR?
wa an y “inangaly”
“cuv akng”?A thermistor can be deined as having an interchangeabiit
toerance o ±0.1°C over the range rom 0° to 70°C. This means
that a points between 0° and 70°C, are within 0.1°C o the
nomina resistance vaues or that particuar thermistor curve.
This eature resuts in temperature measurements accurate to
±0.1°C no matter how man dierent thermistors are substi-
tuted in the appication.
wa an y ‘”Pn mad”?
A standard thermistor is caibrated and tested at 25°C to a toer-
ance o ± 1%, 2%, 5% or ± 10%. Since these thermistors on
have one controed point o reerence or ‘point matched’ tem-
perature, the resistance at other temperatures are given b the"Resistance vs. Temperature Conversion Tabes" or the appropri-
ate materia curve. The resistance vaue at an temperature is
the ratio actor times the resistance at 25°C.
In addition to the industr
standard o point matching
thermistors at 25°C, Quait
Thermistor can point match
to a speciic temperature
range. Exampes o this
woud be the reezing point
o water (0°C) or human
bod temperature (37°C).
AVAiLAbLe iNterchANGeAbLe toLerANces
0Cº to +70ºC
A3 = +/- 1ºC
B3 = +/- 0.5ºC
C3 = +/- 0.2ºC
D3 = +/- 0.1ºC
-20Cº to +50ºC
A2 = +/- 1ºC
B2 = +/- 0.5ºC
C2 = +/- 0.2ºC
0Cº to 100ºC
A4 = +/- 1°C
B4 = +/- 0.5°C
C4 = +/- 0.2°C
+20Cº to +90ºC
A5 = +/- 1ºC
B5 = +/- 0.5ºC
C5 = +/- 0.2ºC
+20Cº to +50ºC
A6 = +/- 1ºC
B6 = +/- 0.5ºC
C6 = +/- 0.2ºC
D6 = +/- 0.1ºC
Closed end tube with
flange, ideal for
rivet mounting.
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HOW MUCH RESISTANCE DO I NEED?
With an NTC thermistor, resistance decreases as the temperature
rises. One main actor in determining how much resistance ou
need at 25°C is to cacuate how much resistance ou wi have at
our critica temperature range.
I the tota wire resistance is a substantia percentage o the
resistance change at our critica temperature range, ou shoud
consider increasing our base resistance at 25°C.
Determine i the resistance change at our critica temperature is
arge enough to compensate or an other errors in our sstems
design. I not, ou shoud increase our base resistance at 25°C.
exAMPle –1,000 Ω curv Z trmistor at 25°C
Btwn –29°C and –28° C, tr is a rsistanc cang of
990 oms. Btwn 118° and 119° C, tr is on a rsistanc
cang of 1.1 oms.
Resitance R/T@25ºC Part# Curve
500 QTMC-1 Z
2,250 -7 Z
2,500 -8 Z
3,000 -9 Z
5,000 -11 Z
10,000 -14 Z
20,000 -19 Z
1,000 -27 y
2,000 -28 y
100,000 -43 V
Resitance R/T@25ºC Part# Curve
1 Meg -65 P
9.8 Meg -70 R
100 -78 X
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WHAT’S A CURVE AND WHICH CURVE DO I CHOOSE?
I ou reca our deinition o a thermistor (An eectrica resistor
making use o a semiconductor whose resistance varies sharp
in a ver predictabe manner with temperature.) We can use the
Stein-Hart Hart equation to predict how the thermistor reacts
to temperature. I we pot these points on a graph, it orms a
repeatabe curve. Thermistor manuacturers can ater the chem-
istr o a thermistor, thereb changing the sope o a curve.
your curve seection shoud be based on how steep the curve is
or our critica temperature range, size constraints and the
target resistance vaue. Since a thermistor is based on buk
resistivit, the size o the sensor m not be easibe or ourappication. Unike the RTD and Thermocoupes, thermistors do
not have industr standards or their curves. However, most
thermistor manuacturers have curves that are simiar. An
exampe o this is Quait Thermistors ‘Z’ curve it’s b ar the
most common curve in the industr and most major thermistor
manuacturers have a ver simiar curve oerings.
Curve ZCurve W
Curve X
Curve Y
Curve V
Curve S
Curve M
Curve R
4
R M u l t i p l i e r
Temperature (ºC )
3
2
1
0
0 10 20 30 40 50 60 70
RESISTANCE VAlUE IS AlSO A FUNCTION OF CURVE
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THERMAl TIME CONSTANT
The therma time constant is the time required or a thermis-
tor to change to 63.2 percent o the tota dierence between
its initia and ina bod temperature when subjected to a step
unction change in temperature under zero power conditions.
The United States Department o Deense has a ver speciic
method or measuring the therma time response o a thermistor
(see Mi Spec 23648)
Pace thermistors in a sti air controed chamber (chamber tem-
perature: 25°C ±1°C) with a minimum voume o 1,000 times the
thermistor bod and test ixture.
4 Se heat the thermistor to 75°C. Aow 15 minutes (max-
imum) or stabiization o thermistors.
4 Prepare to measure time rom the instant the power is
cut to the time the bridge indicator passes through the
nu point (43.4°C)
4 Record this time: This is the time constant o the thermis-
tor is register a 63.3% change in temperature.
ta’ g, DD span al pn
a a an a a 32° ang!
Some thermistor manuacturers choose to use a 50°C change.
Be sure and consut the product speciications when making a
comparison.
THERMAl CONDUCTIVITy
Heat moves through a materia at a speciic rate. The rate it
traves depends on the materia itse: some materias aow
heat to move quick through them, some materias aow heat
to move ver sow through them. Beow is a ist o dierent
materias and how the conduct heat.
mAteriAL thermAL coNDUctiVitY (w/m K)
Siver - Best 429
Copper (pure) 401
God 317
Auminum (pure) 237
Brass (70Cu-30Zn) 110
Titanium 21.9
316 Stainess Stee 13.4
PEEK pastic 1.75
Therma Conductive Epox 1.25
UHMW pastic 0.42
ba ng a p aal ad lly n
nduvy. cn an, , ng and
analy a all ky a.
WHAT IS THERMAl TIME CONTANT? (Mi-PRF 23648 & Mi-PRF 32192)
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WHAT IS THERMAl DISSIPATION CONSTANT?
WHAT IS SElF HEATING?
THERMAl DISSIPATION CONSTANT
The therma dissipation constant o a thermistor is the power
required to raise the thermistors bod temperature b 1°C. The
dissipation constant is expressed in units o mW/°C (miiWatts
per degree Centigrade).
Dissipation Constant can be aected b:
4 Mass o the thermistor probe
4 How the probe and sensor are mounted
4 Therma dnamics o the environment
The dissipation constant is an important actor in appica-
tions that are based on the se-heating eect o thermistors.
Speciica, the change in resistance o the thermistor due to
change in dissipation constant can be used to monitor eves or
ow rates o iquids or gasses. As an exampe as the ow rate
increases, the dissipation constant o the thermistor in a uid
path wi increase and the resistance wi change and can be
correated to the ow rate.
Stated another wa, the dissipation constant is a measure o
the therma connection o the thermistor to its surroundings. It
is genera given or the thermistor in sti air, but sometimes in
we-stirred oi.
SElF-HEATING EFFECTS
When current ows through a thermistor, it generates heat,
which raises the temperature o the thermistor above that o its
environment. This o course wi cause an error in measurement
i not compensated or. Tpica, the smaer the thermistor, the
ower the amount o current needed to se-heat.
The eectrica power input to the thermistor is just
P E = IV
where I is current and V is the votage drop across the thermis-
tor. This power is converted to heat, and this heat energ is
transerred to the surrounding environment. The rate o transeris we described b Newton's aw o cooing:
P T = K (T (R) - T 0)
where T(R) is the temperature o the thermistor as a unction o
its resistance R, T0 is the temperature o the surroundings, and
K is the dissipation constant, usua expressed in units o mi-
iwatts per °C. At equiibrium, the two rates must be equa.
P E = P T
The current and votage across the thermistor wi depend on
the particuar circuit coniguration. As a simpe exampe, i the
votage across the thermistor is hed ixed, then b Ohm's law
we have I = V / R and the equiibrium equation can be soved or
the ambient temperature as a unction o the measured resis-
tance o the thermistor:
T 0 = T (R) -
The dissipation constant is a measure o the therma connection
o the thermistor to its surroundings. It is genera given or
the thermistor in sti air, and in we-stirred oi. Tpica vaues
or a sma gass bead thermistor are 1.5 mw/°C in sti air and
6.0 mw/°C in stirred oi. I the temperature o the environ-
ment is known beorehand, then a thermistor ma be used to
measure the vaue o the dissipation constant. For exampe, the
thermistor ma be used as a ow rate sensor, since the dissipa-
tion constant increases with the rate o ow o a uid past the
thermistor.
V 2
KR
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Another probem with seecting materia based on therma con-
ductivit aone is that i the mass o high conductive probe
housing can actua act ike a heat sink and pu additiona heat
out o the sstem. This can obvious create measuring inac-
curacies.
To oset this, ou can combine dierent materias whie design-
ing our probe. A ow therma conductive housing with a
sma high conductive probe tip is a good soution.
In some cases, our appication ma require a sow therma timeresponse. An exampe o this woud be an outdoor sign that dis-
pas the temperature. A arge over moded probe wi insuate
the thermistor and even out quick uctuations in temperature
changes.
CONFINED SPACE
Due to a thermistors miniature
size, the can be potted intoamost an size housing. Current,
the smaest avaiabe thermistor
is 0.023” max diameter. Hoow-
tube rivets, set screws, hpodermic
needes and direct epox attach are
some common methods or con-
ined space thermistor appications.
lIQUID
For iquid appications, it’s best
to use a threaded probe. Possib,
with some tpe o eastomeric seaike an o-ring. QTI aso oers a
compete ine o NPT probe hous-
ings. Some appications require
over moding the thermistor into
the pastic housing o the product.
Another option is to use a gass
encapsuated bead. It provides a
hermetic sea that is as cose to
‘waterproo’ as Mother Nature wi
et us. Remember the Titanic?
GAS/AIR
Gas and air appications have a
variet o choices. Probes can
be surace mounted in the ow
stream or the can be projected
into the air stream b means o a
cosed or open-end tube. When
measuring gas or air under pres-
sure, we recommend using some
tpe o thread/o-ring combination.
SURFACE
B ar the most common method
or surace measurement is thering ug. Due to the sma size o
the thermistor eement, it can be
potted into most ring ug barres.
Be careu that the wire gauge
does not exceed the inside dimen-
sion o the barre. Another option
or surace measurement is direct
attachment o a thermistor using a
stainess stee disc.
HOW DO I DESIGN A PROBE?
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WIRE INSUlATION PROPERTIES
hala- PVc- tfn- Ply- tzl thermAL PVc e-ctFe myla Kyna PFA suln FeP Kapn tFe etFe
Maximum ContinousRating (Cº) 105 135 105 135 260 150 200 200 260 150
low Temperature (Cº) -50 -100 -60 -70 -200 -100 -200 -200 -200 -100
Non-Fammabiit Ver Good Exceent Ver Good Exceent Exceent Good Exceent Exceent Exceent Exceent
Soder Resistant Good Ver Good Ver Good Ver Good Ver Good Ver Good Exceent Exceent Exceent Exceent
Smoke Moderate Sight Moderate Sight None Moderate None None None Sight
hala- PVc- tfn- Ply- tzl eLectricAL PVc e-ctFe myla Kyna PFA suln FeP Kapn tFe etFe
Voume Resistivit
(ohm-cm) 1012 1013 1016 2x1014 1018 5x1016 2x1018 1018 1012 1016
Dieectric Strength (1 mi fm)
VPM, 1/8” thick 350 490 350 450 430 400 430 420 430 400
Dieectric Constant 5.70 2.60 3.50 7.70 2.06 3.13 2.00 2.40 2.00 2.60
Dissipation Factor
(1 kHz) .09 .002 .03 .02 .0002 .001 0.4 .001 .0002 .0008
Capacitive Frequenc
Stabiit Fair Exceent Good Poor Exceent Good Exceent Exceent Exceent Exceent
hala- PVc- tfn- Ply- tzl mechANicAL PVc e-ctFe myla Kyna PFA suln FeP Kapn tFe etFe
1.68 (67%Densit (gm/cc) 1.36 1.68 1.48 1.76 2.15 1.24 2.18 poimide) 2.20 1.70
Tensie, psi 4,000 7,000 15,000 6,000 4,000 10,000 2,700 17,000 2,500 6,500
Eongation, % 250 200 50 250 300 100 250 75 225 100-400
Abrasion Resistance Fair Fair Good Exceent Good Exceent Good Exceent Good ExceentCut-through Resistance Good Good Exceent Exceent Fair Exceent Fair Exceent Fair Exceent
Bondabiit Good Good Good Good Good Exceent Good
hala- PVc- tfn- Ply- tzl eNViroNmeNtAL PVc e-ctFe myla Kyna PFA suln FeP Kapn tFe etFe
100 200 approx.100Nucear Radiation Fair megarads Fair Exceent Fair Good Fair megarads Fair megarads
UV Radiation Fair Exceent Fair Exceent Exceent Fair Exceent Exceent Exceent Exceent
hala- PVc- tfn- Ply- tzl
chemicAL PVc e-ctFe myla Kyna PFA suln FeP Kapn tFe etFe Water Absorbtion 0.7% .01% .06% .04% .03% .05% .01% .8% .01% .1%
Acids Good Exceent Good Ver Good Exceent Good Exceent Fair Exceent Exceent
Akai Good Exceent Poor Ver Good Exceent Good Exceent Fair Exceent Exceent
Acoho Fair Exceent Fair Ver Good Exceent Fair Exceent Ver Good Exceent Exceent
Ceaning Sovents Sight
(tri-chor, carbon, tetr) Swe Exceent Good Ver Good Exceent Crazes Exceent Ver Good Exceent Exceent
Aiphatic Hdrocarbons Sight
(gasoine, kersosene) Swe Exceent Fair Ver Good Exceent Good Exceent Ver Good Exceent Exceent
Aromatic Hdrocarbons Sight
(benzene, touene) Swe Exceent Fair Ver Good Exceent Crazes Exceent Ver Good Exceent Exceent
long Term Stabiit Fair Exceent Good Ver Good Exceent Ver Good Exceent Exceent Exceent Exceent
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CONVERSION TABlES
eQUiVALeNt tAbLes Dal/n/
sandad sud tnalsud sz Da hl Da.U.s. () in. () in. ()
#2 .0866 .090M2 (2.18) (2.29)
#4 .112 .118(M2,5) (2.84) (3.00)
#5 .125 .127(M3) (3.18) (3.23)
#6 .138 .146(M3,5) (3.51) (3.71)
#8 .164 .173(M4) (4.17) (4.39)
#10 .190 .198(M5) (4.83) (5.03)
1/4” .250 .270(M6) (6.35) (6.86)
5/16” .312 .330(M8) (7.92) (8.38)
3/8” .375 .385(M10) (9.53) (9.78)
1/2” .500 .520(M12) (12,7) (13.21)
5/8” .625 .650(M16) (15.88) (16.51)
3/4” .750 .810(M18) (19.05) (20.57)
Da Da o p osz in 1000 p k
20 AWG 0.032 0.813 10.15 33.29
21 AWG 0.029 0.724 12.80 41.98
22 AWG 0.025 0.645 16.14 52.94
23 AWG 0.023 0.574 20.36 66.78
24 AWG 0.020 0.511 25.67 84.20
25 AWG 0.018 0.455 32.37 106.17
26 AWG 0.016 0.404 40.81 133.86
27 AWG 0.014 0.361 51.47 168.82
28 AWG 0.013 0.320 64.90 212.87
29 AWG 0.011 0.287 81.83 268.40
30 AWG 0.010 0.254 103.20 338.50
31 AWG 0.009 0.226 130.10 426.73
32 AWG 0.008 0.203 164.10 538.25
33 AWG 0.007 0.180 206.90 678.63
34 AWG 0.006 0.160 260.90 855.75
35 AWG 0.006 0.142 329.00 1,079.12
36 AWG 0.005 0.127 414.80 1,360.00
37 AWG 0.005 0.114 523.10 1,715.00
38 AWG 0.004 0.102 659.60 2,163.00
2.0 mm 0.008 0.203 169.39 555.61
1.8 mm 0.007 0.178 207.50 680.55
1.6 mm 0.006 0.152 260.90 855.75
1.4 mm 0.006 0.152 339.00 1,114.00
1.25 mm 0.005 0.127 428.20 1,404.00
1.12 mm 0.004 0.102 533.80 1,750.00
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FREQUENTly ASKED QUESTIONS
How does aging affect thermistor stability?“Thermometric drit” is a speciic tpe o drit in which the
drit is the same amount o temperature at a temperatures o exposure. For exampe, a thermistor that exhibits a -0.02°C shit
at 0°, 40° and 70°C (even though this is a dierent percentage
change in resistance in each case) woud be exhibiting thermo-
metric drit. Thermometric drit: (1) occurs over time at varing
rates, based on thermistor tpe and exposure temperature, and
(2) as a genera rue, increases as the exposure temperature
increases. Most drit is thermometric.
How do thermistors fail?
SIlVER MIGRATION
This aiure can occur when one or more o the oowing
three conditions are present: constant direct current bias, high
humidit, and eectrotes (disc/chip contamination). Moisture
inds its wa into the thermistor and reacts with the contami-
nant. Siver (on the thermistor eectrodes) turns to soution,
and the direct current bias stimuates siver crsta growth
across the thermistor eement. The thermistor resistance
decreases, eventua reaching zero O (short) (probab the
most common aiure mechanism).
MICRO CRACKS
Thermistors can crack due to improper potting materias i a
temperature change causes potting materia to contract, crush-ing the thermistor. The resut is a thermistor that has erratic
resistance readings and is eectrica “nois.”
FRACTURE OF GlASS ENVElOPE
Tpica caused b mishanding o thermistor eads, this aiure
mechanism induces ractures in the gass coating at the ead/
thermistor interace. These cracks ma propagate around the
thermistor bead resuting in a catastrophic upward shit in
resistance. Mismatching o epoxies or other bonding materias
ma aso cause this. Careu handing and the proper seection
o potting materias can eiminate this aiure.
AGING OUT OF RESISTIVE TOlERANCE
I thermistors are exposed to high temperatures over time,
sometimes reerred to as “aging,” their resistivit can change.Genera the change is an upward change in resistivit, which
resuts in a downward change in temperature. Seecting the
proper thermistor or the temperature range being measured
can minimize the occurrence o this aiure. Temperature
ccing ma be thought o as a orm o aging. It is the cumua-
tive exposure to high temperature that has the greatest inu-
ence on a thermistor component, not the actua temperature
ccing. Temperature ccing can induce shits i the compo-
nent has been buit into an assemb with epoxies or adhesives,
which do not match the temperature expansion characteristics
o the thermistor.
What happens if my application exceeds thetemperature rating?
Intermittent temperature incursions above and beow the oper-
ating range wi not aect ong-term survivabiit. Encapsuate
epox tpica begins to break down at 150°C and the soder
attaching eads to the thermistor bod tpica reows at about
180°C. Either condition coud resut in aiure o the thermistor.
Are thermistors ESD sensitive?
Per MIl-DTl-39032E, Tabe 1, thermistors b deinition are not
ESD sensitive.
What is the resolution of a thermistor?
There is no imit to the resoution o a thermistor. The imitationsare in the eectronics needed to measure to a speciied resou-
tion. limitations aso exist in determining the accurac o the
measurement at a speciied resoution.
Are QTI thermistors RoHS compliant?
(What i I don’t want a ead ree part?)
Quait Thermistor maintains two separate manuacturing ines
to meet the speciic environmenta needs o our customers. One
ine is dedicated to RoHS compiance and the other is main-
tained or traditiona tin/ead parts or miitar, aerospace and
medica appications.
Does the ength o wire impact the accuraco a thermistor?With a thermistor, ou have the beneit o choosing a higher
base resistance i the wire resistance is a substantia percentage
o the tota resistance. An exampe o this woud be a 100-ohm
thermistor vs a 50,000 ohm thermistor with 10’ o 24 AWG wire.
Tota wire resistance = 10’ x 2 wires x 0.02567 ohms per oot =
0.5134 ohms
The amount of drift over a period of time is dependent on the aging
temperature. Please note that not all thermistor manufactures age at
the same temperature so drift data may be different. This chart shows
typical drift when parts were aged at 125°C.
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N t c t h e r m i s t o r D e s i G N G U i D e
Quait Thermistor, Inc. a eader in thermistor innovation
is peased to announce the Therma Bridge. The Therma
Bridge incorporates a bridge resistor with the thermistor
providing a more inear signa or conditioning. B incorporating
a bridge resistor with a thermistor in a singe precision assem-
b, temperature sensing is impemented without the need or
caibration, potentionmeters, precision externa components and
with no concern or cocking and bus issues.
Temperature is determined b a ratio o the
input versus output votage across the sensor
aowing inexpensive and precise tempera-
ture measurement capabiit or near anMicroprocessor based
sstem. With wide avaiabe embedded
mixed signa processors and A-D converters,
Design Engineers can easi condition the
non-inear signa o NTC thermistors.
FEATURES AND BENEFITS OF USING THE
THERMAl BRIDGE:
•Operatingtemperaturerangeof-55
to 150ºC
•Accuracyupto+/-.2ºC
rom 0–70ºC
– Up to +/-1ºC rom -55 to 100ºC
– Up to +/-1.5ºC rom -55 to 150ºC
•Availableinmanyprobeconfigurationsorasacircuit
board mounted component
•Highstabilitywithnocalibrationrequired
•Longsensorlife-span
•Dynamicresponseforeaseofmeasurement
•Wideoperatingvoltagerange,upto48VDC
•Monolithicthermistorsensorexhibitsnegligible
capacitance and inductance
•Noerrorintroducedduetonoise,andrandomnoise
se-cances
•Lowpowerconsumption,170uWmaximum
-55
20
0
40
60
80
100
-45 -35 -25 -15 -5 5 15 25 35 45 55 65 75 85 95 105 115 125
V o u t ( % V i n ) C
NEW PRODUCTS
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HOW SMAll CAN yOU MAKE A THERMISTOR?
Part Number Bead Dia. Resistance Toerance
QT06002-524 .023" 10,000 +/- 0.1ºC (0ºC to 70º)
QT06002-525 .023" 10,000 +/- 0.2ºC (0ºC to 70º)
NANo tUbe 0.023" mAx oD epox fed poimide tube with insuated #38 AWGsoid nicke eads, parae bonded, 6" (76.2 mm)
Part Number Bead Dia. Resistance
QTMB-14 .038" 10,000
QTMB16 .038" 15,000
miNi beAD 0.038" mAx oD epox coated bead with #34 AWGPo-non insuated bifar eads, twisted pair, 6" (152.4 mm). Toerance+/- 0.2ºC (0ºC to 70º)
c o N F i N e D s P A c e t h e r m i s t o r s & t e m P e r A t U r e P r o b e s
• Exceptiona ast therma response time•Suitableforsmallertemperatureprobehousings
•Customandsemi-customproductsmaybespecied
•Availableinpointmatchedandinterchangeabletolerances
Part Number Bead Dia. Resistance
QT06002-529 .031" 2,252
QT06002-530 .031" 3,000
QT06002-531 .031" 5,000
QT06002-532 .031" 10,000
micro tUbe 0.031" mAx oD epox fed poimide tubewith pourethane non insuated #32 AWG soid copper eads, twistedpair, 6" (152.4mm). Toerance +/- 0.2º (0ºC to 70º)
Part Number Bead Dia. Resistance
QT06002-526 .037" 2,252
QT06002-533 .037" 3,000
QT06002-527 .037" 5,000
QT06002-528 .037" 10,000
miNi tUbe 0.037" mAx oD epox fed poimide tube withpourethane non insuated #32 AWG soid copper eads, twisted pair, 6"(152.4mm). Toerance +/- 0.2º (0ºC to 70º)
ReSISTANCe
Temp(ºC) 2,252 3,000 5,000 10,000
0 7,355 9,798 16,330 32,6605 5,720 7,620 12,700 25,400
10 4,481 5,970 9,950 19,900
15 3,538 4,713 7,855 15,710
20 2,813 3,747 6,245 12,490
25 2,252 3,000 5,000 10,000
30 1,815 2,417 4,029 8,058
35 1,471 1,960 3,266 6,532
40 1,199 1,598 2,663 5,326
45 984 1,310 2,184 4,368
50 811 1,081 1,801 3,602
55 672 896 1,493 2,986
60 560 746 1,244 2,488
65 469 625 1,041 2,082
66 453 603 1,005 2,010
67 437 582 971 1,941
68 422 563 938 1,875
69 408 544 906 1,812
70 394 525 876 1,751
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Qualified Test Lab
To ensure the quait o our QTI
brand thermistors, Quait
Thermistor has an extensive test
ab or a wide range o testing
services. In addition, this aciit is avaiabe or customers or
the oowing services:
•Powerburn-in
•Temperaturecycling
•Moisturetesting
•Shockandvibrationtesting
•Temperaturecharacterization
•Space-levelscreening
•QCIMilitarytesting
Custom Design
With a u sta o experienced temperature appication
engineers, Quait Thermistor can provide custom design services
at an step aong the design process. Experts in temperature
measurement, compensation, and contro, Quait Thermistor
engineers can work with our in-house engineers or contractors,
or as a u-support design team to sove our appication.
•Components
•Probes
•Boards
•Systems
•Controlandsignal
conditioning
Private Labeling
The QTI brand is recognized in man industries or high-quait
manuacturing and measurement accurac and reiabiit.
However, in situations where private abeing is required, Quait
Thermistor wi provide components with no abe or with our
abe to ensure the integrit o our branding strateg.
•Yourdesign,yourlabel
•Ourdesign,yourlabel
•Yourdesign,theQTIlabel
Assembly
Quait Thermistor oers expert, time component and board
assemb services in our we-equipped Tecate, Mexico, aciit.
In addition, to ensure product is deivered on time, the aciit’s
capabiit is mirrored at our Idaho pant.
•Highly-trainedassemblers
•High-volumeproduction
•Competitiveprices
•Probeassembly
•PTCandNTCdevices
SPECIAl SERVICES
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For more information on QualityThermistor, Inc., or on QTI brandthermistors, probes, and engineeringservices, contact Technical Support.
Quait Thermistor, Inc.2108 Centur Wa
Boise, ID 83709
www.thermistor.com
800-554-4784 U.S.208-377-3373 Wordwide208-376-4754 [email protected]
QTI, leach Guard, and Hdroguard are
trademarks o Quait Thermistor, Inc.