Technical Review of the MY-207 Thermal Conductivity Meter: How the Transient Planar Heat Source Method Has Brings Thermal Conductivity Measurement into the "5-Second-Level" Era
The thermal conductivity coefficient is the fundamental physical quantity used to quantify a material's thermal conductivity performance; it directly influences product decisions in areas such as electronic heat dissipation design, building energy efficiency assessment, and the research and development of new energy materials. Traditional steady-state methods (e.g., the protected plate method) require several hours to complete a single measurement and impose stringent requirements on sample preparation. The MY-207 thermal conductivity meter employs transient planar heat source technology (TPS), which compresses a single measurement to 5–160 seconds while covering an extremely wide range of 0.0001–300 W/(m·K); a single test can therefore simultaneously provide both the thermal conductivity coefficient and the thermal diffusivity. This review examines the device from four dimensions: technical parameters, testing procedures, methodological comparisons, and practical implementation challenges.
▎I. Technical Parameters and Probe System
The core measurement range of the MY-207 spans six orders of magnitude—from insulating materials (0.0001 W/(m·K)) to highly thermally conductive metals (300 W/(m·K))—with segmented coverage achieved through three probes of different diameters. The complete technical specifications are provided below.
| Parameter Items | Qualification | Explain |
|---|---|---|
| Test specification | 0.0001 ~ 300 W/(m·K) | From insulating materials to highly conductive metals |
| Accuracy | ±3% | Achievable at ±0.5% under optimal conditions |
| Repeatability error | ≤3% | Consistency of multiple measurements of the same sample |
| Measurement time | 5–160 seconds | Can be configured based on material properties |
| Sample temperature rise | ≤15℃ | Non-destructive testing; samples can be reused |
| Total power | ≤500W | |
| source | AC 220V | |
| Temperature range | -20°C ~ 200°C | An external temperature control device must be selected and configured. |
Three-Probe Range-Matching Solution
The equipment's wide-range coverage depends on the segmented matching of three types of probes. The basic logic for selecting a probe is as follows: use a small probe for low thermal-conductivity materials (heat is concentrated, resulting in higher temperatures), and use a large probe for high thermal-conductivity materials (heat spreads rapidly, requiring a larger heating area).
| Probe | Diameter | Applicable Materials | Single-sample size requirements | Maximum power |
|---|---|---|---|---|
| Probe No.1 | 7.5mm | Low thermal conductivity thin materials (thermal insulation boards, foam, etc.) | ≥15×15×3.75mm | < 0.4W |
| Probe No.2 | 15mm | General-purpose (plastics, rubber, ores, etc.) | ≥30×30×7.5mm | < 14W |
| Probe No.3 | 30mm | High thermal conductivity materials (metals, ceramics, etc.) | ≥60×60×20mm | < 7W |
[Technical Note] The TPS probe consists of a thin sheet with a continuous double-spiral structure, fabricated from a conductive alloy through etching and coated with a double-layer insulating protective layer. The probe simultaneously functions as a heat source and a temperature sensor: the thermal resistance coefficient of the alloy exhibits a linear relationship with temperature; therefore, by measuring changes in resistance, temperature changes can be inferred without the need for an external temperature sensor. This "heat source as sensor" design constitutes the core innovation of the TPS method.
▎II. Testing Procedure: From Sample Preparation to Data Reading
The testing procedure for the MY-207 is significantly more streamlined than that of the conventional steady-state method; its core step consists of a sandwich configuration in which "two samples are held between a single probe." The complete operating procedure is provided below.
Step 1: Probe Selection and Sample Preparation
Select the probe model based on the estimated order of magnitude of the thermal conductivity. Prepare two samples whose dimensions meet the specified requirements—each should have a length and width of at least twice the probe diameter—and whose surfaces are relatively flat and smooth. No special polishing or machining is required; it is sufficient that the surface of the bulk solid be relatively smooth. For samples with a smooth surface and high viscosity, multiple thin samples can be stacked together to meet the required thickness.
Step 2: Probe Installation and Sample Clamping
Place the selected probe between the two samples to form a sandwich configuration. Use the sample stage's adjustment mechanism to clamp the samples, ensuring good surface contact between the probe and both sample surfaces. The quality of this contact directly affects measurement accuracy: the heat generated by the probe must be fully absorbed by the samples; any gap will cause heat loss and measurement bias.
Step 3: Parameter Configuration and Startup Test
Set the heating power and test duration on the color LCD touchscreen. The power setting depends on the probe model and the thermal conductivity characteristics of the material: use low power for low thermal conductivity materials (to prevent the temperature rise from exceeding the 15°C upper limit), and use high power for high thermal conductivity materials (to ensure a sufficient temperature response signal). The test duration can be selected from 5 to 160 seconds; for low thermal conductivity materials, a longer test duration is typically used to obtain a complete temperature response curve. After startup, the ARM microprocessor controls the data acquisition chip to continuously record the probe resistance (i.e., temperature) in real time with high resolution as it undergoes transient changes over time.
Step 4: Data Calculation and Result Output
Upon completion of the test, the core algorithm performs mathematical model fitting on the transient temperature–time data acquired by the probe. Based on the theory of the transient temperature response of a step-heated disk heat source in an infinite medium, the TPS method enables direct determination of the two parameters—thermal conductivity and thermal diffusivity—through model fitting, without requiring the input of the sample density (a distinction from the laser method). The results are displayed on a touch screen and can also be exported via a communication interface to a computer for report processing.
[Technical Note] Compared with the laser method: The laser method (flash method) directly measures the thermal diffusivity and specific heat; the thermal conductivity must be calculated after additionally inputting the sample density. In contrast, the TPS method provides the thermal conductivity directly in a single step, thereby reducing the sources of error introduced by intermediate conversions. Furthermore, the laser method imposes strict requirements on sample preparation (the sample must be disk-shaped and have a specified thickness), whereas the TPS method imposes no special requirements on sample shape.
▎III. Overview of Application Scenarios
The MY-207 offers an exceptionally broad range of test materials, covering everything from high thermal-conductivity solids such as metals and ceramics to low thermal-conductivity thermal insulation materials such as foam plastics and mineral wool; it can also test powders and particles, as well as liquids, colloids, and paste-like substances. The following are five typical application areas.
Thermal Performance Assessment of Building Energy-Saving Materials
Thermal conductivity testing is performed on building materials such as cement walls, mineral wool, cement–polystyrene boards, sandwich concrete, and composite panels with fiberglass-reinforced plastic panels, providing the necessary thermal parameters for building energy efficiency design. Probe No.2 (15 mm) is suitable for routine testing of most building materials, while Probe No.3 (30 mm) is suitable for large-size samples, such as cement concrete.
Selection of Electronic Packaging and Thermal Interface Materials
Measure the thermal conductivity of thermal interface materials such as thermal silicone sheets, thermal grease (paste), phase-change materials, and thermal pads, thereby providing material selection data for the thermal dissipation design of electronic devices. Paste and colloidal materials represent the unique advantage of the TPS method; the laser method and the protective plate method are ill-suited for handling samples in this form.
Research and Development of Polymers and Composite Materials
Thermal and physical property characterization is performed on materials such as polymer matrix composites, fiber-reinforced plastics, paper honeycomb panels, and fabrics, thereby supporting material formulation optimization and process improvement. The nondestructive testing capability means that samples from the same batch can be reused for subsequent mechanical testing or other analyses, reducing sample consumption.
Thermal Management Verification for New Energy Materials
Perform thermal conductivity assessments on new-energy-related materials, including battery separators, phase-change energy storage materials, and thermal insulation layer materials. With a lower limit measurement capability of 0.0001 W/(m·K), the system can meet the testing requirements for ultra-insulating materials, such as aerogel felts.
Quality Control for Powder and Granular Materials
Rapid thermal conductivity measurements are performed on powdered raw materials and granular fillers for quality control during production batches. A test duration of 5–160 seconds makes in-line sampling inspections feasible; compared with the several-hour measurement cycles required by the traditional steady-state method, efficiency is increased by dozens of times.
▎IV. Typical Testing Challenges and Solutions
Although the TPS method simplifies the testing process, several issues still arise in practical implementation that require proper handling. The following outlines eight frequently encountered or challenging problems and their corresponding countermeasures.
Challenge 01: Poor contact between the probe and the sample results in underestimation of the measured value
High frequencyObservation | The thermal conductivity of the same sample differs by more than 5% between two tests (repeatability indicator ≤ 3%), and the measured values are systematically low. A slight gap is visible between the probe and the sample.
Root Cause | The fundamental premise underlying the measurement in the TPS method is that all heat generated by the probe is completely absorbed by the sample. Poor contact causes part of the heat to be conducted through the air gap (the thermal conductivity of air is only 0.026 W/(m·K)); this is equivalent to inserting a thermal resistance layer in series between the probe and the sample, resulting in a measured thermal conductivity value lower than the true value. The primary causes include an uneven sample surface, insufficient clamping force on the sample stage, or uneven sample thickness, which leaves one side of the probe unsupported.
Countermeasures | ① Confirm that the sample surface is relatively flat, with no protrusions or depressions (mirror-grade polishing is not required, but the surface should feel smooth and free of burrs); ② Adjust the sample stage's clamping mechanism to ensure that the probe is evenly pressed against both sides of the sample; use a 0.02 mm feeler gauge to check the gap between the probe edge and the sample (the gap should be too small for the gauge to pass); ③ For samples with rigid surfaces, apply an extremely thin layer of thermal grease between the probe and the sample to fill microscopic gaps (note that the thickness of the grease layer must be extremely thin; otherwise, it will itself become a thermal resistance layer).
Challenge 02: Incorrect probe model selection results in insufficient signal strength or excessive temperature rise
CommonObservation | When using Probe No.2 (15 mm) to test highly thermally conductive metals (e.g., pure copper, approximately 400 W/(m·K)), the temperature response signal is extremely weak, the fitted curve exhibits significant noise, and the result deviates by more than 10%. Alternatively, when using Probe No.1 (7.5 mm) to test low-thermal-conductivity foams, the temperature rise exceeds the 15 °C upper limit, triggering the protection mechanism.
Root Cause | The fundamental principle in probe selection is matching: heat dissipates more slowly in low thermal-conductivity materials, so a small probe (7.5 mm) can concentrate heat and generate a sufficient temperature-rise signal; in high thermal-conductivity materials, heat dissipates rapidly, requiring a larger probe (30 mm) to provide adequate heating area and power. Selecting an inappropriate probe can result in an insufficient signal-to-noise ratio or uncontrolled temperature rise.
Mitigation measures | ① Before testing, estimate the order of magnitude of the material's thermal conductivity: use Probe No.1 for values ≤ 0.1 W/(m·K); Probe No.2 for values between 0.1 and 50; and Probe No.3 for values> 50; ② If the value is uncertain, first conduct a trial measurement using Probe No.2 (the universal probe), then adjust the settings based on the temperature rise and signal quality; ③ Strictly observe the maximum power limit for each probe (Probe No.1: <0.4 W; Probe No.2: <14 W; Probe No.3: <7 W) to prevent probe damage caused by exceeding the power rating.
Challenge 03: Boundary effect interference caused by insufficient sample size
High frequencyObservation | Test results vary with sample size—when the sample size is increased, the measured values rise and stabilize; for small-sized samples, the measured values are systematically lower.
Root Cause | The mathematical model underlying the TPS method is based on the assumption of an "infinite medium": the heat generated by the probe within a finite period of time has a limited diffusion range; if the sample size is insufficient to be regarded as "infinite," the heat reflects upon reaching the sample boundary, thereby violating the model's boundary conditions and resulting in measurement bias. The instruction manual specifies that the sample's length and width should be at least twice the probe's diameter; however, practical experience has shown that twice the diameter is merely the lower limit.
Mitigation measures | ① Strictly adhere to the minimum size requirements: for Probe No.1, the sample should be ≥15×15 mm; for Probe No.2, ≥30×30 mm; and for Probe No.3, ≥60×60 mm; ② For materials with a high thermal conductivity (which dissipate heat rapidly), it is recommended that the sample size be increased to 3–4 times the probe diameter to fully satisfy the "infinite" assumption; ③ Sample thickness is likewise critical—the thickness of the sample on one side of the probe should exceed the probe radius; if the sample is too thin, multiple samples can be stacked together.
Challenge 04: Probe sinking or bubble adhesion during liquid sample testing
DifficultPhenomenon | When measuring the thermal conductivity of a liquid, the probe sinks in the liquid due to its own weight, or tiny bubbles adhere to the probe surface, resulting in abnormal fluctuations in the measurement results.
Root Cause | The TPS probe is designed to be clamped between two solid samples; when testing a liquid, the probe must be immersed in the liquid. The probe's metal spiral structure has a certain weight and may slowly sink and shift position in low-viscosity liquids; the insulating layer on the probe surface readily traps air bubbles when immersed in the liquid. Since air bubbles are poor thermal conductors, they effectively create an additional thermal resistance layer on the probe surface.
Mitigation measures | ① Use a dedicated liquid test container and fix the probe at the center of the container to prevent sinking or displacement; ② Before immersing the probe, dip a lint-free cloth into a small amount of the same type of liquid and moisten the probe surface to reduce bubble adhesion; ③ After immersion, allow the probe to stand for 30 seconds so that bubbles can escape naturally, then gently tap the container wall to assist in bubble release; ④ For low-viscosity liquids, the testing time may be appropriately extended to obtain a more stable average signal.
Challenge 05: Improper test-time configuration leads to large fitting residuals
DifficultObservation | When the test duration is set to a minimum of 5 seconds, the fitting residuals are relatively large (the residual curve does not follow a random distribution but exhibits a systematic trend), resulting in unstable thermal conductivity data. After extending the duration to 60 seconds, the results improve significantly.
Root Cause | The TPS method determines the thermal conductivity by fitting a transient temperature–time curve. If the test duration is too short, the collected data points are insufficient to cover the complete transient heat diffusion process; consequently, the mathematical model lacks sufficient data within its fitting window, resulting in non-convergence or convergence to an incorrect solution. If the test duration is too long, heat diffusion may extend beyond the sample boundaries, thereby violating the "infinite" assumption.
Recommendations | ① Principle for setting test duration: for materials with low thermal conductivity (slow heat diffusion), set a longer test duration (60–160 seconds); for materials with high thermal conductivity (rapid heat diffusion), set a shorter test duration (5–30 seconds); ② Observe the fitted residual curve—the residuals should be randomly distributed around zero; if a systematic trend is present, adjust the test duration and retest; ③ When testing a material for the first time, it is recommended to conduct comparative measurements at 2–3 different test durations and select the value at which the fitted residual is minimized and the results have converged.
Challenge 06: The Impact of Contact Thermal Resistance in Multi-layered Overlaid Samples on Measurement Accuracy
High frequencyObservation | When multiple thin samples are stacked to meet dimensional requirements, the measured values are low and repeatability is poor. The greater the number of stacked layers, the larger the deviation.
Root Cause | The instruction manual states that "if the surface of the sample being tested is smooth and flat and exhibits adhesion, the sample may be stacked"; however, stacking introduces interlayer contact thermal resistance. Microscopic air gaps exist between each two layers, forming a series of thermal resistance layers. The TPS method itself is not affected by probe–sample contact thermal resistance (this is its advantage); nevertheless, the contact thermal resistance between sample layers cannot be eliminated. The value measured by the probe is the "equivalent thermal conductivity" including interlayer thermal resistance, which is lower than the material's intrinsic value.
Mitigation measures | ① Prioritize the use of a single intact sample that meets the dimensional requirements to avoid stacking; ② When stacking is necessary, select samples with smooth surfaces and high flatness, and apply an extremely thin layer of thermal grease between the layers; ③ The number of stacked layers shall not exceed two (per side of the probe); ④ Specify the stacking test conditions in the report and state that the measured value represents the "equivalent thermal conductivity including interlayer thermal resistance," rather than the intrinsic material property.
Challenge 07: Testing for excessive temperature rise causing changes in sample properties
DifficultPhenomenon | When testing thermally sensitive materials (such as phase-change materials and low-melting-point alloys), heating the probe causes the local temperature of the sample to exceed its phase-change point or softening point, resulting in a change in the sample's appearance before and after testing.
Root Cause | The TPS method measures thermal response by inducing a temperature rise through probe heating; the instructions specify that the sample temperature rise must be ≤15°C. For phase-change energy storage materials (whose phase-change temperatures typically range from 20–60°C) or low-melting-point materials, a temperature rise of 15°C is sufficient to trigger phase change or softening; at this point, the material's thermal properties themselves have changed, and the measurement results do not represent the material's true thermal conductivity at the target temperature.
Mitigation measures | ① Reduce the heating power and keep the temperature rise within 2–5 °C (although the signal will weaken, this prevents changes in material properties); ② Shorten the test duration to reduce the total heat input; ③ For materials with a known phase-change temperature, conduct testing at a temperature sufficiently below the phase-change temperature; ④ If the thermal conductivity near the phase-change temperature needs to be measured, use an external temperature-control device to preset the sample to the target temperature and then perform the test at minimum power.
Challenge 08: Data Acquisition Abnormality—Touchscreen display communication failure or data loss
CommonIssue | After the test is completed, the touchscreen displays "Communication Failure" or "Data Acquisition Abnormality"; the results cannot be displayed; and the data files exported to the USB drive are empty or corrupted.
Root Cause | Data communication links involve three stages: data acquisition chip → ARM microprocessor → touchscreen/USB flash drive. Communication failures may arise from: ① Incompatibility of the USB flash drive's file system (devices have the best compatibility with the FAT32 format; exFAT or NTFS may cause write failures); ② Poor contact at the USB flash drive or a capacity exceeding the device's supported limit; or ③ Power fluctuations during testing causing an interruption in data transmission between the ARM microprocessor and the data acquisition chip.
Mitigation Measures | ① Use a small-capacity USB flash drive formatted in FAT32 (preferably under 8 GB); avoid using exFAT or NTFS formats; ② Ensure that the USB flash drive is fully inserted and do not touch it during testing; ③ If communication fails, do not immediately retest—power off the device and restart it first, then check whether the system self-diagnostic process operates normally; ④ If communication failures occur frequently, use a multimeter to check the stability of the AC220V power supply; if necessary, install a voltage regulator; ⑤ Contact the manufacturer to obtain the latest version of the experimental software and update the USB drive driver.
▎V. Comparison between the TPS Method and Other Thermal Conductivity Testing Methods
To objectively assess the technical advantages of the TPS method, it is compared below with three mainstream thermal conductivity testing methods.
| Comparison dimension | TPS method (this unit) | Laser method | Hotline method | guarded-plate method |
|---|---|---|---|---|
| Measuring principle | Unstable state | Unstable state | Unstable state | Steady state |
| Obtain parameters | Thermal conductivity + thermal diffusivity | Thermal diffusivity + specific heat capacity | Thermal conductivity | Thermal conductivity |
| Scope of application | Solid/liquid/Powder/Paste/Gel/Particle | Solid only | Solid/liquid | Solid only |
| Sample preparation | No special requirements | Complex sample preparation | Specific requirements apply | Large size |
| Optimal accuracy | ±0.5% | ±10% | ±5% | ±3% |
| Thermal conductivity range | 0.005~300 | 10~500 | 0.005~10 | 0.005~5 |
| Testing time | 5–160 seconds | A couple of minutes | Several dozen minutes | Several hours |
[Technical Note] The TPS method offers comprehensive advantages across three dimensions: scope of application (full coverage of solids, liquids, powders, pastes, adhesives, and particles); sample preparation difficulty (no special requirements); and testing time (5–160 seconds). Its only limitation is that the measurement of ultra-high thermal conductivity materials (>300 W/(m·K)), such as pure copper and diamond, requires supplementation with the laser method. For conventional engineering materials (0.005–300 W/(m·K)), however, the TPS method remains the overall optimal choice.
Review Conclusion
The MY-207 thermal conductivity meter is based on TPS transient planar heat source technology. It achieves a measurement accuracy of ±3% (optimally ±0.5%) across a wide range of 0.0001–300 W/(m·K); a single test requires only 5–160 seconds; it imposes no special requirements on sample geometry; and it is nondestructive and repeatable. The three-probe system and the dual-spiral probe design form the technical foundation for its wide-range coverage. In practical operation, appropriate probe selection and matching, sample dimensions that satisfy the "infinite" assumption, guaranteed contact quality, and properly set test times are the four key control points for ensuring data reliability. For sample forms that are difficult to handle using conventional methods—such as pastes, colloids, liquids, and powders—the TPS method offers an irreplaceable advantage in terms of applicability.