Annex E
(Informative)

Load transmission to the load cell

This Annex is taken from the WELMEC 2.4 (European cooperation in legal metrology) Guide for Load Cells (Issue 2, published in August, 2001). With permission from WELMEC, the following portion of that Guide is reprinted here to provide guidelines for load cell evaluators, during load cell performance evaluations. Recognising the critical role that load cell receptors and load transmission devices play in accurate measurements, this Annex is intended to provide information regarding the effect of load transmission and recommendations for test design and procedure. The annex is informational and not to be considered required practice.

For some types of load cells, the kind of load transmission to the load cell has an influence on the measurements and therefore on the test results.

In this Annex the standard load transmission devices are listed.

The manufacturer should define whether the load cell works with all standard load transmission devices for the type of load cell or with selected standard load transmission devices or with a load cell specific load transmission devices.

This information may be considered for the load cell tests and may be marked on the certificate.

Standard load transmission devices

Tables E.1 and E.2 identify different types of LCs, (compression, tension, …​) and typical load cell mounting devices suitable for them. The symbols below classify the mobility between one point of contact on the load cell and its counterpart on the load receptor or mounting base.

Symbol	Description
	Movement possible normal to load axis
	Movement possible normal to load axis, with reversing force (spring-back effect)
	Inclination possible
	Indicates auto-centring effect of the complete mounting assembly of one load cell

Remarks on the standard load transmission devices presented in Tables E.1 and E.2 :

All combinations of load cell and transmitting device shown in Tables E.1 and E.2 can also be utilised in a completely reversed manner.

The load transmission device is independent of the encapsulation, potting or housing which are shown in the examples.

1. Compression LCs (Table E.1, upper part)

   • The load transmissions 1 to 8 are presented for canister type LCs. Instead, all load transmissions may be constructed for S-type or ring type load cells.

   • 6a shows a pendulum construction build as a complete unit.

   • 6b and 6c show external pendulum rocker pins combined with ring-type LCs.

   • The bearings for all compression load cells may be installed either below or above the LC.

2. Tension LCs (Table E.1, lower part)

   • The load transmissions 1 and 2 are presented for canister type LCs. Alternatively, both load transmissions may be used for S-type LCs.

3. Beam LCs (Table E.2, upper part)

   • The drawings present double bending and shear beams, as well as plastic potted and encapsulated constructions; all these constructions may be combined with either of the load transmissions 1 to 10.

   • The direction of loading, which is given by the manufacturer, has to be observed.

4. Single point LCs (Table E.2, middle part)

   • The load transmissions 1 to 10 for the beam LCs may be applied to all single point LCs.

   • The direction of loading, which is given by the manufacturer, has to be observed.

5. Double bending beam LCs (Table E.2, lower part)

   • The table shows examples of common constructions. Variations are possible provided the constructions allow enough horizontal flexibility between both ends.

   • The direction of loading, provided by the manufacturer, has to be observed.

The single bending beams had been exempted for general acceptance, because very small displacements of the “force transducing point” may lead to a change of span and linearity.