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1. What if the UV doesn't cool quick enough to restart
after 1 minute?
A UV lamp has to be cool enough in order to be re-ignited.
The amount of cooling a lamp gets after it has been
shut down is usually controlled by a Cool Down Timer
(or Blower Run On Timer). On some common UV Systems,
this is labeled as T3. The Cool Down time should typically
be around 60 seconds in order to allow, not only the
lamp, but the electrical components within the irradiator
enough time to adequately cool before a lamp re-start.
If after this time the lamp has difficulty starting,
check the blower filter to ensure that enough clean
air is being allowed through to the lamp. Shortening
the Cool Down time may allow the lamp to be started
sooner after it has been powered down, but it may also
allow excessive heat to build up within the irradiator
and so damage the lamp leads or other components.
2. What causes UV Lockout?
A UV Lockout is when the UV System does not allow ignition
of the UV Lamps. This can be during a warm up cycle,
a cooldown cycle, or any other time the UV System
deems unsafe to ignite the lamps. A UV Lockout on
a MetalBox system is caused by the Lockout Relay
(R1/R2) which is switched on when the Current Relays
(CR1/CR2) do not detect any current draw after a
lamp is ignited.
3. What is UV Fault?
UV Fault is caused when a lamp fails to ignite or fails
to reach a ready condition. A UV Fault may have nothing
to do with a lamp, but may be caused by some other
component within the UV System.
4. What should the Current Relay be set at?
The Current Relay (CR1/CR2) should be set to between
1 and 5 amps. It is not too important as the relay
is there just to sense current to see if the lamp
is lit. After the lamp is ignited, the Lamp Start
Timer has to expire to activate the Current Relay.
This is to give the ignitor enough time to light
the lamp. If the Current Relay does not read any
current after this time, it is assumed that the lamp
did not light.
5.What signal tells the machine that the UV is up
to power and ready?
The Voltage Relays (VR1/VR2) signal the lamp has reached
its normal operating voltage. This signal is used to
start the cooling blower and to notify the printer.
The normal operating voltage for a MetalBox lamp is
anywhere between 250 and 310 volts, hence the Voltage
Relay is normally set to the lower value.
6. How do you know if the cooling blower is working
properly?
Most UV systems have some form of detector or switch
that looks to see if the cooling blower is functioning.
On a Metalbox system this takes the form of a pressure
sensor in the UV irradiator. The pressure sensor is
connected to the Cooling Pressure Switch Relay (labeled
PR) that has to be enabled for the system to run. Although
most systems can detect that the cooling blower is
functioning, they cannot always tell you that you have
enough or too much cooling. Regular inspection of the
lamp is necessary to really ensure adequate cooling.
7. How often should reflectors be cleaned/changed?
Whenever the lamp is changed, or sooner if it is dirty/damaged.
The importance of the reflector cannot be stressed
enough, most of the curing power of the lamp comes
from the reflected light.
8. How can you tell UV lamps need changed?
Over time the running voltage of a lamp will drop.
Once the lamp falls beneath the voltage set be the
Voltage Relay it will fail to send a Lamp ready signal
to the Press. If a lamp becomes swollen due to overheating,
this will also reduce the running voltage of the
lamp. Swollen lamps will also not be as effective
at curing. If all other components within the UV
system are operating correctly, lamps should be changed
when they fail to start, fail to reach ready, fail
to cure, are too discolored or are swollen. 99% of
lamp failures are normally misdiagnosed and are actually
failures by other components in the system, such
as capacitors, ballasts or ignitors.
9. What tells the system that the UV is cool enough
to restart?
The Delay Start Timer (T2) is used to lock-out a re-start
once the UV system is powered down.
10. What is the procedure to check the capacitors with
a meter?
- Disconnect all wires from the capacitor terminals.
- Short
the two terminals using a screwdriver with an insulated
handle.
- Connect the meter to the terminals and
take reading. Replace the capacitor if the reading
is 10% or
more below the capacitors' value.
11. What does the voltage
sensing relay do?
How do
you know it's working properly? The Voltage Sensing
Relays (VR1/VR2) are used to indicate when a lamp has
reached its operating voltage (its ‘Ready Condition'),
which in turn is used to start the cooling blower system.
MetalBox 426 lamps normally run at a voltage between
250 and 320 volts (each lamp is slightly different).
The Voltage Sensing Relay is normally set to the lower
end of this range, typically 240-250 volts. See question
18 to find out what happens if the voltage relay does
not work correctly.
12. What is the pressure sensor relay?
The pressure sensor relay is used to indicate that
the irradiator is pressurized, ie. that the air from
the cooling blower is reaching the irradiator. This
is to verify that there is no problems between the
blower and the irradiator, such as a damaged or blocked
hose, or a choked blower air filter.
13. What does the lamp contactor do? How do you troubleshoot?
The Lamp Contactor (C2/C3) allows power to flow to
the lamps, via the ballasts, capacitors and ignitors.
In essence, these switch on the lamp circuits. The
contactors themselves are energized by a control
signal from the printers' PLC. A contactor, when
engaged, should have the same voltage coming out
as is going in, and should remain closed when the
control signal is applied. A faulty contactor may ‘rattle'
when it is energized and so turn the output voltage
on and off very rapidly. This could cause spikes
in the voltage and damage other components further
down the line. A contactor can normally be pushed
in by a screwdriver in order to turn it on, rather
than be energized by a control voltage. This is useful
when manual control is needed, for example to test
the contactors output voltage or to briefly test
the lamp's circuit.
14. System comes up to power then shuts down. What
is the problem? Depending upon how far up to power the system was at
the time it shut down, could be because one of the
lamps failed to reach a ready status. If Lamp 1 ignited
and then shut down, it will be because lamp 1 did not
achieve ready. Lamp 2 will not ignite until Lamp 1
is ready. If Lamp 2 ignited, then we know already that
Lamp 1 is running OK, but if Lamp 2 does not reach
its ready condition, a UV Fault will be caused and
both lamps will power down. The time a lamp is allowed
to reach its ready condition from when it is ignited,
is controlled from the PLC.
Alternatively, if Lamp 1 reached its ready condition
and then the system went down, it could also be caused
by a blower fault indicated by the Cooling Pressure
Switch Relay (PR), or by the Current Relay for Lamp
2 (CR2) not detecting any current in Lamp 2 once it
has been told to ignite.
15. The UV System tries to
start, flashes and then shuts down. What do I look
for? Check cables, caps,
contactor (Lamp Contactor C2/C3), ballast and ignitor.
Cables should be secure, capacitors should be within
8% of nominal, contactor should hold in when energized
(and have the correct voltage coming out as was going
in), and the ballast should output close to the same
voltage that was input. There are easy steps to follow
for checking capacitors and ballasts (if in doubt,
call for more info), but the best way to check an
ignitor is just to replace it with a new one.
16. The UV lamps looked swelled and black on the ends,
does this mean that they should be changed?
Swelled and blackened lamps are a sign of overheating.
If this is caught very early on, the blower baffle
can be adjusted to allow for more cooling (or even
clean filters installed on the cooling blower), and
some use may still be squeezed out of the lamps. But
generally once a lamp starts to swell, it can lose
some of its curing properties, as well as drop in voltage.
This drop in voltage may not allow the lamp to achieve
its ready condition and so make the lamp more prone
to failure.
17. Are all UV lamps of the same length the same wattage?
No. The power output of the lamp has nothing to do
with its length, other factors such as the amount
of mercury in the lamp and the power supply that
feeds the lamp govern this. For example SPDI produce
a variety of lamps which have a 6 inch arc length,
but they vary from just a couple of hundred Watts
Per Inch to over 1500.
18. UV comes up to full power but the machine doesn't
start, the reflectors burn up and the wires get burnt
to the lamps. What caused this?
It sounds as if the Voltage Sensing Relay is not working
correctly or is set too high. The Voltage Sensing is
used to indicate a Lamps ready status which is used
to start the cooling blower and indicate to the press
to start running. If the Voltage Sensing Relay never
kicks on, the blower will not start and so the lamp
will continue to heat up, and the press will never
get the signal to start. Obviously an un-cooled lamp
will damage anything within and near the irradiator,
including reflectors, cables, junction boxes and the
lamps.
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