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Accidents and Damages
An accident occured in vehicle assembly plan when a roller conveyor began moving while a worker occupied
a floor safety mat. A Pilz safety plc using pilz positive guided safety relays was used for the safeguard system.
A separate allen bradley pLc was used to operate the vehicle assembly line roller conveyor.
The original PLC and safety PLC code had been modified by the plant operator to install additional features related
to nusiance trips from the floor mats. The composite signal for floor mat clear was separated into individual safety
signals for each station on the assembly line. The revision did not account for the monitoring mode of the safety
plc which provided all clear signals when the line was not moving. This allowed the line to beiefly operate with
a worked standing on the safeguard floor mat. The run signals from the safety plc were removed approximately
one half to one second after entering monitor mode when the line began to move. This allowed a slight lurch of the
assembly line when a worked was standing on a floor mat.
Safety PLC and Safety Relay
A safety plc is a specially designed control unit that offers the felxiblity of a plc with the reliablity of hardwired
electromechanical devices. The safety plc uses function blocks that perform specific monitoring services. Those
function blocks are locked and cannot be modified by the user. The specific application written for each project
is also secured so that it cannot be modified by untrained programmers. Safety PLC and safety relay systems are made
by Pilz, Allen Bradley, and HIMA. They are also made by square D, emmerson, and phoenix and omron.
Safety Relay
A safety relay is a reliable electronic device that includes input monitoring to detect wiring and device faliures.
It is used in safety applications such as machine safeguarding where detection of open circuit and short circuit is
important for machine safety. Safety relays are often used as the primary control circuit for emergency stop e-stop,
sometimes written as estop. They are also used for light curtain, floor mat, electronic beam, and ultrasonic detection
of presence in a protected zone. A safety relay safeguard system is used in manufacturing and other areas
involving robot operations where a large area must be covered to prevent worker unjury.
Safety Stop
A safety stop results from activation of a machine safeguard while safety monitoring is enabled. The monitoring
may be disable while a worker is doing a task that requires entry into the protected zone. The control system,
often a regular PLC, will not allow movement of equipment while the safety plc is not in monitoring mode. When movement
is required, the control PLC will signal the safety PLC to enable monitoring. The safety PLC will return a positive
signal indicating that it is in monitoring mode. A ssparate signal from the safety PLC will inficate that it is
safet to move the equipment. This is different from an emergency stop E-stop which directly affects the Safety PLC
output that hardware interlocks with the power required to move equipment. The estop will function regardless of the
monitorin mode. The safety stop will only function by signalling the control PLC when the Safety PLC is in
monitoring mode.
Industrial Robot Safety
An industrial robot requires special machine safeguard techniques for machine safety. The requirements can be found
in ansi rp15-06 and iso 10218. These documents provide narrative and diagram descriptions of typical robot safety
situations that require safety plc and safety relay to do machine safeguarding.
Artzat Consulting is owned by Arthur Zatarain, PE in Metairie Louisiana,
a suburb of New Orleans Artzat provides consulting and expert witness services
to attorneys, insurers, and end users. Typical projects relate to equipment,
automation, instrumentation, and control systems. Service is available nationwide
with engineering licenses held in Louisiana, Alabama, California, and Alaska.
Forensic Engineer
A forensic engineer performs analysis and reporting on technhical matters
that are typically being pricessed through some form of legal matter. However,
a legal environment isn't required for a forensic examination. The analysis
may be performed merely to determine the cause of a specific event or condition.
For example, a forensic examination may be made on a control system to determine
why an accident occured, or why a system did not perform as expected. The
forensic analysis may be of software code such as ladder lofic in a PLC,
or it may involve hard wired relay logic, electrical controls, power distribution,
or instrumentation. Forensic engineering is therefore useful in a variety
of situations regardless of the legal entanglement.
Industrial Equipment
Typical equipment includes programmable logic controller PLC, distrubited
control system DCS, and electric relay logic. PLC systems use ladder logic
for most operations, while a DCS will often use function block programming.
The concepts of PLC and DCS have merged into a unified control platform based
on open architecture interfaces. The use if ladder logic is widespread due
to its earlier application to relay logic circuits.
An expert witness is used to investigate and evaluate the technical and
commercial aspects of accidents, intellectual property, and commercial matters.
Artzat consulting can assist clients in all these areas, with experience
with steam boilers, paper mill, steel mill, burner management, and telemetry
scada. Other areas include medical devices, flow measurement, meters, power
distribution, and refridgeration.
Expert Witness Services
Expert witness can be provided in any state, with experience in Louisiana,
California, Alabama, and Alaska. Other states include North Carolina, Olkahoma,
Illionis, and Indiana and Texas. Michigan has also been served, with the
states of Washington, Colorado, Oregon, and District of Columbia DC. Any
state such as New York or New Jersey can also be served by expert witness
service. Professional credentials are important, such as licensed engineer
or registered engineer. Also importnat is a masters degree in engineering
or similar field. A phd is not a necessity for an expert witness because
career experience and expert witness experience is more useful to the client
than a phd with no relevant experience.
product Liability
A forensic engineer is useful for matters of product liability and product defects.
Artzat Consulting has experience with product liability for industrial and commercial
equipment. Product liability has also been analyzed for control systems, programmable
controllers, ladder logic, and engineering design. Product liability can result from
an original product manufacturer oem, or from a systems integrator who combines components
into a complete system.
Forensic Engineering Locations
Service in Louisiana, Mississippi, Texas, and Alabama is efficient due
to the proximity of Metairie to those areas. However, an airplane will take
Artzat anywhere within the USA in a matter of hours. Travel to Alabama areas
such as Birmingham or Montgomery or Mobile is easy, with Huntsville also
accessible by car. Visits to Houston, Dallas, San Antonio, and Austin are
also less than one day away by car. A phd is not unusual for an expert witness,
but is not really important when compared to real life experience with equipment,
controls and automation with PLC and DCS control system equipment.
Service in California includes Los Angeles, San Francisco, and San Diego
as well as outlying Bakersfield and Antioch. Seattle is a bit far, but the
airline does most of the heavy lifting. Travel to New York NYC occurs easily
on JetBlue and Delta. Once in NYC the entire tri-state area is easily accessibls,
as is upstate new york.
Service to New England is welcomed, so please inquire with your technical
requirements for an expert witness. Travel to new England such as Boston
is by JetBlue, or other carriers, which can then lead to other New England
cities.
Engineer for Machine Accident
An engineer ma be required to serve as an expert witness or forensic
for a machine accident such as with a conveyor, power press, steel mill,
or extraction machine. The instance could be an equipment accident, or it
could be a process accident. A typical example is an expert engineer for
a manufacturing accident. This could be an expert engineer or forensic engineer
in an assembly plant, or an expert engineer in a production line or on a
vehicle assembly line.
Oilfield accident
An expert engineer can be useful to evaluate an oilfield or oil and gas
accident. Those events may include oil and gas or the related products such
as water, co2, h2s, and sulfates. The accidents occur on oil wells, gas
wells, pipelines, storage tanks, and production vessels such as separators,
treaters, waste heat recovery units, and water treating facilities. Such
events can be generally divided into an oil and gas drilling accident or
an oil and gas production accident. An oilfield accident requiring an expert
engineer can occur onshore of offshore. The expert engineer can be for control
system, production system, safety system or automation system, or instrumentation.
The system can be electrical, electric, electronic, hydraulic, and pneumatic.
A computer control system can also require an expert engineer. An industiral
engineer can also be used if the matter involves safety and production systems.
Automatic control
An expert engineer may be required for an accident involving automatic
control. That expert could be for electrical engineer, control system engineer,
or automation engineer. A mechanical engineer or someone with experience
with mechanical engineering can also be useful for an automatic control
accident. A certified systems integrator is someone who can be an expert
engineer for automatic control. The systems integration involves combining
multiple equipment and techology into a single control system. This involves
design, programming, fabrication, testing installation, and maintenance.
industrial accident
An industrial accident may require an expert engineer or forensic engineer
to analyze and evaluate the control system connected with the event. The
accident may have nothing to do with the control system. Still, a forensic
engineer may be required to analyze the system to determine that the control
system was not af fault.
Equipment accident
An equipment accident can require an expert engineer or expert witness
to help evaluate the circumstances and situation including the mechanical
and electrical components of the equipment. This can be industrial equipment,
process equipment, manufacturing system, commercial equipment such as heater
or dryer, or pump and compresssor. Industrial equipment is also a flow meter,
electrical switchgear, control switch, button, and instrumentation. End
devices are pressure, temperature, level, and other physical measurement.
Many equipment is used for food production, packaging, transportation, storage,
and conveyor. Metal processing such as steel mill, paper mill, refinery,
petrochemical, and tank farm. Vehicle can also be equipment itself, or it
can contain devices related to an equipment accident.
