You’ve probably heard the term “platinum resistance” regarding thermometers. If you haven’t, you may not understand why you should care.
As Process Parameter explains (https://www.processparameters.co.uk/temperature-probes/), the reason is that most thermometers are not accurate enough to be used for critical applications.
That’s why you need to choose a thermometer that is certified for use with platinum-based alloys.
In this post, we’ll discuss what you need to consider when choosing a platinum resistance thermometer.
We’ll also cover the benefits of using a platinum-based alloy thermometer in your lab.
What Is A Platinum Resistance Thermometer?
Platinum is used to determine the temperature in the platinum resistance thermometers. Platinum is a non-reactive metal that may be easily fashioned into tiny wires.
Platinum is utilised as a sensing element in thermometers because of its characteristics. It operates on the premise that the resistance of platinum varies with temperature.
The thermometer measures temperatures are ranging from 200°C to 1200°C.
Professor H. L. Callendar, C.B.E., F.R.S., introduced and developed the platinum resistance thermometer, the most precise and sensitive temperature measuring technique.
What To Look For In A Platinum Resistance Thermometer
The platinum is often made into fine or thick sheets, or its wire is stacked in helical coils, the more coils are used, the greater the sensitivity.
The film or wire is enclosed in glass or ceramic and supported by loose or compacted MgO.
The probe unit is connected to the thermometer electronics through platinum-based leads, which convert the electrical signal to temperature.
P.R.T.s are widely classified into two types based on sensitivity and robustness: Industrial P.R.T.s (IPRTs) and SPRTs. P.R.T.s are classified into various classes by ASTM and I.E.C., each having its own set of standards.
Temperature Sources
Dry-wells and calibration baths are the most often used temperature sources for P.R.T. calibration.
Dry-wells are employed in situations where probe uniformity is required, but only a moderate level of precision is required.
Calibration baths should be used when accommodating probes of various shapes and sizes or when more precision is desired.
Use an LN2 comparison device for the lowest temperatures and a calibration furnace for the highest temperatures.
The two most crucial factors to examine are uniformity and stability. The level of immersion is also a concern. Calibration mistakes will occur if the immersion depth is insufficient.
Furthermore, if the reference probe is a glass sheath SPRT, some protection should be applied at higher temperatures to avoid glass sheath devitrification and contamination of the platinum sensor.
Calibration of short U.U.T.s involves several challenges due to the temperature source. It would be best to properly submerge the probe without exposing the transition junction to high temperatures.
In these cases, dry-well temperature sources are frequently a preferable alternative. Some calibration baths contain fluid level adapters that elevate the fluid level to the top of the bath lid.
You can also use these adapters to calibrate short probes satisfactorily. The application itself is the most crucial factor, regardless of the sort of temperature source employed.
Even if an instrument is outstanding, it may not work well in a certain application if it is not well matched.
To guarantee a good match, carefully examine the requirements before picking the temperature source.
Types of Usage
P.R.T.’s are used in many industries, and each industry will require a different type due to the difference in usage.
A contemporary passenger plane may include up to fourteen resistance thermometers. These are needed to monitor the temperatures of the oil, gasoline, cabin air, outside air, and de-icing mats.
Base metal thermocouples could be used to monitor such temperatures, but they would need to be controlled or adjusted for the cold junction temperature, and their low output would require a piece of highly sensitive measurement equipment or some amplification.
Platinum resistance thermometers with stainless steel sheaths are thus recommended when used in combination with ratio-meter indications.
Resistance thermometers, often with Wheatstone bridges and multi-point indications, are used in power plants to measure steam, gas, and water temperatures.
Nearly a hundred platinum resistance thermometers connected to multi-point indications may be seen aboard ships transporting chilled meat or fruit, whereas, in the regulation of space-heating in huge structures such as theatres, a lot of instruments will be similarly coupled to one indicator.
The chemical industry, one of the main consumers of platinum resistance thermometers, uses the devices for accurate laboratory measurements and indication, recording, and control in process plants across the business.
Advantages & Disadvantages Of Platinum Resistance Thermometers
There are many benefits for platinum resistance thermometers; here are some of the reasons you should consider using one.
Advantages
The drawbacks of platinum, thermal resistance are as follows:
- Temperature measuring using a platinum resistance thermometer is simpler than with a gas thermometer
- The metre provides an accurate temperature measurement
- The thermometer has a temperature range of 200 to 1200° Celsius
- The thermometer is quite sensitive
- At the same temperature, platinum has the same resistance
- The resistance-temperature connection is widely understood
- IPRTs are built to last, and the cost of an IPRT is cheaper than that of an SPRT
- For specialised uses, numerous forms and sizes are available
- You can use it in conjunction with digital temperature reading equipment
Disadvantages
The drawbacks of platinum, thermal resistance are as follows:
- The delayed reaction of the thermometer
- The thermometer’s melting point is 1800° Celsius. However, when the temperature of platinum exceeds 1200°C, it begins to evaporate
- Drift is caused by mechanical stress and vibration
- Lead-wire compensation is required for 2- and 3-wire devices
- IPRTs that are not hermetically sealed will decay in damp situations
- Not as precise as an SPRT
Platinum Resistance Thermometers: Final Thoughts
Platinum resistance thermometers play an essential role no matter what industry you work in. They come with their advantages and disadvantages, but one outweighs the other.
They are not the best for standard uses at home or medical uses, but they excel in other industries that are concerned with and require thermometers with much higher and lower temperature measurements and sensitivities.
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