Armored Thermocouple vs Armored Thermal Resistance: A Visual Guide to Selection
Which is better: armored thermocouples or armored thermal resistors? This is the most frequently asked question in industrial temperature measurement system selection. A wrong choice can lead to insufficient accuracy and shortened lifespan at best, or even distorted data across the entire production line at worst. This article provides a comprehensive comparison across five dimensions—temperature measurement principles, accuracy, response speed, lifespan, and cost—to help you make the right decision in just three minutes.
Figure: Comparative schematic of Armored Thermocouple versus armored thermal resistor structures
I. Different Principles: Thermoelectric Effect vs Resistance Change
The Armored Thermocouple operates on the thermoelectric effect (Seebeck effect): two different metal wires are welded together at one end to form the hot junction, while the other end serves as the cold junction. The temperature difference between the two junctions generates a thermoelectric potential, which is measured to determine the temperature. The signal is in the millivolt range.
The armored thermistor operates based on the temperature-dependent resistance characteristics of metals: the resistance values of platinum wire (PT100/Pt1000) or copper wire (Cu50) change linearly with temperature, allowing temperature calculation through resistance measurement. The output signal is the resistance value (Ω).
| Counter Item | armoured thermocouple | Armored thermal resistor |
| Principle of Temperature Measurement | Thermoelectric effect (temperature difference → electric potential) | Resistance change (temperature → resistance value) |
| output signal | Millivolt-level voltage (mV) | resistance value （Ω） |
| mode of connection | two-wire system | Three-wire system/Four-wire system |
| Reference terminal required | Yes (cold-end compensation) | deny |
II. Comprehensive Comparison of Core Parameters
| Dimension for Comparison | armoured thermocouple | Armored thermal resistor |
| Temperature measurement range | -200℃ ~ 1600℃ | -200℃ ~ 850℃ |
| Maximum Precision | Type E ±0.2°C | Pt1000 ±0.01℃ |
| Common Precision | K-type ±0.5°C | PT100 ±0.1℃ |
| response time | Millisecond level (30–80 ms) | Second-level (1–3 s) |
| capacity of resisting disturbance | Weaker (interference rate 23%) | Strong (interference rate <5%) |
| life length | 1 to 5 years | 3 to 10 years |
| Calibration Cycle | 1–2 years | 1–2 years |
| Annual calibration cost | 400–800 yuan | 200–1200 yuan |
III. How to Choose Among the Three Major Types of Thermocouples
| model | Temperature measurement range | accuracy | response time | Common Scenario |
| K mould | -200~1350℃ | ±0.5℃ | ≤50ms | Chemical pipelines, heating furnaces, boilers |
| E mould | -200~800℃ | ±0.2℃ | ≤30ms | Laboratory, Aerospace |
| S mould | 0~1600℃ | ±1.0℃ | ≤80ms | Metallurgical furnace, ceramic sintering |
⚠ Important Reminder: K-type thermocouples must not be used to measure temperatures exceeding 1200°C, as this will cause the nickel-chromium alloy wire to melt, resulting in measurement failure and safety hazards.
IV. How to Choose Among the Three Major Types of Thermistors
| model | Temperature measurement range | accuracy | response time | Common Scenario |
| PT100 | -200~850℃ | ±0.1℃ | ≤2s | Chemical reaction vessels, electrical equipment |
| PT1000 | -200~850℃ | ±0.01℃ | ≤3s | Precision Laboratory, Medical Equipment |
| Cu50 | -50~150℃ | ±0.5℃ | ≤1s | Air conditioning system, cold storage facility |
⚠ Important reminder: Cu50 thermistors must not be used to measure temperatures above 150°C, as the copper wire will oxidize and fail.
V. Model Selection Decision: 5 Questions to Help You Make Your Choice
① What is the temperature measurement range?
>850°C → Only thermocouples (S-type) are acceptable; <850°C → Both types are acceptable, depending on the required accuracy.
② What is the required level of accuracy?
Within ±0.1°C → Resistance Temperature Sensor (PT100/PT1000); within ±0.5°C acceptable → K-type thermocouple is sufficient
③ What are the requirements for response speed?
Millisecond-level rapid warning → Thermocouple; Second-level stable monitoring → Thermistor
④ Environmental electromagnetic interference?
Strong electromagnetic environment (near the motor or inverter) → A thermistor must be selected; ordinary environment → Both options are acceptable.
⑤ Budget and maintenance?
Low cost and long service life → Thermistor (PT100 has a lifespan of 5–8 years); High temperature and low cost → K-type thermocouple
VI. One Table for Everything: Scenario → Quick Model Selection
| Industrial Scenario | temperature range | Recommended Selection | Recommended model |
| Chemical reaction kettle | 0~400℃ | Armored thermal resistor | PT100 three-wire system |
| Heating furnace/boiler | 300~1200℃ | armoured thermocouple | K mould |
| Metallurgical furnace chamber | 800~1600℃ | armoured thermocouple | S mould |
| electrical power unit | -40~150℃ | Armored thermal resistor | PT100 Class A |
| Cold storage/air conditioning | -50~50℃ | Armored thermal resistor | Cu50 |
| food handling | 0~200℃ | Armored thermal resistor | PT100 + Sanitary grade |
| Near the frequency converter | 0~300℃ | Armored thermal resistor | PT1000 (anti-interference) |
| Rapid temperature fluctuation | wantonly | armoured thermocouple | Type E/K |
💡 Technical Note: For medium-to-long-range (＞10 meters) temperature measurement, resistance thermometers must employ a four-wire wiring system to eliminate lead errors, while thermocouples require compensation wires.
VII. Procurement Pitfall Avoidance Checklist
Confirm the graduation number: Types K, E, and S must not be used interchangeably; the graduation number must be specified during procurement.
Selection of armor material diameter: Commonly used diameters are Φ3/Φ4/Φ5/Φ6/Φ8 mm. Smaller diameters offer faster response but are more brittle.
Insertion depth: Generally not less than 8 to 10 times the diameter of the protective tube; insufficient depth results in inaccurate temperature measurement.
Wiring box rating: For outdoor use, select IP65 waterproof type; for explosion-proof areas, choose flameproof or intrinsically safe type.
Compensation wire matching: Type K requires KC compensation wire, Type S requires SC compensation wire; they must not be used interchangeably.
Calibration Certificate: Request the factory calibration report upon procurement; only those within the validity period guarantee accuracy.
────────────────────────────────────────
When choosing between armored thermocouples and armored thermal resistors, three key factors must be considered: whether the temperature range is sufficient, whether the accuracy meets the required standards, and whether the device can withstand environmental conditions. Clarifying these three aspects eliminates any hesitation in selection. For any selection inquiries or customization needs, please contact our technical team for professional solutions.