Characteristics of Thermocouples Standardized Thermocouple Types In the United States, nine material combinations presently are letter-designated by the American Society for Testing and Materials (ASTM) as thermocouple types: B, C, E, J, K, N, R, S, and T. Representative properties of letter-designated thermocouples are summarized in Table 1. To view that Table, Please Follow the […]
Applications of Functional Model A representative T/X sketch, Figure 1, for a dual-reference junction thermocouple with two extensions, Figure 2, illustrates T/X application. It shows one deliberately inappropriate yet plausible temperature distribution. It reveals how particular segments of thermoelements, variably, are thermally paired in electrical effect, with different segments that may be remote in the
T/X Sketch of Dual-Reference Junction Circuit An informal T/X sketch, Figure 1, plots one present distribution of temperatures, T, of all junctions against the sequence, X, in which those junctions occur in the circuit. (X is not a space variable; slopes do not represent temperature gradients.) A T/X sketch is not rendered to scale. It
Functional Model of Thermoelectric Circuits The commonplace obscure problems of thermoelectric circuits are difficult to visualize without a graphic tool. Conventional electrical circuit diagrams conceal the actual thermoelectric emf sources, unrecognized thermoelements, incorrect pairings, incidental junctions, and changing functions that often cause significant hidden thermometry error. The spurious “junction-source” model conceals the fact that all
Extensions of Thermocouple In the Figure given below, pairs P′N′, P″N″ and any additional thermoelement pairs are optional circuit extensions. A connector is an extension. Every thermoelement must be homogeneous. Only two junctions may function as the essential reference junctions. Which two depends on the type of extensions? If there are no extensions, b and
Basic Thermocouple Circuits Conventional electric circuit schematics represent passive conductors that often all are of copper. Distinctively, in thermoelectric circuits, paired legs are of very different materials and the “conductors” are the emf sources. Much more is involved than circuit connectivity. True thermoelectric schematics must explicitly acknowledge each leg material, all junctions, essential relative junction
The self-generating thermocouple is one of the more widely used (but most misunderstood) sensors for routine and specialty thermometry because of its versatility, simplicity, ease of use, and low cost. It employs the Seebeck thermoelectric effect that, unlike the related Peltier and Thomson thermoelectric effects, alone converts heat to emf. The physical cause of thermoelectric
The most significant errors affecting thermistor thermometers are: Errors in Thermistor Thermometers due to Self-heating In order to measure a resistance, a current must be passed through the thermistor, which leads to Joule heating and a small temperature increase called the self-heating error. The error, ∆T, is proportional to the power dissipated and the thermal
Thermistors are temperature-sensitive semiconducting devices. There are several types used in a wide variety of temperature measurement, switching, and sensing applications. This article will focus primarily on negative temperature coefficient (NTC) thermistors designed specifically for temperature measurement. While NTC thermistors are used over a very wide range of temperatures, from 1 K to 1000°C, we
Errors in Platinum Resistance Thermometers To fully understand the accuracy of a temperature measurement, it is imperative that all the sources of errors are understood and where possible quantified. Accuracy is not a statement of the correctness of a temperature sensor independent of its system. It is the total accuracy of the sensor system, and