Testing in half the time

More efficient testing with CO₂ cooling technology

The new CO₂ cooling technology in climate simulation not only meets the requirements of the EU F-Gas Regulation for single-stage cooling systems, but also accelerates processes in test laboratories. With the extended temperature range of the new test chambers down to -50°C, changes to previous test programs are possible. In some cases, this leads to significant time savings.

According to IEC 60068-2-14 (Ed. 7), for example, test runs can be performed in less than half the time previously required, depending on the selected parameters. A typical test situation is the testing of electronic components with the preferred temperatures TA -40°C and TB +85°C according to test case Na. The “Increased Severity” described in the standard allows the temperature load on the test object to be adjusted. The temperature settings of the test are set below or above the target temperatures (e.g. -40°C and +85°C) for a certain period of time. It must be noted that the target temperatures are selected from IEC 60068-2-1, unless otherwise stated in the relevant test specification. Based on this information, the next preferred temperature would be -50°C. It often makes sense to apply the same temperature difference of 10 K for the upper value TBi. If the set temperature of the test chamber is temporarily adjusted to -50°C and +95°C for the “ts*” periods of the test standard, the temperature change of the test object can be significantly accelerated.

The actual comparison of the described test, which was carried out in otherwise identical 600 l test chambers with -40°C R-449A refrigeration technology and -50°C CO₂ refrigeration technology with a 10 cm aluminium cube as test object and a waiting time of t1 = 10 h, yielded these values:

Average cooling rate of the test object to a core temperature of -40°C

Cooling time to a core temperature of -40°C

Even without “Increased Severity”, the temperature change of the test object is about three hours faster with CO₂ cooling technology. This is mainly due to the strong drop in cooling capacity of the R-449A system with a possible final temperature of -40°C. It takes a long time to temper the test object from -30°C to -40°C.

The further reduction of the test time in the example is possible with the temporary temperature hold of -50°C. The incoming air quickly reaches -50°C and is only regulated to -40°C when the core temperature of the test object approaches the target temperature of -40°C (∆Ts). For those who want to make programming more efficient, an accessory package is available for the Weiss Technik test chambers. This includes a temperature sensor and suitable test programs.

Time savings can also be achieved with -70°C devices. However, the energy consumption is higher. Further reductions through even larger deviations in holding temperatures are difficult because this can quickly lead to an undesirable intensification of the test (especially at high temperatures). If time savings are not the leading parameter, greater efficiency can also be achieved by increasing the number of test objects in the test chamber that are simultaneously re-tempered. The higher performance of CO2 devices, in combination with the modified standard specifications, creates a larger test capacity. This also applies to tests according to IEC 60068-2-2, test cases Bd and Be.

If test chambers need to be replaced, replacement with CO₂ cooling technology that can reach -50°C is always sufficient in the case of an old device with a low temperature of -40°C. In many cases, it is also possible to replace a device with a low temperature of -70°C at a significantly lower investment cost. The cooling capacity of a -50°C test chamber with CO₂ technology is approximately half as high at -40°C as that of a -70°C cascade. This is sufficient for the requirements of IEC 60068-2-1, test cases Ab, Ad and Ae.

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Posted by Weiss Technik Netherlands