Platinum temperature sensors

Sensors in Household Appliances (Sensors Applications Volume 5). 

Copyright 2003 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 3-527-30362-6 

Pnotollthograpti Icall y structured platinum thin film 

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Temperature control is one of the longest established and most important functions in household appliances. One example of modern thin film fabrication technology of platinum temperature sensors with application examples in the kitchen in hot plates and ovens is given in Chapter 5.1. 

Fig. 5.1 Schematic diagram of the structure of a platinum temperature sensor.

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. 

For each type of sensor, a classification framework sets precision tolerance ratings. Platinum temperature sensors have a positive temperature coefficient which is defined as ... 

An economic large-scale production of platinum temperature sensors is now possible due to the application of modern manufacturing techniques based on thin-film technology. This development has led to price levels which were previously the exclusive domain of NTC elements. 

Given this situation, it is not surprising that, over the last few years, products based on platinum thin film technology have been finding their way into the home. With the growing use of electronic control systems in the new generation of domestic appliances, platinum temperature sensors have been more widely used in ovens where they have replaced electromechanical regulators such as capillary tubes, solid expansion thermometers and NTC thermistors. Typical sensor applications in the food preparation sector are shown in Fig. 5.3. 

Intelligent process control based on platinum temperature sensors and tailored electronics provides an effective method of improving both kitchen safety and the user friendliness of kitchen appliances, and also contributes to reducing energy consumption. 

A novel microhotplate design was proposed to overcome the CMOS operating temperature limit and to avoid polysilicon-induced drift problems. A cross-sectional schematic of the device is shovm in Fig. 4.11. Instead of using a polysilicon resistor as temperature sensor, a platinum temperature sensor is patterned on the microhotplate. The Pt-metallization process step was used to simultaneously fabricate the electrodes and the temperature sensor. The CMOS-Al/Pt contacts are located off the membrane... 

The voltage drop across the platinum temperature sensor is small since the platinum resistor has a nominal resistance of only 75 Q. The fully-differential LNA amplifies the minute voltage drop in order to provide an useful feedback signal to the differential-analog proportional controller. A simplified schematic of the fully-differential low-noise amplifier is shown in Fig. 5.18. 

The mixture was used as purchased from Fluka AG. The submitters have occasionally used, as a bath liquid, petroleum ether (bp 40-60°C) of unknown composition or pure isopentane (mp — 160°C). In such cases, temperature control is necessary it was achieved with a platinum temperature sensor inside the reaction mixture. 

The principle discussed above has been used to develop an electronically adjustable miao chemostat valve allowing feedback control to keep constant concentration of certain species in solution. " The chemostat consists of silicon-based upper and bottom plates as well as a circuit card for the elertric connection to the PC-controlled power supply. The upper plate carries a platinum temperature sensor and contains a hydrogel chamber ((600 x 600 x SSOjpm ), which is covered by a perforated membrane. The bottom plate has similar con-stmction with an integrated platinrrm heating element (Figure 36(a)). ... 

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