What are the differences between Loadshackles and dynamometers?

Why would you choose one over the other?

Recommended calibration frequency

Getting the right tool for the job is essential.

Below we answer the most common questions on load monitoring

What are the differences between Loadshackles and dynamometers?

Simply we could summarise that “Loadlinks are for load measurement and loadshackles are for load monitoring”. In more detail, what does that mean?

Below are some simple criteria to evaluate both options and help you choose the right lifting load cell for your application. At Elevate we use the terms ‘loadlink’, ‘dynamometer’ and even ‘load indicating device’ (LID) interchangeably. They refer to the Straighpoint, specific name, the generic term and also the term used by ASME B30.26-2010. For the user there is little or no difference between each.

How they work?

First a bit about how they work which will help us understand accuracy.

Loadshackles

Load shackles work in shear. During manufacturing SP remove the pin of a standard bow shackle, bore a hole down the middle and bond strain gauges through the centre of the pin. Now, the shackle pin has become a loadpin.

Those strain gauges are aligned with two shear grooves that are visible from the outside of the pin. The groove depth is precisely calculated in terms of position and depth to allow the best loadpin performance but stay within our strength and safety guidelines. Advanced finite element analysis (FEA) software is used to model and prove our calculations.

The area between those grooves is the ‘load area’. When load is applied a shear force occurs across those grooves. This shearing effect is measured by the strain gauges which, once the load pin has been calibrated is translated into an actual force or weight reading for the user.

Loadlinks/Dynamometers

The original loadlink plus

Loadlinks work in tension. Strain gauges are bonded to the body of our aluminium load cells. The process of bonding the strain gauges to the load cell body that is flexing under load is similar to load shackles, but in this case the strain gauges are flexing directly in line with the pull on the load cell, so straight line and in tension.

This direct tension force on the body of the load cell while under load gives us a very clear, linear signal from the strain gauges. This is what gives load links superior accuracy of 0.3% of applied load vs load shackles at +/- 1%.

To achieve the best accuracy with a load pin it is essential to use the full ‘load area’ as described above. You will notice that Straightpoint Wireless load shackles use a bobbin or collar to achieve this

Quick guide comparison loadlinks v shackles

Advantages of loadshackles

  • Limited headroom
  • A loadlink consists of a top and bottom shackle in addition to the height of the loadlink body itself.
  • As a result a load shackle typically uses around 1/3 the headroom of a loadlink.

Handling

  • For those who do mobile testing and carry around load cells with them a loadshackle gives you a one-piece measuring device and especially for heavier capacities this may offer easier handling.

Familiarity and ruggedness

  • Riggers like load shackles. They are familiar with size, weight and working load limit (WLL) of each component.

Simple swap to load monitoring

  • In a rigging setup it is easy to swap standard shackles for wireless loadshackles for a simple load monitoring solution. No change in headroom or configuration.

Multi-point lift monitoring

  • Once loadshackles are in place the banksman leading the lift has visibility of the individual load on each shackle as well as the total load from one display. It allows them to lead the lift, giving them confidence and control for heavy lifts and when moving bulky or out-of-gauge cargoes.

Advantages of loadlinks

  • Accuracy
  • A loadlink (+/- 0.3% of applied load) is around 3 times as accurate as a loadshackle (+/- 1% of applied load).
  • As such it is often chosen for weighing applications, precise force measurement or to calibrate other devices such as safe load indicators (SLI’s) on cranes.
  • Calibration interval should not exceed 12 months.

Frequency Of Calibration

The frequency of calibrations should be determined by the user of the load cell based on the following factors:

Frequency of use

  • Severity of service conditions
  • Nature of loading
  • Experience gain using other similar products in same application

Once these factors are established the user may then establish the calibration frequency:

  • Normal use – calibration every 12 months
  • Severe use – calibration monthly to quarterly
  • Special service – as recommended after consultation with SP engineering team and user.
  • A written record of the most recent periodic inspection shall include the condition of the load cell.

Periodic Inspection Recommendations

  • A complete inspection of the load cell shall be performed by a designated person trained to National Standards. The load cell shall be examined for conditions such as those listed below and a determination made as to whether they constitute a hazard.

Removal Criteria:

A load cell and its indicator, if applicable, shall be removed from service if damaged such as the following is visible and shall only be returned to service when approved by a qualified person:

  • Missing or illegible manufacturers name/trademark, or serial number, or rated load identification.
  • Indications of heat damage, including weld splatter or arc strikes.
  • Excessive pitting or corrosion.
  • Bent, twisted, distorted, stretched, elongated, cracked, or broken load-bearing components.
  • Excessive nicks or gouges.
  • Any reduction of the original or catalogue dimension at any point outside of the load-sensing zone.
  • Illegible display or readout.
  • Damaged of deformed component hardware.
  • Evidence of unauthorised welding.
  • Other conditions, including visible damage that cause doubt as to the continued use of the load cell.

For further information please contact our customer service team on 1300 437 842