Download OFSTP-27

TIA/EIA-526-27
OFSTP-27
Procedure for System-Level
Temperature Cycle Endurance Test
Contents
Foreword……………………………………………………………………………………………..
iii
1. Introduction……………………………………………………………………………………….
1
2. Normative references……………………………………………………………………………..
2
3. Apparatus………………………………………………………………………………………….
2
4. Sampling and specimens…………………………………………………………………………..
3
5. Procedure…………………………………………………………………………………………..
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6. Calculations or interpretation of results…………………………………………………………….
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7. Documentation………………………………………………………………………………………
11
8. Specification information…………………………………………………………………………… 11
Annex…………………………………………………………………………………………………… 14
References………………………………………………………………………………………………. 16
TIA/EIA-526-27
Procedure for System-Level
Temperature Cycle Endurance Test
Foreword
(From EIA Standards Proposal No. 3177, formulated under the cognizance of TIA FO-2.6/6.10,
Subcommittee on the Reliability of Fiber Optic Systems and Active Components.)
This OFSTP is part of the series of test procedures included with Recommended Standard TIA/EIA-526.
Key words:
Fiber Optic Transport System
Reliability
Temperature Cycling
TIA/EIA-526-27
Introduction
1.1
Intent
This procedure details a temperature-cycle endurance test that is meant to demonstrate the capability of
fiber-optic telecommunications equipment to operate reliably in uncontrolled environments.
1.2
Scope
This procedure is applicable to a fiber-optic equipment whose designed application is for the uncontrolled
loop environment. The fiver-optic equipment include all major fiber-optic transport systems (e.g., OC-12
fiber-in-the-loop terminals) and other smaller fiber-optic units (e.g., optical fiver amplifier units).
1.3
Background
Increasing amounts of fiber-optic telecommunications equipment are being deployed in the loop. This
equipment included digital terminals, multiplexers, fiber-in-the-loop, and other fiber-optic transport
equipment. This equipment will typically be located in housings without environmental controls, such as
aboveground cabinets, pedestals, and pole-mounted enclosures. The conditions that the equipment
encounters inside these housings can be extreme. The natural temperature cycling that will be experienced
represents a major stress on this equipment, a stress that is will continually be subjected to throughout its
service life.
Temperature-cycle endurance testing is important to assess the long-term reliability of equipment to be
used in the uncontrolled loop environment because temperature cycling imposes significantly different
stresses on components and assemblies than are imposed under the typical constant elevated-temperature
conditions.
1.4
Hazards
This procedure involves potentially hazardous operations as discussed in this section. During the
measurement, a laser will emit non-visible light. Personnel are strongly cautioned never to look directly
into the laser at anytime. Although the optical output power is generally not very high, virtually all the
power is concentrated into a narrow frequency band, which implies that the energy can be focused into a
very intense spot on the retina by the lends within the viewer’s eyes.
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Normative references
The documents listed in this section form a part of this OFSTP to the extent specified herein. Users of this
procedure are encouraged to utilize the latest edition of the documents, when they are applicable.
Where applicable, TIA FOTPs shall be used to measure the parameters listed in Section 5.
ANSI Z136.2, American National Standard for the Safe Use of Optical Fiber Communications Systems
Utilizing Laser diode and LED Sources, shall be used to determine safe operating practices when
performing tests with fiber-optic communications systems.
3.
Apparatus
The following apparatus and equipment is required to perform this temperature-cycle test on the System
Under Test (SUT).
3.1
Ancillary Equipment
Ancillary equipment is needed to make the SUT operational. First, other systems may be needed to provide
control information, data, or power to the SUT. Second, media are needed to provide communications
between the SUT and the other systems. Media components can include cables, connectors, splitters,
attenuators, splices, etc.
3.2
Test Equipment
Since there are many types of fiber-optic equipment, this OFSTP does not provide a comprehensive list of
test equipment. The necessary test equipment depends on the system performance measurements outlined
in 5.3.1. The following test equipment provides an example necessary to make system performance
measurements for a digital fiber-optic transport system:
 Bit Error Ratio (BER) Test Set: To compute BER, (Burst) errored seconds, and % error-free
seconds.
 Jitter Generator: For jitter generation and jitter tolerance measurements.
 Digital Oscilloscope: To view the low-speed (Dsn) output pulse shape and transmitter eye pattern.
 Variable Attenuator: For receiver sensitivity measurements.
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Optical Power Meter: To measure transmitter output power.
Optical Spectrum Analyzer: To compute central wavelength and spectral width.
DC Power Supply: To test input voltage tolerance.
Transmission Impairment Measurement Set: For system loss, amplitude tracking, idle-channel
noise, signal-to-distortion, and impulse noise measurements.
Impedance and Return Loss Measuring Set: To measure echo and singing return loss.
Longitudinal Balance Test Set: For longitudinal balance measurements.
Sampling and Specimens
The test sample shall be a fiber-optic transmission system as defined in the Detail Specification of the SUT.
The test sample should be production equipment, of if pre-production, the circuit design and physical
design should be representative of what production equipment will be.
The test sample shall not be pre-screened or otherwise tested, operated, or stressed in a way different from
the routine process applied to all systems.
5.
Procedure
5.1
Test Conditions
This subsection defines the temperature cycle profile (in terms of temperature extremes, test length, soak
time, and ramp rate). Constraints on humidity are also defined.
For US Military applications only, and unless otherwise specified by the (US Military) Detail Specification
of the SUT, the test environment shall be in accordance with the controlled ambient conditions of EIA/TIA526.
5.1.1
Temperature Extremes and Test Length
System testing can be performed at different levels, identified by the temperature extremes and test length
used for testing. The system ambient temperature shall cycle between temperature extremes and shall run
for the test length without interruption, except for brief pauses for detailed measurements.
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5.1.1.1
The systems ambient temperature refers to the air temperature surrounding the SUT 1 For
a system located inside any type of housing in the field, this is the mid-air temperature between the system
hardware and the housing walls. When the system is tested inside an environment chamber without a
housing, this is the temperature controlled by the chamber.
5.1.1.2
The system can be tested at varying levels by choosing different values for the
temperature extremes and the test length. The test length is characterized by the number of consecutive
cycles the system undergoes during the test. Different values for these parameters will expose the system
to varying amounts of stress. Table 1 lists the temperature extremes and test length alternatives. For
example, a 100-cycle test with temperature limits of -40ºC and +65ºC would be identified as Test Conditon
Cc.
Table 1. Temperature Extremes and Test Length Alternatives
Temperature
Extremes
A
0/+50ºC
B
-25/+65ºC
C
-40/+65ºC
Test Length
(# cycles)
a
5
b
25
c
100
D
Other
Specified
d
Other
Specified
5.1.1.3
The two temperature extremes of -40ºC and +65ºC are the assumed operating
temperature extremes for loop equipment placed in environmentally uncontrolled housings. A sufficient
number of locations in the US experience temperatures of -40ºC (or below) to warrant this lower limit. A
system temperature of +65ºC, or as otherwise specified in the customer Detailed Specification, is
considered the worst-case upper operating condition, where high-power equipment is placed in an outside
housing with no fans, at maximum outside temperature, maximum solar loading, and maximum power
dissipation.
5.1.2
Soak Time
Soak time is the period for which the chamber temperature is kept constant after the SUT has reached
equilibrium (at a temperature extreme) for that part of the cycle. As a minimum, the soak time should be
minimum 30 minutes.
5.1.2.1
The SUT can be considered to be at thermal equilibrium when the rate of change in the
“hot-spot” temperature is no more than 3ºC per hour. A practical way to determine whether all parts of the
SUT have thermally stabilized is to monitor the temperature of some “hotspots” in the SUT. These “hot
spots”
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This system temperature must be distinguished from the component temperature, which is the temperature
of the air surrounding a component in the system. Due to heat dissipation, the maximum temperature of
active components is typically specified for higher operation (up to and exceeding 85 C in some instances).
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are typically found near high-power components in the system. Air temperatures around such components
are normally higher than the chamber temperature setting, due to their heat generation (even when
stabilized), and lag behind the chamber temperature during cycling.
5.1.2.2
The minimum 30 minutes soak time after the SUT has thermally stabilized is required to
monitor the steady-state system performance at each temperature extreme. Testing experience shows that
the time for the SUT to reach thermal equilibrium is usually 1 hour or more, depending on the thermal mass
of the system and the heat generation of the system.
5.1.3
Ramp Rate
Ramp rate refers to the rate of change in chamber temperature during cycling. The ramp rate between the
two temperature extremes in either direction shall be at least 20ºC per hour. It should be reasonably
constant throughout the entire temperature range (i.e., between -40ºC and +65ºC).
5.1.3.1
A higher ramp rate than 20ºC per hour will save time in testing and is preferred. For
example, the preferred ramp rate is a 105ºC change in a half hour if -40ºC and 65ºC are chosen as the
temperature extremes.
5.1.3.2
In choosing an appropriate ramp rate for testing a particular SUT, the major factor in the
decision is the objective of uncovering potential reliability problems in the system. IT may be desirable to
employ a ramp rate higher than the minimum criterion of 20ºC per hour to save time in testing. While the
capability of the environment chamber will set an upper bound for the ramp rate chosen, extremely fast
ramp rates (e.g., 1200ºC per hour [20ºC per minute] or higher, achieved with direct spraying of cold gases)
could approach thermal shock conditions which are not desirable for this test.
5.1.3.3
Some systems might have performance problems during a high rate of temperature
change, possibly due to the designs of their temperature compensation circuitry. However, this
phenomenon should be transitional and should disappear once the system has thermally stabilized (during
soak). If such a transitional problem occurs during ramping, the problem should be continuously monitored
throughout the course of temperature-cycle testing. If there is no general trend of increase in the magnitude
of the problem with the number of cycles, the problem is not considered to be a long-term reliability
problem. However, it must then be verified that the ramp-induced problem will not occur when the ramp
rate is reduced to 20ºC per hour and below.
5.1.4
Humidity
The humidity level inside the chamber during the test can be left uncontrolled, but there must be no
condensation of “snowing” at any time. The specific humidity should not exceed 0.024 pounds of moisture
per pound of dry air at any
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time. The actual humidity values during temperature cycling should be monitored and reported for future
reference.
Controlling humidity beyond these constraints would require more elaborate environment test chambers,
and would also significantly limit temperature ramp rates. High humidity/temperature and temperature
cycling impose very different kinds of stresses on equipment, and are better addressed separately from a
life-test standpoint.
5.2
Test Configurations
5.2.1
SUT Configuration
5.2.1.1
For a system that consists of two terminals of different designs, both terminals should be
tested simultaneously in an end-to-end link configuration
5.2.1.2
For a system that consists of only a signal terminal or two terminals of identical designs,
one terminal may be tested in an optical loop-back configuration.
5.2.1.3
In both cases, the optical transmission link should be configured for the worst-case
scenario in terms of attenuation, reflection, and dispersion as specified for the system by the supplier.
5.2.2
Enclosures
In the temperature-cycling test, the system should be placed in the environment chamber without any
cabinet or enclosure.
Depending on its design and capacity, a system can be as small as equipment located in a pedestal or polemounted enclosure, or it can consist of one or more shelves or equipment (typically configured in racks).
In other words, the “open” system should be tested, since the temperatures set in the chamber care intended
to be the ambient temperatures that equipment would encounter inside its housing.
5.2.3
System Loading and Operation
Throughout the test, the system should be configured to its maximum capacity and in full operation. All
channels in the system should be tested. Channels can be daisy-chained together to accomplish this
purpose. Of course, all other equipment for measurement purposes should be kept outside the chamber.
5.2.4
Ancillary Equipment
Whether or not the media (cables, connectors, splices, etc ) between terminal equipment should be included
in eth chamber for testing depends on whether the media are provided as part of the system.
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5.2.4.1
Where the media are part of the system, they should be placed inside the chamber
together with the system equipment for testing.
5.2.4.2
Where the media are not part of the system, they should be kept outside the chamber and
under ambient conditions, except for short lengths of jumpers or cables necessary for making connections
to the system inside the chamber.
5.2.5
Example Test Setups
The following two figures show example setups of equipment for a temperature-cycle test.
Figure 1 - SONET Terminal Multiplexer Test Setup
Figure 2 – Optical Network Unit (ONU) Test Setup
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5.3
Measurements
This subsection outlines the parameters to be measured for the temperature cycle test and their frequencies.
5.3.1
Measurement Parameters
Sufficient system-level measurements should be made to fully characterize all system functions and
performance that could be impacted by temperature cycling. Since temperature cycling is intended to
qualify and demonstrate the reliable operation of the equipment, a meaningful set of parametric
measurements is necessary. The measurements are not only used as pass/fail criteria, but are also useful for
detecting potential reliability problems (hence for improving reliability designs).
Since there are many types of loop equipment, this OFSTP does not provide a comprehensive list of
parametric measurements. A typical minimum set of measurements for digital and analog systems is given
below. Additional parameters that might be appropriate can be found in the Detailed Specification of the
SUT.
5.3.1.1
In the case of digital fiber-optic transport systems, a typical minimum set of required
measurements is as follows:
 Bit error ratio (BER), also known as bit error rate
 (Burst) errored seconds
 % error-free seconds
 Jitter generation
 Jitter tolerance
 Low-speed (DSn) output pulse shape
 Transmitter output power
 Central wavelength
 Spectral width
 Transmitter eye pattern
 Receiver sensitivity
 Input voltage tolerance
 Protection and alarms
 System restoration and startup
5.3.1.2
In the case of systems with electrical analog interfaces, a typical minimum set of required
measurements is as follows:
 Echo return loss
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5.3.2
Singing return loss
Longitudinal balance
System loss
Amplitude tracking
Idle-channel noise
Signal-to-distortion
Impulse noise
Intermodulation distortion
Channel crosstalk
Transmitter output power (if applicable)
Central wavelength (if applicable)
Spectral width (if applicable)
Receiver sensitivity (if applicable)
Input voltage tolerance
System restoration and startup
Frequency of Measurements
Any trends or changes in system behavior can be determined by measuring specific parameters at several
times (before, during, and after the temperature-cycle test). This can be as important as simple pass/fail
results.
5.3.2.1
All measurements should be made at room temperature and at each temperature extreme
before and after the test.
5.3.2.2.
The same measurements at each of these temperatures should also be made at least two
more times during the course of temperature cycling (to establish trends of changes in system behavior, if
any).
5.3.2.3
Continuous monitoring should be preformed on the following critical parameters to track
the overall performance of the system throughout the entire test.
a.
BER, burst errored seconds, and % error-free seconds shall be monitored continuously throughout the
test to track the overall digital system. For BER monitoring, it is recommended that repetitive
measurement intervals be set such that there are at least two measurement intervals in each soak and
each ramp of a temperature cycle. This method helps determine precisely when a problem begins and
whether it is repetitive. BER data shall be recorded for trend analysis at the end of the temperaturecycle test.
b.
For any analog output of the system, Carrier-to-Noise Ration (CNR) or Signal-to-Noise Ration (SNR)
shall be monitored continuously throughout the test (in place of BER).
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6.
Calculations of interpretation of results
6.1
Pass Criteria
6.1.1
Pass
A system is deemed to pass the temperature-cycle test if all the parameters measured at the stated frequency
(as discussed in citation 5) are within the system suppliers specifications throughout the entire test.
6.1.2
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6.2
Conditional Pass
As discussed in Section 5.1.3.3, the occurrence of a transitional problem during temperature
ramping may be observed. If such a problem has not shown a general trend of increase in
magnitude with the number of test cycles, and if it has been demonstrated that the problem does
not recur when the ramp rate is reduced to 20ºC per hour and below, then such a problem would
not constitute a failure of the test.
There may be occasions when a system passes the temperature-cycle test but some of its
parameters who signs of degradation as a result of the test. Such findings should be reported and
made not of; they may serve as warnings of some potential problems. They may be useful for
reliability design improvements.
Fail Criteria
The system fails the test if any of the following occur:
 Any parameters exceed the supplier’s specifications as measured during the test or as its end
 Any circuit packs require replacement due to performance degradation (outside the supplier’s
specifications) or total failure, as determined by the system’s internal diagnostics or by parametric
measurements made during the test or at its end
 Protection switching automatically occurs as a result of any internally detected problem.
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7.
Documentation
7.1
Reporting requirements
Report the following information for each test:
7.1.1
Date of test
7.1.2
Procedure used for test (OFSTP–6)
7.1.3
SUT identification
SUT Identification. The SUT shall be identified by manufacturer name, product name, application speed
( e.g., OC-12), and serial code (if available).
7.1.4
Test results
Test results documented in the report shall include parameters measured before, during, and after the
temperature-cycle test, and how the measurements compared to the pass/fail criteria. A statement of
whether the criteria are met (see 6.2) shall also be included.
7.2
US military applications
United States military applications require that the following information also be reported for each test. For
other (nonmilitary) applications, this information need not be reported but shall be available for review
upon request.
7.2.1
Test personnel
7.2.2
Test equipment and date of latest calibration
8.
Specification information
The following information shall be specified in the Detail Specification for the SUT:
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8.1
Product Specifications
Obtain the following test conditions and other information from the Detail Specification for the SUT:
 System voltage and/or current requirements
 Data rate and input signal characteristics
 Input/output measurement conditions:
o Minimum and maximum wavelength
o Minimum and maximum transmitter optical power
o Transmitter and receiver mating connector types
o Receiver sensitivity requirements (minimum and maximum receiver input)
o Maximum spectral width
o Maximum dispersal limit
o Maximum back reflection limit.
 Environment operating conditions (i.e., minimum and maximum temperature limits, maximum
humidity limit, and maximum temperature change rate, if applicable) with and/or without the cover
installed
 Special services such as cooling fans
 Minimum and maximum transmission distance over a specific type of transmission medium.
8.2
Procedure references
Obtain the following test conditions and other information from the Detail Specification for the SUT:
Include a reference to this test procedure if it is o be used,
8.3
Exceptions or deviations
Note any exceptions or deviations that apply to this test procedure.
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8.4
Acceptance or failure criteria
The equipment supplier and its customers should have accumulated sufficient experience performing
system testing to develop a reasoned judgment regarding the degree of confidence on the pass/fail criteria.
Additional thoughts should be spent on the system configurations and specific applications.
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ANNEX
Comparison Between This OFSTP and IEC, ISO, or CCITT Requirements
(Nonmandatory Information)
A.1
IEC
It should be noted that, as of this publication date, there are not known IEC test methods comparable to this
OFSTP.
A.2
ISO
It should be noted that, as of this publication date, there are no known ISO test methods comparable to this
OFSTP.
A.3
CCITT
It should be noted that, as of this publication date, there are no known CCITT test methods comparable to
this OFSTP.
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Annex A
Comparison between this OFSTP and IEC or ITU-T requirements
TIA’s FO-2 and FO-6 Committees and their various subcommittees have an established policy of making
every reasonable effort to “harmonize” their test methods with those published by IEC (International
Electrotechnical Commission) and ITU-T (International Telecommunication Union Telecommunication
Standardization Sector).
A.1
IEC
As of the date of the final ballot for this OFSTP, there are no known test methods in IEC comparable to it.
A.2
ITU-T
As of the date of the final ballot for this OFSTP, there are no known test methods in ITU-T comparable to
it.
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References
“T.S. Frank Lee, “Results of Accelerated Life Tests on a Fiber Optic System Designed for Loop
Application,” Proceedings of the National Fiber Optic Engineering Conference (NFOEC), (1991).
GR-416-CORE, “Generic Reliability Assurance Requirements for Fiber Optic Transport Systems”, Issue 1
(Bellcore 1997).
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