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Tower 332

Platform Leveling System Issues and Corrective Actions

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Platform Leveling System (PLS)

• 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.

• 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.

3Platform Leveling Sys – Master Cylinder

4Platform Leveling Sys – Slave Cylinder

5Platform Inclinometer - Original Location

Platform Inclinometer

Platform Controller

6Aerial Operations - Hydraulic Spool Valves

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Electrohydraulic Actuators

Hydraulic and Electronic Systems

Spool Valves

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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.

9Initial Occurrence July 2010 – Approx 25 Degree Tilt

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Event History/Timeline

• 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)

• 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)

• 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)

• 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

• 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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Deutsch Electrical Connector - Used to Connect Platform Inclinometer Leads to the Platform Controller

Silicone Elastomer Seal

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Initial PLS Corrective Actions

• 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.

• 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.

17Platform Inclinometers (2) - New Location

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Platform Inclinometers (2) Installed Inside Sealed Box

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Mobile Electronics Control Systems

3rd Party Evaluation of the PLS

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

• 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)

• 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.

• 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

28TW331 Platform Control Console

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PLS Modifications - Conclusion

• 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

• 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)

• 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.

33TW332 Platform Controls (New)