"If tensile forces will be measured in addition to compressive forces, convex load application is naturally unsuitable. For tensile force transducers or force transducers that are suitable for tensile and compressive forces, the components that apply the force to the transducer are therefore screwed together with the transducer. Some force transducers, for example the Z4A or U2B, have an external thread on the top and an internal thread on the bottom. Force transducers of series U10M and U10S are fitted with internal threads on both connection sides. Internal threads are considerably more compact. This makes them suitable for force transducers that must be flat. In external threads the distance between the screw connection and SG installation is naturally greater, which has a positive effect on various metrological properties (hysteresis!). Force transducers for tensile and compressive loading with very high requirements for accuracy and reproducibility therefore generally have an external thread. An internal thread is only used on the non-critical side. For internal thread: For every bolted connection of a force transducer, sufficient surface pressure must be exerted on the force transducer by the nut.
There are two different ways to do this:
a. A bolted connection with application of force that is greater than the largest operating force
b. Mounting with suitable torque
Note that the torque required for mounting must never be applied through the transducer. If it is, the transducer may be destroyed. For force transducers with external thread: The component to be connected must at least be fixed in place by a locknut. This requirement is eliminated for purely static force measurements. The torques are specified in the operating manuals for the force transducers. ; The Z4A (right) is only locked on the internal thread. Locking with a nut is always required for the external thread of the U2B (left) HBM offers knuckle eyes for almost all transducers that are suitable for tensile and compressive forces. If force transducers are mounted using at least one knuckle eye, torsional moments are not applied to the transducer. If two knuckle eyes are used, bending moments and forces must not be applied to the force transducer at an angle. Use of two knuckle eyes for calibration of a U10M with a maximum capacity of 500 kN Knuckle eyes are normally not suitable for measuring dynamic forces because bearing play increases over time, which can lead to measurement errors. Furthermore, the frequency range within which knuckle eyes can be used is limited to about 10 Hz. For dynamic requirements we therefore recommend the use of pliable elements to apply forces."