Download View a sample Flame Safety training solution

Developed by
Niels Bogh
March 2006
Objective
• At the end of the class you will be able to
explain the differences of the three main
types of flame safety devises used in the
plants.
– Flame rods
– UV Mini peeper
– UV self checker
Flame Supervision
• The flame supervisory system consist of a
single or multi channel controller in
connection with individual flame sensors
that ensures the flame is present during
operation.
• If flame failure is detected the systems
shuts down in a pre-determined safe
manner.
Flame safeties
• Flame controllers
• Flame Sensors
– Flame rods
– UV sensors (Purple peepers)
– UV Self checker
Flame rod.
The flame rod is the safest flame supervision
available since it inherently can not fail in the ON
position like some of the UV detection systems. A
flame must be present for the system to work.
However with the micro amps generated in an
industrial environment there are possibilities for
failures where the system will not stay on. The
following reviews the flame rod theory.
Flame rod
• FLAME CONTROLLER
• . The controller applies alternating voltage between the flame
sensing rod and the base of the flame (ground)
• HOW DOES IT WORK?
• The flame rod is positioned such that the high temperature sensing
rod would be in contact with the flame.
• The flame creates an ionized "path" between the center
electrode/rod and the electrical ground.
• The excitation voltage induces a current flow across this "path". This
results in a very small DC offset current. DC offset is small, only
micro amps.
• This current is a stable, measurable signal which can then be used
in the appropriate control scheme. If there is a flame present, the DC
offset is detected by the controller, which tells the gas valve to
remain open.
Flame rod basic components
Flame rod
Furnace/burner
110V -360V AC
depending on
manufacturer.
Insulator
Ground.
Flame rod
• The figure show a flame present but no path for the DC current
since the flame do not ionize so a ground is established.
Flame but no path.
Flame rod
• A signal is established and the controller can amplify this
signal so the flame safety will keep the gas valve open
Flame with a ionized
path for the rectified
signal
Micro Amp DC
generated.
Flame rod
• Below are areas to keep in mind when using flame rods. The current
detected is micro Amperes, wiring and other issues affect the
reliability of the system.
–
–
–
–
–
–
–
–
Moisture (Resistive leakage)
Ignition interference (induced)
High resistance connections (series resistance)
Lead capacitance to ground (shunt)
Line voltage (sensor output variations)
Line transient or floating ground
Low rod ground ratio (flame rod)
Sot on flame rod
• In short: The flame must hit the flame rod and create a path to the
ground for the system to work. This can be done directly at the flame
rod or between the flame rod and the burner body if the flame hits
the body.
Attachment of Flame rod and Igniter connectors
UV Flame safeties
Typical Honeywell Self Checker UV
Scanner
UV “Mini peeper’s”
UV Flame Detection
• An UV flame detector is a device that
looks for a specific ultraviolet light emitted
by the flame.
• The light gets amplified by an optical lens
and is projected to a lead sulfide coating
on the back of the sensor.
• The generated current is detected by the
controller and is recognized as a flame.
Mini Peepers
• Will fail in the on position.
• Can be used on equipment which gets
shut down once every 24 hours and has
automatic startup check.
• Flame controller will fail flame if sensor is
ON when gas is OFF during start check.
• Manual check is still allowed.
Self Checker
• A self checker will interrupt the light signal
from the flame a few times per minute and
self check to ensure the flame sensor is
still working.
• A small shutter is activated and blocks the
light from hitting the sensor surface.
• The electronics keeps the flame signal on.
• Used on continuous running equipment
Flame controllers
Flame safeties from GN Electronic and Honeywell