CABLE TENSION MONITORING
CABLE TENSION MONITORING
WHAT WEARS OUT/DESTROYS CABLE

Fatigue
 Tight-loose-tight-loose
ie tension cycles
 Bending around sheaves - forth and back
 Vibration

Abrasion
 On
the ground
 On and off the drum
 Recoil on the drum
WHAT WEARS OUT/DESTROYS CABLE

Burning it
 On
the ground/rocks
 Over logs
 Line wrap

Abuse
 Kinks
 Grapples
 Neglect
WHAT WEARS OUT/DESTROYS CABLE
But out of all the ways that we can damage
 or destroy a piece of wire rope, what is the
 most common cause of the destruction of
 wire rope in logging?

TENSION
We shorten the life of and destroy more
cables and especially skylines by over
 loading or over tensioning them.

HOW DOES A CABLE REACT TO TENSION
_________SWL_________EL________CBS
1/3
2/3
3/3
0

SWL = Safe Working Load (Design Load)
 EL = Elastic Load (Damage Starts)
 CBS = Catalog Breaking Strength

CUMULATIVE DAMAGE
Every time you go over the Elastic Limit of a
cable you do damage, you weaken it and
reduce it’s strength.
 It will now break at something less than the
original breaking strength.

HOW DO WE MONITOR TENSION

Historically
 By
the seat of the pants (pucker factor)
 By Design (Calculate payloads, engineering)
 By Visual indicators ( belly in the line, vibration)
 By Audible Indicators ( hear the cable talking)
 Mechanical…. Brake settings
 By Breaking cable
SEAT OF THE PANTS
When does it kick in?
 What is it telling us?

 “If
I pull any harder, something is going to break”
Where are we in the strength profile of the
cable when this occurs?
 Probably somewhere between the elastic limit
and the breaking tension.

BY DESIGN/ENGINEERING
How many do payload analysis during
planning?
 How many give this to the logger?
 How many loggers/rigging slingers can tell you
what the weight of a turn is?
 Great planning tool
 Difficult to implement on the ground

VISUAL INDICATORS

Belly in the cable/deflection
 Hard

to visualize on the ground
Vibration
 Frequency
of vibration is a function of length,
weight (lbs/ft) , and tension
 Good for comparing tension in guylines
 Not very useful in determining absolute tension
AUDIBLE

When does the cable start talking to us?
Just before it breaks, so we are in the red zone
between the elastic limit and breaking.
Already doing damage
MECHANICAL
We can set the brakes to slip.
 How do we know where to set them?
 Some machines have a chart the helps to
determine the air pressure setting.
 These are based on an engineering calculation,
not actually measurements.
 Based on the original brake lining and ideal
conditions of humidity and temp.

ELECTRONICALLY
System are available to monitor cable tension
through the use of load cells and digital read
outs.
TENSION MONITORING SYSTEMS
How do they work?
 Replace the pin in the sheave of the line you
want to monitor.

TENSION MONITORING SYSTEM

Replace with a pin that has one or two load
cells built into the pin.
TENSION MONITORING SYSTEM
This system puts the tension of the skyline in
front of the operator at all times.
 Can give the crew feedback as to what is going
on.
 Avoids overloading the system and breaking
…………stuff.
 Avoids underloading the system and losing
productivity.

TENSION MONITORING SYSTEMS
Two “Warning” lights and a buzzer.
 Amber light is set, usually at SWL or 1/3 of CBS
 Red Light is set at 50% of CBS
 Buzzer goes off when red light comes on.

TENSION MONITORING SYSTEMS
TENSION MONITORING SYSTEM
Most yarders require a pin with two load cells
set at 90 degrees to each other because the
angle of the skyline over the pin is constantly
changing. (Dual axis pin)
 There are a few yarders (071, 171, 172 Madills)
that have a deflector sheave where the angle of
the cable over the pin doesn’t change and
those only require one load cell. (single axis
pin)

TENSION MONITORING SYSTEM
Crew gets immediate feed back concerning
under and over loading.
 They quickly get a sense of what is a “good”
turn.
 The yarder operator can set the skyline brake to
slip at a tension that is less than what will
damage the skyline.

TENSION MONITORING SYSTEM
Encourages crew to chase deflection.
 Give real data, as opposed to a “feel”
 Protects your investment in time, cable,
carriages, yarder.
 At one time there was an insurer who was
willing to give a discount.
 Eliminates the need for “fuse links” in over
spec’d skylines.

FUSE LINKS
Yarder is designed for the breaking strength of
the skyline, mainline, and haulback that it is
plated for.
 As long as your system stays under this load it
is legal and safe.
 50% of 1-1/8th PowerPac/double swaged is
approximately 83% of 1-1/8th EIPS.

TENSION MONITORING SYSTEM
Cost of tension monitoring system. $7000
 Cost of skyline ??
 Cost of carriage ??
 Cost of down time??
 Cost of lost production from under loading??

TENSION MONITORING SYSTEMS

Load sensing shackles are available for
monitoring guylines.
TENSION MONITORING SYSTEMS

These load sensing pins are being integrated
into tethering machines to control operations
??QUESTIONS??
 Brian
Tuor
bltuor@skyride.net
 509-894-4610
 www.cableloggingspecialist.com

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