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Load pin selection starts with the force at the proposed joint. On a sheave, that force is the resultant of the rope pulls; on a linkage, it depends on the mechanism position. Neither is automatically equal to the suspended load shown on a display. A useful design drawing therefore shows the loads and supports around the pin, not just the hole into which it must fit.
Load pin selection: calculate the local force first
Draw a free-body diagram of the sheave, clevis or linkage member. Mark the direction and magnitude of each force, the bearing contact regions and the reactions. Repeat the calculation for positions that change during operation. Include the supported parts' own weight and the relevant acceleration or braking conditions in the equipment assessment.
For an ideal sheave with two equal rope tensions T, the magnitude of their resultant is R = 2T cos(theta/2), where theta is the included angle between the two force arrows acting on the sheave. This is not necessarily the angle called the wrap angle on a machinery drawing. Define the arrows before using the equation.
| Included force angle | Resultant for T = 10 kN | Meaning of the example |
|---|---|---|
| 60 degrees | 17.32 kN | The resultant exceeds either individual rope tension. |
| 90 degrees | 14.14 kN | A change in geometry changes pin force without changing the assumed rope tension. |
| 120 degrees | 10.00 kN | Equality with one rope tension is specific to this ideal geometry, not a general rule. |
These are illustrative static calculations, excluding sheave weight, friction, unequal tensions and dynamic effects. They do not select a sensor capacity or approve lifting equipment. With unequal tensions, calculate the vector sum using the actual forces. A fixed conversion to hook load is unsuitable when the relationship changes with position or reeving unless the measurement system accounts for that change.
Decide whether the joint is a practical measurement point
Inspect the proposed load path before committing to a pin design. The supporting lugs and bushes must place the reactions where the sensor drawing expects them. Uncontrolled gaps, uneven contact or wear can alter the stress distribution. Nominal double-shear geometry alone is not enough to establish the measurement behaviour.
Show which member rotates and how the sensing orientation remains defined. Rotation of a sheave around a stationary pin is different from rotation of the pin itself. The retaining and orientation arrangement must suit the selected sensor, and the cable must remain clear of movement. Where the force direction changes materially, request confirmation that the proposed measurement arrangement can resolve it; do not assume a single output measures every direction.
Access also matters. A measurement point that cannot be inspected, unloaded or removed safely may be a poor choice even if it is compact. Include cable protection, connector access and the maintenance support arrangement in the initial drawing.
Compare METRAVON candidates by their own drawings
The MV-LC0005 reference gives a technical maximum of 5 t; confirm the offered rating and joint arrangement before selection. The MV-LC0006 covers 2-30 t with capacity-dependent dimensions. Both published bridge configurations list nominal 1 mV/V output and 10-12 VDC excitation. Shared electrical figures do not mean shared mounting geometry.
Choose the candidate from the calculated joint load and the space for the complete assembly, then obtain the exact capacity drawing. The published overload figure must not be substituted for normal measuring capacity or for verification of the lugs, bearings and retaining parts. Ask separately for evidence relevant to repeated loading and environmental exposure.
Specify what the instrument will report
Decide whether the required output is local pin force, rope tension or estimated suspended mass. Write down the conversion and its valid configurations. A PLC receiving a number without a clear definition cannot distinguish a genuine load change from a geometry change.
The bridge version needs suitable excitation and conditioning. Check the useful signal at the minimum decision load as well as the maximum. If the controller requires 4-20 mA, RS485 or Modbus RTU, identify the device that supplies that interface and verify its actual scaling and fault information. Those protocols are not implied by a nominal mV/V specification.
Before ordering, send the joint drawing, force calculations, operating positions, duty cycle, environment and readout requirements through METRAVON enquiries. State whether the measurement is advisory or used in a protective function. The latter needs a separate assessment of the complete function, not an assumption based on the sensor family.
Questions before releasing the joint drawing
Q1. Can a catalogue calibration replace an installed test?
It characterises the sensor under its calibration conditions. It does not establish the conversion through a different sheave or linkage. Agree an installed verification method using an appropriate reference and include the positions or configurations that affect that conversion.
Q2. What must be reviewed if a bush is replaced later?
Confirm that fit, contact length, alignment and clearance still match the accepted assembly. Compare the measurement with its earlier baseline and carry out the required re-verification before relying on it. A bush can affect force introduction even when the sensor and instrument are unchanged.
Summary
Locate the measuring point with a force diagram, then approve the pin and surrounding joint together. Keep the local force calculation separate from any displayed hook-load conversion. For an existing-machine retrofit, the replacement checks add the wear, wiring and historical calibration evidence needed before ordering.
