Temperature measurement 285 Table 14.1 Accuracy of digital instrument, temperature sensor and overal temperature accuracy of combined thermometer Instrument(°C) Sensor(C)Both(°C) Type k thermocouple Tvpe T thermocouple latinum ±0.4 hermit 0.3 Table 14.2 Response times(s)of sensors in air ensor Air condition Still M Bare thermocouple Bare thermistor Shrouded thermocouple Shrouded thermistor 260 Shrouded platinu 365 sensors are shrouded to improve their robustness their response times increase substantially (Table 14.2) Most manufacturers supply a range of cased sensors(probes)normally made of stainless steel suitable for most applications. These include blunt ended probes for general purpose use, needle-point or hypodermic probes for inserting into solid or semi-solid food, probes with spring-loaded ends for measuring surface temperatures or very robust probes that can be screwed or hammered into frozen meat Probe length is not important for measuring air and liquid temperatures. However, to check the deep leg temperature of a side of beef the probe needs to be at least 15 cm long to measure the temperature at the deepest 14.1.2 Temperature recorders There may often be a requirement to measure the values of temperatures at many different positions at the same time. The simplest solution to this problem is often to attach a multipole switch to a digital thermometer A number of temperature sensors can then be connected to the switch and their temperatures monitored in succession. This procedure is com- monly used in central plant rooms where an operator can routinely look at and record the temperatures at many different locations. A hand-held digital thermometer will provide information on one temperature at onesensors are shrouded to improve their robustness their response times increase substantially (Table 14.2). Most manufacturers supply a range of cased sensors (probes) normally made of stainless steel suitable for most applications. These include blunt￾ended probes for general purpose use, needle-point or hypodermic probes for inserting into solid or semi-solid food, probes with spring-loaded ends for measuring surface temperatures or very robust probes that can be screwed or hammered into frozen meat. Probe length is not important for measuring air and liquid temperatures. However, to check the deep leg temperature of a side of beef the probe needs to be at least 15 cm long to measure the temperature at the deepest point. 14.1.2 Temperature recorders There may often be a requirement to measure the values of temperatures at many different positions at the same time. The simplest solution to this problem is often to attach a multipole switch to a digital thermometer. A number of temperature sensors can then be connected to the switch and their temperatures monitored in succession. This procedure is com￾monly used in central plant rooms where an operator can routinely look at and record the temperatures at many different locations. A hand-held digital thermometer will provide information on one temperature at one Temperature measurement 285 Table 14.1 Accuracy of digital instrument, temperature sensor and overall temperature accuracy of combined thermometer Instrument (°C) Sensor (°C) Both (°C) Type K thermocouple ±0.3 ±1.5 ±1.8 Type T thermocouple ±0.3 ±0.5 ±0.8 Platinum ±0.2 ±0.2 ±0.4 Thermistor ±0.2 ±0.1 ±0.3 Table 14.2 Response times (s) of sensors in air Sensor Air condition Still Moving Bare thermocouple 20 5 Bare thermistor 45 20 Shrouded thermocouple 150 40 Shrouded thermistor 260 50 Shrouded platinum 365 65