Interesting thread. If I had to measure click rate, I’d use a ‘scope, not too high frequency at that, and count trigger events over time. I once detected a “click” problem at a Telephone Central Office with a ‘scope and a loop antenna. Sometimes we need to look at more than 9 (10, 100, 120) KHz.
Discontinuous refers to each event as it happens; it can still be periodic, and the CISPR-14 relaxation works as a QP correction. If we use a QP detector, clicks can be pretty high before they show up near a limit. Off topic (sort of): Given present very high bandwidth ‘scopes, enough gain ahead of them, and shielded chambers, FFT may not be needed for a lot of things. But you do need to know how to set up the equipment. Cortland Richmond (writing only for me; not my employer) From: [email protected] [mailto:[email protected]] On Behalf Of Grace Lin Sent: Wednesday, August 03, 2011 10:53 AM To: Mike Violette Cc: [email protected] Subject: Re: [PSES] FCC Exempted Devices Good Morning, Mike, It is good to hear from you. I would like to share with you and members my findings/thoughts, based on some measurement I took lately. Turning on and off relays with 16A/heavy load (high current?) creates big spikes (clicks). The amplitude of the spikes does not comply with FCC §15.107 conducted emission limits (for continuous disturbance?). Turning on and off relays without load creates much smaller spikes (clicks). The amplitude of the spikes complies with FCC §15.107 conducted emission limits (with good margins). Most of household appliances are high curent devices. CISPR 14-1 / EN 55014-1 gives relaxation for click noise. In order to apply for the relaxation, click rate must be measured. Most of spectrum analyzers, from my understanding, have no capability to measure click rate. R&S has a free download software, "Click Rate Analyzer", for its certain models of the EMI receivers wtih FFT option (a +$8,000 option). My guess is: FCC exempts appliances in order not to increase labs' (tax payers') financial burden. Agree? If you agree with my thoughts, here is my question: should a 16A load device with relays be exempted? Thank you very much for sharing your comments. Best regards, Grace Lin On Wed, Aug 3, 2011 at 10:06 AM, Mike Violette <[email protected]> wrote: The appliance manufacturers had an effective lobbying campaign when the rules were written! Mike Violette Washington Laboratories & American Certification Body [email protected] +1 240 401 1388 <tel:%2B1%20240%20401%201388> On Aug 3, 2011, at 9:39 AM, Grace Lin wrote: Dear Members, Does anyone know the reason FCC exempts devices listed under FCC §15.103(d) as quoted below? “(d) A digital device utilized exclusively in an appliance, e.g., microwave over, dishwasher, clothes dryer, air conditioner (central or window), etc.” FCC KDB 772105 clarify the exempted household appliances: “Exempt household appliances are electrical machines intended for household tasks that assist persons in washing and drying clothes, household cleaning, cooking, or food preparation; or is equipment that is directly involved in conditioning the supply of household water and air (heating, cooling and humidifying) in a residence. This includes appliances such as a vacuum cleaner, washing machine, dishwasher, clothes dryer, air conditioner (central or window), etc. This exemption is limited to basic housekeeping appliances and is not intended to apply to all home-use products that may contain digital logic.” I wonder (and would like to learn from members) if the exemption is due to the discontinous disturbance as stated in the EN 55014-1 (CISPR 14-1), the emission requirements for household appliances in the EU. I list several paragraphs excerpted from CISPR 14-1: 2005 for reference: “Switching operations in thermostatically controlled appliances, automatic programme controlled machines and other electrically controlled or operated appliances generate discontinuous disturbance. The subjective effect of discontinuous disturbance varies with repetition rate and amplitude in audio and video presentation. Therefore distinction is made between various kinds of discontinuous disturbance. “(CISPR 14-1 Clause 4.2) “The limits for discontinuous disturbance depend mainly on the character of the disturbance and on the click rate N ....” (CISPR 14-1 Clause 4.2.1) “For discontinuous disturbance, the click limit Lq is attained by increasing the relevant limit L (as given in 4.1.1) with: 44 dB for N<0.2, or 20 lg (30/N) dB for 0.2≤N<30 “ Thank you very much for your time and look forward to your comments. Best regards, Grace Lin - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at http://product-compliance.oc.ieee.org/ Graphics (in well-used formats), large files, etc. can be posted to that URL. 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