Testing Heatsink Temperatures with the Tenma 72-7712 Data-Logging Dual Thermocouple

The 72-7712 Digital Thermometer from Tenma Test Equipment is a dual thermocouple meter with internal logging capability, USB output for saving logged data, and software up-link.  This unit can become an integral part of a PC testing arsenal by allowing for isolation of case hot spots, heat sink testing, and liquid nitrogen/dry ice work. The limitations start to change and the performance bar can be raised when you know where it is hot and where it is not.

Features and Specifications

• Compatible with K-, J-, T- and E- thermocouples (others should work, but these are the recommended types)
• User programmable offsets
• Internal memory stores 100 sets of temperature readings that can be transferred to PC software
• Data logging software for real time testing (good for working with fan and component placement and viewing their effects in real time)
• Ability to export data sets from software in .xls format to do comparative studies and graphing

The graph capabilities of the 72-7712 software are not phenomenal, it does however serve the intended purpose. Though dual software readout (T1 & T2) would be preferred; the logging capacity and decent feature set, as well as an Excel export feature make up for the software weaknesses.

By pressing the T1, T2, T1-T2 button on the meter your view will also change on the software output screen.

Pressing again will display the variance on the software output screen.

XLS output is a useful feature.

Thermal Conductivity

The thermal conductivity of the heatsink material is an important factor in air cooling. Copper and aluminum are the most widely used materials in PC HSF (heat sink & fan) construction. The thermal properties of these two materials are critical to proper cooling of the processor. The chart below shows the thermal conductivity of materials for comparison. The only three that matter for this testing are aluminum, copper, and air (water and the other items may be of interest to those who like to get a little wet).

Note: Fourier’s Law expresses conductive heat transfer as q = k.A.dT / s where q = heat transferred per unit time (W/h), A = heat transfer area (m²), k = thermal conductivity of the material (W/m.K), dT = temperature difference across the material (K) and s = material thickness (m).

Testing the Efficiency

Methodology: Air can only dissipate a fixed load of heat due to its low thermal conductivity. Having a material of higher thermal conductivity does not always mean better temperatures, but it does allow a potential for lower temperatures, depending on other contributing factors. Testing the two most common heat sink materials to see these differences helps gain an understanding of what the conductivity numbers really mean.

Copper: 56.8 seconds to reach maximum efficiency with a variance of 3.9 degrees centigrade

Aluminum: 59.8 seconds to reach maximum efficiency with a variance of 7.9 degrees centigrade

This is the point where temperatures stabilize (temperature increases are such that after a pre-determined amount of time, ~20 seconds in this case, there is no change)  and heat is dispersed through natural convection. Although this was not the most rigorous and scientific test (not all variables were controlled) this test does show that copper will transfer heat faster and more evenly. A two minute test of both materials (copper and aluminum) showed a 3.7 degree centigrade variance, copper being hotter (this is good, it means it will draw that much more heat to be dissipated). It must be taken into consideration that these heat sinks did not have a fan and the variance may have been different during operation.

Testing Your Heat Sink and Fan Assembly

Using an Arctic Cooling AF64 PRO

Temperature above ambient

If the HSF is not equalizing temperatures within a reasonable variance or running 10+ degrees above ambient case temperature (check the temperature at the intake area of the HSF to eliminate the possibility of a hot spot causing the problem), then a re-seat of the HSF may be needed and possibly a replacement HSF of higher quality may be in order.

Comparative Heatsink Testing

The setup: thermocouples were inserted in aluminum transfer blocks alloy for accurate temperature measurement without the risk of potential damage to other costly components.