Tenma 72-7712 dual channel temp probe, what happens with temperatures inside a PC.

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 LN2/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.

• 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 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.

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Thermocouple 1 reading

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Thermocouple 2 reading

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Thermocouple 1 – thermocouple 2 reading. Temperature difference. This screen is most effective when trying to move case temperatures closer to ambient room temperature.

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Example of exported data to .xls format

Thermal conductivity of the heat sink 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 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).

:More information about thermal conductivity and conductive heat transfer:

Some simple ideas for improving the PC enthusiast experience:

Checking the case for hot spots.

Keeping your entire case as close to ambient is probably the most important thing that can be done to keep the HSF operating at its maximum efficiency. A heat sink can not lower temperatures below case ambient and will usually level out 4-12 degrees centigrade above case ambient no matter how much money is spent on it.

By identifying hot spots, proper fan placement can be made. Though 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; especially: a circular current : whirlpool) which in turn, remain hot and by cross circulation make  air circulating 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, 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 allows for fixes that otherwise would not be possible.

Testing for efficiency.

Methodology: Air can only dissipate a fixed amount 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 and Aluminum heat sinks tested for conductivity.

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 and heat is dispersed through natural convection. This is not a scientific test as the blocks were not exactly the same and some variables were omitted. What it does show is that copper will transfer heat faster and more evenly.

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A double boiler is used to allow for better temperature control

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Test equipment and stop watch used (phone) for testing. A Tenma 72-8540 is used as a control.

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The copper and aluminum heat sinks used for the test

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 would have been lower during operation.

The results of this test correlate directly to the previous test results.

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.

Using information gathered 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.

Shots of the 72-7712

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All display elements

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Temperature readout screen

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Variance screen

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Setup: Offset adjustment screen

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Front view of meter showing controls

Conclusion

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 features the 72-7712 makes an excellent addition to the tool box of the overclocker or small PC mod shop.