Calibration bath or dry-well calibrator – which is the right choice?

Temperature sensors – like all other sensors – must be calibrated at regular intervals. This ensures they deliver accurate and consistent measured values. Temperature calibration (e.g. using a calibration bath or dry-well calibrator) is generally carried out by measuring temperature points within the temperature range of the probe. The results are then compared with a reference instrument. Fixed points such as the triple point of water can also be used. This is determined on the international temperature scale from 1990 (ITS-90). By means of the fixed-point method, laboratories can measure and check high-accuracy thermometers such as SPRTs (“standard platinum resistance thermometers”) using a predefined point.

For temperature calibration, various tools can be used depending on the environment, application and industry. Two of the most common tools – with a similar functionality and stability – are the calibration bath and the dry-well calibrator. Both instruments can reach different levels of uncertainty and act as a stable temperature source. The evaluation of their differences and the decision on which of the two to use depends on the application.

Calibration bath – functionality and application possibilities

For a higher degree of temperature uniformity, industry experts recommend calibration baths. Depending on the temperature to be measured for calibration, the bath is either filled with water or with certain types of oil. The probes are immersed for measurement. The water or oil circulates in the calibration bath so that the desired temperature is maintained. Depending on the liquid and the temperature controllers used for heating and cooling, operators often use several baths with different temperature ranges. The sensors can therefore be calibrated at a wide variety of temperatures.

Calibration baths are available either in the form of portable instruments or as large, permanently installed laboratory equipment. They achieve the lowest calibration uncertainties as a result of the stable and uniform temperature environment they generate. Another advantage is that probes of all sizes and shapes can be calibrated, so long as they can be completely immersed. However, the design of a calibration bath can also be restrictive. Since the test item is immersed in oil or water, calibration baths cannot be used in sterile environments (in which there must be no contamination). A probe which is used in the food industry for temperature measurement of milk, for example, might contaminate the product if it is immersed in oil for calibration.

Dry-well calibrator – functionality and application possibilities

Sterile industries generally rely on dry-well calibrators to calibrate their temperature probes. Their use can be both portable and also stationary in calibration laboratories. Dry-well calibrators are fitted with inserts. These are used to perfectly adapt the probe to the temperature in the block. For calibration, the test item is inserted into the hole provided in the calibration insert. Here, care must be taken that the probe is firmly seated. There should be a maximum of a few millimetres of clearance in order to prevent air flow around the temperature probe which is being checked. The ambient air can influence the measured values and thus falsify the calibration results. If a built-in controller is used, the dry-well calibrator heats or cools to the set temperature in order to check the measurements of the probe and to carry out the necessary calibrations.

Dry-well calibrators are often preferred as a portable calibration method. The user is thus spared having to handle any liquids. They also have the advantage that the probes do not come into contact with other substances that could be harmful to the end product. However, calibrating several probes at once can be a challenge if they have measuring heads which can interfere with each other. In this case, the number of calibrations that can be carried out simultaneously is limited. The user must also purchase several inserts – suitable for the various probes. Most inserts are made of brass or aluminium, although these are not well suited for calibrations at extremely high temperatures. In these applications, ceramic sleeves should be used to ensure a more stable temperature.

Conclusion

Ultimately, the choice between calibration bath and dry-well calibrator depends on the requirements of the respective application. The criteria for consideration are: temperature range, portability, handling of liquid media and temperature stability.

Author: Danica Schwarzkopf
Product Management, WIKA Alexander Wiegand SE & Co. KG

WIKA INSTRUMENTS (Pty) Ltd.
Tel: (011) 621 0000

sales@wika.co.za
www.wika.co.za



Latest


28 Sep 2020
Analysing Mercury and other hydride forming Metalloids with PS Analytica

P S Analytical is a leading company in the manufacture and supply of instrumentation for the analysis of Mercury (Hg),…

Analysing Mercury and other hydride forming Metalloids with PS Analytica

P S Analytical is a leading company in the manufacture and supply of instrumentation for the analysis of Mercury (Hg), Arsenic (As), Selenium (Se), Antimony (Sb), Bismuth (Bi) and Tellurium (Te) in all matrices. Systems generally utilise Atomic Fluorescence Spectroscopy which offers many advantages over other techniques (such as Atomic…

27 Aug 2020
Electromagnetic flowmeters upgrade

Instrotech has announced that the Kobold magnetic inductive flowmeters MIM and MIS have been upgraded and further developed. Kobold MIM,…

Electromagnetic flowmeters upgrade

Instrotech has announced that the Kobold magnetic inductive flowmeters MIM and MIS have been upgraded and further developed. Kobold MIM, for measuring and monitoring of conductive liquids, is available for nominal sizes, ½” to 2”, and measuring ranges from 15ml/min to 350l/min. The new remote version, still manufactured in stainless…

26 Aug 2020
Labotec’s Precision Furnace Series

The Labotec Precision Furnace Series consists of ashing, muffle, fibre and ceramic chamber furnaces. They provide an excellent fit for…

Labotec’s Precision Furnace Series

The Labotec Precision Furnace Series consists of ashing, muffle, fibre and ceramic chamber furnaces. They provide an excellent fit for scientific laboratories, educational institutions, ceramic studios, medicine and industry as they are designed for material testing and heat treatments firing up to 1 300°C. Fibre chamber furnaces The high accuracy…

26 Aug 2020
Call for papers: analytica Lab Africa

Exhibition organiser Messe Muenchen South Africa has issued a call for papers, seeking expert industry speakers for analytica Lab Africa,…

Call for papers: analytica Lab Africa

Exhibition organiser Messe Muenchen South Africa has issued a call for papers, seeking expert industry speakers for analytica Lab Africa, set for 13-15 July 2021 at Gallagher Convention Centre, Johannesburg. analytica Lab Africa will bring together key industry stakeholders from across Africa and abroad for three days of high-level engagement…


Top stories


04 Aug 2020
Pandemic fast-tracks progress in air freight supply chain

No going back to the old normal for the pharma air freight supply chain Few – if any – air…

Pandemic fast-tracks progress in air freight supply chain

No going back to the old normal for the pharma air freight supply chain Few – if any – air freight supply chain stakeholders envisaged a global pandemic and air traffic shutdown in their business continuity plans, and all had to react quickly, collaboratively and innovatively to cope with the…

04 May 2020
Pfeiffer Vacuum showcases Hena 50 and Hena 70 powerful vacuum pumps for mass spectrometer systems

Air and Vacuum Technologies represent Pfeiffer Vacuum in South Africa and supply Hena 50 and 70 vacuum pumps.

Pfeiffer Vacuum showcases Hena 50 and Hena 70 powerful vacuum pumps for mass spectrometer systems

Air and Vacuum Technologies represent Pfeiffer Vacuum in South Africa and supply Hena 50 and 70 vacuum pumps.

10 Mar 2020
Treating wastewater with ozone could convert pharmaceuticals into toxic compounds

With water scarcity intensifying, wastewater treatment and reuse are gaining popularity. But some methods for killing microbes in wastewater create…

Treating wastewater with ozone could convert pharmaceuticals into toxic compounds

With water scarcity intensifying, wastewater treatment and reuse are gaining popularity. But some methods for killing microbes in wastewater create disinfection byproducts (DBPs) that could be harmful to human health. Now researchers have found that ozone treatment and subsequent chlorination can convert trace amounts of some pharmaceuticals in wastewater into…

02 Mar 2020
Cannabis compound acts as an antibiotic

Public health agencies worldwide have identified antibiotic resistance of disease-causing bacteria as one of humanity’s most critical challenges. However, scientists…

Cannabis compound acts as an antibiotic

Public health agencies worldwide have identified antibiotic resistance of disease-causing bacteria as one of humanity’s most critical challenges. However, scientists haven’t discovered a new class of antibiotics in more than 30 years. Now, researchers reporting in ACS Infectious Diseases have uncovered the hidden antibiotic potential of a non-psychoactive cannabis compound called cannabigerol…


Visit the official COVID-19 government website to stay informed: sacoronavirus.co.za