Temperature

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Precise process control is one of the most important factors in maintaining high quality in production, just as precision and accuracy are the key to research.

Precise process control is one of the most important factors in maintaining high quality in production, just as precision and accuracy are the key to research. Temperature is a crucial variable in both production and research.

Glass and metal thermometers use thermal expansion to measure temperature. This method uses a physical law which gives a false sense of reliability, since one assumes the measurement is “true” because he or she can see how it works. This system is no longer suitable for many reasons and their accuracy and range are very limited. Glass construction is fragile and can be dangerous to a person’s health, as well as to the environment. For these reasons, an alternative way of measuring temperature has become necessary. Hanna electronic thermometers are designed to withstand mechanical stress and extreme environments while maintaining high accuracy.

Electronic thermometers have provided the versatility, speed and accuracy requested by operators in all areas of temperature measurement. Speed is important when the reactions being monitored change rapidly. Small, compact sensors are preferable for tightly arranged areas, such as electronics and other miniature applications. Electronic thermometers allow users to monitor maximum, minimum and even average temperatures.

Dedicated research teams, precision process control, integrated production facilities and an overall team effort is required to meet the demanding applications of our users. Hanna’s extensive professional thermometer line constitutes the true dedication Hanna commits to thermometer design and production.

Measurement Unit

Temperature is one of the most common physical properties in our everyday life. It is defined as the property of a body that determines the transfer of heat to or from other bodies. Physically, temperature affects variations in the macroscopic parameters of a body such as volume and pressure, among others.

The fundamental temperature scale is the absolute, thermodynamic or Kelvin scale. The Kelvin (K) unit of thermodynamic temperature, is the fraction 1/273.16 of thermodynamic temperature of the triple point of water. The triple point of water is a standard fixed point at which ice, liquid water, and water vapor are in equilibrium.

Two empirical temperature scales are in common use: the Celsius and Fahrenheit scales. These scales are based on two fixed points.

The Celsius (formally Centigrade) temperature scale uses the Celsius (°C) units, defined as 1/100th of the difference between the temperature of boiling (100°C) and freezing points (0°C) of water. The relationship between the Kelvin and Celsius scales is given by:

K = °C + 273.15

The Fahrenheit scale uses Fahrenheit (°F) units, where the temperature of boiling water is taken at 212°F, and the temperature of the freezing point at 32°F.The scale originally used the temperature of a mixture of ice and common salt as 0°F, and the inventor’s approximate body temperature as 96°F.The relationship between the Fahrenheit and Celsius scales is calculated by:

°F = °C • 9/5 + 32

Achieving Thermometer Accuracy

Even though it is easy to show resolutions of 0.1°C with digital thermometers, there is no relationship between resolution and accuracy of measurements.

Here is a list of the main causes that can have an effect on accuracy in temperature measurements:

  • Instrument: The instrument may have an extended scale and 19,000 points of measurement may be obtained. Within these 19,000 points, the instrument may perform differently because of internal linearity.
  • Electronic components: The internal electronics have a drift that depends on the ambient temperature. For this reason, the accuracy of the instrument is stated at a specific temperature of 20 or 25°C, and the drift has to be specified for each degree of variation with respect to the reference temperature.
  • LCD Liquid crystals: have an operating limitation which is a function of temperature. Their normal range is between 0 and 50°C, but there are components capable of performing between -20 and 70°C.
  • Batteries: Instrument battery power supply also has limitations of use.
  • Temperature sensor: This is a separate accuracy, which is to be added to the instrument’s error.

Also, if the probe supplied is connected to the meter during factory calibration, the probe error is eliminated but will reappear if the probe is replaced.

With all the possible forces influencing accuracy, calibration verification is essential. Hanna’s CAL Check™ can verify an accurate calibration quickly and easily.

Importance of Accuracy

Up to a few years ago, accuracy was not a very critical aspect and tolerances of a few degrees did not jeopardize a process. From the time that hazard analysis and critical control points (HACCP) programs became a necessity, measurement accuracy has become a discriminating factor. Due to health risk factors, now an error of a few tenths of a degree can decide whether food can still be kept or must be discarded. In 1990, Hanna began to produce thermometers for our customers’ HACCP programs to comply with new governmental regulations. Soon after, Hanna became the market leader in Europe as a result of the technological solutions offered to our users.

User Calibration of Typical Thermometers

To calibrate typical thermometers, you need:

  • For thermocouple thermometers: A simulator of the emf (electromotive force) generated by the thermocouple
  • For thermometers with NTC/PTC sensor: At least two thermostatic baths
  • For Pt100 thermometers: A resistance simulator
  • For infrared thermometers: A heat source (panel) at controlled temperature

Few users can afford this investment in time and materials for checking their thermometers’ accuracy. Hanna’s exclusive CAL Check™ is a quick and cost effective way to verify accuracy.

Hanna CAL Check™ Calibration Feature

As previously described, the electronic components of an instrument shift with time. Hanna has made it possible for users, with the simple touch of a button, to verify whether the response of the instrument is within the tolerance limit of ±0.02°C.

The CAL Check™ system acts by substituting the sensor with an internal resistor which corresponds to 0°C; thus, simulates the response that the temperature probe would have at 0°C.

Standardization

Hanna has designed a series of pre-calibrated temperature probes with a maximum error of 2°C for trouble-free replacement.

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