Thermocouples are often required to work in hostile environments, usually very hot or cold, often corrosive, sometimes subject to vibration and flexing, conditions that cause thermocouples to deteriorate. Deterioration causes errors, so thermocouples must be replaced periodically. Thermocouple probes have various types of sensors designed to measure surfaces, gas, liquids and so on. Selecting the right probe is very important. Each application has its set of problems requiring careful probe selection and careful use.