Temperature measurement 289 14.2 Calibration Any temperature measuring system should be tested over the operating range at regular intervals to ensure accuracy and should also have a current calibration certificate from its manufacturer or official standards laboratory The system can be checked by means of a calibration instrument, or against a reference thermometer that is known to be accurate Melting ice(which if made from distilled water should read 0C, or-006C if made from tap water with 0. 1% salt)may be used to check sensor accuracy. The ice should be broken up into small pieces and placed in a wide-necked vacuum flask with a depth of more than 50mm. The system should be agitated frequently and the temperature read after a few minutes when stable If differences of more than 0.5C are found, the instrument should either be very carefully adjusted or sent for calibration. Other simple calibration systems are available. These consist of a small stirred tank that can be filled with water or oil. The temperature of the stirred liquid is measured using a standard calibrated platinum resistance thermometer. The temperature sensors to be calibrated are placed in the liquid and compared with the standard measurement. The temperature of the liquid can be raised or lowered to different values by the addition ice, cold liquid or hot liquid 14.3 Measuring temperature data Accurately determining the temperature of chilled meat throughout the cold chain is difficult. Training and experience are required to locate posi tions of maximum and minimum temperature in abattoirs, stores, vehicles and display cabinets. The problem is further exaggerated by changes in posi tion with time caused by loading patterns and the cycling of the refrigera tion plants. Obtaining a relationship between environmental temperatures that can be measured relatively easily) and internal meat temperatures is not a simple process. Relating temperatures obtained in a non-destructive manner with internal meat temperatures again poses problems. Determin- ing the temperature of cuts of meat with regular shapes is quite simpl doing so for irregular cuts of meat is more difficult All the temperature measurement problems associated with chill foods will equally apply to quick-frozen foods. In addition, there are a number of other problems. Many instruments have sensors that will accurately measure temperatures of-20.C and below, but the instruments themselves become inaccurate or fail to operate at low temperatures. If frozen foods tre removed from their low temperature environment to one suitable for the instrument the surface temperature rises very rapidly. However, the main problem is that of actually inserting a temperature sensor into frozen meat14.2 Calibration Any temperature measuring system should be tested over the operating range at regular intervals to ensure accuracy and should also have a current calibration certificate from its manufacturer or official standards laboratory. The system can be checked by means of a calibration instrument, or against a reference thermometer that is known to be accurate. Melting ice (which if made from distilled water should read 0°C, or -0.06 °C if made from tap water with 0.1% salt) may be used to check sensor accuracy. The ice should be broken up into small pieces and placed in a wide-necked vacuum flask with a depth of more than 50 mm. The system should be agitated frequently and the temperature read after a few minutes when stable. If differences of more than 0.5 °C are found, the instrument should either be very carefully adjusted or sent for calibration. Other simple calibration systems are available. These consist of a small stirred tank that can be filled with water or oil. The temperature of the stirred liquid is measured using a standard calibrated platinum resistance thermometer. The temperature sensors to be calibrated are placed in the liquid and compared with the standard measurement. The temperature of the liquid can be raised or lowered to different values by the addition of ice, cold liquid or hot liquid. 14.3 Measuring temperature data Accurately determining the temperature of chilled meat throughout the cold chain is difficult. Training and experience are required to locate posi￾tions of maximum and minimum temperature in abattoirs, stores, vehicles and display cabinets.The problem is further exaggerated by changes in posi￾tion with time caused by loading patterns and the cycling of the refrigera￾tion plants. Obtaining a relationship between environmental temperatures (that can be measured relatively easily) and internal meat temperatures is not a simple process. Relating temperatures obtained in a non-destructive manner with internal meat temperatures again poses problems. Determin￾ing the temperature of cuts of meat with regular shapes is quite simple but doing so for irregular cuts of meat is more difficult. All the temperature measurement problems associated with chill foods will equally apply to quick-frozen foods. In addition, there are a number of other problems. Many instruments have sensors that will accurately measure temperatures of -20 °C and below, but the instruments themselves become inaccurate or fail to operate at low temperatures. If frozen foods are removed from their low temperature environment to one suitable for the instrument the surface temperature rises very rapidly. However, the main problem is that of actually inserting a temperature sensor into frozen meat. Temperature measurement 289