Hi Grace
I was working at the FCC lab at the time (Mike is just a kid compared to me)
and that's pretty much the thinking that was going on.
best regards
Tom Cokenias
T.N. Cokenias Consulting
P.O. Box 1086
El Granada CA 94018
On Aug 3, 2011, at 9:37 AM, Mike Violette wrote:
Hi Grace,
Good to hear from you, too.
I think the FCC exempted appliances because during the original
incarnation
of the Rules (Docket 20780 circa 1979—yes, I am dating myself) there was
scant idea that microprocessors would be so widely dispersed and installed in
almost any device imaginable.
Also, the appliance manufacturers (as well as the vehicle and medical
device
folks) had a strong influence on the manufacturers.
I don’t think it had anything to do to reduce lab operators’ capital
outlay, but rather the economics favoring the exempted industries.
Just a notion.
Mike Violette
[email protected]
Washington Laboratories & American Certification Body
Radio Frequency, Electrical Safety & Wireless
Cell: 240 401 1388
________________________________
From: Grace Lin [mailto:[email protected]]
Sent: Wednesday, August 03, 2011 10:53 AM
To: [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
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