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SEMI S15-0200 © SEMI 2000 3 6.13 Enviro nmental Cond itions — W h a t are the temperature and relative humidity specification s for the gas detection syste m for normal operation as well as for storage of consumable part…
SEMI S15-0200 © SEMI 2000 2
5.2.5 latching — relative to discrete alarm contacts,
the alarm relay will not reset when the alarm condition
ceases to exist. The alarm must be manually or
remotely reset by operator interface.
5.2.6 poisoning — the interaction of a gas/chemical
other than the target gas/chemical that temporarily or
permanently disables the sensor from reliably detecting
the presence of the target gas/chemical, or otherwise
renders the device inoperable.
5.2.7 span drift — the percentage change in a known
calibration point or span of a sensor or gas detection
system over time.
5.2.8 surrogate gas/chemical — a substitute
gas/chemical that is more benign than the gas/chemical
it is replacing. This concept is used in the calibration of
gas/chemical sensors when a highly toxic or corrosive
challenge gas is undesirable. The surrogate
gas/chemical will simulate the interaction with the
sensor of the gas/chemical for which it is substituted.
5.2.9 target gas — the specific gas intended to be
detected.
5.2.10 zero drift — the percentage change in the zero
point or baseline of a sensor or gas detection system
over time.
6 Performance Characterist ics
6.1 The performance characteristics (the test results of
which should be reliable and repeatable) are as
identified below. These are factors one should consider
in the evaluation of a gas detection system (from the
point of detection through the output signal) for a
specific application. A form for compiling a
comparison table is provided as Appendix 1.
6.2 Accuracy — What is the stated accuracy of the
system? Over what time period will that accuracy be
valid (before calibration of the gas detection system is
necessary)?
6.3 Alarms — What is the range for setting the alarms
for each gas detection point? Are the alarms user-
adjustable for set and reset time delays, latching or non-
latching, normally open or closed, fail-safe or non fail-
safe? How many alarm levels are available per
detection point? Is there a fail alarm and what
conditions will activate that alarm? Are the alarms
dedicated to each detection point or are they common to
a group of monitoring points?
6.4 Calibration
6.4.1 Is calibration required? If so, how often? How
is it accomplished? Can it be done away from the point
of detection or must it be done on site? What
equipment is needed to perform the calibration? Can a
surrogate gas be used for calibration? Can the
calibration be accomplished by one individual? Is
calibration accuracy affected by humidity?
6.4.2 During start-up, how much time must elapse
before the gas detection system can be calibrated?
6.5 Certifications and Classifications — Does the gas
detection system have the necessary performance or
safety approvals for the specific application and
location (e.g., UL, CE, SEMI S2)?
6.6 Communications (serial) — What types of serial
communication are available from the gas detection
system? What communication protocols are supported?
Is it one-way or two-way communication?
6.7 Conditioning Requirements — Is the monitoring
equipment always ready and able to detect a gas leak or
must it be preconditioned on a periodic (regular) basis
to ensure response times are achieved?
6.8 Cost of Ownership — What is the initial cost for
the equipment and installation? What is the long-term
cost of ownership of the system (consumables,
calibration equipment, and labor)? What is the cost
(hardware and installation) to expand the system
(additional points of detection) and/or change the gas
configuration?
6.9 Data Archiving — Are data documentation or data
archiving system available as a part of the gas detection
system?
6.10 Diagnostics — What system diagnostics are
included? Can electrical or mechanical failures within
the system be detected? Will a fault alarm be
activated? Are diagnostics communicated over analog
and/or digital outputs? Are faults archived by the gas
detection system? Will an inoperative system be
identified through a self-activated alarm (fail-safe)?
Will the system alert the user that a calibration is
required? Are communication outputs supervised?
6.11 Display — What local displays are available on
the gas detection systems? Where is the display
located? Does the display show gas concentration level
with engineering units and identify active alarms with
signal lights? Are other diagnostic and control
functions displayed when activated? Is the display easy
to read from a distance?
6.12 Drift — What is the zero and span drift over 30,
60, 90, and 180 days? Does the gas detection system
compensate for drift?
SEMI S15-0200 © SEMI 20003
6.13 Environmental Conditions — What are the
temperature and relative humidity specifications for the
gas detection system for normal operation as well as for
storage of consumable parts? Could environmental
changes such as quick humidity transients or
temperature changes cause the gas detection system to
spike or drift into an alarm condition?
6.14 Equipment Failure — Is the gas detection system
capable of reporting all single point failures that disable
detection? What failure mode disables both detection
of gas and reporting failure?
6.15 Expansion Flexibility — Is the gas detection
system capable of expansion to accommodate
additional detection points? How easy is it to integrate
into the user’s system (hardware, installation,
programming, etc.)?
6.16 Extraction Detection Systems
6.16.1 Sampling Distance — What is the maximum
sampling distance for the gas detection system? Will
all the gas entering the sample line at the point of
detection reach the central monitor? What is the
sample loss due to the challenge gas absorbing onto the
sample tubing walls?
6.16.2 Sample Cycle Time — How frequently, if
multiple points are sampled, is the same detection point
surveyed by the extraction detection system, at the
desired alarm level?
6.16.3 Sample Contamination — What, if any, is the
potential for contamination of the sample line tubing
and manifolding equipment when multiple gases are
monitored within the same extraction system? What
combination of gases should be avoided due to
chemical interaction on wetted materials?
6.17 Filter Lag — Does the gas detection system use
any mechanical, chemical or electronic filters (for cross
sensitivity, particles, etc.) which could slow the
sampling response? If so, what lag time is expected for
each gas type?
6.18 Installation - Wiring Configuration — How many
wires are required per detection point? Can the system
be wired in a highway configuration (bus, ring, star,
etc.)? Are special barriers or grounds required to
ensure no earth loop faults exist?
6.19 Isolation — Does the gas detection system
require any special electrical isolation or grounding?
6.20 Limits of Detection
6.20.1 Lowest Alarm Level — What is the lowest
alarm level setting for the gas detection system which
will not activate due to sensor drift or insufficient signal
to noise ratio?
6.20.2 Limit of Detection — What is the absolute
lowest value that a sensor can detect, for each gas?
6.20.3 Upper Limit of Detection — What is the
highest level of gas that can be quantified reliably by
the gas detection system?
6.21 Linearity — What is the linearity over the full
measuring range of the gas detection system output?
6.22 Maintenance Interval — What is the
manufacturer’s recommended maintenance frequency?
What is involved to perform this maintenance? What
items potentially require maintenance or periodic
replacement (pumps, sensors, tapes, etc.)?
6.23 Other Utilities — In addition to electrical power,
what other utilities are required to operate the system
(e.g., compressed air, hydrogen, oxygen, etc.)?
6.24 Outputs — Does the gas detection system have
analog, digital, and relay outputs? How many are
available per system?
6.25 Physical Size — What is the physical size of the
gas detection system for both the detection head (or
sampling point) and the control systems or central
monitor, including the required floor space?
6.26 Poisoning — Is the gas detection system
susceptible to gases or vapors which would reduce the
performance (ability to detect gas) of the system or
render it contaminated and inoperative?
6.27 Position Effect (Attitude Sensitivity) — Is there a
specific orientation of the sensor, detector, or sampling
point required for the gas detection system to function
optimally?
6.28 Power Outage — When system power is lost,
what happens to the gas detection system? Once power
is restored, what is the time lag before the system is
fully functional?
6.29 Power Requirements — What are the power
requirements (i.e., AC, DC, voltage, and amperage) of
the system? What is the power draw of the total gas
detection system?
6.30 Recovery Time — What is the amount of time it
takes the gas detection system, once exposed to
challenge gas, to recover to 10% of the original target
gas concentration value?
SEMI S15-0200 © SEMI 2000 4
6.31 Repeatability — What is the ability of the gas
detection system to produce the same detection results
within a certain percentage, when repeatedly exposed to
the same gas concentration?
6.32 Reliability — What is the expected life of the
various portions of the gas detection system (including
the main unit, detection sensors, and consumables)?
6.33 Replacement/Replenishment — Does the system
contain consumable items? How frequently must they
be replaced? Can they be replaced by the user or is a
factory person required for servicing?
6.34 Resolution — What is the level of resolution for
changes in gas concentration? That is, to what extent
can the gas detection system detect a changing
challenge gas concentration? Is this user selectable?
6.35 Response Time — From the point of release of
the challenge gas, how long does it take the gas
detection system to reach 90% of the challenge gas
concentration?
6.36 RFI/EMI Susceptibility — Does the gas detection
system meet the requirements for CE Marking for
RFI/EMI immunity and per SEMI E33?
6.37 Self-Test — Does the gas detection system have
an automatic or user initiated self-test routine? How is
it accomplished? What is the interval for the self-test?
Can the operator override the self-test? Is the self-test
just an electrical check or is gas actually generated? Is
the generated gas the target gas?
6.38 Sensor Exchange — Do sensors require on-site
calibration only or can they be factory calibrated? Are
additional adjustments or programming operations
required when replacing a sensor? Is there a warm-up
period for the sensors before they are functional (for
calibration purposes)? If so, how long?
6.39 Sensor Specificity — Are gas specific sensors
available for every gas that must be monitored? What
are the known interferences to the gas detection system
that could cause a false alarm or mask a real alarm?
6.40 Service & Support — What is the manufacturer’s
capabilities to service and support their equipment once
it is has been installed? Does the manufacturer have a
24 hour/7 day service support program in place?
6.41 Spare Parts Availability — What is the
availability of spare parts from the manufacturer? Are
emergency spare parts always available?
6.42 Special Handling Considerations — Are there
items that require special handling, storage, or disposal?
If so, what are the considerations?
6.43 Storage and Shelf-Life Requirements — What are
the storage (environmental) requirements for the
consumable items (e.g., electrochemical sensors and
paper tapes)? Do these items have a shelf-life and if so
how long?
6.44 System Check — Does the gas detection system
have a system check facility? If so, is this done on a
continuous or interval basis? What is the interval?
6.45 System Expandability & Flexibility — Is the gas
detection system universal, in the sense that the user
can change from one gas sensor to another by only
exchanging the sensing elements? How much
modification is required? Can this be done in the field
by the user or must the detection system be returned to
the manufacturer for service?
6.46 Wake Up Requirement — Does the gas monitor’s
sensor require periodic doses of challenge gas or
electrical charges to ensure the sensor will continually
operate? If so, what is the interval required for each gas
type or electrical challenge?
6.47 Warm Up Period — Upon installation or sensor
replacement, how long does it take for the gas detection
system’s sensor to stabilize after power is applied?
6.48 Warranty — What is the warranty period of the
gas detection system?
7 Gas Detection Technologies Available
7.1 Several gas detection technologies are described in
the following paragraphs. As additional technologies
become available, they should be considered, using the
performance characteristics described above.
7.2 Acoustic (Hydrogen Gas Measurement Only) —
Piezoelectric crystals send and receive pulsed
ultrasound. These sound waves travel through two
tubes of air, one tube filled with sample air, the other
with reference air. The returned pulses are counted,
normalized for temperature, and compared. Through
mathematical calculations the result represents the
concentration of hydrogen gas present in percent by
volume or percent LEL.
7.3 Catalytic — Catalytic gas sensors measure
flammable gases by comparison of the change in
resistance across a Wheatstone bridge. The sensor
contains two resistive elements (beads), one active
which increases its resistance when exposed to gas, and
the other which maintains a constant resistance. The
sensor output is then conditioned by the gas detection
system and generates a current output proportional to
the gas concentration in percent of lower explosive
limit (LEL).