Sensors Seebeck effect

When different regions of an electric conductor or semiconductor are at different temperatures, there is an electric potential between these regions that is directly related to the temperature differences. This phenomenon, known as the Seebeck effect, can be used to produce a temperature sensor, a thermocouple, by taking a wire of metal or alloy A and another wire of metal or alloy B and connecting... 

Thermocouple (Fig. 2) is one of the most widely used sensors for temperamre measurement and control. The mechanism underlying the function of thermocouples is the so-called thermoelectric effect or Seebeck effect, named after the German-Estonian physicist Thomas J. Seebeck in 1821. 

Flow measurement using thermoelectric devices and sensors implies the use of heat transfer and temperature measurements in microchatmels to determine the near-wall velocity. With appropriate calibration procedures, the mean fluid flow velocity or mass flow rate can be determined by measurements of the local wall temperature. Thermoelectric temperatrue probes and sensors, also known as thermocouples, rely on the Seebeck effect, where a temperatrue difference between two different metal contacts induces a voltage drop which can be electrically mea-strred. An electrical resistance heater introduces a heat flux into the fluid flow. The temperature is measured directly either at the heater, in its vicinity, or at the wall downstream of the heater. Often, the upstream mean temperature of the fluid flow is also measured to provide a comparison. Thermoelectric flow rate measurement is a very common measuring technique and for laminar flow one of the most accurate, reliable, and cost effective. 

Due to their compactness and standard fabrication technology, the temperature in thermal flow sensors is often measured by thermocouples, which rely on the thermoelectric effect. The thermoelectric effect describes the coupling between the electrical and thermal currents, especially the occurrence of an electrical voltage due to a temperature difference between two material contacts, known as the Seebeck effect. In reverse, an electrical current can produce a heat flux or a cooling of a material contact, known as the Peltier effect. A third effect, the Thomson effect, is also connected with thermoelectricity, where an electric current flowing in a temperature gradient can absorb or release heat from or to the ambient [10, 11]. The relation between the first two effects can be described by methods of irreversible thermodynamics and the linear transport theory of Onsager in vector form. 

Thermocouples are rugged and versatile temperature sensors frequently found in industrial control systems. A thermocouple consists of a pair of dissimilar metal wires twisted or otherwise bonded at one end. The Seebeck effect is the physical phenomena which accounts for thermocouple operation, so thermocouples are known alternatively as Seebeck junctions. The potential difference (Seebeck voltage) between the fi ee ends of the wire is proportional to the difference between the temperature at the junction and the temperature at the fi ee ends. Thermocouples are available for measurement of temperature as low as —270°C and as high as 2300°C, although no single thermocouple covers this entire range. Thermocouples are identified as type B, C, D, E, G, J, K, N, R, S, or T, according to the metals used in the wire. 

Thermocouples/Thennopiles. Thermocouples operate on the basis of the Seebeck effect. If wires fabricated from two different metals or semiconductors are soldered together to form a circuit, any temperature difference that exists between the joined points leads to a measurable potential difference, the magnitude of which depends on the extent of the temperature difference and the materials involved. The use of several thermocouples connected in series thermopiles) increases the sensitivity of the sensor, but if a single thermocouple is damaged the entire sensor is affected. It is more difficult to miniaturize thermoelectric sensors than resi.stance devices, and the long-term stability of thermocouples is often not good, A typical response time is less than one second. 

McAleer JE, Moseley PT, Bourke P, Norris JO, Stephan R (1985) Tin dioxide gas sensors use of the Seebeck effect. Sens Actuators 8 251-256... 

Additional information can be provided by measurements performed at the same conditions, with results so far not commonly used as sensor signals. Examples include monitoring work function changes [135,136], catalytic conversion of CO to CO2 [98], mobilities [156,157], AC impedance spectroscopy and frequency dependent resistance data [35,36], simultaneous calorimetric and resistive measurements [13,14], and Seebeck effect [33,34,158],... 

Siroky, K. Use of the Seebeck effect for sensing flammable gas and vapours. Sensors Actuators B 1993,17,13-17. 

Vlachos, D.S., Papadopoulos, C.A., and Avaritsiotis, J.N. A technique for suppressing ethanol interference employing Seebeck effect devices with carrier concentration modulation. Sensors Actuators B 1997, 44, 239-242. 

In modem electrical engineering, measurement of temperature can performed by various different methods, starting from a most basic bimetal temperature switches up to laser pre-celebrated semiconductor sensors with high accuracy (Boyes, 2010). The most basic principle of measuring temperature in industrial plants is the use of thermocouple probes by exploiting the thermoelectric effect in metals (called the Seebeck effect) that... 

---