more than technology
” High Accelerated Life Test : Translating
Theory in to Design Solutions for the
Implementation Tool”
“solid-edge design”
INTRODUCTION
 The
Environmental Test Chambers are today
compulsory for developing any product
reliability,
 The one which is becoming more and more
popular is the chamber for : Highly Accelerated
Environmental Test or “HALT”. The chamber is
easy recognized by high environmental
performance and integrated shaker, but… this is
not all what is required to an environmental
chamber to perform accelerated tests
ACCELERATED TESTING
 The
theory behind the accelerated testing has been
explored in many academic contexts, the advantages
have been broadcasted all over the world for the
benefit of every one
 The object is now how to translate the accelerated test
requirements in the proper technical solutions for the
tool which has to implement the test : the
environmental test chamber.
 basic philosofy for accelerating environmental tests :
to provide high stress to the product by rapid cycling
between extreme environmental conditions and by
strong stimulation of the full spectrum failure modes.
ACCELERATION FACTOR FORMULAS
Coffin-Manson Fatigue Acceleration Model :
Ntest = Nactual( Tactual/ Ttest)2.5
Pecks Model for Temperature Humidity :
AF = (Mact/Mtest)-n e -(EA/K)(1/Tact-1/Ttest)
Arrhenius Reaction Rate Model :
in case of different temperatures :
-(EA/K)(1/Tact - 1/Ttest)
AF = tact /ttest = Ae -(EA
HALT requires Outstanding
Performance
1 - Extreme change rate chamber
2 - Multi-axis Random Vibrations
3 - Maximum Vibration Transmissibility
4 - Maximum Thermal Transmittance
5 - Adjustable Air Flow
6 - Reliability and Usability
7 - Supplier qualification
1- Extreme Temperature Change Rates
 When
temperature rate goes to extreme (20 - 30
°C/min), the cost effective solution for the
cooling ramps is to use the evaporation of LN2
(Liquid Nitrogen).
 Being the evaporation temperature at ambient
pressure -196°C and the calorific value 40-50
Kcal/Kg, it gives the LN2 a very high cooling
power to rapidly cool down the systems which
include : the air inside the chamber, the walls and
components of the chamber and…. the specimen.
1- Extreme Temperature Change Rates
 Considering
also a price which all over the
world is under the 0.25 USD per Kg, the LN2
solution is convenient when the LN2 supply
facility is already available in the laboratory.
Traditional compressor refrigeration system
for this application would require tenths of HP,
even if the electrical energy consumption cost
will save some money in comparison with the
LN2 consumption.
1- Extreme Temperature Change Rates
 As
far as heating the solution refers to the
traditional technology of electrical heat
dissipation from resitors : easy to
implement and fast to be controlled. The
associated power has to be adequately
increased, for a 1 m3 chamber with 20 kg of
electronic specimen to be heated at
60°C/min, the dissipated, and electrically
supplied, power is in the range of 100 Kw !
2 - Multi Axis random Vibration
 Accelerating
the test means also to test "in parallel"
as it can be done with a multiaxial shaker which wich
avoids rotation of the specimen and test repeatition.
Furthermore it has been demonstrated that some
product failures are detected by :
- correlation effect of multiple axes vibration ;
- application of a vibration signal which is random as
far as possible (flat and extended frequency band).
The cost-effective solution is to use multiple pneumatic
actuators.
2 - Multi Axis
random Vibration
 This
experimented system
satisfy the technical
requirements but also is
available at costs which are
considerably less than
complex 6 DoF system
which use different
technology (i.e
electrodynamic).
 Vibration levels
up to 60 G’s.
Multi-Axis Repetitive Shock
Vibration
 The
instateneous pressure
of the supplied air controls
the "movement speed" of each
actuator, viceversa when the
actuator works it affects the
instaneous air pressure and
consequently the "speed" of
other actuators, pratically each of the actuators moves
randomly and in different direction. Not only the intensity
of the acceleration vector is random but also the direction
Multi Axis random Vibration
 Wide
frequency band in the PSD
A potential disadvantage is that the vibrations are basically
not controllable as far as spectrum shape (they are random
only) but they can be controlled only in total rms level.
Nevertheless this is what HALT requires.
3 - Maximum Vibration
transmissibility
Mounting products
on Aluminum
standoffs provides
maximum
transmissibility of
vibration input from
table
4 - Powerful Airflow
Thermal power is nothing without the ability to
transfer the power to the the real subject of the test :
the specimen. One of the most important parameter
affecting the thermal transfer is the “thermal
resistance” between the air and specimen. It depends
from material and shape of the specimen, density
(temperature and pressure) and humidity of the air,
airspeed.
The factor controllable by the chamber is the airspeed :
the higher is the airspeed the lower is the thermal
resistance and the most part of the thermal energy is
transferred to the specimen.
4 - Powerful Airflow
High airspeed for a
given volume requires
powerful fans (2 - 4
HP of total power),
likely two fans which
in combination with a
flexible configuration
of air ducts give a
good airflow
distribution.
5 - Adjustable Airflow
Precise
control of
air direction
provides faster
product change rates
Up to four ducts can
direct air onto
different products
Adjustable Air Flow
 Air
slot can be open or closed
 When slot is closed, air is directed to the
ducts allowing air to be directed onto the
product
 Allows
flexibility in controlling airflow to
maximize air velocity across the product
Adjustable Air Slot
6 - system reliability & safety :
Vibration
 Top
of the line
Teflon Coated
Impactors for long
life and high
MTBF
6 - system reliability & safety :
CE Mark
The system has to comply with the latest
requirements of the European
Community.
The package includes :





proper grounding procedures,
specified components,
screw type terminal connections,
Electromagnetic shielding/immunity
as well as filters for the heating system to
reduce electrical noise
6 - “Usability”
 Convenient Table
Height
 Front and Rear doors for unrestricted
product access
 18” X 18” Windows for observation
 Access Ports for product interconnect, and
product monitoring sensors
 Access Panels
7 - Supplier Qualification
 Broad
product line and experience in environmental
chambers
 Turn-Key System : chamber, controls, and vibration
system.
 Local Sales and Service. Provide factory trained
professionals.
 In house design and manufacturing of the system,
from sheetmetal to electronics, electrical
subsystems, etc. This assures full control of the
production.
Efficiency considerations
 Saving
energy is today an "ambientalist" issue
but also affect very much the money budget to
run a particular chamber like an accelerated test
chamber which use 100 kW of electrical power
and hundreds of kg of LN2.
Efficiency considerations
 do
not waste energy special care has to devoted to :
- minimize the thermal capacity of the chamber
internal elements in order do not absorb useless
energy especially during the temperature transients
- minimize the thermal capacity of the chamber walls
and of the shaker table having the necessary
thermal insulation;
- improve the thermal transfer characteristics with an
adequate airspeed and good air circulation around
the specimen ;
Efficiency considerations
- minimize the pressure drop and turbolence along
the airflow circuit in such a way to reduce the
dissipated power, the fan motor power and its
heating transferred inside the chamber.
Careful consideration the above points can
considerably reduce the energy consumption
Chamber Typical Performance
Temperature
Range:
Temperature variation rate:
Air
speed:
Acceleration:
Frequency range:
Vibration table size:
Chamber internal dimension:
Vibrator features:
Heating:
Cooling:
Noise
pressure level :
-100°C / +200°C
60°C/min cooling from +150°C to –60°C
60°C /min heating up from –60°C to +150°C
20 m/sec
Up to 60 grms
Up to 10000 Hz
36 x 36 inches
1000 litres (adjustable)
The system provides vibration using impact
excitors with 6 degrees of freedom equally
distribuited il all 3 axes and in all 3 rotations
100,000 Watts by Nicrome heaters
Liquid nitrogen expansion
76 dB(a)
HALT & HASS Chamber
Mod.UHS 300
UHS 1200
HALT & HASS Chamber
Mod.UHS300
Temperature
Range:
Temperature variation rate:
-70°C / +150°C
30°C/min cooling from +120°C to –40°C
30°C /min heating up from –40°C to +120°C
Air speed:
5 m/sec
Acceleration:
Up to 60 grms
Frequency range:
Up to 2000 Hz
Vibration table size:
24 x 24 inches
Chamber internal dimension: 300 litres
Vibrator features:
The system provides vibratio using impact
excitors with 6 degrees of freedom equally
distribuited il all 3 axes and in all 3 rotations
Heating:
Nicrome heaters
Cooling:
Liquid nitrogen expansion
Power:
45 kW