Tower 332
Platform Leveling System
Issues and Corrective Actions
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Platform Leveling System (PLS)
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The leveling of the platform is accomplished by two different methods, primary
(hydraulic) and secondary (electronic):
– Primary: the majority of the platform leveling is performed by the master/slave
hydraulic cylinders as the aerial is raised or lowered.
– Secondary: minor adjustments or corrections to the platform leveling are made
electronically via inputs from an inclinometer sensor that is mounted in the platform.
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The leveling adjustments via the inclinometer input are required to keep the
platform level to the horizon during aerial operations and to level the platform
to the truck chassis after the aerial is bedded into the cradle.
The inclinometer sends low-voltage signals to the platform controller which
processes the signal and sends it down the ladder through the CAN cable to
the valve driver controller (located inside the turntable pedestal) and then on to
the electrohydraulic actuator on the leveling hydraulic spool valve.
The microcontroller in the actuator processes the signals from the valve driver
controller and moves the leveling spool valve to allow oil flow to the platform
slave cylinders to make the required leveling adjustments to the platform.
The focus of this presentation is on the secondary/electronic leveling
part of the PLS. This is area where the problems have occurred.
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Platform Leveling Sys – Master Cylinder
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Platform Leveling Sys – Slave Cylinder
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Platform Controller
Platform Inclinometer
Platform Inclinometer - Original Location
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Aerial Operations - Hydraulic Spool Valves
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Electrohydraulic
Actuators
Spool
Valves
Hydraulic and Electronic
Systems
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Key Issue with the PLS
• Crimson Tower PLS is equipped with a safety feature described in the
Operator’s Manual as follows: “A safety feature is installed in the
leveling system where if the platform becomes +/- 5 degrees out
of level the electronic leveling system will shut down.”
• The PLS safety has failed to prevent the platform from tilting
downward excessively (significantly exceeding the 5 degree
limit) on separate occurrences in Jul – Nov 2010 and Nov 2012.
• The malfunctions of the PLS and subsequent failure of the safety to
function could be caused by the following factors:
– Signal Generation Error - the platform inclinometer sending incorrect
signals to the controllers and the actuator.
– Signal Processing Error - leveling spool valve actuator microcontroller
incorrectly processing the signals from the inclinometer.
– Signal Integrity Issue – transmission issues with the signals being
sent from the inclinometer to the leveling spool valve actuator.
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Initial Occurrence July 2010 – Approx 25 Degree Tilt
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Event History/Timeline
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18 Jul 2010 – Initial malfunction of the PLS (previous photo)
9 Aug 2010 – Platform inclinometer replaced; failure analysis of the sensor
by the manufacturer revealed nothing wrong with unit.
31 Oct 2010 – Second occurrence of PLS malfunction (Sunflower Dr.)
14 Nov 2010 – Third occurrence of PLS malfunction (Gairloch Pl.)
1 Dec 2010 – Truck taken to Crimson facility (Ephrata PA) for repairs to the
PLS and other warranty items. Was determined that the
platform inclinometer had been installed incorrectly (was not
properly grounded) that caused erroneous signal output.
22 Dec 2010 – Truck returned to Bel Air and placed back in service.
3 Aug 2012 – Informed that Crimson was working on a modification to the
PLS to add a 2nd platform inclinometer to improve the
function of the safety feature of the PLS.
13 Nov 2012 – Serious malfunction of the PLS occurred causing severe
downward tilt of the platform, contacting the top of the cab.
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Event History/Timeline (Cont’d)
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29 Nov 2012 – Truck taken to Crimson facility for repairs to the PLS and
the truck cab. Later determined that the PLS malfunction
was likely caused by water contamination in the electrical
connector for the platform inclinometer leads.
30 Jan 2013 – Truck returned to Bel Air but not placed back in service
pending discussion with Crimson regarding the modifications
made to the PLS and possible evaluation by a 3rd party.
12 Feb 2013 – Meeting held with Crimson management personnel to
discuss modifications made to the PLS but no failure analysis
was provided. It was decided to have a 3rd party evaluation
of the PLS to determine if additional modifications were
required. Crimson concurred with the 3rd party involvement
and recommended an engineering firm (Logical Control Systems)
that they had used previously in support of their aerial control
systems design work.
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Event History/Timeline (Cont’d)
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5 Mar 2013 – Truck taken back to Ephrata for evaluation by the 3rd party
firm (Logical Control Concepts, Electro – Hydraulic Control
Specialists) recommended by Crimson.
7 Mar 2013 – LCC personnel examined the PLS on TW332 that included
the recent modifications made by Crimson to include the
addition of a second platform inclinometer.
27 Mar 2013 – Received the PLS evaluation report from LCC which
provided several recommendations to further improve the
function and reliability of the PLS.
9 Apr 2013 – Following the review of the LCC report, it was decided to
meet with Scott Jones (President of LCC) to discuss the
report to support a final decision on what additional
modifications should be made to the PLS.
23 Apr 2013 – Met with Scott Jones and made the decision to go with all
of the recommended modifications to the PLS that were
highlighted in the LCC evaluation report.
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Event History/Timeline (Cont’d)
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May – 14 Aug 2013 – Crimson ordered the required components and made
the requested modifications to the PLS. New
waterproof inclinometers were installed but required a
6-week lead time by the mfg. A new CAN cable was
installed but the cable model had to be changed due to
fit issues related to the installed bend radius. The new
inclinometers were installed and calibrated and the
PLS tested. Repairs were also made to aerial lift
cradle to fix minor damage.
15 Aug 2013 – Truck picked up at Crimson and driven to Penn Diesel for
repairs to the Diesel Particulate Filter (DPF) regen system.
16 Aug 2013 – Repairs to DPF regen completed by Penn Diesel, truck
returned to Bel Air.
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Cause of PLS Failures
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Following the 1st PLS malfunction, the platform inclinometer was inspected by
the manufacturer (Rieker) and was found to be functioning satisfactorily with
no malfunctions or abnormalities detected.
Following the Jul – Nov 2010 platform leveling issues, it was determined that
the platform inclinometer had been installed incorrectly. The inclinometer had
been improperly grounded to the common 12v chassis ground causing a
ground loop effect with other circuits creating noise that in turn caused signal
distortion. The inclinometer requires a dedicated 5v ground.
Following the Nov 2012 incident, the troubleshooting of the leveling problem
included a functional checkout of the leveling spool valve hydroelectric
actuator. The actuator was found to be operating properly.
It was later determined that the cause of the Nov 2012 incident was the
corruption or distortion of the platform inclinometer signal being sent to the
spool valve actuator due to water contamination in the electrical connector
that connects the inclinometer leads to the platform controller.
Moisture in the connector caused a change in characteristic impedance and
an increase in signal reflection causing the signal to become distorted
resulting in incorrect values being transmitted to the microcontroller in the
leveling spool valve actuator.
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Silicone Elastomer Seal
Deutsch Electrical Connector - Used to Connect
Platform Inclinometer Leads to the Platform Controller
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Initial PLS Corrective Actions
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Previously, it was found that the platform inclinometer had not been
grounded properly when first installed. This was corrected by Crimson
in Dec 2010.
Following the Nov 2012 incident, the following fixes were made to the
PLS by Crimson:
– The platform inclinometer was remounted inside a sealed plastic box at
the LR corner area of the platform. This relocation also included the move of
the electrical connection providing power to the inclinometer inside the box
as well for weather protection.
– The addition of a second (redundant) inclinometer that was also placed
inside the plastic box. The purpose of the 2nd inclinometer is to support a
sanity check of the signal being sent for the other platform inclinometer.
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The purpose of the above fixes was to protect the inclinometers and the
electrical connections and to better ensure that the leveling commands
(signals) being sent by the platform inclinometers are fully valid before
leveling adjustments are made by the leveling spool valve actuator.
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Platform Inclinometers (2) - New Location
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Platform Inclinometers (2)
Installed Inside Sealed Box
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3rd Party Evaluation of the PLS
Mobile
Electronics
Control Systems
LCC is described as a full service systems integrator that specializes in the
integration of electronics and hydraulics into robust, user-friendly control
systems. They specialize in custom design of control systems using the
Sauer-Danfoss PLUS+1 GUIDE microcontroller systems that is used in
many aerial ladder systems to include the Crimson aerial control systems.
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3rd Party Evaluation of the PLS
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LCC evaluated the PLS after Crimson had added the 2nd platform
inclinometer and placed both inclinometers inside a sealed plastic box.
The evaluation was only done on the modified version of the PLS and not
on the original configuration with the single platform inclinometer.
Crimson added a 2nd inclinometer to the platform with the original
inclinometer controlling the platform leveling and the other inclinometer
handling the safety function to disable the leveling if the platform gets
more than +/- 5o off the horizon. However, neither the platform controller
or the valve driver controller (inside the turntable pedestal) were
programmed to compare the signals received from the two platform
inclinometers for a redundancy check. LCC indicated concern about this.
LCC noted that the Controller Area Network (CAN) cable that runs the
length of the aerial ladder connecting the platform and valve driver
controllers does not conform to CAN 2.0 A/B standards that requires a
shielded cable with an impedance of 120 ohms to enhance protection
against high EMI/RFI that is common around high voltage lines and radio
transmitters.
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3rd Party PLS Evaluation (Cont’d)
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Following the evaluation, LCC issued a System Design Review report of
the modified Crimson PLS highlighting the following points:
– Recommended that the signals from both platform inclinometers be
compared by the platform controller and if the measure angle signals of both
inclinometers and not within a specified window that the platform leveling be
disabled (shut off).
– Recommended that the cable be replaced with a different model cable that
fully conforms to the CAN standards to enhance signal integrity of the
transmissions between the platform and the turntable.
– Noted that Crimson should consider using sealed (fully waterproof)
inclinometers rather than water-resistant inclinometers with either fully potted
cable or M12 electrical connectors as a general improvement to the overall
reliability of the PLS.
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The LCC report summary included the following:
– The installation of the PLS hardware was satisfactory and only provided
recommendations to further improve the reliability of the PLS.
– A program change of the platform controller was justified and stressed that
the comparison of the signals from the two platform inclinometers will provide
a higher degree of safety and reliability to the control system.
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Follow-On PLS Modifications
• Immediately prior to the LCC evaluation of the PLS, on the request of
the BAVFC, Crimson installed shut off switches on the turntable
and platform control consoles that disable the electronic leveling
of the platform. TW331 features similar mushroom switches at both
the turntable and platform that perform exactly the same function.
• Following the LCC evaluation, the following modifications were made
to the PLS as directed by the BAVFC:
– Program change of the platform controller to include a redundancy
(comparison) check of the signals received from both of the platform
inclinometers as was recommended by LCC.
– Replacement of the two platform inclinometers with a fully sealed
(waterproof) inclinometer model.
– Replacement of the CAN cable that runs up the aerial ladder connecting
the platform and valve driver controllers with a new cable model that fully
conforms to the CAN specifications.
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New Sealed (Waterproof)
Platform Inclinometers
Installed Inside Sealed Box
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New Platform Electronic Leveling On/Off Switch
TW332 Turntable Control Console
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New Platform Electronic Leveling On/Off Switch
TW332 Platform Control Console
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New Platform Electronic Leveling On/Off Switch
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TW331 Turntable
Console
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TW331 Platform Control Console
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PLS Modifications - Conclusion
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The problems experienced with the PLS leveling were primarily caused
by component installation issues and less than optimal electrical wiring
procedures that were used for the platform inclinometer.
The distortion or corruption of the signals from the single platform inclinometer
caused the electronic leveling of the platform to malfunction and more
significantly, prevented the PLS leveling safety from functioning as intended.
The key concern is considered to be the failure of the electronic leveling
safety to prevent the platform from becoming considerably out of level, a
very significant safety issue.
The addition of the 2nd platform inclinometer in conjunction with the
program change of the platform controller is the most significant modification
of the PLS. These changes and the improved installation of the related
components greatly improve the function and reliability of the safety feature
of the PLS.
With the modifications made to the PLS, it is much less likely that the leveling
signals will become distorted or corrupted causing the electronic leveling of
the platform to malfunction. But most importantly, the PLS safety now has
a much better chance to function as intended to prevent the platform
from tilting more than 5 degrees out of level.
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Aerial Operation with the Electronic PLS Disabled
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The Electronic PLS (E-PLS) can be disabled by shutting off the power to
the platform inclinometers either by the use of the new switches on the
turntable or platform control consoles or if the PLS senses a fault and
automatically shuts down the electronic leveling of the platform.
The electronic leveling of the platform on TW331 can also be disabled by
shutting off the leveling (mushroom type) switch at either the turntable or
platform control consoles.
The aerial can still be operated with the E-PLS disabled but the
platform will likely not remain level to the horizon since the platform
inclinometer will not be able to make the required leveling corrections.
The leveling misalignment will be primarily noticed when the aerial is
cradled (stowed). On TW332, the platform will not align itself to the truck
chassis unless the E-PLS is turned back on or the platform is leveled
manually. On TW331, the platform always remains level to the horizon
(not the truck chassis) when the ladder is stowed if the E-PLS is activated.
It can also be leveled manually without the use of the electronic leveling.
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Aerial Ops with the E-PLS Disabled (Cont’d)
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If the E-PLS is disabled on either TW331 or TW332, the platform can be
expected to get out of level with the horizon as the aerial is raised or lowered.
However, in most cases, the amount the platform will likely be out of level is
relatively small and is practically unnoticeable by the platform operators.
With the E-PLS off, the TW331 platform will drop below the horizon
(downward tilt) as much as 3.5 to 4 degrees as the aerial is raised up to max
elevation. However, the TW332 platform will actually rise above the horizon
(upward tilt) approximately the same amount as the aerial is raised. For
reference purposes, a 4 degree tilt of the platform is illustrated below.
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Other Modifications Made to TW332
• Deadman foot switch in the platform was removed.
• Aerial controllers at the platform console were replaced with new
controllers that are equipped with sliding collars similar to the
controllers on TW331.
– The sliding collars lock the control levers in the neutral (centered)
position unless the collars are lifted upward allowing the levers to be
moved to initiate aerial functions.
– In lieu of the deadman, the locking collars on the control levers provide
a positive means to prevent unintentional movement of the aerial per
NFPA 1901 requirements.
• The removal of the deadman switch and the aerial controller
modification now makes the functionality in the platform
exactly the same as TW331.
• All of the aerial rung covers were also replaced.
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TW332 Platform Controls (New)
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