Introduction
In this session we are gonna discuss about the procedures to install a thermocouple in to a process.The thermocouple is a delicate instrument and should be handled with care.
(1). Keep element protected from contamination prior to installation.
(2). Avoid excessive bending of lead wire.
(3). Insure proper element is installed in proper location/environment.
How to install a Thermocouple in to a process
1. Insert the thermocouple into the thermowell. By inserting a spring loaded stem, a positive contact with the bottom of the well will be achieved. Make sure that the cables in the connection head do not twist during insertion. If the cables start to turn, disconnect the wires from the terminals and reconnect them after screwing the sensor into the thermowell.
2. Thermocouple wire of the same type as the sensor must be used to hook the thermocouple up to its instrumentation. Make sure the wire ends are clean and provide good electrical contact with the terminals.
3. When hooking up the extension wire, match up wires so the same colors are connected. (Thermocouple wire is color coded – the negative leg is always red, and the positive leg varies, e.g. type K = yellow; J= white; E = purple; T = blue)
4. Install the thermocouple and extension wire at least one foot away from AC power lines for best results. Do not run thermocouple wires in conduit with other wires.
5. The thermocouple connection head should not exceed 400 deg. F, and best results are obtained when the head is as near as possible to room temperature.
Maintenance
1. Calibration frequency: Thermocouple calibration will gradually deteriorate at a rate that varies with different applications. The frequency of calibration must be determined in each case by the user. Heat transfer compound is available.
2. Calibration is achieved by comparing thermocouple output with a working standard. It is preferred to calibrate the thermocouple in its installed position. If the sensor is removed for calibration, the thermocouple should be returned to the same location and immersion depth for greatest reliability.
3. Periodically check the thermowell surface and the sensor sheath for corrosion or damage. If damage has occurred, replacement may be considered.
4. Moisture can cause corrosion and decalibration in some thermocouple wire (for instance, the positive leg of a J thermocouple is iron, and will readily rust). Take care to prevent moisture buildup at thermocouple wire terminals.
Also read about the types of thermocouple by clicking in the link below
https://automationforum.co/2018/02/thermocouple-basics-types-thermocouple.html
