Everything about NTC vs PTC Thermistor
A microwave oven is perfectly normal in your daily life, for you often have microwavable foods at home, but there are countless components at work behind the machine's operation. Among them is a component called NTC Thermistor, which helps control the internal temperature and the wide temperature range. There's another thermistor called PTC Thermistor, widely used in many fields. Now let's explore NTC vs PTC Thermistor from several aspect.
The History of Thermistors
Michael Faraday (1791-1867), a British physicist and chemist, initially gained recognition for his research in electromagnetic induction and electrochemical processes. The less known compound is Ag2S (silver sulfide), which can be examined first. Document the semiconductor characteristics of NTC thermistors.
Due to the challenges in producing early thermistors and the restricted application of technology, the commercial manufacturing and utilization of thermistors commenced only a century later. In the early 1940s, Bell Telephone Lab created technologies to enhance the reliability and reproducibility of manufacturing methods. Initial commercial thermistors were of the ceramic variety, and by current standards, their tolerances were rather broad. These devices are mainly employed for controlling, safeguarding, and adjusting temperature in electronic circuits.
During the 1950s and 1960s, the demand for enhancing the aviation sector through more precise and stable apparatus prompted various advancements in the materials utilized for producing glass beads and disc thermistors. During the 1960s and 1970s, the need for affordable high-torque tolerance equipment spurred the advancement of chip thermistors.
As the reliability of these devices improved in the 1980s, the adoption of electronic thermometers in the healthcare sector has grown. The increasing expense of sterilizing materials and worries about potential cross-contagion between patients has resulted in low-cost disposable thermometers, making chip thermistors a highly appropriate necessity. During the 1980s and 1990s, the use of NTC thermistors kept increasing in the automotive, food processing, and HVAC sectors.
What are Thermistors?
Definition
Thermistors are a special type of resistors that function like a temperature-sensitive resistor, which indicates they possess higher resistance than conductive materials but lower resistance than insulating materials. To determine a temperature reading, the recorded electrical resistance of a thermistor can be related to the temperature of the surroundings where that thermistor is placed.
The word 'thermistor' is a combination of terms - it comes from THERMally sensitive ResISTOR - and these devices offer a highly accurate and economical choice for measuring temperature.
The reasons thermistors remain favored for temperature measurement are: Their increased resistance change per degree offers better resolution - Consistent high repeatability and stability (±0.1).
These components help extend device lifespan, reduce stress on components, and enhance reliability.
Composition of Thermistors
Thermistors are semiconductor devices made from sintered mixtures of metal oxides such as copper, manganese, nickel, and cobalt, which are formed into beads, rings, and discs. They achieve a considerable resistivity with a high resistance/temperature coefficient.
Depending on their design, thermistors can exhibit resistances at 20°C that range from 1 ohm to several mega-ohms. The relationship between a thermistor's temperature and its resistance is significantly influenced by the specific materials used in its fabrication. Manufacturers meticulously evaluate this property, as it is the primary concern for thermistor buyers.
These devices are composed of metallic oxides, binders, and stabilizers, which are compressed into wafers that are later cut into chip sizes, kept as discs, or molded into various shapes. The precise ratio of the composite materials determines the resistance/temperature "curve," and manufacturers closely monitor this ratio to ensure optimal thermistor performance.
Working Principles of Thermistors
The core concept of a thermistor is that its resistance changes with temperature fluctuations. This resistance is assessed with an ohmmeter, which measures electrical resistance. It's essential to understand that thermistors do not yield direct measurements; rather, their resistance alters due to changes in temperature. The degree of resistance is determined by the material employed in the device. In contrast to linear sensors, thermistors exhibit non-linearity, and their temperature-resistance correlation is depicted by a non-linear graph.
Grasping how changes in temperature affect a thermistor's resistance enables the computation of temperature measurements from the collected information. This connection is non-linear, producing a curve instead of a straight line.
Every resistor shows variations in resistance due to temperature, measured by the temperature coefficient of resistance. Although standard resistors exhibit some changes in response to temperature, thermistors are specifically engineered with a high temperature coefficient of resistance to facilitate accurate temperature readings.
A thermistor is placed inside a device to track its temperature and is connected to an electrical circuit. As the device's temperature fluctuates, the resistance of the thermistor adjusts correspondingly. The connected circuit detects this change in resistance and adjusts it to correspond with the appropriate temperature.
Thermistors usually have two wires, one linking to a power source that gauges the thermistor’s voltage. The main benefit of thermistors is their capacity to show a significant alteration in resistance with temperature changes, offering very sensitive and accurate measurements.
Thermistors operate based on the Steinhart-Hart equation, which is a mathematical method for achieving precise temperature measurements. The Steinhart-Hart equation was created by John Steinhart and Stanley Hart in 1968, this polynomial equation is utilized to find the connection between temperature and resistance in NTC thermistors. The equation enables the determination of resistance if the temperature is established, and alternately, it enables finding the temperature if the resistance is unspecified.
Types of Thermistors
There are two types of thermistors: Negative Temperature Coefficient (NTC Thermistors) and Positive Temperature Coefficient (PTC Thermistors). The resistance of an NTC Thermistor declines as its temperature rises. The resistance of a PTC Thermistor rises with a rise in temperature.
NTC Thermistors are primarily utilized for measuring temperature, whereas PTC Thermistors are mainly employed for safeguarding circuits.
Thermistors consist of substances that have a known resistance. As the temperature rises, the resistance of an NTC Thermistor will rise in a non-linear manner, adhering to a specific “curve.” The characteristics of the materials composing the thermistor dictate the form of this resistance versus temperature graph.
Thermistors come in different base resistances and exhibit various resistance in relation to temperature curves. Applications at low temperatures (-55 to about 70°C) typically utilize thermistors with lower resistance values ranging from 2252 to 10,000Ω). Applications involving higher temperatures typically utilize thermistors with greater resistance (over 10,000Ω). Certain materials offer greater stability than others. Resistances are typically defined at 25°C (77°F). Thermistors provide accuracy of around ± 0.2°C within their designated temperature range. They are typically sturdy, enduring, and cost-effective.
Thermistors coated with epoxy can operate at lower temperatures [usually -50 to 150°C (-58 to 316°F)]; additionally, thermistors with glass coatings are suitable for higher temperatures [generally -50 to 300°C (-58 to 572°F)]. These coatings shield the thermistor and its connecting wires from moisture, corrosion, and mechanical strain.
Overview of NTC Thermistors
Operational Principles
Every resistor displays variations in resistance due to temperature, measured by the temperature coefficient of resistance. Although standard resistors exhibit some fluctuation in reaction to temperature, thermistors are engineered to possess a substantial temperature coefficient of resistance for accurate temperature readings.
Self-heating caused by the current is released from the thermistor's surface, preventing any temperature increase. Nonetheless, as the heat generated increases, the temperature of the NTC thermistor body increases and the resistance value diminishes.
Types of NTC Thermistors
Bead Thermistors:
These thermistors consist of lead wires made from a platinum alloy that are directly sintered into the ceramic structure. They typically provide quicker response times, greater stability, and enable functioning at elevated temperatures compared to Disk and Chip NTC sensors, but they are more delicate. It is typical to encase them in glass, to shield them from physical harm during assembly and to enhance their measurement stability. The usual sizes vary from 0.075 to 5 mm in diameter.
Disks and Chips Thermistors:
They feature metalized surface connections. They are bigger and, consequently, exhibit slower response times compared to bead type NTC resistors. Nonetheless, due to their dimensions, they possess a greater dissipation constant (energy needed to increase their temperature by 1 °C). Because the power lost by the thermistor is related to the square of the current, they manage higher currents significantly better than bead type thermistors. Thermistors of the disk type are produced by compacting a mixture of oxide powders into a circular mold and subsequently sintering at elevated temperatures. Chips are typically produced through a tape-casting method in which a material slurry is applied as a thick film, dried, and then cut to form. The usual sizes vary from 0.25 to 25 mm in diameter.
Glass Encapsulated Thermistors:
These are NTC temperature sensors enclosed in a sealed glass bubble. They are intended for applications involving temperatures exceeding 150 °C, or for use in printed circuit board assembly, where durability is essential. Encasing a thermistor in glass enhances the sensor's stability and shields it from environmental factors. They are created by tightly sealing bead type NTC resistors inside a glass enclosure. The standard sizes vary from 0.4 to 10 mm in diameter.
Benefits of NTC Thermistors
They are very adaptable and responsive.
As a temperature sensor, it is capable of sensing temperature.
The thermistors provide both high accuracy and interchangeable capabilities simultaneously.
NTC thermistors are dependable, precise, function effectively, and exhibit strong heat resistance.
Different sizes and tolerances can be found.
The primary benefit of NTC thermistors compared to other temperature-dependent resistors is their heightened sensitivity.
Even slight temperature variations can activate these thermistors.
Their capability to sense a wave under one degree within a temperature span is outstanding.
Limitations of NTC Thermistors
Due to their high sensitivity, NTC thermistors can cause damage to entire devices if they experience overheating.
If the thermistor is damaged, the dryer will be completely non-operational.
Substitution is not feasible because these are custom-made.
Selecting an NTC thermistor necessitates confirming the central temperature operating point.
Application of NTC Thermistors
NTC thermistors are found throughout our daily lives, and due to their resistance traits where the resistance value drops as temperature increases, they are utilized in temperature sensors like thermometers and air conditioners, as well as in temperature regulation devices such as smartphones, kettles, and irons. In a preventive role, thermistors lower the likelihood of appliances, such as microwaves or portable heaters, overheating and causing a fire. Additional devices comprise computers, air conditioning units, and smoke detectors.
Operational Principles
PTC thermistors operate on the properties of specific semiconductor materials, usually incorporating barium titanate or comparable compounds. At reduced temperatures, these substances exhibit a crystalline arrangement that permits a relatively unhindered movement of electrons, leading to minimal resistance.
Types of PTC Thermistors
Chip Thermistors:
These PTC thermistors are compact and typically have a square or rectangular shape. Electronic circuits are frequently utilized for sensing and controlling temperature.
They are produced with semiconductor materials like barium titanate and show a positive temperature coefficient, indicating their resistance rises with temperature.
Chip thermistors are used in devices such as temperature sensors, heating components, and circuits for overcurrent protection.
Bead Thermistors:
Bead thermistors are generally compact, spherical parts enclosed in a protective substance like glass or epoxy resin.
They are frequently utilized for measuring temperature across different sectors, such as automotive, medical, and HVAC systems.
Bead thermistors offer precise temperature-detection features; producers frequently incorporate them into probes or sensors for particular uses.
Disk Thermistors:
Disk thermistors are larger than chip and bead thermistors. They are ideal for uses that demand greater power dissipation.
Electronic devices frequently utilize them for initiating motors, safeguarding against overcurrent, and compensating for temperature variations.
Because of their increased surface area, disk thermistors are capable of managing higher currents and power levels, rendering them appropriate for challenging industrial uses.
Glass-Covered Thermistors:
Producers cover these thermistors with a delicate glass layer to shield them from environmental influences such as moisture, chemicals, and physical stress.
Glass-coated thermistors are frequently utilized in challenging conditions where precision and dependability in temperature sensing are essential.
They are utilized in automotive, aerospace, and industrial automation sectors, where the sensors encounter severe conditions.
Surface-Mounted Thermistors:
Surface mount thermistors are made for simple incorporation onto printed circuit boards (PCBs) utilizing surface mount technology (SMT).
They are available in different package sizes and forms, providing adaptability in design and positioning on PCBs.
Surface mount thermistors are commonly utilized in consumer electronics, telecommunications, and industrial machinery for temperature detection and regulation.
Thermistor Probes:
Probe thermistors include a sensing component enclosed in a metal or plastic casing, typically featuring a sharp tip for insertion into liquids, gases, or solids.
They are utilized for precise temperature readings in food processing, HVAC systems, and scientific research purposes.
Probe thermistors provide quick response times and excellent precision, making them ideal for industrial and laboratory settings.
Benefits of PTC Thermistors
Temperature Sensing Precision: PTC thermistors provide precise temperature sensing abilities, enabling accurate oversight and regulation of temperature-critical systems.
Quick Response Time: These thermistors demonstrate swift reactions to temperature fluctuations, making them suitable for applications demanding immediate detection and response.
Self-Regulating Characteristics: PTC thermistors feature a positive temperature coefficient, indicating that their resistance rises with increasing temperature. This self-regulating action aids in preventing circuit overheating by restricting current flow as temperature increases.
Extensive Operating Temperature Range: PTC thermistors function efficiently over a wide range of temperatures, from sub-zero levels to several hundred degrees Celsius, rendering them ideal for various applications.
Dependability and Longevity: When designed and managed appropriately, PTC thermistors can serve as very dependable and long-lasting elements, able to endure severe environmental situations and mechanical pressure.
Limitations of PTC Thermistors
Nonlinear Response: PTC thermistors demonstrate a nonlinear relationship between resistance and temperature, potentially complicating calibration and measurement in certain applications.
Restricted Operating Voltage: These thermistors possess a maximum voltage limit, exceeding which they could face thermal runaway or irreversible harm. Thoughtful assessment of voltage levels is essential to avoid overloading.
Temperature Hysteresis: PTC thermistors can show temperature hysteresis, implying that their resistance values may change slightly based on whether the temperature rises or falls. This feature necessitates precise adjustment in particular contexts.
Responsiveness to Environmental Conditions: PTC thermistors may react to environmental conditions like humidity, pressure, and vibration, potentially impacting their performance and dependability.
Manufacturing Variability: Fluctuations in production techniques and materials may cause discrepancies in performance and features among PTC thermistors, necessitating stricter quality control practices for uniform outcomes.
Restricted Current Handling Capability: Although PTC thermistors can offer overcurrent protection, they have constraints on the amount of current they can manage before reaching the high-resistance state, which might not be ideal for high-power uses.
Application of PTC Thermistors
PTC thermistors are commonly employed to control temperature in industrial devices like medical machinery, HVAC systems, electronic parts, and automotive elements. They are utilized to identify overcurrent situations and safeguard delicate electronic devices from unintentional overvoltage or overcurrent.
Moreover, they may serve to manage or activate machinery in packaging lines and automated assembly processes. A PTC thermistor can be utilized to detect temperature variations between two distinct locations, aiding in the prevention of overheating, monitoring machine performance and safety, or enhancing efficiency.
Comparative Analysis of NTC vs PTC Thermistors
As noted, the main distinguishing characteristic of thermistors is the polarity of the TRC. NTC and PTC thermistors are utilized in various circuit applications.
NTC
In reference to the current passage, an NTC thermistor is similar to an inductor facing inrush current, even though the underlying processes are completely different. An NTC resistor displays a certain level of resistance at room temperature prior to a rise in temperature caused by power dissipation across the resistor (the principle of Ohmic heating). The resistance decreases when the temperature rises above the ambient level, enabling more current to flow. Applications of this method involve:
Temperature-sensitive operations - Industries in biology and chemistry that depend on cold chains can oversee a thermistor's output to detect hazardous temperature conditions.
Present limiters - Thermistors regulate the flow of current to safeguard delicate components and replaceable items such as fuses and circuit breakers. They additionally diminish power loss since the current is minimal when resistance is high (and the reverse holds true).
Predictive maintenance - Monitoring process fluids can show that a decrease in resistance may signal possible early failure of system parts.
Battery chargers - The output can monitor rising temperatures that may suggest the onset of thermal runaway situations.
PTC
In contrast to NTC, PTC thermistors have a self-regulating feature: the resistance rises as current flows through the resistor and its temperature exceeds the ambient level. This corrective measure allows PTC thermistors to shine in sustaining a constant temperature. If the circuit and material conditions allow the PTC thermistor to avoid self-damage, then the necessity for temperature management is unnecessary. The thermistor's capacity to prevent current spikes renders it useful as a resettable fuse alongside sensitive circuits. Additional PTC positions consist of:
Heating elements - The variable resistance of a thermistor is useful in temperature-sensitive operations such as diesel engines prior to fuel injection.
Present divider - Parallel elements with significant resistance variations can result in current hogging/starvation. PTC thermistors arranged in series will actively equalize the current across the branches.
Silistor - Silicon thermistors provide enhanced linearity compared to conventional ceramic material PTCs.
Why Unikey is a Good Choice?
When it comes to choosing top-notch thermistor solutions, Unikey distinguishes itself for many convincing reasons:
Outstanding Product Excellence
Unikey is well-known for its dedication to quality in producing thermistors. The firm employs cutting-edge technology and strict quality assurance protocols to guarantee that every thermistor—be it NTC or PTC—adheres to demanding performance criteria. This dependability is essential in situations that require precise temperature measurement and current regulation.
Variety of Choices
Unikey provides a comprehensive range of NTC and PTC thermistors designed for different applications. Ranging from automotive and consumer electronics to industrial applications, their offerings are tailored to meet diverse environmental conditions and functions. This flexibility positions Unikey as a comprehensive resource for engineers and designers in need of tailored thermal management solutions.
Customization Features
Each application is distinct, and Unikey recognizes that varying demands necessitate tailored solutions. They offer design assistance and customization choices, enabling clients to define resistance values, sizes, and other crucial parameters in their thermistor products. This adaptability guarantees ideal incorporation into any system.
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Conclusion
In summary, recognizing the differences between NTC and PTC thermistors is essential for choosing the appropriate temperature sensor or control device for your unique application. NTC thermistors are crucial for accurate temperature readings and are perfect for uses that demand sensitive thermal reaction and precision. Their capacity to reduce resistance as temperature increases enables them to operate efficiently across various areas, such as medical equipment, HVAC systems, and automotive diagnostics.
Conversely, PTC thermistors are outstanding in protective and self-regulating functions, rendering them ideal for equipment that needs to avert overheating or control inrush currents. Their ability to enhance resistance at higher temperatures is beneficial in applications that include circuit protection, heating elements, and current balancing modules.
Engineers and designers can select the appropriate type of thermistor to suit their unique requirements, given the range of choices offered by reputable brands such as Unikey. Regardless of whether they are standard items or tailored solutions, Unikey’s dedication to quality and flexibility in various applications guarantees that clients can seamlessly incorporate thermistors into their designs.
In the end, the decision between NTC and PTC thermistors should be determined by your project's needs, taking into account elements such as sensitivity, response time, operating conditions, and safety attributes. Using the appropriate thermistor technology can enhance your quality of life.Recommended Reading：
