Thermistors vs. RTDs

Thermistors and resistance temperature detectors (RTDs) are both types of resistors, able to be used for measuring temperature by gauging electrical resistance in modern heating, ventilating, air conditioning, and refrigerating systems. Despite falling into a similar category of products, the exact design of these parts and their uses differ. As such, this article will explore thermistors, RTDs, and their differences from one another that make them useful in varying applications.

Made of a metal semiconductor, a thermistor is a resistor designed to carry out large, predictable, and precise adjustments in electrical resistance in response to changed temperatures. Overall, such devices are cheap and simple to use, and they come in the form of NTC and PTC variations. Negative Temperature Coefficient (NTC) thermistors lose electrical resistance when subjected to heightened temperatures, while Positive Temperature Coefficient (PTC) thermistors experience increased electrical resistance under the same conditions. NTC thermistors are the most common option, though they need to be kept at a low temperature to avoid false results. Most thermistors are able to operate in temperatures ranging from -100 degrees to +600 degrees Fahrenheit, and because of their predictable traits and durability, they are often considered to be the most advantageous sensor for a large number of applications, including for temperature measurement and control.

Thermistors work under the principle that their resistance is dependent on temperature, that of which can be measured using an ohmmeter. The amount of change in resistance depends on the type of material that has been utilized in a thermistor, and the relationship between its temperature and resistance will be non-linear. Thermistors tend to be constructed of ceramic or polymer, and they are available in shapes like beads, rods, and disks. Starting small, they can range in diameter from 1 millimeter to significantly larger sizes that can tolerate a notable amount of current.

On the other hand, a Resistance Temperature Detector (RTD), sometimes referred to as a resistance thermometer, is defined by the American Society for Testing and Materials (ASTM) as a device meant for measuring temperature. Generally, an RTD is constructed of a resistance thermometer element, internal connecting wires, a protective shell that can mount a connection head, or a connecting wire and other fittings. There are typically 3 to 4 wires, and the resistive element senses temperature. The resistive element is often made of platinum because this durable material has a wide temperature range, but they are also constructed from nickel or copper.

Though both thermistors and RTDs are electrical components used to measure electricity and monitor the temperature of certain devices for regulation, they differ in that thermistors tend to be made of ceramic and polymer materials, while RTDs are made of pure metal. Thermistors are also almost always superior in terms of their accuracy and they can be wired with thousands of feet of cabling, while RTDs can only offer use slightly over a hundred feet. This means that transmitters need to be used alongside RTDs. Moreover, thermistors are able to sense sudden changes in temperature much more quickly than RTDs.

Those searching for high-quality thermistors, RTDs, and more can count on our team at ASAP Supply Chain to provide them with reliable products with great rates and rapid lead times. Those facing time constraints will be pleased to know that our expansive supply-chain network allows us to expedite shipping for both domestic and international customers. We may even be able to offer same-day shipping rates for those experiencing an AOG situation, so be sure to call or email our team at any time to see if this applies to your operations. As an AS9120B, ISO 9001:2015, and FAA AC 00-56B accredited distributor, we are proud to source all of our products from leading global manufacturers that are on our Approved Vendor List (AVL). Moreover, we subject countless parts to rigorous quality control measures to guarantee their fit, form, and functionality. Get in contact with us or submit an RFQ form to commence the procurement process with a reliable partner today!