Thermistor vs RTD: Key Differences, Accuracy, and Applications

In Thermistor vs RTD (Resistance Temperature Detector sensor) the key difference lies in their application context. Both resistance temperature detector sensors are used extensively in industrial and hobby electronics. Both sensors operate based on the changing resistance proportional to the changing temperature. However, the difference in Thermistor vs RTD lies in their construction, material, behavior, accuracy, and their respective suitable applications.
In this detailed guide, we’ll clearly explain what Thermistor vs RTD differences are, what their working principles are, and carefully compare their key differences in terms of accuracy, range, linearity, cost, form factor, and suitability. We’ll also explore typical questions like “What is the difference between an RTD and a thermistor?”, “Do Thermistors have polarity?”, “Is a PT100 sensor a Thermistor or RTD?”, etc.
Whether you’re an electronics engineer, PCB designer, or hobbyist, this guide will help you understand when to use a Thermistor vs an RTD for temperature sensing.

What is a Resistance Temperature Detector Sensor (RTD)?

A Resistance Temperature Detector sensor (RTD) is a temperature-sensing device that measures temperature by correlating the resistance of a pure metal element (Typically Platinum-Pt, Nickel-Ni, or Copper-Cu) with temperature. RTDs are regarded as resistance thermometers as well.

RTD Construction & Materials

Most RTDs consist of fine metal wire (Pt, Ni, or Cu) wound on ceramic or glass core. They are also spread of the ceramic substrate in thin film, for thin-film RTDs. Platinum is most commonly used metal for RTD construction because it has stable, very predictable, nearly linear temperature-resistance response curve (with a 100Ω at 0°C).

Resistance Temperature Detector Working Principle

Here we provide  abreif resistance temperature detector working principle. Resistance temperature detector sensor is a passive temperature sensor – that is, it does not produce any voltage on its own. To measure temperature using an RTD, you pass a small amount of excitation current through the RTD and measure the voltage drop at the other end of the coiled wire to calculate its resistance. Since the RTD resistance rises linearly with temperature, you can also extrapolate the voltage drop to estimate the temperature. Effectively, the resistance temperature detector working principle is based on the varying resistance based on the varying temperature.

RTD Types (Platinum, Nickel, Copper)

RTD types are mostly based on the material and construction type. In material wise categorization, the Platinum (Pt), Nickel (Ni), and Copper (Cu) are common. Platinum RTDs have near linear resistance-temperature response. The RTDs made with platinum include Pt100, pt500, and Pt1000. They have excellent temperature range from –200 °C to 600+ °C.

Sample Probe Style Pt100 RTD

On the other hand, Nickel (Ni) based RTDs have higher temperature coefficient, but limited temperature range.

Copper (Cu)-based RTDs have a very linear resistance–temperature relationship like Platinum, but because copper oxidizes even at moderate temperatures, you cannot use it for applications requiring temperatures over 150 °C.

Key Characteristics of RTDs

The most common, and widely acknowledged characteristics of the RTDs are:

• Accuracy
• Stability and
• Linearity.

RTDs, because of these excellent characteristics, are, however, more expensive than thermistors. RTDs are also slightly larger than in form factor (more details coming up) than thermistors as well. See later in this article.

What is a Thermistor?

The name ‘Thermistor’ originates by merging the two terms ‘Thermal’ and ‘Resistor’ which discloses its type: temperature-sensitive resistor. Typically when refereing to thermistors, we mean the NTC Thermistors. We’ll discuss the difference between NTC Thermistors and PTC Thermistors later in this article. Unlike the RTDs (which are made up of pure metal like Platinum), thermistors are made of semiconductor metal-oxides. The key characteristic of thermistor is that by changing the temperature, its resistance changes non-linearly. Thermistors exhibit large resistance change with small temperature variation, making them more sensitive temperature sensors in specific ranges.

Thermistor Types (NTC vs PTC)

In general, the thermistors have two major types:

• NTC: Negative Temperature Coefficient. In NTC, the resistance decreases as the temperature increases
• PTC: Positive Temperature Coefficient. In PTC type thermistor, the resistance increases as the temperature rises

NTC is the most common type of thermistor for temperature measurement. When talking about thermistor, an NTC type thermistor is implied unless specified otherwise. The temperature-resistance curve of an NTC thermistor is logarithmic rather than linear. This effectively means, at low temperatures a small increase in temperature causes a big drop in resistance, whereas at higher temperatures the resistance changes more gradually.  The temperature coefficient of various metals is given in the graph below:

The PTC thermistors have two categories:

• Switching PTCs: These PTC thermistors jump in resistance at a threshold temperature,
• Silistor linear PTCs: Manufacturers create these thermistors using doped silicon, hence the name—a combination of “Sili” (from Silicon) and “tor” (from Thermistor). They change resistance more gradually with a positive coefficient and sometimes serve in temperature compensation applications.

How Thermistors Work

Manufacturers construct thermistors from mixtures of metal oxides (such as oxides of nickel, copper, iron, etc.) and press them into specific shapes such as bead, disk, or probe. They then sinter this pressed metal at high temperature to form a ceramic semiconductor. Going through this process makes this ceramic semiconductor, a highly sensitive resistor.

A common 10 kΩ NTC thermistor will change by several hundred ohms per degree at near-room temperature. This resultant change is much larger than a platinum RTD which changes fractions of an ohm per degree change in temperature.

However, this higher sensitivity has a side effect too. Due to very high change in resistance for smaller temperature changes, the overall range of operation for thermistors is much lower than a typical RTD.

Thermistor Construction & Packages

Thermistors are available in many forms and packages. From tiny bead thermistors to larger disk or surface mount thermistors. Like many other electronic components, surface mount thermistors are also popular for circuit board temperature sensing or compensation. For example, a standard 0603 surface mount thermistor chip can measure PCB board or ambient temperature. Following image demonstrates various thermistor forms, and packages:

Thermistor vs “Standard” Resistor

A common question arises, “Is a thermistor just a resistor?”. The answer is Yes, in terms of symbol and similar two terminals as the resistor. However, unlike a resistor, a thermistor is made of material that gives it a strong temperature coefficient. Effectively, thermistors are highly temperature-sensitive resistors in comparison with standard resistors.

Key Characteristics of Thermistors

Since the resistance vs temperature curve of the thermistor is quite steep compared to an RTD, you can achieve a precision of ±0.05 °C in a narrow span by calibrating the thermistor. The Comparative Resistance Graph of Thermistor vs RTD below depicts the strongly non-linear behavior of thermistors versus the linear behavior of RTDs.

Thermistor vs RTD – Comparative Resistance Graph

A substantial drawback (or additional step, really) of thermistors is that you must either use the specific temperature-resistance chart from the thermistor’s data sheet or obtain Steinhart-Hart coefficients for that part to convert resistance to temperature.

Thermistor vs RTD: Key Differences in Performance

Both thermistors and resistance temperature detector sensor are temperature sensors based on resistance. However, they have significant differences in characteristics. below is a comparison of key aspects of thermistors vs RTDs:

Operating Temperature Range of Thermistor vs RTD

Due to their high sensitivity and significant resistance changes with minor temperature variations, thermistors operate within a limited temperature range. Standard NTC thermistors typically operate between −50 °C up to +150 °C. On the other hand, Platinum resistance temperature detector sensor operate in much wider range between −200 °C to +650 °C. Due to higher temperature coverage, RTDs are more suitable in industrial high-temperature applications where Thermistors cannot survive or stay as accurate.

Accuracy and Precision

In NTC Thermistor vs RTD, both sensors can be very accurate in specific range and context. NTC Thermistors are extremely accurate in limited range. For example, Class-A NTC Thermistors can be accurate to ±0.05 °C or ±0.1 °C in the range around room temperature.
On the other hand, RTDs have good accuracy in broader range. For example, a standard Class-A resistance temperature detector sensor (RTD) is about ±0.15 °C at 0 °C (increasing slightly with temperature).

Practically, thermistors are more accurate than typical Class-B RTDs in Thermistor’s narrower operating range.

Linearity of Thermistor vs RTD

The major difference between Thermistors, and RTDs is Linearity of both devices. RTDs have a linear resistance – temperature relationship, which makes the conversion from resistance to temperature simple, often a polynomial or look-up table suffices for this.

On the other hand, Thermistors are highly non-linear. Their response follows an exponential curve as indicated in the comparative Resistance Graph previously.

For example, resistance of an NTC thermistor might decrease from 30 kΩ to 5 kΩ within a 30 °C span—a substantially non-linear change. Since engineers can linearize the thermistor’s output using the Steinhart-Hart equation, they program microcontrollers to handle the non-linearity. Effectively, engineers accommodate thermistor non-linearity with an additional processing step.

Thermistor vs RTD – Response Time

NTC Thermistors respond far quicker than RTDs. This is possible for thermistors due to their smaller sensing elements manufacturability with low mass. Thermistors are also faster because they are in direct contact with the environment they are sensing, compared to RTDs which have longer and enclosed probes. Typical response times (to 63.2% of a step change) might be on the order of 0.2 to 10 seconds for thermistors, versus 1 to 50 seconds for RTDs, though depending on packaging.

Although engineers can also find faster RTDs (thin-film or exposed element types) and slower thermistors (with large epoxy blobs), thermistors generally respond far more quickly than RTDs.

Size and Form Factor of Thermistor vs RTD

As described earlier in detail, Thermistors are very small sizes and can be found in numerous forms. For example, thermistors can be in SMD chip packages, small beads, or integrated into probe assemblies.

Resistance temperature detector sensors historically are wire-wound and larger. However, modern engineering has enabled thin-film RTDs which can also be made as small surface mount chips – for example, 1206 size platinum RTD elements are commonly available.

Traditionally however, manufacturers produce RTDs as probe-style sensors encased in metal tubes, while they supply thermistors more commonly as discrete PCB components or potted in small housings.

Similarly, surface mount thermistors are also widely available for PCB, and wide array of circuit board ambient temeprature sensing.

Excitation and Measurement Circuitry of Thermistor vs RTD

When comparing Thermistor vs RTD for measurements circuitry, we see that both sensors are passive sensors. However, because of wide resistance-temperature curve differences of the two sensors, their circuit design varies.

An NTC Thermistor exhibits large resistance changes for small temperature variations, allowing engineers to read them easily through a voltage divider connected to an Analogue-Digital Converter (ADC). Because the sensor’s resistance is high, the resistance of lead wires becomes negligible. However, their non-linear output requires engineers to use software implementing the Steinhart-Hart equation or an op-amp circuit when needed. An interesteing benefit over RTD is that surface mount thermistors are also availabe with this capability.

RTDs on the other hand produce small resistance in response to the temperature change, hence small voltage change. In RTD’s case, the leads resistance is non-negligible. The voltage of the RTD is measured with a constant current source and a precision ADC or Wheatstone bridge.

A Pt100 with 1 mA current only uses about 0.1 mW, practically negligible to heat the sensor. However, some circuits use 5 mA using 2.5 mW—enough to warm a small RTD by about 0.1 °C in still air. Thermistors, like a 10kΩ type, can use very low currents (around 100 µA) and still produce a clear signal, so they have almost no self-heating.

Thermistor vs RTD – Summary Table of Characteristics

Thermistor vs RTD – Common Applications and Uses

Both thermistors and RTDs have extensive applications due to their distinct features and limitations. Below we take a look at common applications of thermistors and RTDs:

Thermistors in Everyday Electronics

Since thermistors are small in size and respond quickly to temperature changes, they are often used in digital thermostat, and HVAC applications. Consumer appliances such as refrigerators, microwave ovens, and coffee makers use thermistors as temperature sensors because of fairly good accuracy within device’s operating range.

Small size, and high sensitivity make thermistors ideal for BMS (Battery Management Systems) applications in Electric Vehicles, mobile phones, PC motherboards, and laptops. Thermistors are also abundantly used in 3D printers, where they are embedded in the extruder system to regulate the nozzle temperature.

RTDs in Industrial & Laboratory Settings

Engineers regard resistance temperature detector sensors, especially the Pt100, as the gold standard for accurate temperature measurement in industrial processes. They frequently use them in industrial settings because a single sensor type can cover temperature ranges from cryogenic levels (e.g., monitoring a freezer at –100°C) up to high heat (steam at 250°C).  In aerospace, RTDs measure environment temperatures where accuracy is paramount and conditions may vary widely.

Thermistors for Inrush Current Limiting & Protection

NTC thermistors have an interesting application due to their inherent temperature-dependent resistance variation characteristic. They are used as surge suppressors in power supply circuits. As the power supply starts up, an NTC thermistor is cold with high resistance, limiting the inrush current. As current flows through it, thermistor heats up, its resistance drops, and it allows normal current flow – effectively protecting against initial surges.

PTC thermistors act as resettable fuse in similar applications. When operating under normal current, PTC Thermistors are cool with low resistance. However, as current increases to too high, they self-heat and trip to a high resistance state, effectively limiting the current.

These two applications are not measurement based, but they are very important applications of thermistor technology in circuit protection.

NTC Thermistor vs RTD – Automotive Sensors

The automotive industry uses thermistors abundantly. They are used as temperature sensors for coolant, air intake, oil and are often NTC thermistors encased in a threaded brass housing.

However, in very high-temperature areas like exhaust gas temperature, engineers use specialized RTDs instead because typical thermistors cannot survive such conditions. In automotive applications, thermistors serve well for engine coolant, outside ambient temperature sensing, and climate control cabin temperature, but engineers often measure exhaust or catalytic converter temperature with a thermocouple or RTD.

Conclusion

Although both thermistors and RTDs serve as reliable temperature sensors, their unique characteristics make them better suited for different applications.

Thermistors excel in compact designs where high sensitivity over a limited range is needed. Examples for Thermistor’s applications include consumer electronics and HVAC systems. RTDs, particularly platinum-based models like Pt100 and Pt1000, offer superior long-term stability, accuracy, and a wider operating range, making them ideal for industrial process control, and precision engineering.

Choosing between the two ultimately depends on the required temperature range, accuracy, response time, and budget. understanding these trade-offs ensures optimal sensor selection for any project.

Frequently Asked Questions (FAQs)

Definitions

What does “platinum RTD” or Pt100 mean?

Platinum RTD refers to the resistance temperature detector sensor built with Platinum material as sensing element. Platinum is the most common element material for RTDs due to its stability and linearity.

Pt100 on the other hand, is particular RTD built with platinum that has 100Ω resistance at 0 °C. The Pt100 has a standardized temperature coefficient: α ≈ 0.00385 Ω/Ω/°C (calculated using  ,  resistance of sensor at  and resistance of sensor at ) for the common IEC standard.

What are the different types of RTDs?

RTDs can be categorized by material or by construction. The main types by material are:

• Platinum RTDs: These are very common and standardized RTDs. Examples include Pt100, Pt500, Pt1000 etc.
• Nickel RTDs: Beyond 300, Nickel has non-linear curves, therefore they are not commonly used. They are still applicable to specific old applications. Their typical examples include Ni120, and Ni1000.
• Copper RTDs: Copper RTDs have very specific use cases for extremely linear behavior; however, limited only to up to 120due to oxidation issue.

By Construction, the RTDs are divided into following categories:

• Wire-wound RTDs: In these RTDs, a fine platinum wire is wound around glass or ceramic core. Although they are delicate, they can handle up to cryogenic range of temperature as discussed in detailed in blog above.
• Thin-Film RTDs: In these RTDs, manufacturers deposit a thin Platinum film on a flat ceramic substrate and trim the excess film using a laser to set the correct resistance. Typical Pt100 RTD elements use thin-film construction unless specified otherwise. These RTDs resist vibrations better and suit SMD application designs.
• Coiled Element in Ceramic: Some RTDs have a strain-free coil loosely threaded in a ceramic tube; this enables slight expansion and gives good accuracy over a range particularly used in high-precision lab sensors.

RTDs also come in 2-wire, 3-wire, 4-wire lead configurations (the sensor itself is the same; the extra wires are for measurement accuracy as explained earlier)

Do NTC thermistors have polarity? Are thermistors directional?

Unlike diodes or electrolytic capacitors, there is no anode/cathode or positive/negative lead for a thermistor. Thermistors do not have any polarity sensitivity, so they are non-polarized electronic sensors. You can connect the thermistor in any way you like just the way you would connect the resistor. Similarly, thermistors are not directional. You can connect them in any direction you like, and they function the same way.

What would you use a thermistor for? (Use-cases)

Thermistors perform well whenever you need to measure or respond to temperature changes in a circuit or device. Some common use cases include:

• Temperature Measurement: Sensing temperature inside the circuit such as in Battery, or CPU temp. measurement
• Temperature Control: In 3D printers or heat pumps for temperature adjustment based on the device feedback
• Over/Under Temperature Protection: Thermistor-based alarm triggering for too cold or too hot environment
• Temperature Compensation: Built on top of other devices to compensate for temperature coefficient of the device downstream. For instance, designers can incorporate an NTC thermistor into the bias network of a transistor amplifier to compensate for temperature-induced variations in the transistor’s gain.

What are the disadvantages of using an NTC thermistor?

Thermistors have many disadvantages as we describe below:

• Non-linearity: Thermistor do not offer linear response. This non-linearity complicates the output interpretation. You might often need proper calculations in restricted range for proper interpretation.
• Temperature Sensing Range: Most thermistors do not function effectively for very high temperature sensing (above 150°C) or very low temperature (cryogenic temperatures).
• Fragility: Small beed thermistors especially the ones encapsulated in glass can be fragile if mishandled, or rapidly thermally shocked.
• Long-term Drift: Although tier-1 and top of the shelf thermistors do not have long-term drift, the low-quality, worn-out thermistors, and thermistors exposed to higher temperatures drift more over time. Epoxy coated thermistors age due to moisture, however the glass encapsulated thermistors might be able to resist the moisture avoiding the long-term drift.
• Calibration: The thermistor’s construction usually does not follow any standard. This is why their use in high-precision applications is not recommended. If necessary, perform proper calibration before using thermistors in high-precision applications.

Despite their disadvantages, thermistors have wide range of applications, and withing their scope they perform well.

Differences

What is the difference between PT100 and PT1000 thermistors?

Pt100 and Pt1000 are usually called resistance temperature detector sensors, not thermistors. The difference:

• Pt100 has 100 Ω at 0°C.
• Pt1000 has 1000 Ω at 0°C.

The only difference is the nominal resistance and thus the impedance level of the sensor. Pt1000 has 10× the resistance of Pt100 at all temperatures, which gives it some advantages in reducing wire resistance errors and increasing signal level.

What is the difference between a thermistor and a thermocouple?

Thermistor and thermocouple are completely different types of sensor technologies as explained below:

• Thermocouple: Thermocouple sensors are made of two dissimilar metals joined at one end. The sensor produces tine thermoelectric voltage (called the Seebeck voltage). This Seeback voltage is proportional to the temperature difference between the junction and wire ends. Thermocouple is an active sensor that generates voltage and can measure extremely high temperatures. It has, however, nonlinear voltage output which is not very accurate either (±1°C or worse is realistic expectation). Finally, they also require their millivolt signal amplification yielding its own share of losses.
• Thermistor: Thermistor is a passive resistive sensor that produces no voltage itself just because of temperature. It is however, much more accurate than the thermocouple and presents large resistance change at temperature variations. Due to substantial change in resistance due to temperature variations, NTC thermistor does not require additional signal amplification.

What’s the difference between a thermistor and a thermostat?

The Thermistor, and Thermostat are two different things and the confusion between them arises due to similar names. An NTC thermistor is an electronic component that changes its resistance as the temperature varies. However, Thermostat refers to a temperature-regulating device or a switch.

An electronic thermostat may use a thermistor as its temperature detection device to control the HVAC system. However, the two are not necessary for each other since a thermostat can use different temperature sensors than a thermistor.

What is the difference between a thermistor and an LDR?

A thermistor (thermal resistor) also available in surface mount thermistors form changes its resistance based on the change in temperature, whereas an LDR (Light-Dependent Resistor, also called a photoresistor) is changes its resistance based on the intensity of light. They are similar in a sense that both are resistors that change value with an external condition:

• Thermistor: Resistance changes with temperature.
• LDR: Resistance changes with light intensity.

Structure and Characteristics

What is the temperature range of an RTD?

For a standard Platinum RTD (Pt100/Pt1000 per IEC 60751), the range is –200 °C to +850 °C for Class B, and –200 °C to +650 °C for Class A accuracy. In practice, most industrial resistance temperature detector sensor probes are used up to about 400–600 °C.

Does an RTD have three wires? Why?

RTD probes may come with 3 wires. The 3-wire RTD is a compromise wiring that allows the measurement system to cancel the resistance of the lead wires. Here is how 3^rd wire helps reduce the resistance of the longer lead wires:

In a 2-wire configuration, the resistance is R_sensor + R_leads. If the leads run long distances or have significant resistance, this introduces error. The measurement device can use the third wire to measure the drop in one lead and reflect that for other leads with similar drops, thereby subtracting it out.

What are the disadvantages of using an RTD?

• Response Time: RTDs have larger mass, which results in slower response to temperature changes compared to a tiny thermistor
• Self-Heating Error: If the current is too high, an RTD will heat itself and read a slightly above actual temperature. So, you must trade-off measurement noise vs self-heating by choosing an appropriate excitation current
• Higher Cost: Platinum resistance temperature detector sensors with probes are more expensive than thermistors in general.

Does an RTD provide cold junction compensation?

No, RTDs do not require or provide cold junction compensation. Cold junction compensation (CJC) is a concept specific to thermocouples.

Can I replace an RTD with a thermocouple (or vice-versa)?

In general, the answer to this question is no, not without changing the measurement hardware and considering the differences. RTDs and thermocouples have different types and characteristics. So, if the question is from a user perspective: “My RTD broke, can I stick a thermocouple in its place?” – The answer is yes, but only if you modify the instrumentation to read a thermocouple properly. Many devices support both but require switching a setting. Without proper interface, the swap will work.

NTC Thermistor vs RTD vs Thermocouple – which one is right for me?

• Use a thermocouple if you need to measure very high temperatures (hundreds of °C beyond RTD/thermistor range), or need a very robust small sensor, and you can deal with lower accuracy and the need for calibration/CJC.
• Use an RTD (Pt100 etc.) if you need high accuracy over a wide range (e.g., -50 to 300°C) and can afford a more expensive sensor and the circuitry.
• Use a thermistor if the temperature range is moderate (e.g., -40 to +125°C) and cost or circuit simplicity is a concern, or you need a very small sensor with fast response.

Following is the generic Radar chart of NTC Thermistor vs RTD vs Thermocouple depicting strong and weak attributes of each temperature device

Radar Chart of Thermistor vs RTD vs Thermocouple