Platinum resistance thermometer | Working and Construction | diagram
Fig. Platinum resistance thermometer
What is a platinum resistance thermometer? (FAQ – Thermal)
A Pt thermometer (PRT) may be a device that determines the temperature by mensuration the resistance of a chunk of pure Pt wire.
The piece of Pt wire is observed as a temperature device.
When factory-made rigorously these devices supply a superb combination of sensitivity, vary and dependability.
The resistivity of five metallic elements plotted
on a linear scale as a operate of temperature.
The data for Pt is that the results of severalclosely-spaced measurements and is plotted as a continuous curve. The data for Al, Cu, Ag and Au consists of simply a number of points with lines drawn to connect the data points.
How do PRTs work?
The electrical resistance of many metals (e.g. copper, silver, aluminium, platinum) will increase around linearly with temperature and this feature makes them helpful as temperature sensors.
The resistance of a wire of the fabric is measured by passing a current (AC or DC) through it and mensuration the voltage with an appropriate bridge or meter, and the reading is regenerate to temperature employing a standardisation equation.
The most reproducible kind of device is created from Pt as a result of it’s a stable unreactive metal which may be drawn right down to fine wires however isn’t too soft.
Using terribly pure wires, thermometers may be created with closely similar resistance characteristics and reachs} good dependability in use.
The length and diameter of the Pt wire employed in a measuring system area unit typically chosen in order that the resistance of the device at around zero ºC is a hundred ohms.
Such a device may be a referred to as a PT100 device, and its resistance changes by around zero.4 ohms per degree.
Using a typical 1 mA measuring current, at around 0 ºC a PT100 sensor would have a voltage drop of around 100 mV across its terminals and this would
change by around zero.4 mV per degree Celsius, which thus makes sensitive thermometry available to anyone with a high resolution voltmeter or resistance bridge.
In several instruments the measure is regenerate in order that the reading is directly in temperature.
Platinum sensors care factory-made to go with a regular curve at intervals a nominative tolerance.
The international normal, IEC 751, is printed within the kingdom as baccalaureate nut 60751.
The Class A tolerance for a PT100 device is ± zero.25 ºC over the range 0 ºC to ±200 ºC.
However, higher uncertainties may be achieved if the device is appropriately protected in a very steel probe and graduated on an individual basis.
For the very best accuracy, special glass-sheathed normal PRTs, usually of 25 ohms at 0 °C, are calibrated at the fixed points of the International temperature scale 1990 (see above)
NPL calibrates normal Pt resistance thermometers, victimisation fixed-points to produce reference temperatures over the ranges laid out in the ITS-90.
he Pt platinum thermometer may be a versatile instrument for temperature measuring within the vary from — 200° to 1000°C.
It is used each for preciseness measurements of the best accuracy and for routine industrial work.
This article discusses the event and construction of resistance thermometers and their uses in a very big selection of industries.
The Pt resistance thermometer—in that the principle of measuring is that the variation within the resistance of a Pt wire as a perform of temperature—is usually accepted because the most correct
temperature measuring device out there.
Its sensitivity and reliableness area unit evident from the actual fact that it had been initial utilized in 1928 to outline the International system of measurement from −190° to 660°C and has therefore
been the first international normal for over thirty years.
But it’s different blessings that realize several and increasing applications in business.
It is notably appropriate wherever measurements area unit to be revamped a comparatively slim vary of temperature, wherever the purpose of measuring is a few distance from the recording instrument,
and wherever there area unit many measure points and readings area unit-needed at one central panel.
In addition to the measuring of elevated temperatures, the Pt platinum thermometer-is additionally finding variety of applications wherever the correct-determination or management of sub-zero temperatures is required.