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.
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).
|Thermal Conductivity (k) / WmK|
|Material||at 0°C||at 25°C||at 125°C||at 225°C|
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
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.
This shows the HSFs ability to pull off heat, notice that the stock HSF just can’t compete. Powering up the fans shows how well each can dissipate heat:
What Else Can You Do?
One simple idea for improving the PC enthusiast experience is to check the case for hot-spots. Keeping your entire case as close to ambient as possible is probably the most important thing that can be done to keep the HSF operating at its maximum efficiency. A heatsink can not lower temperatures below case ambient and will usually level out 4 to 12°C above case ambient no matter how much money is spent on it. By identifying hot spots, proper fan placement can be made. Although these areas may not seem relevant to CPU cooling, they are. Air circulating throughout the case creates eddies (a current of air running contrary to the main current; a special case is a circular current, whirlpool) which remain hot and by cross circulation make air around them heat up. Working in a similar fashion to the eddy, dead zones (hot area where there is no mechanical air circulation) may seem harmless, but it is critical to circulate or eliminate this air to alleviate convection (heat transfer in a gas by the circulation of currents from one region to another). For dead zones, a fan may not be an option and directed air may be needed. If directed air is not possible, then closing in/sectioning off this area may be the only option.
Knowing where the hot areas of the case are located allows for fixes that otherwise would not be possible. Gathering information with a good temperature meter will help guide the process of lowering case temperatures and in turn allow for a cooler processor, memory, and hard disk drive.
Thermocouple test probes useful for PC applications:
Shots of the 72-7712
Using a dual probe temperature meter with capabilities comparable to the 72-7712 is a definite step up from the volt meter type single probe units that were used in the past. With the data logging capabilities and other features available with this unit, it is much easier to maximize case cooling and potentially gain a few hundred MHz from a heat limited overclock.
With acceptable quality, useful software and adequate features the 72-7712 makes an excellent addition to the tool box of the overclocker, enthusiast or small PC mod shop.