〰️ Test Fc — sinusoidal vibration — PN-EN 60068-2-6

Electronics and EMC PN-EN 60068-2-6

Overview

THIS STANDARD DOES NOT SAY HOW SEVERE THE TEST IS TO BE — IT SAYS HOW TO CONDUCT IT. This is the most important thing for a reader who sees in an accreditation scope the line "badanie wibracji sinusoidalnych wg PN-EN 60068-2-6" [badanie wibracji sinusoidalnych wg = sinusoidal vibration testing according to] and wants to know what exactly was tested. The answer is: this cannot be known from the number of the standard alone.

SCOPE, QUOTED FROM THE TEXT OF THE STANDARD (clause 1): "This part of IEC 60068 gives a method of test which provides a standard procedure to determine the ability of components, equipment and other articles, hereinafter referred to as specimens, to withstand specified severities of sinusoidal vibration." The decisive word is SPECIFIED — the severity is SET from outside, and the standard gives the procedure for setting and checking it. PURPOSE OF THE TEST, from the same clause: "to determine any mechanical weakness and/or degradation in the specified performance of specimens and to use this information, IN CONJUNCTION WITH THE RELEVANT SPECIFICATION, to decide upon the acceptability of the specimens". So the standard itself does not even decide on passing — passing is decided by the product specification, read together with the result. THE INTRODUCTION SAYS IT DIRECTLY: "The relevant specification writer is expected to choose the testing procedure and values appropriate to the specimen and its use." Annexes B and C (informative) give EXAMPLES of severities — B for components, C for equipment — that is, proposals to choose from, not requirements.

A MEASUREMENT ON THE TEXT THAT SHOWS THE SCALE OF THIS REFERRAL: in the extract of the standard that we read (15 pages of the IEC 60068-2-6:2007 edition), the phrase "the relevant specification" occurs 21 times. Almost every decision that the reader would like to find in the standard — the condition of the specimen, the method of mounting, the severity, the pass criterion, what is to go into the report — is referred in it to the product document. WHAT FOLLOWS FROM THIS IN PRACTICE: an accreditation scope line citing PN-EN 60068-2-6 alone describes a TECHNIQUE, not a test. To know what was tested, one has to know the second document — the product standard or the client's specification — and it is that document that gives the frequency range, the amplitude, the number of cycles and the axes.

WHAT THE STANDARD DOES DECIDE BY ITSELF — and the product specification does not change this without an explicit provision: • SWEEPING: "The sweeping shall be continuous and the frequency shall change exponentially with time. The sweep rate shall be one octave per minute with a tolerance of ±10 %" (clause 4.1.6). The rate of one octave per minute is therefore a feature of the METHOD, not of the severity. • CROSS-AXIS MOTION: the amplitude in the axis perpendicular to the specified one does not exceed 50 % of the specified amplitude up to 500 Hz and 100 % above 500 Hz; for small specimens the specification may limit this value to 25 % (clause 4.1.2.1). • AMPLITUDE TOLERANCES: control signal at the reference point ±15 %, at the check points ±25 % up to 500 Hz and ±50 % above (clauses 4.1.4.1 and 4.1.4.2). These tolerances INCLUDE instrumentation errors. • FREQUENCY TOLERANCES for endurance by sweeping: ±0.05 Hz up to 0.25 Hz; ±20 % from 0.25 Hz to 5 Hz; ±1 Hz from 5 Hz to 50 Hz; ±2 % above 50 Hz (clause 4.1.5.1). • SIGNAL DISTORTION: unless the specification states otherwise, the signal tolerance does not exceed 5 % (clause 4.1.3), the measurement covering frequencies up to 5 000 Hz or five times the driving frequency — whichever of the two is lower.

A TRAP THAT THE STANDARD ITSELF POINTS OUT: "SWEEP CYCLE" MEANS SOMETHING DIFFERENT IN THE STANDARD AND IN THE EQUIPMENT HANDBOOK. Definition 3.4 reads: "traverse of the specified frequency range once in each direction, for example 10 Hz to 150 Hz to 10 Hz" — that is, a traverse of the range IN BOTH DIRECTIONS. Immediately after it, the standard places a note: "Manufacturers' handbooks for digital sine control systems often refer to a sweep cycle as f1 to f2, and not f1 to f2 to f1." The same number "10 cycles" therefore means twenty traverses of the range in the standard, and ten in the controller handbook. A report that gives only the number of cycles, without indicating according to which definition it was counted, does not allow the duration of the test to be reconstructed.

WHAT WE DO NOT GIVE IN THIS ENTRY: Table A.1 ("Number of sweep cycles and associated endurance times per axis") or Tables B.1, C.1 and C.2 with examples of severities. We read an extract of the standard covering clauses 1–4; we did not have the annexes, so we do not quote any number from them.

Method principle

The specimen is mounted on the table of the vibration exciter and subjected to sinusoidal vibration with a specified frequency range and a specified amplitude — swept continuously at a constant rate of one octave per minute or held at a fixed frequency. The motion is controlled with the signal from transducers at the check points and at the reference point, keeping it within the tolerances of the standard. Mechanical weakness and degradation of the specimen's performance are assessed by initial, intermediate and final measurements, and passing is decided by the product specification.

Applications

• Products exposed in transport or in service to vibration of a harmonic nature originating from rotating, pulsating or oscillating masses
• Electronic components and subassemblies — assessment of mechanical weakness and categorisation on the basis of the severity withstood
• Equipment installed in vehicles, mobile machinery and on ships
• Railway equipment and alarm system equipment, where product standards cite this test as part of the test programme
• Investigation of the dynamic behaviour of a product — determination of critical frequencies and resonances
• Products tested in packaging — the standard distinguishes an unpackaged specimen (test specimen) from a product with its packaging, where the specimen is the whole

Key parameters

Standard

Standard number

PN-EN 60068-2-6:2008 (wersja angielska; wprowadza EN 60068-2-6:2008 [IDT], IEC 60068-2-6:2007 [IDT])

Title (PL)

Badania środowiskowe — Część 2-6: Próby — Próba Fc: Wibracje (sinusoidalne)

Title (EN)

Environmental testing — Part 2-6: Tests — Test Fc: Vibration (sinusoidal)

Step-by-step procedure

1. Establishing the severity from the second document

   Before the test, the following are read from the product specification: frequency range, amplitude, number of cycles or duration, axes and condition of the specimen. Without this document the test cannot be set — the standard does not contain these values.

2. Initial measurements

   The specimen is inspected and checked electrically and mechanically to the extent required by the specification.

3. Mounting the specimen

   The specimen is mounted in accordance with IEC 60068-2-47. The fixing points are to move substantially in phase and along straight parallel lines.

4. Vibration response investigation (if required)

   An exploratory sweep serves to determine the critical frequencies — those at which malfunction, degradation of performance or mechanical resonance occurs. The sweep rate here may be different from that in the endurance test.

5. Endurance test

   Endurance is carried out by sweeping the range or at fixed frequencies — in the latter case usually at the previously determined critical frequencies, also with a limited sweep in the range 0.8–1.2 of the critical frequency.

6. Control of motion during the test

   The amplitude is kept within the tolerances of ±15 % at the reference point and ±25 % (up to 500 Hz) at the check points; cross-axis motion does not exceed 50 % of the specified amplitude up to 500 Hz.

7. Intermediate measurements

   If the specification requires it, the operation of the specimen is checked during exposure — the standard states that their extent and timing are determined by the specification.

8. Final measurements and assessment

   After the test, the inspection and checks are repeated. The result is assessed TOGETHER with the product specification: the standard provides information on weakness and degradation of performance, but acceptability is decided by the product document.

9. Recording in the report together with the severity

   The report gives the specified severity, the actual test conditions, the sweep cycle definition used and — if excessive cross-axis or rotational motion occurred — its value.

Required equipment and apparatus

Health and safety (OHS)

• Exciter and fixture in motion — access to the table only with the system stopped; the specimen and accessories secured against being thrown off
• The sound level at large amplitudes and low frequencies can be high — hearing protection at the test station
• Large and heavy specimens can induce unintended rotational motion of the table — the standard requires the permissible level to be set in the specification and the level reached to be recorded
• Resonances at critical frequencies lead to a sharp increase in amplitude — the overload protection system is kept ready
• The power amplifier and the exciter cooling remain live throughout the test

Frequently asked questions