If you’ve ever worked in industrial temperature measurement—whether in food and beverage processing, pharmaceutical manufacturing, or power generation—chances are you’ve relied on a Head Type RTD (Resistance Temperature Detector) at some point. As someone who’s been supplying these sensors for over a decade, I’ve heard every question under the sun about them, but one I get more than any other is: “How stable is this thing over time?” Head Type RTD
It’s a fair question. Stability is the backbone of reliable temperature measurement. If your RTD drifts after a few weeks, your entire process could be off-spec, leading to wasted product, compliance issues, or even safety hazards. Early in my career, I saw a client in the petrochemical sector lose $200,000 in a single quarter because their old, off-brand Head Type RTDs drifted 3°C in just six months. That’s when I realized this wasn’t just a technical detail—it was a make-or-break factor for customers.
So let’s break down Head Type RTD stability over time, from what causes drift, how we (as a supplier) engineer for longevity, real-world performance data, and what you need to look for when specifying these sensors.
First, let’s get clear on what a Head Type RTD is, just to make sure we’re on the same page. Unlike a bare RTD element, which is just the fine wire or thin-film sensor itself, a Head Type RTD integrates the sensing element, terminal block, connection housing (the “head”), and often a transmitter right into one unit. It’s designed for field installation, which means it’s exposed to more environmental stress than a lab-grade sensor—temperature swings, vibration, moisture, sometimes corrosive atmospheres. That environment is a big part of its stability.
Now, the two main types of RTD elements are wire-wound and thin-film, and their stability characteristics are very different. Wire-wound elements use a coiled length of platinum wire, usually wound around a ceramic or glass core, and encased in a protective sheath. Thin-film elements are a thin layer of platinum deposited onto a ceramic substrate, then passivated with a glass or polymer coating. From a stability standpoint, wire-wound elements have a long-held reputation for superior long-term stability, while thin-film are often cited for better short-term performance and lower cost—but that general rule is changing as manufacturing processes improve.
But stability isn’t just about the element. The head assembly, the materials used, and the sealing are equally critical. A common failure point we see from low-quality competitors is poor sealing. If moisture gets into the head, it can corrode the terminal connections or leach contaminants onto the RTD element, causing resistance shifts. Similarly, using cheap terminal blocks made of plastic that deforms at high temperatures can create mechanical stress on the element, leading to drift over time.
Let’s talk about real data, because numbers matter. Our own in-house testing, which we run in our ISO 17025-calibrated temperature lab, tracks RTD drift rate over 5, 10, and 15-year periods under standard industrial operating conditions (up to 200°C, constant vibration typical of pump or conveyor installations, and ambient humidity around 50%). For our standard-grade wire-wound Head Type RTDs (which we call our “Industrial Series”), the average drift after 10 years is less than 0.15°C. Even after 15 years, that number jumps to just 0.22°C. For our premium grade, which uses a platinum wire with higher purity (99.999% vs. 99.95% for standard) and a hermetically sealed head, the drift after 15 years is a negligible 0.1°C.
Thin-film Head Type RTDs, on the other hand, perform well for shorter periods—our tests show less than 0.1°C drift over 5 years—but that increases to ~0.5°C after 10 years, and ~0.9°C after 15 years. That’s not to say thin-film are bad; they’re perfect for applications where you need accurate temperature measurement for 3-5 years, like HVAC systems or food service equipment. But if you’re running a process that requires 10+ year measurement lifecycles, wire-wound is the way to go.
But wait—what about extreme conditions? Our data is for standard operating ranges, but many customers use Head Type RTDs in harsh environments: like 500°C in kilns, or in saltwater for marine applications, or in industries with high levels of sulfuric fumes. We’ve found that stability drops linearly as environmental stress increases, but even here, proper engineering can mitigate that. For example, our marine-grade Head Type RTDs use a Hastelloy sheath and a hermetically sealed head with O-rings made of Viton, and we test them in a salt spray chamber for 1,000 hours before they leave the facility. In our tests, these units only drift 0.18°C over 10 years in marine ambient conditions, which is well within most industry tolerances.
Another factor that affects stability is calibration. RTDs are calibrated to match a standard resistance-temperature curve, usually the ITS-90 (International Temperature Scale of 1990). Every Head Type RTD we supply is pre-calibrated at three points (0°C, 100°C, and 300°C) before shipping, but re-calibration over time is not optional. Even the most stable RTD will drift a small amount, and re-calibrating every 2-3 years (depending on application) will keep your measurement accurate. We always advise customers to build re-calibration into their maintenance schedule, and we offer on-site calibration services as well as send-in options, because we know how critical that is to long-term stability.
A common misconception I hear is that “all Head Type RTDs are the same, so stability is just about the brand.” That’s simply not true. We’ve had customers send us Head Type RTDs from big-name industrial suppliers that they’ve had for 7 years, and when we test them in our lab, we see drift as high as 1.2°C. When we look inside the head, we find things like plastic terminal blocks that have cracked, moisture buildup on the RTD element, and platinum wire that wasn’t properly annealed. Annealing is a key step in wire-wound RTD manufacturing: it involves heating the platinum wire to near its melting point to relieve internal stresses, which prevents resistance shifts over time. Many low-cost suppliers skip this step to cut costs, leading to higher drift in the first few years of operation.
We also invest a lot in quality control at every stage of production. For example, every Head Type RTD’s head assembly is leak-tested with helium at 10,000 psi to ensure there are no micro-cracks that could let moisture or contaminants in. The terminal blocks are made of high-grade PEEK plastic that can withstand temperatures up to 250°C without deforming, and the RTD elements are annealed in a controlled atmosphere furnace for 48 hours before assembly. These steps add a small amount to the unit cost, but in the long run, they save our customers money by reducing downtime, product waste, and calibration costs.
Let’s put this in context with a real customer story. A few years ago, a pharmaceutical manufacturer came to us after having issues with RTDs in their freeze-drying process. They were using a competitor’s Head Type RTDs that were drifting 2°C in just 8 months, leading to batches of vaccine that were out of temperature spec and had to be destroyed. They switched to our premium wire-wound Head Type RTDs 5 years ago, and when they sent us samples for testing recently, the drift was only 0.08°C. They told us that since switching, they haven’t had a single batch rejection due to temperature measurement errors, saving them an estimated $500,000 annually. That’s the kind of impact that stable RTDs can have.
Now, what are the limits of Head Type RTD stability? No sensor is infinitely stable, but when properly selected and maintained, a high-quality Head Type RTD can provide reliable measurement for 15-20 years in many industrial applications. The key variables that affect this lifespan are operating temperature (higher temperatures accelerate drift), environmental exposure (moisture, chemicals, vibration), and calibration frequency. For example, an RTD operating at 400°C will drift faster than one at 100°C, even with the same quality element and head. That’s why we always work with customers to select the right grade based on their specific operating conditions, not just a one-size-fits-all product.
Another point to consider: long-term stability vs. short-term accuracy. Short-term accuracy is about how close the sensor reads to the actual temperature right after installation. Long-term stability is about how much that reading changes over time. You can have an RTD that’s accurate to ±0.05°C when it’s new, but if it drifts 1°C after a year, it’s not a stable sensor. All of our Head Type RTDs are specified for both initial accuracy and long-term drift, so customers know exactly what to expect over the lifespan of the product.
If you’re in the market for Head Type RTDs, or you’re looking to replace sensors that are drifting and causing issues in your process, there are a few things to keep in mind. First, don’t just go for the cheapest option—pay attention to the materials used in the head assembly, the purity of the platinum element, whether the element is annealed, and the testing the supplier does. Ask for drift rate data over 5, 10, and 15 years, not just a vague claim of “high stability.” And make sure the supplier offers calibration and support, because even the best RTDs will need re-calibration periodically.
At the end of the day, stability is what makes Head Type RTDs a better choice than other temperature sensors like thermocouples for long-term, high-accuracy applications. Thermocouples have a wider temperature range, but they drift much more over time—often several degrees after just a few years. RTDs, especially high-quality wire-wound Head Type RTDs, are designed to hold their calibration for years, which is why they’re the gold standard in industries where accuracy and reliability are non-negotiable.
If you’re looking for Head Type RTDs that are engineered for long-term stability, or you have questions about which grade is right for your application, we’d be happy to help. Our team has decades of experience working with industrial, pharmaceutical, food and beverage, and petrochemical customers, and we can provide custom solutions, testing, and support to meet your specific needs. Reach out to our team today to discuss your requirements, get a quote, or learn more about our stability testing processes.
Wire Type Thermocouple References:
- Measurement Canada. (2021). Industrial Temperature Measurement: RTD Stability and Calibration Practices.
- ASME PTC 19.3-2010. (2010). Thermometers and Thermowells for Process Measurement.
- Kubin, L., & Vojtech, L. (2018). Long-term stability of platinum RTD elements under industrial operating conditions. Journal of Sensors and Actuators A: Physical, 277, 212-219.
- International Organization for Standardization. (2015). ISO 9001:2015 Quality Management Systems Requirements for Design, Development, and Production of Temperature Sensors.
Chongqing Haichen Instrument Co., Ltd.
Chongqing Haichen Instrument Co., Ltd. is one of the most professional head type rtd manufacturers and suppliers in China for over 20 years, featured by good service and competitive price. Please rest assured to buy high quality head type rtd for sale here from our factory. For customized service, contact us now.
Address: No.11 Gusheng Road, Caojie Street, Hechuan District, Chongqing City, P.R. China
E-mail: sales@hcsensor.com
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