Explain Thermocouples Measuring Junction?
An exposed (measuring) junction is recommended for the measurement of flowing or static non-corrosive gas temperature when the greatest sensitivity and quickest response is required. An insulated junction is more suitable for corrosive media although the thermal response is slower. In some applications where more than one thermocouple connects to the associated instrumentation,insulation may be essential to avoid spurious signals occurring in the measuring circuits. If not specified, this is the standard. An earthed (grounded) junction is also suitable for corrosive media and for high pressure applications. It provides faster response than the insulated junction and protection not offered by the exposed junction. Thermocouple Standards ASTM E 235: Standard Specification for Thermocouples, Sheathed, Type K and Type N for Nuclear or for other High-Reliability Applications. ASTM E 839: Standard Test Methods for Sheathed Thermocouples and Sheathed Thermocouple Materials. ASTM E 220: Test Methods for Calibration of Thermocouples by Comparison Techniques ASTM E 230: Specification and Temperature-EMF Tables for Standardized Thermocouples. ASTM E 585: Standard specification for compacted MI, MS, base metal thermocouple cables. ASTM E 608: Standard specification for compacted MI, MS, base metal thermocouples. ASTM E 696: Standard specifications for tungsten – rhenium alloy thermocouple wire. ASTM E 1652: Standard specification for Magnesium oxide & Alumina oxide powder & crushable insulators used in metal sheathed PRT’s, base metal thermocouples & noble metal thermocouple. IS 12579: Specification for Base Metal Mineral Insulated Thermocouple Cables and Thermocouples. GB/T 1598- 2010: Chinese standard for platinum thermocouples. IEC 584: International standard for thermocouples.
