Temperature instruments are designed for temperature monitoring and analysis. Temperature indicators either come equipped with an integral sensor, or require sensor input. Approximately 16% of all process instrumentation measures, indicates, or controls temperature. In many industrial applications it is necessary to collect temperatures as a permanent record due to government or manufacturing requirements, or to provide historical data that may later be used to determine problems within a system. Data collection methods in industry vary from simple manual systems using inexpensive portable indicators to sophisticated DCS (Distributed Control Systems) that both log and control data. The most inexpensive portable indicators do not provide any "recording" or memory features. Readings from portable temperature indicators must be recorded by hand. Some portable indicators are available with memory so that a number of measurements may be collected and later downloaded into a personal computer. A chart recorder is another device used to record temperature data. These recorders usually offer digital readouts and give a digital indication of the process temperature of selected points or of scanned points. Distributed control systems also offer datalogging as a part of their overall capabilities. Since these systems are computer based, the datalogging functions are programmable to almost any needed configuration.
Important general specifications to consider when searching for temperature indicators include the sensed temperature range, input options and number of inputs or channels. The sensed temperature range refers to the temperature range the device is rated for sensing. Choices for input options include permanent sensor or probe, thermocouple inputs, RTD inputs, thermistor inputs, and solid-state inputs. The number of inputs or channels specifies the number of inputs available for probe or sensor attachment. Interface and display options are also important to consider. Local interfaces include digital front panels and analog front panels. Display options include digital readouts, analog meters or indicators, video display terminals or no displays. Communications interfaces for devices that can be controlled remotely by a computer include serial and parallel interfaces.
Mounting is also important to consider when searching for temperature indicators. Mounting choices include portable or hand held, self-contained or stand-alone, panel mount or meter, and rail or track mounted. The display scale can be Fahrenheit or Celsius. Fahrenheit is defined by 32 degrees at the ice point and 212 degrees at the boiling point of water at sea level. Celsius is defined by 0 degrees at the ice point and 100 degrees at the boiling point of water at sea level. Additional specifications to consider when searching for temperature indicators include battery powered, detachable probes, datalogger or data collection capabilities, recording of minimum or maximum values, internal timers or counters, controller functionality, math or statistical function performance, and self-test diagnostics.