TEMPERATURE SENSOR EXPERTS - Quality Thermistor Inc.

temperature 

sensor 

experts 

THERMISTOR PROBES 

NTC THERMISTORS 

PTC THERMISTORS 

INSTRUMENTATION 

www.thermistor.com

Surface 

They have been used for many years to measure 

probes 

hat is an RTD 

sistance Temperature Detectors (RTDs) are 

mperature sensors that contain a resistor that 

anges resistance value as its temperature changes. 

ey have been used for many years to measure 

mperature in laboratory and industrial processes, 

d have developed a reputation for accuracy, 

peatability, and stability. 

What is an RTD 

Resistance Temperature Detectors (RTDs) are 

temperature sensors that contain a resistor that 

changes resistance value as its temperature changes. 

temperature in laboratory and industrial processes, 

and have developed a reputation for accuracy, 

repeatability, and stability. 

Custom solutions: 

ture Detectors (RTDs) are 

s that contain With a resistor QTI Probes that you have the flexiblilty of applying a 

value as its temperature changes. 

variety of sensor options with the housing of your choice. 

d for many years to measure 

ratory and industrial processes, 

a reputation for accuracy, 

ability. 

THERMISTOR USB HERMETICALLY SEALED SENSOR 

Flag ring lug probes 

n Available in a variety of sizes with or without insulation 

n Standard lug sizes #4 to #12 with additional styles available 

n Recommended wire sizes #24-28 AWG 

n Material: Tinned Copper or ni plated steel 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

ring lug probes 

n Available in a variety of sizes with or without insulation 

n Standard lug sizes #4 to #12 with additional styles available 


n Material: Tinned Copper or ni plated steel 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

. 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

flat disc probes 

n Versatile, multi-purpose surface sensor 

n Standard sizes are 0.33” and 0.21” 


n Can be overmolded 

n Material: Stainless Steel, Copper, Aluminum 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

MOlded Ring luG probes 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

n Ideal for high humidity environments 

n Operating Temp range: -40ºC - to 80ºC 

n Recommended wire sizes #22 AWG 

n Material: Molded Plastic 

. 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

Pipe mount probes 

100% 

n GUARANTEED Ideal for high humidity environments 

HERMETICALLY 

SEALED 




100% 

GUARANTEED 

HERMETICALLY 

SEALED 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

2 www.thermistor.com | Probes 

100% 

GUARANTEED

Waterproof 

Temperature 

sensor 

IP68 rated product 

QTI’s Hydroguard IP68 Series of parts combines a highly stable precision thermistor 

encapsulated with an extremely durable waterproof housing. The temperature sensor 

offers excellent performance during harsh freeze thaw cycles. The over molded probes 

are a great solution where waterproof and moisture resistance is critical. 

Features 

n Precision NTC Thermistor 

n Long term stability 

n Double insulated thermoplastic rubber 

n Ruggedized housing and corrosion resistant cable 

n Waterproof rating to IP68 

n Based on the most common curves in the industry 

Applications 

n Refrigeration and freezer applications 

n Air-conditioning 

n Under floor heating 

n Climate control systems 

n High humidity environments 

n Maximizing refrigerator equipment life 

temperature range 

cable 

resistance values @ 25ºC 

dielectric strength 

-55ºC to 105ºC (-67ºF to 221ºF) continuous 

Also avialable up to 150º C (302ºF) 

2’, 5’, 10’, 25’ (custom lengths available) 

#24 AWG stranded copper, VDE Approved 

Insulation Resistance 100MOhm at 1000 VDC 

Color coded wire available 

2.25k, 5k, 10k, 20k, 100k, Other values available. 

3750 VAC 

accuracy Point Matched: +/- 1%, 2%, 5% and 10% 

Interchangeable 0º-70ºC (32-158ºF): +/- 0.2ºC 

moisture resistance 

Meets or exceeds IP68 

Probes | www.thermistor.com 

3

Liquid 

probes 

Pipe & SAE Threaded Fitting with Tube 

n General purpose, rugged high pressure design 


n Material: Stainless Steel, Brass, Titanium 

n Straight thread option with or without O-rings. 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

Closed End Tube 

n 100% 

GUARANTEED 

Versatile, multi-purpose sensor 

HERMETICALLY 

n SEALED 

Standard sizes are 0.040” to .250” in diameter 


n Material: Stainless Steel, Brass, Titanium, Inconel, Hastelloy 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

Composite Probes 

n 100% Ideal for reducing thermal time response 

GUARANTEED 

HERMETICALLY 

n Materials: Brass or Stainless Steel with high temp plastic 

SEALED 

n Available with or without O-rings. 

n Wide selection of connectors and strain relief. 

n NPT or straight threads 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

Hex Nut Probes 

n 100% Available in a variety of sizes .060” to 0.50” 

GUARANTEED 

HERMETICALLY 

n General purpose, rugged high pressure design 

SEALED 


n Material: Stainless Steel, Brass, Titanium, Aluminum 

n Available with or without O-rings. 

n Available in Metric and reverse threads. 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

Inspection Probes 

n 100% Ideal for spot inspection 

GUARANTEED 

HERMETICALLY 

n Recommended wire/cable sizes #22-28 AWG 

SEALED 

n Material: Stainless Steel with plastic or metal handle 

n Available with straight or T handle 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

Fast Response-Stepped Housings 

n Available in a variety of sizes from .040” to 0.080” 

100% 

GUARANTEED 

HERMETICALLY 


SEALED 

n Material: Stainless Steel 

n Available with stepped housings 

n Food Grade Stainless Steel 

100% 

100% 

GUARANTEED 

GUARANTEED 

HERMETICALLY 

HERMETICALLY 

SEALED 

4 SEALED 

www.thermistor.com | Probes

Air-Gas 

probes 

rivet style probes 

n Available in a variety of sizes 

n Designed for harsh environments 

n Ideal for over molding 

n Material: Stainless Steel, Anodized Aluminum 

T0220 Style Probes 

n Ideal for heat sink surface temperature 

n Standard T0220 package size 

n Material: Thermoset Plastic 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

flanged, open tip 

n Available in a variety of sizes with or without brazed flange 

n Flange can be screwed or riveted in place 


n Material: Stainless Steel 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

polyimide tube 

n Versatile, multi-purpose sensor with high dielectric strength 

n Standard sizes are 0.040” and 0.136” in diameter 


n Material: Polyimide tube 

. 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

MOlded tube probes 

n Ideal for high humidity environments 




100% 

GUARANTEED 

HERMETICALLY 

SEALED 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 

100% 

GUARANTEED 

HERMETICALLY 

SEALED 


100% 

GUARANTEED 

HERMETICALLY 

5

how do I 

use a 

thermistor 

Closed end tube with flange, 

ideal for rivet mounting. 

What is meant by “Interchangeability” 

or “Curve tracking” 

A thermistor can be defined as having an interchangeability 

tolerance of ±0.1°C over the range from 0° to 

70°C. This means that all points between 0° and 70°C, 

are within 0.1°C of the nominal resistance values for 

that particular thermistor curve. This feature results 

in temperature measurements accurate to ±0.1°C no 

matter how many different thermistors are substituted 

in the application. 

What is meant by ‘”Point Matched” 

A standard thermistor is calibrated and tested at 25°C 

to a tolerance of ± 1%, 2%, 5% or 10%. Since these 

thermistors only have one controlled point of reference 

or ‘point matched’ temperature, the resistance 

at other temperatures are given by the "Resistance vs. 

Temperature Conversion Tables" for the appropriate 

material curve. The resistance value at any temperature 

is the ratio factor times the resistance at 25°C. 

In addition to the industry standard of point matching 

thermistors at 25°C, Quality Thermistor can point match 

to a specific temperature range. Examples of this would 

be the freezing point of water (0°C) or human body 

temperature (37°C). 

Available Interchangeable Tolerances 

-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 +50ºC 

A6 = +/- 1ºC 

B6 = +/- 0.5ºC 

C6 = +/- 0.2ºC 

D6 = +/- 0.1ºC 

0Cº to +70ºC 

A3 = +/- 1ºC 

B3 = +/- 0.5ºC 

C3 = +/- 0.2ºC 

D3 = +/- 0.1ºC 

+20Cº to +90ºC 

A5 = +/- 1ºC 

B5 = +/- 0.5ºC 

C5 = +/- 0.2ºC 

What is 

Thermal 

Dissipation 

Thermal Dissipation 

The thermal dissipation of a thermistor is the power 

required to raise the thermistor’s body temperature 

by 1°C. The dissipation is expressed in units of 

mW/°C (milliwatts per degree Celcius). 

Dissipation can be affected by: 

4 Mass of the thermistor probe 

4 How the probe and sensor are mounted 

4 Thermal dynamics of the environment 

The dissipation is an important factor in applications 

that are based on the self-heating effect of thermistors. 

Specifically, the change in resistance of the 

thermistor due to change in dissipation can be used 

to monitor levels or flow rates of liquids or gasses. 

As an example, as the flow rate increases, the dissipation 

of the thermistor in a fluid path will increase 

and the resistance will change and can be correlated 

to the flow rate. 

Stated another way, the dissipation is a measure of 

the thermal connection of the thermistor to its surroundings. 

It is generally given for the thermistor in 

still air, but sometimes in well-stirred oil. 

What is 

self-heating 

Self-heating effects 

When current flows through a thermistor, it generates 

heat, which raises the temperature of the thermistor 

above that of its environment. If this effect is not 

compensated, it will cause an error in measurement. 

Typically, the smaller the thermistor, the lower the 

amount of current needed to self-heat. 

The electrical power input to the thermistor is just 

PE = IV 

where I is current and V is the voltage drop across 

the thermistor. This power is converted to heat, and 

this heat energy is transferred to the surrounding 

environment. The rate of transfer is well described by 

Newton’s law of cooling: PT = K(T(R) - T0) 

where T(R) is the temperature of the thermistor as a 

function of its resistance R, T0 is the temperature of 

the surroundings, and K is the dissipation constant, 

usually expressed in units of milliwatts per °C. At 

equilibrium, the two rates must be equal. 

PE = PT 

The current and voltage across the thermistor will 

depend on the particular circuit configuration. As a 

simple example, if the voltage across the thermistor 

is held fixed, then by Ohm’s Law we have I = V / R 

and the equilibrium equation can be solved for the 

ambient temperature as a function of the measured 

resistance of the thermistor: 

V 2 

T0 = T(R) - 

KR 

The dissipation constant is a measure of the thermal 

connection of the thermistor to its surroundings. It is 

generally given for the thermistor in still air, and in 

well-stirred oil. Typical values for a small glass bead 

thermistor are 1.5 mw/°C in still air and 6.0 mw/°C 

in stirred oil. If the temperature of the environment 

is known beforehand, then a thermistor may be used 

to measure the value of the dissipation constant. For 

example, the thermistor may be used as a flow rate 

sensor, since the dissipation constant increases with 

the rate of flow of a fluid past the thermistor. 

6 www.thermistor.com | THERMISTORS

Available 

Tolerances 

Precision USB 

thermometer 

precision temperature 0.1º C: 0 ºC to 100 acquisition ºC or +/- 0.5°C (0-70°) system 

1.5º C: -55 ºC to 150 ºC 

n Accuracy +/- 0.1°C (0-100°C) or +/- 0.5°C (0-70°) 

n Custom probe and cable configuration 

n NIST Traceable - Certification available 

n Data logging and alert notification software included 

n Able to run multiple sensors 

Customizable USB Probe 

AVAILABLE 

TOLERANCES 

RESOLUTION 

RoHS COMPLIANT 

CURRENT DRAW 

+/- 0.5°C (0-70°C) 

+/- 0.1°C (0-100°C) 

+/- 0.05°C (0-70°C) 

0.01 ºC 

Yes 

< 100mA 

DirecTempº Software 

(HID configuration only) 

Available Interface Options 

HID Configuration 

(Plug & Play, DirecTempº Software Included) 

n Automatic driver installation in MS Windows 

n DirecTemp data logging software included for Windows 

n Stream data to a plot and record to file for future analysis 

n Compatible with Windows 2000 and newer 32 bit systems 

USB-Serial Configuration 

(Virtual Com Port, For OEM & Proprietary Software Applications) 

n Virtual serial device 

n Designed for integration with custom third party software applications 

n Free demo software & LabVIEW VI included 

n Communication protocol information available upon request 

n Compatible with Linux, Windows, and MacOS systems 

n Additional programming language examples available. 

*Windows 32 bit versions work with included DirecTempº software 

**User specified single point temperatures and tolerances available 

Warning: Do not use in human life support applications. 

This device is not designed nor intended to operate in situations where human injury will result in the event of a failure. 

THERMISTORS | www.thermistor.com 

7

NTC 

thermistor 

Elements 

Why QTI 

Brand 

www.thermistor.com 

The QTI brand temperature sensing probes found 

in this catalog use NTC thermistor technology. NTC 

thermistors are the most reliable, sensitive, and cost 

effective technology for temperature measurement 

& control. 

Experts in Thermistor Manufacturing: 

Quality Thermistor manufactures the ceramic based NTC 

thermistor elements used in our temperature probes. 

We assure our customers are receiving the most stable, 

accurate, and reliable sensors available. 

100% Final Testing: 

All of the temperature probes manufactured by Quality 

Thermistor are 100% inspected for accuracy in temperature 

controlled baths to ensure proper electrical 

and curve-fit tolerances. “Set-point” tolerances can be 

specified at any temperature between -55C & +200C. 

Calibration data is available as an option on all of the 

probes we manufacture. 

Attention to Detail: 

The proprietary manufacturing processes and materials 

used in manufacturing our temperature probes ensure 

proper sensor placement to optimize thermal time 

response. Closed-end Stainless Steel probe housings 

feature “rolled” ends which maintain the specified wall 

thickness throughout the entire enclosure. This optimizes 

thermal time response and minimizes the thermal 

load on the sensing element. 

design assistance: 

QTI is AS9100 and ISO 9001 registered. 

While we trust that the information provided within 

this design guide will assist you in the selection of the 

appropriate materials, there is no substitute for candid 

one-to-one dialog. We encourage you to contact the 

Quality Thermistor factory or field sales representative 

in your area to discuss specific design, sales or customer 

support needs. “Live” design assistance is also available 

Monday through Friday (8 am - 5 pm MST) at www. 

thermistor.com 

Why use a 

thermistor 

Resolution - Large change in resistance for a small 

change in temperature 

Another advantage of the thermistor is its relatively high 

resistance. Thermistors are available with base resistances 

(at 25° C) ranging from tens to millions of ohms. 

This high resistance reduces the effect of resistance in 

the lead wires, which can cause significant errors with 

low resistance devices such as RTD’s. An example of this 

is the traditional RTD, which typically requires 3-wire 

or 4-wire connections to reduce errors, caused by lead 

wire resistance; 2-wire connections to thermistors are 

usually adequate. 

The thermistor has been used primarily for high-resolution 

measurements over limited temperature ranges 

(-55° to 150°C). The classic example of this would be a 

medical application where the user is only concerned 

with body temperature. However, widespread improvements 

in thermistor stability, accuracy, and interchangeability 

have prompted increased usage of thermistors in 

all types of industries. 

Cost 

Thermistors are by far the most economical choice 

when it comes to temperature sensors. Not only are 

they less expensive to purchase, but also there are no 

calibration costs during installation or during the service 

life of the sensor. In addition, if there is a failure in the 

field, interchangeable thermistors can be swapped out 

without calibration. 

Speed 

Due to their small size, thermistors can respond very 

quickly to slight changes in temperature. Caution must 

be taken when designing probes because materials and 

mass play an important role in the reaction time of the 

sensor. See section on “Thermal Time Constant” and 

“How do I design a probe” for further details. 

No Calibration Required 

Properly manufactured thermistors are aged to reduce 

drift before leaving the factory. Therefore, thermistors 

can provide a stable resistance output over long periods 

of time. 


NTC 

thermistor 

Elements 

Epoxy Coated NTC Thermistors (QTMC, QTLC) 

n Available in a variety of wire types and lengths 


n Leads: Kynar, PVC, Teflon, Tin Plated Copper 

n Resistance values from 100 ohms to 9.8 M ohms 

n Typical dissipation Constant = 2mW/°C in still air 

n Typical time constant in still air = 10 seconds 

n Temp Range: -55°C to 155°C 

n RoHS compliant parts available 

glass beAd - qtgb 

n High Stability 

n Ideal for high temperature environments 

n Available as interchangeable or point matched 

n Hermetic, glass encapsulated bead 

n Operating temp range -55°C to 300°C 

n Dissipation Constant: .75mW/°C in still air 

n #36 AWG Platinum clad, Ni-Fe wires 

n Standard 10k and 30K ohms at 150°C 


high temperature glass beAd - qtgbht 

n High Stability 

n Ideal for high temperature environments 

n Available as interchangeable or point matched 

n Hermetic, glass encapsulated bead 


n Dissipation Constant: .75mW/°C in still air 

n #36 AWG Platinum clad, Ni-Fe wires 

n Standard 2252, 5000 and 10k ohms at 25°C 


Miniature Thermistors (QTUT, QTMB) 

n Available in 0.020” and 0.040” diameter 

n Operating Temp range: -55°C –to 125°C 


n Leads: Poly Nylon, Bi-Filar 

n Material: Epoxy coated or Polyimide tube 


n Typical time constant in still air = 1 second 



9

NTC SMD 

thermistor 

Elements 

ntc thermistor die (QTC11) 

n Part Size: 0.040” x 0.040” x 0.020” 

n Resistance values from: 100 ohms to 20 Mohms 

n Available with Gold or Silver terminations 

n Hybrid attachment (wire bond/epoxy) 

n RoHS compliant 

n Typical dissipation Constant = .0625W, derate to 0 at 125C 


n Tolerances: 1%, 2%, 5%, 10% 

qt0805 ntc series thermistors 

n Standard EIA 0805 package size 

n Resistance values from: 50 ohms to 10 Mohms 

n Available with Gold, pure tin or Tin/lead terminations 

n Typical dissipation Constant = 2 mW/°C in still air 

n Typical time constant in still air = 8 seconds max 

n Tolerances: 1%, 2%, 5%, 10% 

n Operating range: -65°C to 150°C 

n Power rating: 0.125 watts max 

n Available waffle packed or tape and reel 

n Available in K, X, T, Y, Z,P, S & V curves 

How Much Resistance Do I Need 

With an NTC thermistor, resistance decreases as the temperature rises. One main factor in 1determining = a + how b 1n much (R) resistance + c 1n you 3 (R) need at 25°C is to calculate 

how much resistance you will have at your critical temperature range. If the total wire resistance T is a substantial percentage of the resistance change at your 

critical temperature range, you should consider increasing your base resistance at 25°C. Determine if the resistance change at your critical temperature is 

large enough to compensate for any other errors in your systems design. If not, you should increase your base resistance at 25°C. 

T 

1 

EXAMPLE: 

ºc = – 273.15 

C+B (1n R) + C (1n R) 3 

 

1,000 ohm curve Z thermistor at 25°C Between –29°C and –28° C, there is a resistance change of 990 ohms. 

Between 118° and 119° C, there is only a resistance change of 1.1 ohms. 

What’s a Curve And Which Curve Do I Choose 

A thermistor is an electrical resistor whose resistance varies sharply in a very predictable 

manner with temperature. We can use the Stein-Hart Hart equation to predict how the 

thermistor reacts to temperature. 

If we plot these points on a graph, it forms a repeatable curve. Thermistor manufacturers can alter the chemistry of a thermistor, thereby changing the slope 

of a curve. Your curve selection should be based on how steep the curve is for your critical temperature range, size constraints and the target resistance value. 

Since a thermistor is based on bulk resistivity, the size of the sensor may not be feasible for your application. Unlike the RTD and thermocouples, thermistors do 

not have industry standards for their curves. However, most thermistor manufacturers have curves that are similar. An example of this is Quality Thermistor’s 

‘Z’ curve. It’s by far the most common curve in the industry and most major thermistor manufacturers have very similar curve offerings. 

Resistance vs. Temperature tables and calculators are available online at www.thermistor.com 


NTC Military and Space Level 

thermistor Elements 

RTH44 MIL-PRF-23648/20 

n Resistance values from 300 ohms to 500k ohms 


n Meets or exceeds MIL-PRF 23648 


n Tolerance: 1, 2, 5, 10% 

n Power rating: 0.2 watts @25°C max 

n Complete specifications can be obtained by contacting DSCC 

(Defense Supply Center, Columbus) 

RTH06 MIL-PRF-23648/1 



n Thermal time constant in still air or = 80 seconds max 

n Temp Range: -55°C to 125°C 





M32192/3 NTC Thermistor die 

n Resistance values from 15 ohms to 20 Mohms 

n Typical dissipation Constant = .625mW/°C in still air 

n Thermal time constant in still air = 10 seconds max 

n Power rating: 0.0625W, derate to 0 at 125 

n Available with a variety of termination finishes 



M32192/4 NTC EIA 0805 package 








M32192/5 NTC EIA 1206 package 

n M32192/5 NTC EIA 1206 PACKAGE 

n Thermal Time Constant: 8 seconds max in still air 

n *Dissipation Constant: 2 mW/°C min in still air 

n *Power Rating: 0.25 W at 25°C, derate to 0 W at 125°C 

n Resistance @25°C: 470 ohm to 10 Mohm 

n Operating temperature range: -55°C to 125°C 

n Storage temperature range: -65°C to 150°C 

n *Thermal Time Constant and Dissipation Constant may vary 

depending on mounting 

space level NASA GSFC S-311-P-827/01, 02, 03 & 04 

n Available in 50k and 100k ohms 

n Interchangeable tolerances to +/- 0.5°C (0-70°C) 

n Acceptable for use in NASA space programs specifying 

quality level (Grade) 1 parts 

n Available with Sn/Pb or Gold termination 

n Meets Level 1 classification per EEE-INST-002 

n Single lot traceability 

11

PTC Military 

thermistor 

Elements 

RTH22 MIL-PRF-23648/9 

n Positive Temperature Coefficient: 0.7%/°C 




n Tolerance: 5, 10% 

n Power rating: 0.5 watts @25°C 




RTH42 MIL-PRF-23648/19 





n Tolerance: 5, 10% 

n Power rating: 0.250 watts @25°C 




M32192/1 PTC Thermistor die 



n Typical dissipation Constant = 1.25mW/°C in still air 


n Power rating: 0.125W, derate to 0 at 125 



M32192/2 PTC EIA 0805 package 









PTC Space Level 

thermistor 

Elements 

space level NASA GSFC S-311-P-827/31, 32 




n Available with Sn/Pb or Gold termination 



space level NASA GSFC S-311-P-827/33,34 

n Resistance values from 75 ohms to1.5k ohms 





design engineers for high-reliablity military and aerospace markets are faced with challenges when given the assignment of redesigning legacy 

applications which have a high count of radial and axial leaded passive components, or generating a new design which needs to incorporate a high percentage of 

surface mount passive components. Quality Thermistor’s high reliablity surface mount thermistors are manufactured to meet or exceed the MIL-PRF-32192 military 

specification, as well as the newly introduced NASA-GSFC S-311-P-827 specifications. 

The Defense Supply Center Columbus (DSCC) 

introduced a new surface mount thermistor specification 

in November of 2006. MIL-PRF-32192 now gives 

the design Engineer fully qualified DSCC options for 

two PTC and three NTC surface mount package styles. 

MIL-PRF-32192/1 

Bare PTC thermistor die available in resistance values 

from 10 ohms to 10,000 ohms. This specification 

should be considered in new designs and for 

legacy designs which used either MIL-PRF-23648/9 

or MIL-PRF-23648/19. 

MIL-PRF-32192/2 

Basic EIA 0805 PTC surface mount package avaialble 

in resistance values from 22 ohms to 5,600 ohms. 

This specification should be considered for nw designs 

as well as an alternative to MIL-PRF-23648/9 

and MIL-PRF-23648/19. 

MIL-PRF-32192/3 

Bare NTC thermistor die avaialble in resitance values 

from 15 ohms to 20 Mohms. This is ideal for new 

board designs which contain other bare die, wire 

bondable components could easily integrate this 

part style. This specification should be considered 

for legacy replacements which usd either MIL- 

PRF-23648/1 or MIL-PRF-23648/20. 


MIL-PRF-32192/4 

Basic EIA 0805 NTC surface mount package. Any 

new high reliablilty application PCB design can 

take advantage of this part style. This specification 

should be considered for new designs as well as 

an alternative to MIL-PRF-23648/1 and MIL- 

PRF-23648/20. 

MIL-PRF-32192/5 

Basic EIA 1206 NTC surface mount package. Any 

new high reliability application PCB design can 

take advantage of this part style. This specification 

should be considered for new designs as well as 

an alternative to MIL-PRF-23648/1 and MIL- 

PRF-23648/20. 

GSFC approved thermistor specification 

S-311-P-827 gives the Aerospace engineers a costeffective 

option and more. 

As the Aerospace market continues to thrive and 

grow, the push for smaller, lighter, more accurate and 

reliable parts intensifies. While the new DSCC MIL- 

PRF-32192 Specification is sufficient for Defense/Military 

requirements, the Aerospace community requires 

additional screening to qualify parts for flight. 

Many customers have chosen to create their own 

SCD’s that incorporate all or part of the M32192 

specification but also added additional 100% screening 

requirements. This escalates customer costs internally 

and increases the unit cost due to a lack of standardization. 

To meet the demands of our Aerospace customers 

and help “standardize” the aerospace test regimen, 

Quality Thermistor engineers worked jointly with 

engineers at NASA/GSFC to create a GSFC approved 

SMD thermistor specification. This new specification, 

S-311-P-827, incorporates PTC thermistors (both EIA 

0805 and hybrid 0303 die) and NTC thermistors (EIA 

0805). All devices procured to this specification will 

meet the requirements for Level I classification per 

EEE-INST-002. 

There are two NTC thermistors currently listed in 

the specification. These parts are availble in “interchangeable” 

tolerances of either ± 0.5C or ± 1.0C 

over the range of 0C to 70C. The PTC thermistors are 

all available in 1% or 2% tolerances at the reference 

temperature of 25ºC. 

For more information, contact the engineering 

staff at Quality Thermistor, or see the link below for 

the complete specification on the NASA NEPP website: 

nepp.nasa.gov. 

13

PTC 

thermistor 

Elements 

PTC Thermistor Die (QTC11) 

n Part Size: 0.032” x 0.032” square 

n Part thickness: 0.028”, 0.050” or 0.072” 

n Resistance values from: 10 ohms to 10k ohms 

n Gold terminations 

n Board attachment by either wire bonding or conductive epoxy. 

n RoHS compliant 



n Tolerances: 1%, 2%, 5%, 10% 



QT0805 PTC Series Thermistors 

n Standard EIA 0805 package size 


n Available with Gold or Silver terminations 



n Tolerances: 1%, 2%, 5%, 10% 


n Power rating: 0.250 watts @ 25C derated to 100C (table 1) 

n Available waffle packed or tape and reel 


Glass Axial PTC Thermistors (QTG12, QTG10) 

n Standard DO35 package size 



n Tolerances: 1%, 2%, 5%, 10% 


n Power rating: 0.125 watts @ 100C (table 1) 

n Available loose or tape and reel 

n RoHS compliant available 

n Commercial version of RTH42 (MIL-PRF 23648) 


TABLE 1 Power Derating Curve 

% Rated Power 

100 

80 

60 

40 

20 

0 

0 25 50 75 85 100 125 150 

Temperature (°C) 

14 www.thermistor.com | FREQUENTLY ASKED QUESTIONS

how do I design a probe 

Another problem with selecting material based 

on thermal conductivity alone is that the mass of 

the highly conductive probe housing can actually 

act like a heat sink and pull additional heat out of 

the system. This can obviously create measuring 

inaccuracies. 

To offset this, you can combine different materials 

while designing your probe. A low thermally 

conductive housing with a small highly conductive 

probe tip is a good solution. 

In some cases, your application may require a slow 

thermal time response. An example of this would 

be an outdoor sign that displays the temperature. 

A large over molded probe will insulate the thermistor 

and even out quick fluctuations in temperature 

changes. 

Confined Space 

Due to a thermistor’s miniature size, it can be 

potted into almost any size housing. Currently, 

the smallest available thermistor is 0.020” max 

diameter. Hollow-tube rivets, set screws, hypodermic 

needles and direct epoxy attach are some 

common methods for confined space thermistor 

applications. 

Liquid 

For liquid applications, it’s best to use a threaded 

probe. Possibly, with some type of elastomeric seal 

like an o-ring. QTI also offers a complete line of 

NPT probe housings. Some applications require 

over molding the thermistor into the plastic housing 

of the product. Another option is to use a 

glass encapsulated bead. It provides a hermetic 

seal that is as close to ‘waterproof’ as Mother 

Nature will allow. Remember the Titanic 

Gas/Air 

Gas and air applications have a variety of choices. 

Probes can be surface mounted in the flow stream 

or they can be projected into the air stream by 

means of a closed or open-end tube. When measuring 

gas or air under pressure, we recommend 

using some type of thread/o-ring combination. 

SURFACE 

By far the most common method for surface measurement 

is the ring lug. Due to the small size of 

the thermistor element, it can be potted into most 

ring lug barrels. Be careful that the wire gauge 

does not exceed the inside dimension of the barrel. 

Another option for surface measurement is 

direct attachment of a thermistor using a stainless 

steel disc. 

frequently asked questions 

How does aging affect thermistor stability 

“Thermometric drift” is a specific type of instability in which the deviation in 

measured temperature is the same at all temperatures to which the thermistor 

is exposed. For example, a thermistor that exhibits a -0.02°C shift at 0°, 

40° and 70°C (even though this is a different percentage change in resistance 

in each case) would be exhibiting thermometric drift. Thermometric drift: 

(1) occurs over time at varying rates, based on thermistor type and exposure 

temperature, and (2) as a general rule, increases as the exposure temperature 

increases. Most drift is thermometric. 

What happens if my application exceeds the 

temperature rating 

Intermittent temperature incursions above and below the operating range will 

not affect long-term survivability. Encapsulate epoxy typically begins to break 

down at 150°C and the solder attaching leads to the thermistor body typically 

reflows at about 180°C. Either condition could result in failure of the thermistor. 

Are thermistors ESD sensitive 

Per MIL-DTL-39032E, Table 1, thermistors by definition are not ESD sensitive. 

What is the resolution of a thermistor 

There is no limit to the resolution of a thermistor. The limitations are in the 

electronics needed to measure to a specified resolution. Limitations also exist 

in determining the accuracy of the measurement at a specified resolution. 

Are QTI thermistors RoHS compliant 

(What if I don’t want a lead free part) 

Quality Thermistor maintains two separate manufacturing lines to meet the 

specific environmental needs of our customers. One line is dedicated to RoHS 

compliance and the other is maintained for traditional tin/lead parts for military, 

aerospace and medical applications. 

Does the length of wire impact the accuracy 

of a thermistor 

With a thermistor, you have the benefit of choosing a higher base resistance 

if the wire resistance is a substantial percentage of the total resistance. An 

example of this would be a 100-ohm thermistor vs a 50,000 ohm thermistor 

with 10’ of 24 AWG wire. 

Total wire resistance = 10’ x 2 wires x 0.02567 ohms per foot = 0.5134 ohms 


15

Quality Thermistor, Inc. 

2108 Century Way 

Boise, ID 83709 

www.thermistor.com 

800-554-4784 U.S. 

208-377-3373 Worldwide 

208-376-4754 FAX 

qti@thermistor.com

TEMPERATURE SENSOR EXPERTS - Quality Thermistor Inc.

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