1、 Preparation before installation
Selection matching
Select the corresponding model of armored thermocouple based on the temperature range, corrosiveness, pressure and other parameters of the measured medium (such as K-type suitable for -200~1300 ℃, S-type suitable for high temperature precision measurement).
Confirm that the diameter of the armor wire and the material of the protective sleeve (stainless steel 304/316, ceramic, etc.) match the working conditions, and corrosion-resistant sleeves should be selected for corrosive media.
Equipment and tool inspection
Check whether the thermocouple probe is bent, damaged, or the insulation layer is cracked. Use a multimeter to measure whether the thermoelectric potential is normal and avoid open or short circuits.
Prepare suitable installation accessories: threaded joints, flanges, welding bases, insulation sleeves, etc., ensuring that the specifications of the accessories are consistent with the thermocouple installation end.
On site environment confirmation
High temperature working conditions require confirmation of the load-bearing and heat resistance of the installation location; Prepare anti vibration fixtures for vibration environments; Strong electromagnetic interference environments require proper shielding and grounding.
2、 Core installation essentials (classified by installation method)
The common installation methods for armored thermocouples include threaded installation, flange installation, welding installation, and direct insertion installation. The operating points for different methods are as follows:
Thread/flange installation (suitable for pressure pipelines and containers)
Sealing treatment: Before installation, wrap PTFE tape around the threads or apply high-temperature resistant sealant. For flange installation, install high-temperature resistant gaskets (graphite, metal wrapping gaskets) to prevent medium leakage.
Insertion depth: The insertion depth of the temperature measuring end must be ≥ 10 times the diameter of the thermocouple, and must exceed the centerline of the pipeline (during pipeline installation) to ensure that the probe is in the flow field of the measured medium and avoid interference from the temperature of the pipeline wall.
Tightening force: When installing threads, use a wrench to clamp the joint and tighten it. It is forbidden to directly clamp the armored sleeve (to prevent deformation and fracture of the sleeve); The flange installation needs to tighten the bolts evenly to avoid the flange surface from tilting.
Welding installation (applicable to fixed measuring points without disassembly requirements)
Pre welding treatment: Install the thermocouple base and weld it onto the surface of the tested equipment. The welding area needs to be polished and rust removed to ensure that the welding is firm and free of pores.
Probe fixation: Insert the armored thermocouple into the base, fix it with high-temperature resistant adhesive or weld it to seal it, ensuring that the temperature measuring end is tightly attached to the base and reducing thermal resistance caused by air gaps.
Post welding inspection: After welding is completed, cool down to room temperature and check the insulation performance to avoid damaging the internal insulation layer of the thermocouple due to high temperature welding.
Direct insertion installation (suitable for open containers with normal pressure and no vibration)
Anti bending fixation: Fix the thermocouple cable with a bracket or fixture to prevent the probe from bending due to medium flow or its own weight. The bending radius of the armor sleeve should be ≥ 5 times the diameter of the sleeve to prevent internal armor wire breakage.
Avoid contact with cold sources: Avoid contact with low-temperature components (such as equipment outer walls and cooling water pipes) around the probe, and install insulation layers if necessary to reduce thermal radiation and conduction losses.
3、 Wiring and protection points
Cable laying
The compensation wire of the armored thermocouple should be matched with the thermocouple model (such as K-type thermocouple with K-type compensation wire) to avoid measurement errors caused by model mismatch.
When laying cables, they should be kept away from strong electromagnetic interference sources such as power cables and frequency converters, with a spacing of not less than 20cm. When laying through conduits, metal conduit should be used and grounding shielding should be done.
Avoid right angle bending at cable bends and reserve a certain margin to prevent equipment vibration from pulling the cable.
Environmental protection
A waterproof cover should be installed at the junction box in a humid environment, with the outlet facing downwards to prevent rainwater from seeping in; Corrosive environments require the use of anti-corrosion junction boxes.
In high-temperature environments, thermocouple cables should be kept away from heat sources and high-temperature resistant protective sleeves should be installed if necessary; Low temperature environments require prevention of cable freezing and cracking.
4、 Verification and maintenance after installation
Verification after installation
After installation, conduct a power on test and compare the measured values of the thermocouple with the readings of standard thermometers (such as mercury thermometers and precision thermistors). The error should be within the allowable range (industrial grade usually ≤± 1.5 ℃ or ± 0.75% t).
Check that the wiring of the junction box is secure, without looseness or virtual connections, to avoid temperature fluctuations caused by poor contact.
routine maintenance
Regularly check the wear and corrosion of the probe, especially under conditions of abrasive media. If the casing becomes thinner or damaged, it should be replaced in a timely manner.
Regularly clean the scale and dust on the surface of the probe to avoid increasing thermal resistance and affecting the temperature measurement response speed.
5、 Prohibited operations
It is prohibited to use thermocouples beyond the range to avoid burning the internal armor wire or insulation layer at high temperatures.
Do not forcefully pull or bend the armor sleeve during installation to prevent internal wire breakage.
It is prohibited to expose the thermocouple temperature measuring end to the air to measure fluid temperature, and it must be ensured that it is in full contact with the medium.
It is prohibited to install the probe without a fixed position in areas with severe vibration to avoid fatigue fracture of the probe.