Resistance Temperature Detector

Temperature to resistance equation

The relation between temperature and resistance is given by the Callendar-Van Dusen equation

Here, RT is the resistance at temperature T, R0 is the resistance at 0 °C, and the constants (for an alpha=0.00385 platinum RTD) are

Since the B and C coefficients are relatively small, the resistance changes almost linearly with the temperature.

• Platinum resistance thermometer

Notable characteristics

When pure, the metal appears greyish-white and firm. The metal is corrosion-resistant. The catalytic properties of the six platinum family metals are outstanding. For this catalytic property, platinum is used in catalytic converters, incorporated in automobile exhaust systems, as well as tips of spark plugs.
Platinum's wear- and tarnish-resistance characteristics are well suited for making fine jewellery. Platinum is more precious than gold. The price of platinum changes along with its availability, but its price is normally slightly less than 150% of the price of gold. In the 18th century, platinum's rarity made King Louis XV of France declare it the only metal fit for a king.
Platinum possesses high resistance to chemical attack, excellent high-temperature characteristics, and stable electrical properties. All these properties have been exploited for industrial applications. Platinum does not oxidize in air at any temperature, but can be corroded by cyanides, halogens, sulfur, and caustic alkalis. This metal is insoluble in hydrochloric and nitric acid, but does dissolve in the mixture known as aqua regia (forming chloroplatinic acid). Common oxidation states of platinum include +2, and +4. The +1 and +3 oxidation states are less common, and are often stabilized by metal bonding in bimetallic (or polymetallic) species.The gold is removed from this solution as a precipitate by treatment with iron(II) chloride (FeCl2). The platinum is precipitated out as impure (NH4)2PtCl6 on treatment with NH4Cl, leaving H2PtCl4 in solution.

Applications

As a catalyst in the catalytic converter, an optional (though often mandatory by law) component of the gasoline-fueled automobile exhaust system (see "Notable characteristics" in this article).
As a catalyst in fuel cells. Reducing the amount of platinum required (and thus cost) is a major focus of fuel cell research.
Certain platinum-containing compounds are capable of crosslinking DNA and kill cells by similar pathways to alkylating chemotherapeutic agents. Cisplatin, carboplatin and oxaliplatin are licensed examples of this class of drugs.
Platinum resistance thermometers.
Electrodes for use in electrolysis and electrochemical measurements (e.g., the standard hydrogen electrode).
In the Clark polarographic electrode for measuring oxygen tension.
A wide range of jewellery
As a catalyst in the curing of silicone elastomers.
As a catalyst in glow plugs in some model engines.
Crucibles for high temperature melting of glass (for example) up to 1500°C better if alloyed with rhodium (10–40% of Rh).
In photography, it is sometimes used for archival printmaking. Platinum prints display a greater range of tones than other Black and White printing methods. Additionally platinum's chemical stability makes for extremely long-lasting prints. The disadvantage of this method, in addition to the high cost, is that platinum is less light sensitive and prints must be contact printed at the same size as the negative. Therefore, enlargements can only be made by making an enlarged negative.
In watchmaking, Vacheron Constantin, Patek Philippe, Rolex, Breitling and other companies use platinum for producing their limited edition watch series. Watchmakers highly appreciate unique properties of platinum as it neither tarnishes nor wears out and is ideal for gems setting. Vacheron Constantin started using platinum in watch production as early as in 1820. Today the company has a whole collection of platinum timepieces, Collection Excellence Platine, with the Malte Tourbillon Regulator and the Malte Perpetual Calendar Chronograph models introduced in 2007.