Structural Differences:
Junction Box Type: Consists of an independent sealed junction box, metal protective tube, thermocouple element, and threaded mounting base. The thermocouple leads are crimped to ceramic terminals inside the box and then routed out. It features electrical isolation and electromagnetic shielding, and has a modular assembly structure. The junction box is usually made of cast aluminum or stainless steel, filled with silicone or epoxy resin to enhance moisture resistance. The terminal block supports two-core or three-core leads and is compatible with direct connection of compensation wires.
Clamp Type: This is essentially a non-invasive surface clamping form of a sheathed thermocouple. It has no junction box or threaded base. The sensing end is a miniature spherical or flat head, covered with a 304/316L stainless steel sheath, with a diameter of 3–6 mm. The sensing end is clamped tightly to the outer wall of the pipe or equipment using a stainless steel clamp or band, relying on mechanical pressure for heat conduction. The leads are either exposed directly or equipped with shielded wires. The structure is lightweight and detachable.
Installation Method and Fixing Mechanism
|
Feature |
Junction Box Type (Threaded Mounting) |
Clamp Type (Pipe Clamp) |
|
Fixing Method |
Screws into the pre-drilled internal threaded hole of the equipment (e.g., M27×2, G1/2) |
Clamped onto the outer wall of the pipe, no drilling or welding required |
|
Connecting Part |
Metal threaded base |
Stainless steel clamp ring (adjustable diameter 40–100mm) |
|
Installation Tools |
Torque wrench (20–30 N·m) |
Manual tightening of bolts (1–2 N·m) |
|
Insertion Depth |
≥15 times the outer diameter of the protective tube, penetrating the medium |
No insertion, only contact with the outer surface |
|
Thermal Contact Method |
Direct contact within the medium |
Surface pressure contact, relying on thermal paste or metal contact |
|
Thermal Response Time |
1–5 seconds (depending on the protective tube wall thickness) |
0.2–1 second (ultra-thin casing + direct contact) |
|
Ease of Disassembly |
Requires disassembly of flange or pipe joint |
Can be removed by simply loosening the clamp, supports online replacement |
Protection Level and Environmental Adaptability
|
Dimension |
Junction Box Type |
Clamp Type |
|
Protection Level |
IP65/IP67, dustproof, waterproof, oil-resistant |
No sealing structure, only protects against mechanical damage, not against environmental media |
|
Electromagnetic Interference (EMI) Suppression |
Built-in shielding layer, signal noise <0.5μV |
Relies on external shielded compensation wires, susceptible to interference from inverters and motors |
|
Applicable Medium |
High-temperature steam, corrosive liquids, high-pressure gases |
Solid surfaces: water pipe outer wall, injection molding machine nozzles, bearing housings, metal pipes |
|
Pressure Resistance |
Up to 10MPa or more |
No pressure resistance, only suitable for surface temperature measurement at normal pressure |
|
Long-term Stability |
5–10 years (sealed environment) |
2–5 years (susceptible to oxidation and dust accumulation affecting contact thermal resistance) |
|
Maintenance Cycle |
Open the box every 1–2 years to check insulation resistance and clean terminals |
No maintenance required, replace when faulty |
Application Scenarios and Typical Uses
|
Application Scenario |
Junction Box Type |
Clamp Type |
|
Thermal power plant superheater pipe wall |
Standard configuration |
Not applicable |
|
Petrochemical reactor internal medium |
Required |
Cannot be inserted |
|
Injection molding machine nozzle surface |
Cannot be fitted |
Preferred (Huanya, Siemens products) |
|
Water pipe wall temperature monitoring |
Cannot be installed |
Preferred (Siemens QAD series) |
|
Bearing/gearbox housing temperature measurement |
Too large |
Preferred (fast response, easy installation) |
|
Cement kiln shell outer wall |
Difficult to install |
Commonly used (clamp-type armored) |
|
High-frequency vibrating pipes |
Easily loosened |
Applicable (rigid clamping, vibration resistant) |
|
Food processing equipment surface |
Easy to accumulate dirt |
Applicable (easy to clean, no dead ends) |
Product Examples:
Junction box type: Shanghai Automation Instrumentation Factory ZR-1200 series, Honeywell T1000 threaded type, OMEGA TCS-M27.
Clamp type: Huanya Thermal Engineering K-type clamp type, Siemens QAD series, testo pipe clamp probe (0602 0092), OMEGA OSTW-E-M-X-BRLK.
Key Conclusions
"Clamp type" is the common engineering term for "pipe clamp type" and "clip type," essentially a surface clamping installation method for armored thermocouples, completely opposite to the "threaded installation junction box type" in structure, use, and protection.
Junction box type is used for temperature measurement inside the medium, while clamp type is used for non-invasive surface temperature measurement; the former emphasizes sealing and anti-interference, while the latter emphasizes convenience and response speed.
In the market, "clamp type" products are all labeled as "clamp," "pipe clamp," "surface temperature measurement," forming a clear distinction from "junction box type" in naming, structure, and price range.
Core selection logic: If penetration, high pressure, high humidity, and strong EMI environment are required, choose the junction box type; if fast, convenient, and non-invasive surface temperature measurement is required, choose the clamp type.
Cost differences: Junction box type connectors typically cost 2-3 times more than clamp-type connectors, but they have a longer lifespan and lower maintenance costs, resulting in a more advantageous total cost of ownership (TCO).
