Interpretation ID: 1985-01.50
TYPE: INTERPRETATION-NHTSA
DATE: 03/15/85
FROM: AUTHOR UNAVAILABLE; Jeffrey R. Miller; NHTSA
TO: ETL Testing Laboratories, Inc.
TITLE: FMVSS INTERPRETATION
TEXT:
Mr. Gordan Bonvallet Manager, Photometric Division ETL Testing Laboratories, Inc. P.O. Box 2040 Cortland, New York 13045-2040
Dear Mr. Bonvallet:
This is in reply to your letter of February 4, 1985, asking for an interpretation of the humidity testing procedure for replaceable bulb headlamps.
Paragraph S6.8 of Motor Vehicle Safety Standard No. 108 states in pertinent part that after completion of the test cycle in which the headlamp shall have been in an environment of 100oF with a relative humidity of 90+105, it shall then be in an environment with a temperature of 73oF and relative humidity of 30+10% before removal for photometric testing. You believe that this implies an instantaneous transition in temperature/humidity conditions which, in your view, is "impossible to achieve." You have set forth three alternative procedures and ask which is the most acceptable to this agency.
Under your first alternative, the temperature and humidity in the humidity chamber would be reduced to 73oF-43%;, requiring about an hour) whereupon the headlamp would be removed to a "dry box" chamber of the requisite temperature/ humidity before photometric testing. In the second alternative, there would be no such removal before the photometric testing. In the third alternative, the headlamp would be removed from the humidity chamber and immediately carried to a "dry box" with the requisite temperature/ humidity; however, in your test set up this would require three to five minutes elapsed time between chambers.
Paragraph S6.8 does not specify a humidity of 43% in any of its test conditions, and a procedure incorporating the first and second alternatives clearly would not be in accordance with paragraph S6.8. That paragraph, however, does not specify that the temperature/humidity sequences must occur in the same chamber but it does imply that the lower temperature/ humidity soak should take place directly following the higher temperature/humidity one. Therefore, your third alternative is the one that meets the intent of paragraph S6.8. To insure consistency of results, we recommend that no transfer period exceed three minutes and that the headlamp be exposed as briefly and as little as possible to the ambient temperature/humidity of the test laboratory.
Sincerely,
Jeffrey R. Miller Chief Counsel
Office of Chief Consul National Highway Traffic Safety Administration 400 Seventh St. S.W. Washington, DC 20590
Gentlemen:
Subject: Interpretation of Testing Procedure FMVSS 108 Replaceable Bulb Headlamps
Paragraph S6.8 Humidity of FMVSS 108 states a test procedure which implies a headlamp should undergo an instantaneous transition in temperature/ humidity conditions from 100oF-90% relative humidity (tolerances have been omitted here) to 73oF-30% R.H. This, of course, is impossible to achieve. The attached discussion suggests possible testing procedures to resolve the problem. I request an interpretation on which is acceptable and if none are, please clarify how the test can and should be performed. We expect to have headlamps to test within the next couple of weeks, so prompt consideration would be appreciated.
Very truly yours,
Gordon Bonvallet, Manager Photometric Division
GB/mm Enclosure
Docket No. 81-11
Replaceable Bulb Headlamp
FMVSS 108 Paragraph S6.8 Humidity The present ruling requires the headlamp to be subjected to a controlled environment of 100oF + 9o and a relative humidity of 90% + 10%. Following the 20 consecutive 6 hour test cycles, the headlamp is to be "soaked" for 1 hour at 73oF (20oC) and a relative humidity of 30% + 10% before it is removed for photometric testing.
Most environmental chambers (Thermotron, Blue M, for example) do not have the capabilities to reduce the humidity to 30% (or 40%) at the 73oF temperature. We have constructed a special chamber which is capable of about 35% RH at 73oF although this is very dependent on the room ambient temperature and humidity. This chamber is located near the Photometric test range so we can perform the following photometric test in a very short time. Unfortunately, this chamber is located a couple hundred feet from the standard environmental chamber. At the completion of the humidity test, we must remove the headlamp and carry it to the "dry box" for the one hour soak. Men the headlamp is removed from the 100oF environmental chamber, it immediately is subjected to a cooler room ambient, perhaps 65o -70oF and 60% RH.
We have experimented with a procedure which reduces the temperatures humidity of the environmental chamber following the normal humidity cycles, to a range of 73oF and about 43% RH. This procedure takes about one hour to accomplish. We cannot get the humidity any lower with prolonged operation of the chamber. Following this procedure, the headlamp is carried to the "dry box" for the one hour soak.
I know of no standard environmental chambers which can operate at 100oF - 90% RH and reduce in conditions to 73oF - 30 + 10% RH within a short enough period to allow a one hour soak at the final temperature/humidity conditions, period to allow a one hour soak at the final temperature/humidity conditions, other than s chamber designed for thermal shock and these have no humidity control.
I request an interpretation on which of the described procedures should be used.
1. Following the humidity test, reduce the temperature and humidity in the chamber to 73oF - 43% RH in a one hour period, transfer headlamp to the 73oF - 30 + 10% RH dry box for one hour followed by the photometric test.
2. Following the humidity test, reduce the temperature and humidity in the chamber to 73oF - 43% RH in a one hour period, followed by the photometric test.
3. Following the humidity test, remove the headlamp from the humidity chamber, carry it at room ambient conditions (approximately three minutes - five minutes) to the dry box and soak at 73oF and 30 + 10% RH for one hour followed by the photometric test.
If none of these alternatives is acceptable, please clarify exactly how the test can and should be performed.
Gordon Bonvallet, Manager Photometric Division ETL Testing Laboratories, Inc. February 4, 1985