contact thermometers
The term "touch thermometer" means all those thermometers which come into direct contact with the body whose temperature is to be measured. In contrast, the non-contacting measurement methods, Eg with pyrometers.
The contact thermometers include expansion thermometers (liquid and bimetallic thermometers) and all electrical or electronic thermometers that work with temperature sensors. Industrial touch thermometers are used to detect the process temperature, Eg on ovens, reaction vessels or pipelines. Edit the source text
Independent of the sensor principle, its structure is similar. Industrial touch thermometers consist of the temperature sensitive sensor (eg thermocouple, platinum measuring resistor) installed in a pipe sealed at one end for protection; together, this is referred to as a measuring insert; See pictures for resistance thermometers. In many cases, the latter has a clamping socket at the other end for connecting electrical leads. The design is standardized in DIN 43735. Measuring inserts can be installed further in a protective tube with a connection head according to DIN 43772. The protective tube and the connection head together form the so-called protective fitting. This protects the sensitive measuring insert against mechanical and chemical stress as well as the connection terminals from dirt and moisture. It allows the exchange of a measuring insert during operation. Influences Edit source text
The temperature of the medium acts on the contact thermometer, but vice versa, the thermometer also acts on the temperature of the medium, see feedback deviation, whereby the temperature difference to the environment is determined to be too small. As a further effect, a platinum measuring resistor is subjected to self-heating by the measuring current. Both influences are of little importance for flowing liquid media, but should be considered as a source of error in the case of gaseous media.
Temperature changes require heat transfer and a delay. It depends on the medium and its flow velocity as well as on the design of the measuring device. The thermal response time, according to which a measured value follows a temperature jump of 90%, is for a thermocouple measuring insert with a diameter of 6 mm (as a rough guide value according to VDE / VDI guideline 3511: Technical temperature measurements) Edit sourcetext
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