After 15 years of work in CISPR Subcommittee I, the IEC Central Office published CISPR 35 Edition 1.0 on Tuesday, August 16, 2016. The IEC webstore link is https://webstore.iec.ch/publication/25667. In the US, ANSI has the standard available on their website as well. Go to www.ansi.org and type in CISPR 35 in the search window for standards. You must purchase a copy of the standard to see what the specific requirements are.
Now that CISPR 35 is finally published, the questions that you want answered are: What is the same as CISPR 24? What has changed? What is new?
The full title of the standard is, “CISPR 35:2016 Electromagnetic compatibility of multimedia equipment – Immunity requirements”.
The abstract, off the IEC webstore page, states, “CISPR 35:2016 applies to multimedia equipment (MME) having a rated AC or DC supply voltage not exceeding 600 V. The objectives of this document are:
- to establish requirements which provide an adequate level of intrinsic immunity so that the MME will operate as intended in its environment in the frequency range 0 kHz to 400 GHz; and
- to specify procedures to ensure the reproducibility of tests and the repeatability of results.”
Before going into any details, please note that CISPR 35, like other CISPR standards, uses dated references to other standards. Thus, the laboratory must use the version called out in the standard, even if a newer version is available. A particular example where this is necessary is in the use of IEC 61000-4-5:2005 for surge testing. A newer version is available on the IEC website, but CISPR Subcommittee I have determined that for the time being the 2005 version is the one to use.
So, what is different between CISPR 24 (ITE immunity) and CISPR 35?
A key difference is that CISPR 24 provides guidance on testing different types of devices while CISPR 35 focuses on “functions” of the EUT. For example, in the annexes of CISPR 24 there are annexes aimed at telephony terminal equipment, data processing equipment, local area networks, printers and plotters, etc. The annexes in CISPR 35, on the other hand, deal with broadcast reception function, print function, scan function, display and display output functions, musical tone generating function, networking functions, audio output function and telephony function. Testing to CISPR 35 need only be performed for the primary function(s) of the product.
The general types of immunity tests are the same in both CISPR 24 and CISPR 35. There are a few key differences, however.
For continuous RF electromagnetic field disturbances, CISPR 35 adds the option of testing in a TEM cell (IEC 61000-4-20) or a reverberation chamber (IEC 61000-4-21) to the testing method used in CISPR 24 (IEC 61000-4-3). Thus, CISPR 35 offers more choice in testing environments. CISPR 35 adds spot frequencies of 1800 MHz, 2600 MHz, 3500 MHz and 5000 MHz to be tested. 3 V/m is the required test level for all these tests (swept from 80 MHz to 1000 MHz and spot frequencies as noted above). Note that this test level is the rms value of the field prior to turning on the modulation. There are additional spot frequencies required in CISPR 35 for equipment with a primary function of telephony. Devices processing analog composite video signals (for example, PAL, NTSC or SECAM) have a relaxation from performance criteria A to performance criteria B test testing within +/- 1.5 MHz of a relevant subcarrier frequency. The key item to note in this is that laboratories that were equipped to test to CISPR 24 will now have to purchase new test equipment to allow performing radiated immunity testing above 1 GHz and manufacturers of equipment to be tested must be prepared for the addition test time and expense associated with this testing.
Table 2 providing immunity requirements for analogue/digital data ports is an expansion of the requirements contained in CISPR 24. Testing requirements unique to CPE (customer premise equipment) xDSL ports has been added. The test level for continuous induced RF disturbances has been changed. In CISPR 35 this is 3 V from 0.15 MHz to 10 MHz. From 10 MHz to 30 MHz this test level decreases with the logarithm of the frequency to 1 V and is 1 V from 30 MHz to 80 MHz. As noted above, this is the rms value of the voltage prior to turning on the modulation.
Immunity requirements in Table 3 for DC network power ports are the same in CISPR 35 as they are in CISPR 24, except for the change in test level for continuous induced RF disturbances noted above.
There are some changes in Table 4 for AC mains power ports, as well. The change noted above for test levels for continuous induced RF disturbances applies here, as well. For voltage dips and dropouts the voltage reduction is stated in terms of the residual voltage, rather than amount of reduction, although the actual requirements are the same. In addition, CISPR 35 provides requirements for either 50 Hz and 60 Hz distribution systems for the remaining reductions.
Table 5 provided requirements on EUT arrangement with respect to whether the EUT is intended for table top, floor standing, either table top or floor standing, rack mounting or “other” operational arrangement.
CISPR 35 is very much like CISPR 24, except where the two standards are different. If you are familiar with CISPR 24 you have a good start on understanding CISPR 35. However, you must obtain and read CISPR 35 carefully to ensure that you test your product correctly to show compliance with the new standard. And make sure the lab has the new test equipment needed for radiated immunity testing above 1 GHz.
