Resistive temperature sensors

A schematic view of the microhotplate functional elements is presented in Fig. 4.4. A resistive temperature sensor is embedded in the heated area of the microhotplate. The resistance is measured in a four-point measurement The calibration procedure of the temperature sensor will be explained in the next section (Sect. 4.1.4). The heating power dissipation is determined using also a four-point configuration. The external wiring of the heater typically adds another 5% to the heater resistance, which has to be eliminated for an accurate measurement of the dissipated power. A heating current, /heat, is applied, and the voltage drop, Vheat. across the heater is measured on chip. 

Temperature can be measured with resistive temperature sensors, thermocouple temperature sensors, and radiation pyrometers. There are two types of resistive temperature sensors the conductive type and the semiconductor type. Both operate on the principle that the resistance of sensor material changes with temperature. 

Dziedzic A, Golonka LJ, Kozlowski J, Licznerski BW, Nitsch K (1997) Thick-film resistive temperature sensors. Meas Sci Technol 8 78-85... 

The achieved data can be further converted into an output temperature signal by the electronic circuit. The resistive temperature sensor works as the resistance temperature detector (RTD) (Figure 4.14b). The working principle of such sensors is based on the changes of metal electrical resistance related to the temperature (Park et ah, 1993 Beckerath et ah, 1995). 

Figure 4.16 Designs of woven, knitted and textile-integrated printed resistance temperature sensors (Locher et al., 2005 Husain and Dias, 2009 Husain et al., 2014 Kindeldei et al., 2011, 2013).

Afterburn Control. Afterburn is the term for carbon monoxide burning downstream of the regenerator this causes an increase in temperature upstream of the expander. Temperature sensors in the gas stream cause the brake to energize. This provides sufficient resisting torque to prevent acceleration until the afterburn is brought under control by water or steam injection. 

Verifying temperature is the second most important aspect of any compressor operation. As with pressure, the basic form of measurement is a simple temperature gauge. The construction of the gauges is quite varied, ranging from a bimetallic device to the filled systems. When transmis sion is involved, the sensor becomes quite simple, taking the form v)l a thermocouple or a resistance temperature detector (RTD). The monitor does the translation from the native signal to a temperature readout ()r signal proportional to temperature. 

Short Normal Resistivity (after Anadriii). The short normal (SN) resistivity sub provides a real-time measurement of formation resistivity using a 16-in. electrode device suitable for formations drilled with water-base muds having a moderate salinity. A total gamma ray measurement is included with the resistivity measurement an annular bottomhole mud temperature sensor is optional. The short normal resistivity sub schematically shown in Figure 4-273 must be attached to the MWD telemetry tools and operates in the same conditions as the other sensors. 

Because of their high heat capacity, only few of the thermometers described in Chapter 9 can be used as sensors for detectors. Resistance (carbon) sensors were used for the first time in a cryogenic detector by Boyle and Rogers [12] in 1959. The carbon bolometer had a lot of advantages over the existing infrared detectors [13]. It was easy to build, inexpensive and of moderate heat capacity due to the low operating temperature. 

The ambient temperature sensor in the IRT 3000 is a KTY type spreading resistance sensor. The resistance of the sensor can be written as a second order polynomial function... 

Here R0 is the resistance at 0°C, and a and b are coefficients whose values are specified in internationally agreed standards covering platinum temperature sensors, for example DIN EN 60751. The coefficient b is so small that for most applications one can assume a linear relation between Rt and the temperature t. 

Platinum electrodes 2, temperature sensor in the heat transfer medium 3, resistance thermometer 4, product sample 5, heat transfer medium 6, resistance heating. 

Figure 7.9 Scheme of the aneroid dynamic combustion calorimeter designed by Adams, Carson, and Laye [77], A jacket B jacket lid C motor that drives the rotation of calorimetric system D rotation system E bomb (which is also the calorimeter proper) F channels to accommodate the temperature sensor, which is a copper wire resistance wound around the bomb G crucible H electrode I gas valve. Adapted from [77]. 

Figure 8.1 Scheme of a Dewar vessel isoperibol reaction-solution calorimeter. A ampule containing the sample B ampule breaking system C calorimeter head D temperature sensor E stirrer F electrical resistance G Dewar vessel H plunger of the ampule breaking system I, J inlets K plug connecting the calibration resistance to the calibration circuit. 

Figure 12.3 Schemeofa power compensation differential scanning calorimeter. A sample furnace Ar reference furnace B temperature sensor of the sample furnace Br temperature sensor of the reference furnace C resistance heater of the sample furnace Cr resistance heater of the reference furnace D cell S sample R reference.

A cross-sectional schematic of a monolithic gas sensor system featuring a microhotplate is shown in Fig. 2.2. Its fabrication relies on an industrial CMOS-process with subsequent micromachining steps. Diverse thin-film layers, which can be used for electrical insulation and passivation, are available in the CMOS-process. They are denoted dielectric layers and include several silicon-oxide layers such as the thermal field oxide, the contact oxide and the intermetal oxide as well as a silicon-nitride layer that serves as passivation. All these materials exhibit a characteristically low thermal conductivity, so that a membrane, which consists of only the dielectric layers, provides excellent thermal insulation between the bulk-silicon chip and a heated area. The heated area features a resistive heater, a temperature sensor, and the electrodes that contact the deposited sensitive metal oxide. An additional temperature sensor is integrated close to the circuitry on the bulk chip to monitor the overall chip temperature. The membrane is released by etching away the silicon underneath the dielectric layers. Depending on the micromachining procedure, it is possible to leave a silicon island underneath the heated area. Such an island can serve as a heat spreader and also mechanically stabihzes the membrane. The fabrication process will be explained in more detail in Chap 4. 

The suggested procedure to arrive at this goal is presented in Fig. 3.1. It starts with the transfer of a certain microhotplate layout into a geometry model for a complex FEM simulation. This step is shown in Fig. 3.2 and will be explained in more detail in one of the next sections. A complex 3-d FEM simulation is then performed. The results of this simulation are used to produce a lumped-element model. This model is translated into a hardware description language (HDL). Using the resistances of the device elements such as the heater resistance, Rheat> and the resistance of the temperature sensor, Rx. co-simulations with the circuitry can be performed. 

The thermal resistance will be temperature-dependent as canbe seen in Eq. (3.24), which is not only a consequence of the temperature dependence of the thermal heat conduction coefficients. The measured membrane temperature, Tm, is related to the location of the temperature sensor, so that the temperature distribution across the heated area will also influence the thermal resistance value. The nonlinearity in Eq. (3.24) is, nevertheless, small. The expression thermal resistance consequently often refers to the coefficient t]o only, which is used as a figure of merit and corresponds, according to Eqs. (3.24) and (3.25), to the thermal resistance or thermal efficiency of the microhotplate at ambient temperature, Tq. The temperature Tm can be determined from simulations with distinct heating powers. The thermal resistance then can be extracted from these data. 

The temperature sensor in the membrane center is made of polysilicon with a nominal resistance of 10 kQ. An additional reference resistor is needed for the control circuitry (Sect. 5.1). For the resistance measurement of the sensitive layer, platinum electrodes are deposited on top of the CMOS aluminum metallization in order to establish good electrical contact to the sensitive metal oxide. 

For thermal characterization and temperature sensor calibration a microhotplate was fabricated, which is identical to that on the monoHthic sensor chips, but does not include any electronics. The functional elements of this microhotplate are connected to bonding pads and not wired up to any circuitry, so that the direct access to the hotplate components without electronics interference is ensured. The assessment of characteristic microhotplate properties, such as the thermal resistance of the microhotplate and its thermal time constant, were carried out with these discrete microhotplates. 

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