The Role of Temperature Calibration in Protecting Food Safety

Temperature testing is essential to the food industry for maintaining food safety and quality. Consistently controlled temperatures prevent the growth of harmful bacteria in processed and packaged foods and can halt the growth of foodborne illnesses. Complying with food temperature safety regulations helps deliver safe foods with long shelf lives, while noncompliance can result in health issues with serious legal consequences. However, temperature calibration tools such as dry blocks and calibration baths are precise, accurate tools for measuring temperatures during food production cycles. They help enhance food safety and ensure long shelf lives for food products.

Food products are available in many packages, from frozen containers to vacuum-sealed cans. Wide temperature ranges are required to process foods for general consumption and safe, long-term storage, whether in a grocery store or on a home pantry shelf. Dry blocks and temperature calibration baths are both capable of measuring wide temperature ranges with high resolution and accuracy although they work in much diverse ways. A temperature dry block heats or cools a metal block to a precise temperature. The block features predrilled, standardized holes for insertion of industry-accepted temperature sensors and probes for measurements. Once the temperature of a dry block has been set, the temperature of the block must stabilize to achieve uniform temperature consistency within a required tolerance across the block.

In contrast, a temperature calibration bath relies on heating or cooling a liquid across a wide temperature range. The temperature of the liquid must be precisely controlled so that calibration of sensors and thermometers can be performed with a high degree of accuracy across the full volume of the temperature bath. Temperature calibration baths typically achieve better temperature stability and uniformity than dry block calibrators. They are typically floor-standing units with elevated temperature calibration accuracy since they can surround a sensor under test with their temperature-controlled liquid.

When temperature calibration capability is needed in a smaller size, a dry block calibrator may be the suggested choice. The size of a dry block calibrator is determined by the dry block or, in some cases, a dry well. Its temperature test volume must be of sufficient size to accommodate the sizes and shapes of temperature probes and sensors for calibration. Dry-block temperature calibrators can be made significantly smaller and lighter than temperature calibration baths while still providing wide temperature calibration ranges with high accuracy. (For more on calibration baths, see the earlier blog: “Calibration Baths Fine Tune Temperature.”)

Comparing Calibrators

Choosing a temperature calibrator may depend on the size of the unit and the volume of its calibration chamber, but usually starts with temperature range, accuracy, stability and even temperature dynamics, such as the times required to change from room temperature (around +23 or +25°C) to a required hot or cold temperature. Depending on location, availability of diversified temperature units of measure, such as degrees Centigrade (°C), Fahrenheit (°F), or Kelvin (°K), may simplify calibrations.

As an example of the versatile temperature calibrators we carry, the Fluke 9009-B dry-block temperature calibrator, offers an extremely high temperature range of -15°C to +350°C. It fits an enclosure measuring just 7.0 × 10.5 × 9.75 in. (178 × 267 × 248 mm) and weighing 10.1 lbs. (4.5 kg) using two independently controlled temperature blocks. The unit, which can calibrate two temperature probes simultaneously, contains a “hot” block with range of +50°C to +350°C and ±0.6°C accuracy and a “cold” block with range of -15°C to +110°C and ±0.2°C accuracy.

Additionally, the Additel ADT875PC-155-A is a dry-well calibrator with temperature range of -40°C to +155°C; it can display temperature in °C, °F, or °K. It offers 0.01°C resolution, ±0.18°C full-range display accuracy, and ±0.01°C full-range stability after 30 minutes. It measures 12.6 × 6.7 × 13.0 in. (320 × 120 × 330 mm) and weighs 21.8 lbs. (9.9 kg) with rapid heating and cooling times. Heating times are 13 min. from -40°C to +155°C and only 5 min. from -40°C to +23°C. Cooling times are 28 minutes from +155°C to -40°C, 8 minutes from +155°C to +23°C, and 20 minutes from +23°C to -40°C. The dry-well calibrator, with two independently controlled temperature zones, shows temperatures on a 6.5-in. (165-mm) color touch-screen display.

The Jofra RTC-159B super cooler dry-block temperature calibrator, has a temperature range of -100°C to +140°C (-148°F to +311°F) in a slightly larger housing measuring 20.9 × 6.65 × 17.0 in. (531 × 169 × 432 mm) and weighing 33.5 lbs. (15.2 kg). It includes a 5.7-in. full color display with inputs for a reference sensor, dynamic load compensation (DLC) sensor (useful for calibrating multiple temperature sensors simultaneously), and sensors under test. With USB and Ethernet ports for remote control, this dry block calibrator provides fast heating and cooling times. Heating times are 12 minutes from -100°C to +23°C (-148°F to +74°F) and 14 minutes from +23°C to +155°C (+73°F to +311°F). Cooling times are 40 minutes from +155°C to +23°C (+311°F to +73°F) and 65 minutes from +23°C to -80°C (+73°F to -112°F).

While dry-block temperature calibrators are capable of wide temperature ranges in small housings, progress is being made in the miniaturization of calibration baths. For example, the Fluke 7103 Micro-Bath calibrator, with a temperature range of -30°C to +125°C (-22°F to +257°F) and well area of 1.9 × 5.5 in. (48 × 139 mm), fits an enclosure measuring 9.0 × 13.2 × 10.5 in. (23 × 34 × 26 cm) and weighing 22 lbs. (9.8 kg) with thermal fluid. It is accurate within ±0.25°C across the full temperature range with ±0.03°C stability at -25°C and ±0.05°C stability at +125°C. It heats from +25°C to +100°C in 35 minutes and cools from +25°C to -20°C in 45 minutes.

When higher temperatures are needed, the Fluke 6102 provides a temperature range of +35°C to +200°C (+95°F to +392°F) with ±0.25°C full-range accuracy. Its silicone oil thermal fluid makes it a candidate for calibrating liquid-in-glass thermometers and other sealed devices. It fits a smaller enclosure than the model 7103, at 5.5 × 10.38 × 8.0 in. (14 × 26 × 20 cm), and weighs only 10 lbs. (4.5 kg) with thermal fluid.

For cold temperature calibrations, Fluke shows what can be done with dry-block calibrator technology by means of its model 9190A-A Ultra-Cool Field Metrology Well. The dry block calibrator has a temperature range of -95°C to +140°C with ±0.05°C full-range accuracy and ±0.2°C display accuracy. Its LCD can show temperature in °C or °F with ±0.015°C full-range stability. The unit, which incorporates USB and RS-232 interfaces for remote control, can cool from +23°C to -90°C in 80 minutes, from +23°C to -95°C in 90 minutes, and from +140°C to +23°C in 60 minutes. It also heats from -95°C to +140°C in 40 minutes n an enclosure measuring 18.8 × 8.0 × 14.9 in. (480 × 205 × 380 mm) and weighing 35 lbs. (16 kg). More information on any of these dry-block calibrators and temperature calibration baths can be found by contacting a Transcat | Axiom Rental Account Manager for guidance at (760) 806-6600.