Temperature sensores

In modern industrial measurement technology, plant engineering, and process engineering, the temperature sensor is the most frequently used element for precisely monitoring, controlling, and regulating complex thermal processes. In practice, the requirements placed on such measuring equipment are multifaceted: a sensor must not only withstand severe mechanical stress, vibration, and often aggressive chemical media, but also deliver reproducible and highly accurate measurement results over many years. Since no universal measuring element exists in industrial practice that equally satisfies all requirements, our product range is differentiated into various technological approaches.

Which temperature sensor is the right choice for your specific system depends primarily on the required temperature range, the demanded accuracy, the dynamics of the process, and the available mechanical installation options on site. Precise temperature measurement and continuous temperature monitoring not only ensure the consistent quality of your end products, but in many process engineering systems also serve as indispensable overtemperature protection or overload protection for expensive machines, pumps, and downstream electronic components. Investing in the right sensor technology therefore has a decisive impact on overall efficiency and on preventing unplanned downtime in your production lines.

Resistance Thermometers: The Physical Principles of Platinum Measurement Technology

Whenever industrial processes require maximum reproducibility, excellent long-term stability, and the highest measurement accuracy, resistance-based temperature sensors are the first choice worldwide. Their fundamental operating principle is based on a basic physical property of metals: the integrated measuring resistor changes its electrical resistance value directly as a function of the surrounding temperature. Since the electrical resistance of pure metals increases as temperature rises, these materials possess a positive temperature coefficient. In industrial practice, the precious metal platinum has established itself as the global standard material.

Platinum resistors exhibit outstanding chemical resistance, show minimal aging effects, and provide excellent linearity across a very wide temperature range from -200 to over 600 °C. A decisive advantage for plant operators is that these measuring elements are internationally standardized. A worn or defective sensor can therefore be replaced at any time with an identical model without requiring time-consuming recalibration of the connected measuring instrument or programmable logic controller.

Within the family of platinum sensors, distinctions are made according to nominal resistance:

The Pt100 is the absolute classic and the most widely used temperature sensor in industrial process engineering. Its designation is derived directly from its physical properties: it has a nominal resistance of exactly 100 ohms at a temperature of exactly 0 °C. Since the characteristic curve of platinum behaves approximately proportionally to actual temperature changes over wide ranges, the measured resistance value can be converted into a precise temperature value within the measuring instrument with relatively little mathematical effort.

The Pt1000 is becoming increasingly important in modern industrial sensor and automation technology. With a nominal resistance of exactly 1000 ohms at 0 °C, its nominal resistance is exactly ten times higher than that of the classic counterpart. This increase provides technical advantages in signal transmission over longer cable distances, because the inherent electrical resistance of the connection cables becomes proportionally insignificant relative to the sensor resistance. This simplifies electrical installation and reduces error influences.

The Pt500, with a base resistance of exactly 500 ohms at 0 °C, forms a solid bridge between the two primary standards. This variant is mainly used in specific applications such as industrial heat quantity measurement or in specialized legacy systems where the input cards of the evaluation electronics are specifically designed for this intermediate value.

Design and Manufacturing Technologies of Industrial Measuring Resistors

The internal characteristics and mechanical construction of a sensor decisively determine its robustness against thermal cycling and mechanical shock. In our online shop you will find temperature sensors based on various manufacturing technologies in order to satisfy every application.

Historically established, proven, and still indispensable for applications with the highest accuracy requirements is the wire-wound measuring resistor. In this classic design, an ultra-thin, highly pure platinum wire is embedded in fine loops or windings inside a protective enclosure. Robust ceramic materials capable of withstanding extreme temperatures or specially vibration-resistant glass are used as carrier and insulation materials. Glass resistors are characterized by outstanding resistance to vibration and, in certain designs, can even be directly immersed into liquid media because the glass hermetically seals the sensitive wire against chemical attack. However, the wire-wound design is relatively complex to manufacture.

The more modern, economical, and currently most widespread variant in everyday industrial use is the thin-film sensor. In this process, an extremely thin platinum layer is vapor-deposited onto a high-purity ceramic substrate under vacuum conditions and subsequently structured using precise laser technology in order to achieve the exact nominal resistance. Due to its extremely low mass, such a thin-film temperature sensor offers excellent dynamic response and reacts rapidly to thermal changes within the medium.

Furthermore, this manufacturing method is highly automated, making these sensors significantly more cost-effective and economical to procure compared with traditional wire-wound elements. You therefore receive a highly precise measuring element with an optimal price-performance ratio without compromising reliability or industrial service life.

Accuracy, Tolerance Classes, and the Interpretation of Limit Deviations

In industrial metrology, accuracy is not a coincidence but a parameter regulated by strict standards. The globally valid standard defines various tolerance classes for platinum measuring resistors, of which Class A and Class B are the most important pillars in everyday industrial use. A Class B temperature sensor perfectly covers standard requirements in general mechanical engineering, heating technology, and basic plant engineering. The defined limit deviation is entirely sufficient for the vast majority of standard processes.

However, if your process requires particularly precise acquisition of physical values — for example in the pharmaceutical industry, food processing, or critical chemical reactions — you should definitely use Class A sensors. These offer significantly tighter error tolerances. For absolute high-end applications, even narrower classifications such as one-third or one-tenth of Class B are available.

For the design engineer, however, one detail is of outstanding practical importance: the guaranteed tolerance classes universally apply only within a very specific temperature range precisely defined by the standard. If a sensor is operated outside this specified temperature window, it no longer complies with the guaranteed accuracy, and measurement errors can increase asymmetrically and unpredictably. A precise analysis of the expected operating range is therefore essential before purchase.

Selecting the Appropriate Connection Technology: Systematically Avoiding System Errors

To ensure that the resistance value precisely determined by the temperature sensor reaches the evaluating measuring instrument completely unaltered, the connection technology must be selected with great care. Every connection cable possesses its own electrical resistance, which changes as a function of temperature and can massively influence the measurement result.

The simplest but also most error-prone installation method is the 2-wire technique. Here, the sensor is connected to the electronics using only two conductors. The resistance of the lead wires is directly and uncompensatedly added to the actual resistance value of the sensor. In the case of a Pt100, even a few meters of cable length lead to falsification of the measurement result. Although this simple method is considerably less sensitive with the Pt1000 due to its tenfold higher base resistance, it is often still unsuitable for long cable runs. The 2-wire arrangement is therefore recommended only for very short distances or when the downstream measuring instrument allows manual software compensation of the cable resistance.

To eliminate this systematic error without manual effort, the 3-wire technique was developed, which today represents the undisputed standard in industrial process automation. In this arrangement, a third conductor is routed to the temperature sensor. The measuring instrument determines the resistance of this cable loop and mathematically subtracts this value from the measured total resistance. In practice, this automatic temperature compensation of cable error functions perfectly, but requires that all three conductors have exactly the same cross-section, consist of the same material, and are exposed to identical ambient temperatures along their entire length.

For laboratory applications, calibration tasks, or industrial processes requiring absolute uncompromising precision, the 4-wire technique is the only correct choice. A completely constant, defined current is supplied through the sensor via two separate conductors, while the voltage drop across the sensor is measured with extremely high impedance through the other two conductors. Since practically no current flows through the actual measurement leads due to the high internal resistance of the measuring instrument, the cable resistance becomes entirely irrelevant. This method always delivers the absolutely exact resistance value of the measuring element regardless of actual cable length or temperature fluctuations along the cable route.

Another physical effect that every technician must consider during design and commissioning is so-called self-heating. Since an electrical current must flow through the sensor in order to determine the resistance value, a minimal power loss is generated within the measuring element according to the fundamental laws of electrical engineering, which is converted into heat. If the measurement current selected by the measuring instrument is too high, the temperature sensor heats itself and indicates an erroneously elevated measured value. High-quality industrial measuring instruments therefore keep this current as low as possible.

NTC and PTC Sensors for Specific Monitoring Tasks

These sensors are manufactured on the basis of semiconductor materials. Compared directly with Pt100 and Pt1000 sensors — although these also belong to the category of positive temperature coefficient devices — they exhibit a strongly non-linear characteristic curve, but offer high sensitivity within a frequently narrow temperature window, making them predestined for specific applications. A fundamental distinction is made between two opposing operating principles.

Thermistors, universally known in technical terminology and everyday use as NTCs (Negative Temperature Coefficient), drastically reduce their electrical resistance as temperature rises. They react sensitively to the smallest temperature changes, allowing very high-resolution measurement within their primary operating range. This typically lies between -50 °C and +150 °C. Absolute industrial standards include the NTC 5kΩ and the NTC 10kΩ, where these characteristic values always refer to the nominal resistance at an ambient temperature of 25 °C.

To calculate the exact temperature from the measured resistance value of a thermistor, the evaluation electronics use specific material constants, especially the so-called B-value, which describes the progression of the exponential characteristic curve. NTC sensors are an extremely cost-effective and economical solution and are therefore used millions of times in building technology, HVAC systems, and automotive engineering for temperature monitoring. However, care must be taken during selection to ensure compatibility between the sensor and the respective system.

Positive temperature coefficient devices, also known as PTCs, behave in exactly the opposite manner: their electrical resistance increases with rising temperature. A special property of many PTC semiconductor components is their extremely steep, almost abrupt increase in resistance upon reaching a very specific material-dependent nominal temperature. This characteristic behavior makes the PTC sensor the ideal component for use as a binary overtemperature or overload protection device.

Embedded into the windings of electric motors, transformers, or power electronics, they function as reliable guardians: as soon as the permissible operating temperature is exceeded, the resistance of the PTC rises sharply, whereupon the downstream protective switching device immediately disconnects the load circuit. This simple but highly effective protection reliably safeguards expensive machine components against thermal destruction.

Thermocouples: The Indestructible Specialists for Extreme Temperature Ranges

As soon as the required measuring range exceeds the physical limits of conventional resistance thermometers or semiconductor sensors, thermocouples become indispensable. A thermocouple is based on a fundamental physical principle known as the Seebeck effect: if two wires made from completely different metals or metal alloys are welded together at one end and a temperature difference exists between this measuring junction and the open ends, a small electrical voltage can be detected. This thermoelectric voltage exhibits a directly reproducible relationship to the temperature difference between the measuring junction and the so-called reference junction within the measuring instrument.

Thermocouples are characterized by extremely short response times because the actual measuring junction can be made very small. Furthermore, depending on the selected material combination — such as Type K (NiCr-Ni), Type J (Fe-CuNi), or Type N — they cover a monumental temperature spectrum ranging from deep cryogenic temperatures to well above 1000 °C in industrial melting furnaces, hardening plants, or exhaust gas systems. Since this is a purely voltage-generating system into which no external current must be injected, the problem of self-heating simply does not exist in thermocouples.

However, the design engineer must consider that the measuring instrument can only measure the difference between the sensor tip and the connection point. Therefore, precise temperature compensation within the evaluation instrument — often referred to as cold junction compensation — is absolutely required in order to determine the absolute temperature value accurately and without error.

Modern Digital Sensors and the Future of System Integration

In today’s Industry 4.0 environment, measurement technology is increasingly moving away from purely analog, resistance-based sensors toward intelligent, networked systems. Modern digital sensors integrate the actual measuring element, analog signal amplification, characteristic curve linearization, and the analog-to-digital converter onto a single compact silicon chip directly inside the sensor. These highly advanced digital sensors no longer provide analog raw data but instead transmit the precisely calculated measured value as a finished digital signal directly to the higher-level controller via standardized protocols such as IO-Link, Modbus, I²C, or other systems. The tangible advantages of this technology are revolutionizing industrial installation: the digital signal is immune to electromagnetic interference commonly encountered in industrial environments. In addition, all error sources caused in analog systems by cable resistance, inadequate cable shielding, or contact resistance at terminals are eliminated. Complex temperature compensation or extensive scaling within the control computer is no longer required.

These modern sensors are used wherever compact designs, maximum immunity to interference, and comprehensive diagnostic capability down to the field level are required. Nevertheless, the classic robust platinum temperature probes continue to retain their undisputed justification in extremely harsh environments, under very high pressures, or at extremely high temperatures, since silicon chips inherently possess narrower thermal limits.

Mechanical Protection Mechanisms for Maximum Operational Reliability

In practical industrial use, it is by no means sufficient to merely select the electrically appropriate measuring element. Sensitive sensor technology must also be mechanically and chemically protected against harsh environmental conditions at the installation site. In pipelines, reactors, and tanks, sensors are therefore almost always installed in combination with a robust thermowell. This mechanical encapsulation protects the actual measuring element against high flow forces, abrasive particles within the medium, as well as corrosive or aggressive chemical substances. An additional advantage is that the sensor can easily be connected with a lead cable and replaced during maintenance or in the event of a defect while the system remains in operation, without emptying the pipeline or interrupting the process.

On the electrical side, modern evaluation systems must also be comprehensively protected against operator errors, installation faults, and defects. A thoroughly engineered and professionally designed overall temperature monitoring concept therefore combines precise and durable sensor technology with robust mechanical and electrical protection. This guarantees maximum operational reliability, highest process stability, and minimizes the risk of unforeseen and costly production downtime to an absolute minimum for plant operators.