Interpretation ID: nht72-4.22

DATE: 03/17/72

FROM: AUTHOR UNAVAILABLE; Francis Armstrong; NHTSA

TO: Electrical Testing Laboratories, Inc.

TITLE: FMVSS INTERPRETATION

TEXT: Thank you for your letter dated January 19, 1972, to Mr. Eugene Laskin, regarding questions you have reisting to interpretations of demonstration procedure descriptions contained in paragraphs 5.2j and 5.2k of Federal Motor Vehicle Safety Standard (FMVSS) No. 209.

The answers to your questions are as follows:

1. Paragraph S5.2j - The phrase "within a period of 50 milliseconds" refers to the rise time of the acceleration only with the webbing movement measured from start of acceleration to lockup. The movement occurring after lockup due to natural webbing elongation and webbing compaction around the retractor spool is not measured. Webbing movement exclusive of the above-mentioned compaction and elongation can be measured by using a rotary of linear potentimeter reading out on a dual channel oscilloscope or oscillograph along with the readout of the time vs acceleration trace.

2. Paragraph s5.2k - The present standard does not specify any particular sequence for performing the 10,000 lockup cycles on emergency locking retractors as part of the total 50,000 cycles. This office presently has two laboratories performing the compliance tests in the following manner.

Laboratory A - One lockup cycle out of every five using the commercial Carlson cycling apparatus.

Laboratory B - 40,000 cycles of extension and retraction followed by 10,000 lockup cycles.

3. The methods presently employed by our test laboratories in actuating the lockup mechanism is to accelerate the retractor by means of compressed air, thus effecting the lockup.

This method of lockup is employed by our laboratories because a retractor that is sensitive both to vehicle acceleration and tilting would most frequently be locked by acceleration when installed in a vehicle.

This is not to say that you are compelled to cycle your retractors by accelerating them. If the locking mechanism is the name for both modes (e.g. a (Illegible Word)), it may make little difference whether the retractors are accelerated or tilted. However, if our test disclose a cycling failure, you will be obliged to show that your method was, in fact, equivalent to ours.

Should you require any further details or information regarding the test procedure for emergency locking retractors, please contact Mr. R. Jasinski of this office.

Thank you for your interest in auto safety.