## 2. Effect of lateral forces, bending moments and torques

### a. Lateral forces

Lateral forces are forces that are applied **perpendicular to the measurement direction** of the transducer. German standard VDI/VDE2638 refers to a force that acts on a point in the application of the load.

These lateral forces are generated, for example, due to the intrinsic weight of attachments or because a load is applied at an angle. In general a lateral force always induces a **bending moment**, as the lateral force seldom acts at the height of strain gauge (SG) installations. Depending on the transverse sensitivity of the transducer, an **additional error** is generated. This error is well **under 1 %** of the force in the measurement direction (Fz) in most transducers if the lateral force is 10 % of Fz.

### b. Bending moments

Major **angle errors** in the application of force can** destroy **the transducer. A** bending moment often overlays the actual force **to be measured in practice.

The sketch above shows the situation. In addition to the force applied, the transducer is also loaded by a bending moment. A bending moment can be generated for instance by a** lateral force **at the point where the load is applied, for example due to the intrinsic weight of the parts that apply the force when the transducer is mounted horizontally.** Eccentric load application **can also generate a bending moment.

In this case the** torque **(which rotates clockwise in this sketch) relieves load on the transducer on the left side and loads it on the right side. **Rotation-symmetrical force transducers **(C2, U2B or U10M) are especially** insensitive **to bending moments because they compensate for bending moments by using multiple measuring points distributed over the circumference. Force transducers U10M and U10S have a** bending moment alignment **that reduces the influence of the bending moment to 0.01 %. This feature makes use of the fact that when the individual measuring points are combined, the result generated is always the mean value.

Independently of this, a large bending moment can destroy a force transducer. It is important to note, as mentioned above,** that the bending moment is not displayed**.

Bear in mind also that in many cases** bending moments bring with them a lateral force as well **which places additional load on the transducer. Note also the sketches below.

*The bending moment is generated on the left side because the load is applied eccentrically In this case there is no lateral force.*

A bending moment is generated on the** left side **because the intrinsic weight of the load application produces a** lever**. The distance from the center of gravity to the force transducer is the length of the lever. The weight is transformed into a force in this simple case. The moment is obtained by multiplying force times the lever arm. In addition, the weight force acts on the transducer as a** lateral force**. Both** parasitic influences **must be taken into consideration.

### c. Torques

Force transducers designed for** compressive and tensile loading **are supplied with** internal threads **(S9, S2, U10) or **threaded bolts **(U15, Z4, U2B). During installation of the transducer, it is important that these screwed connections are **locked in place **with a suitable torque. The** maximum torque** is frequently exceeded during mounting. Please note: Lock the screw connections in place so that no torque is applied through the transducer. The maximum torque must be kept in mind as well, since the transducer can be permanently destroyed if the limit value is exceeded.

During operation the torque is largely compensated for by the geometry of the transducer body and the installation location of the SG.

### d. Interaction of all moments, torques and lateral force

The** maximum load limits** must always be understood as indicating that the transducer, when loaded with the nominal (rated) force, can also be loaded with one of the parasitic influences. If several effects act simultaneously on the force transducer, then the following applies:

- Several components simultaneously at maximum permitted values will
** destroy **the transducer - If multiple influences act on the transducer simultaneously, these components can be
**added**. The total must not exceed 100 %. Example: 50 % of the permissible torque, 40 % of the permissible bending moment and 10 % of the permissible lateral force are utilized. Then the transducer is at maximum load, as the sum equals 100 %.