I. GENERAL INSTALLATION PARAMETERS
There are many variations of thermocouples and thermocouple assemblies. Even though some may appear to have heavy duty protecting tubes or thermowells, the internal parts can be delicate. Care in handling is a must to insure the sensor integrity. DO NOT DROP. Thermocouples are carefully packed at the factory. Inspect the package when receiving for indications of shipping damage. If shipping damage is noticed report it immediately to the shipping company and make the necessary reports. Marlin ships on a FOB factory basis therefore it is your responsibility to file any claims. Hidden shipping damage can also occur (no evident sign of mishandling). If after carefully opening the package, damage is discovered, save all product and shipping material then notify and file the proper claims with the shipping company immediately.
Store in a dry, clean place. Avoid areas where dropping or stacking may occur.
The thermocouple should “see”, as closely as possible, what the product in the process is experiencing in order to get meaningful temperature measurements. Locate the thermocouple as close to the product as possible. A rule of thumb is to have at least 10 tube diameters immersion in the hot zone. Avoid direct flame impingement or stagnant areas.
DO NOT ATTEMPT to mechanically connect the assembly into the process by tightening at the terminal or connecting head. USE ONLY THE PROCESS FITTING OR THE THERMOWELL FLATS FOR THIS PURPOSE. Terminals or connecting heads that are twisted can be damaged or cause shorts that can adversely affect the operation of the thermocouple. If a thermowell or protecting tube must be welded into the process, carefully remove the thermocouple sensor before welding and be sure to handle carefully, keep clean and replace without forcing or stressing any components. Assemblies with ceramic tubes should be preheated before immersion into high heat in order to avoid any thermal shock.
II. GENERAL MAINTENANCE PARAMETERS
Regularly scheduled maintenance procedures should include inspection and calibration intervals so that life and reliability of the instrumentation is improved and the likelihood of sudden serious failure is reduced. These procedures should be set up by the responsible engineering department and performed by personnel that are familiar with the operating principles upon which the system is based. DO NOT LUBRICATE.
Thermocouples often deteriorate with time, exhibiting a drift from actual temperatures. Deterioration usually is more rapid at higher temperatures and depends on the integrity of the protecting tube or sheath to isolate it from contaminates. Thermocouples should be checked at regular maintenance intervals based on recommendations or on experience.
III. WIRE EXTENSIONS
Use wire extensions of the same thermocouple material type (i.e. “J”, “K”, “T”, “E”, “R”, “S”, “B”, etc.) of the installed thermocouple throughout the circuit. The use of thermocouple grade or thermocouple extension grade wire and the selection of conductor insulation depends on what the environmental conditions dictate.
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“RED” color code is always negative in thermocouple circuits. Ideally run thermocouple circuit wires in separate conduits at least one foot away from power lines. Twisted and shielded constructions may be required to avoid noise in the thermocouple circuit. The overall impedance of the thermocouple circuit must be compatible with your instrumentation. If there is a reversal in the thermocouple circuit the indication will be down scale. A “double-reversal” in the circuit will give an upscale but erroneous reading. Keep the“RED” color coded leg negative throughout the circuit to avoid these reversals.
For more information regarding Marlox Thermocouples please consult your Marlin catalog.