Mainstream Installation Methods and Applicable Scenarios
|
Installation Method |
Structural Features |
Applicable Scenarios |
Installation Key Points |
|
Threaded Installation |
Probe tail has metric threads (M6, M8, M12×1.5) or pipe threads (G1/2, NPT1/2) |
Industrial pipelines, reactors, pressure vessels, hydraulic systems |
- Use sealing gaskets (PTFE or metal wound gaskets) to prevent leakage - Recommended installation torque is 15–20 N·m to avoid deformation of the probe due to overtightening - The threaded hole needs to be pre-tapped to ensure it matches the probe thread |
|
Flange Installation |
The probe is connected to the pipeline/equipment through a flange, often with gaskets and bolts |
High-pressure, high-temperature, large-diameter pipelines (such as steam, chemical reactors) |
- Flange rating must match the system pressure (e.g., PN16, PN40) - Select corrosion-resistant materials (316L stainless steel) - A leak test is required after installation |
|
Magnetic Installation |
The bottom of the probe integrates a strong magnet (neodymium iron boron), which can be adsorbed onto ferromagnetic surfaces |
Motor casings, bearings, fans, temporary temperature measurement |
- Only suitable for environments ≤200℃, magnetic properties attenuate at high temperatures - The adsorption surface needs to be clean and flat to ensure good thermal contact - It is recommended to use thermal conductive grease to improve heat transfer efficiency |
|
Screw-type Installation |
The probe head has mounting holes and is pressed against the metal surface with screws |
Vibrating environments (such as engine blocks, gearboxes) |
- Avoid directly pressing on thin-walled areas to prevent deformation - Use spring washers to prevent loosening - The contact surface needs to be polished flat and coated with thermal paste |
|
Insert-type (Direct Insertion) |
No fixed interface, only the protective sleeve is inserted into the medium |
Atmospheric pressure vessels, ventilation ducts, laboratory equipment |
- Insertion depth ≥200mm, or 1/3–2/3 of the medium diameter - Use matching sealing compression nuts or stuffing boxes to prevent leakage - Suitable for non-corrosive, low-flow media |
|
With Mounting Sleeve (Thermowell) |
The probe is inserted into a metal protective sheath, which is welded/threaded to the equipment. |
Suitable for highly corrosive, high-flow rate conditions requiring online maintenance. |
- Sheath material must be resistant to medium corrosion (e.g., Hastelloy, silicon carbide) - Sheath wall thickness ≤ 3mm to avoid thermal response delay - Allows for "sensor replacement without shutting down the system" |
Installation Core Specifications and Standards
Insertion Depth Requirements:
Pipe diameter < 250mm → Insertion depth ≥ 1/2 to 2/3 of the pipe diameter
Pipe diameter ≥ 250mm → Insertion depth 75–150mm
Laboratory/High-precision measurement → ≥200mm (according to JJG 229-2010)
Air/Gas temperature measurement → The probe must be completely placed in the main flow area, away from the wall and heat source
Standards:
GB/T 30121-2013 (equivalent to IEC 60751:2008): Specifies the structure, graduation, tolerance, and basic installation requirements of platinum resistance thermometers
JJG 229-2010: Specifies the verification procedures for industrial platinum resistance thermometers, including insertion depth and thermal response test methods
IEC 60751:2022: International general standard, emphasizing the effectiveness of thermal coupling between the sensor and the process medium
Wiring Specifications and Lead Treatment
Recommended Wiring Method: Three-wire system (preferred in industry)
Wiring Rules:
One end has 1 red wire (A wire)
The other end has... Two wires of the same color (wires B and C, usually white/green)
Instrument terminal connection: A connects to the measurement terminal, B and C connect to adjacent bridge arms of the bridge circuit.
Key requirements:
The three wires must be of equal length, equal cross-section, and the same material to compensate for lead resistance.
For long-distance transmission (>10m), shielded twisted-pair cables are preferred, kept away from power cables (spacing ≥300mm).
It is strictly forbidden to mistakenly set it to a two-wire system, otherwise, the lead resistance will introduce significant errors (e.g., a 50m cable can cause an error >7℃).
Insulation testing:
After installation, use an insulation resistance tester (500V DC) to test; the insulation resistance should be >100MΩ.
In humid or corrosive environments, it is recommended to retest quarterly.
Recommended installation tools:
|
Tool Name |
Purpose |
Recommended Model/Type |
|
Torque wrench |
Controls the tightening torque of the threaded connection to prevent probe deformation |
0–50 N·m adjustable torque wrench |
|
DC low resistance tester |
Verifies the consistency of the three-wire lead resistance (B-C should be ≈0Ω, A-B/A-C ≈110Ω) |
TH2511, JK2512 |
|
Insulation resistance tester |
Tests the insulation performance between the lead wires and the casing |
Fluke 1507, KYORITSU 3125 |
|
Thermal conductive grease |
Fills the gap between the probe and the mounting surface to improve heat conduction |
Silicone-based, temperature resistance ≥300℃ |
|
Thermal imager |
Verifies whether the temperature distribution of the probe contact surface is uniform after installation |
Fluke TiS series |
Common installation errors and avoidance strategies:
Insufficient insertion depth → Leads to low temperature readings and slow response
Solution: Strictly calculate the minimum insertion depth according to the pipe/container dimensions
Three-wire system mistakenly connected as a two-wire system → Lead resistance is added, and the error can reach ±5℃ or more
Solution: The instrument terminal settings must be consistent with the sensor wiring method; confirm before installation
Lead wires are stressed or bent → Platinum wire breakage or insulation damage
Solution: Leave a slack loop in the lead wire and secure it to the support with a wire clip; avoid pulling on the wire.
No thermal conductive medium used → Poor heat transfer with magnetic/screw mounting
Solution: Apply thermal conductive grease evenly to the contact surface (thickness 0.1–0.3mm)
Incompatible protective sleeve material → Corrosion, scaling, and wear leading to failure
Solution:
Food/Pharmaceutical → 316L stainless steel + PTFE coating
Strong acid/chloride ions → Hastelloy or titanium alloy
High wear → Silicon carbide ceramic sleeve
No insulation testing performed → Leakage in humid environments, signal drift
Solution: Test insulation resistance immediately after installation and record the results.
