Bare Thermocouple vs. MIMS Cable: A Practical Comparison for Industrial Applications
How to Select the Right Thermocouple
Temperature sensing in extreme industrial environments requires careful sensor selection. Thermocouples, among the most widely used temperature sensors, come in multiple configurations. Two of the most common are:
- The bare thermocouple (exposed wires)
- The MIMS thermocouple (Mineral Insulated Metal Sheathed)
Each has unique strengths and trade-offs. Understanding how they perform, and in which environments they excel, is critical to selecting the right solution for your process.
What Is a Bare Thermocouple?
A bare thermocouple consists of two dissimilar metal wires joined at a sensing junction. These wires are unshielded, directly exposed to the environment.
Advantages:
- Fast response to temperature changes (minimal thermal mass)
- Simple design and installation
- Lower cost than protected configurations
Limitations:
- Susceptible to oxidation, corrosion, and mechanical damage
- Shorter lifespan in high-temperature or reactive atmospheres
Bare thermocouples are typically used in lab settings, controlled environments, or applications where quick response is needed and environmental exposure is not a concern.
What Is a MIMS Thermocouple?
MIMS (Mineral Insulated Metal Sheath) thermocouples are more robust. The thermoelement wires are enclosed in a metal sheath and surrounded by compacted magnesium oxide insulation, offering electrical isolation and mechanical protection.
Advantages:
- Excellent resistance to high temperature, moisture, vibration, and contamination
- Longer lifespan and stable performance
- Greater installation flexibility in industrial environments
MIMS cables are well-suited for aerospace, power generation, heat treatment, and metals processing, where environmental stresses and continuous operation demand reliable, long-term measurement.
Drift in High-Temperature Applications
One critical factor often overlooked is thermocouple drift — a gradual shift in measurement accuracy over time.
- Bare wire thermocouples, especially Type K, are more prone to drift at temperatures above 1000°C due to oxidation and metallurgical changes.
- Drift can lead to incorrect temperature readings, posing risks in safety-critical or tightly controlled processes.
MIMS thermocouples significantly reduce drift by shielding the wires from direct exposure, extending sensor life and measurement accuracy.
Junction Types: Tuning MIMS for Speed
While MIMS thermocouples are often viewed as slower due to their insulation, they can be customized for performance:
- Exposed junctions offer fastest response, nearly matching bare wire.
- Grounded junctions provide good speed with noise shielding.
- Ungrounded junctions isolate electrical interference, ideal for instrumentation-sensitive environments.
CEL offers MIMS thermocouples in all three junction types heng customers tune their sensors to application priorities.
| Feature | Bare Thermocouple | MIMS Thermocouple |
|---|---|---|
| Response Time | Very fast | Tunable via junction type |
| Environmental Protection | None – exposed to process environment | High – metal sheath blocks contaminants |
| Drift Over Time | Higher, especially above 1000°C (Type K) | Lower, stable long-term accuracy |
| Mechanical Durability | Fragile, prone to breakage | Excellent – robust for industrial conditions |
| Installation Environments | Best in labs or clean processes | Best for plant, furnace, field applications |
| Lifespan | Short in harsh conditions | Long, especially in oxidizing/corrosive atmospheres |
| Cost | Low upfront cost | Higher, but better long-term ROI |
| Shielding Options | None | Exposed, Grounded, or Ungrounded junctions |
CEL's Role in Industrial Thermocouple Solutions
Cleveland Electric Laboratories brings over 100 years of experience delivering custom industrial temperature sensing solutions to the world’s most demanding industries. CEL designs and manufactures both bare and MIMS thermocouples, supporting clients in:
- Aerospace engine testing
- Heat treatment and metals processing
- Power generation
- Defense and research labs
CEL also provides:
- ISO/IEC 17025-certified calibration
- Custom sheath materials for extreme environments
- Fast-turnaround on high-demand models like Type K
- A Precious Metal Exchange Program for platinum thermocouples (S, R, B types)
Whether you’re replacing sensors in a furnace or specifying instrumentation for new process lines, CEL helps you select the right thermocouple — bare or MIMS — based on temperature, atmosphere, response time, and lifespan.
Final Thoughts
Choosing the right thermocouple isn’t just about cost or availability — it’s about fit for purpose. While bare thermocouples offer speed and simplicity, MIMS thermocouples deliver protection, longevity, and flexibility — especially in high-temperature and industrial applications.
CEL provides expert support to help customers balance performance, cost, and reliability — ensuring better measurement, better decisions, and better outcomes.
