Torque Meter / Torque Tester

Just as forces can cause and influence linear movements, torques can trigger, amplify or reduce rotary movements.
A torque occurs when forces act on a pivoted body at a distance from the pivot point. If the forces act directly on the pivot point, no torque is generated. The magnitude of the torque results from the force multiplied by the distance of this force to the pivot point. This means that the torque acting on the pivot point can be increased by increasing either the force or its distance to the pivot point.

Torque	=	force	*	distance
M	=	F	*	s

If several forces are acting, they are added vectorially – i. e. taking into account the amount and direction.
This can be easily tested on a seesaw on the playground. If the two sides of the seesaw are unevenly loaded, in order to compensate either the side with the lower weight can be loaded additionally or on the other side the higher weight can be brought closer to the pivot point. As soon as the torques are equal, the seesaw is in balance. The up and down movement can then be triggered by slight weight shifts such as simple bending back and forth.

Torques play a major role in tightening screws. For safety-relevant screw connections, the torques to be observed for tightening the screws or nuts are determined depending on the type of screw and the type of connection. When changing tyres on a motor vehicle, for example, the wheel nuts must be tightened with the tightening torque specified for the respective wheels. Too high, but also too low tightening torques can cause the loosening of the wheels while driving. Also the installation of other components on the vehicles should always be carried out with the specified tightening torque. Torque spanners or impact wrenches can be used for installation, where the tightening torque to be achieved can be adjusted. These assembly tools with adjustment possibility are in a certain way also torque meters, but they do not display any measured values, but trigger a signal when a set limit value is reached. In order to determine whether they work correctly, these tools can be tested with another torque measuring device.

Torques are an important measurement variable for many components which are set into rotational motion according to plan or which are subject to torsional stress by static or dynamic loads. This applies to mechanical engineering and vehicle construction as well as to the construction and energy industry.

Torque meter for screw connections
For many screw connections, tightening torques are prescribed with which the screws or nuts must be tightened during assembly. This not only applies to connections of rotating parts, but also, for example, to the fixing of high-strength screw connections in steel construction. These screw connections are often carried out with the tools that signal acoustically and haptically when the preset torque is reached. These tools can be calibrated with another torque measuring instrument.

Torque measuring device in production monitoring
In production monitoring, torque meters can be used not only to monitor and control screw driving processes but also, for example, to determine the viscosity of materials. The thicker a material is, the higher the viscosity and the torque, which must be applied to mix the material by stirring, are.

Torque meters in dynamometers
Torques are often measured and evaluated during the development and also during later inspections of motors, drive shafts, gearboxes and brakes in order to find the ways to increase mechanical performance and improve efficiency.

Torque meters for calibration tasks
Impact spanners, torque spanners and other tools that apply torque to the components can be checked regularly with a torque meter to ensure that the screw connections are tightened to the correct value.

Torque meter for screw caps
On the one hand, the fact that the torque with the screw caps are fixed on the containers, is intended to prevent the contents from leaking or spoiling. On the other hand, the threads must not be destroyed and the cap should not be too difficult to loosen.

Designs of the torque measuring device
Torque meters are available as hand-held devices for mobile use, as table-top units or for fixed installation in test benches or production lines. The sensor for measurement can either be built into the display unit or connected as an external sensor to the display and control unit via a cable. The torque meters with external sensor also allow measurements in places that are difficult to access.

Measuring range, overload protection and resolution of the torque meter
The measuring range should always be selected according to the torques to be tested. If the applied torque exceeds the measuring range, the value can no longer be measured correctly and the sensor will be destroyed if the load is too high. Some torque meters have an overload protection for up to 50 percent of the maximum torque. This means that the torque meter with the measuring range of 100 Nm can measure torques up to 100 Nm and can take loads above 100 Nm up to 150 Nm without being damaged. If the torque measuring device with a very high measuring range is used for small torques, the possible display values are not as finely graded as in the device with a smaller measuring range. For example, the resolution within a device series with the sensor for 10 Nm maximum load is 0.01 Nm and when using the sensor for 100 Nm maximum load, the display can only be shown in 0.1 Nm steps.

Measuring accuracy in the torque meter
For the assessment of the measuring accuracy it is important to pay attention to whether the values given in percent refer to the measured value or to the measuring range. A measurement uncertainty of 0.5 percent of the measuring range at 10 Nm means a possible deviation of 0.05 Nm, for a sensor with 100 Nm maximum load, though a 10-fold – 0.5 Nm.

Here is an example of a measured value of 6.20 Nm which was measured with two different devices:
In the tachometer with 100 Nm measuring range, the applied torque can be between 5.7 and 6.7 Nm at this measured value.
The tachometer with a 10 Nm measuring range may only display this value if the torques between 6.15 Nm and 6.25 Nm are applied.

Measuring rates
The measuring rate indicates how many measured values can be recorded by the torque measuring device within a certain time. No measuring rate can be selected in a very simple torque meter. The devices that are to be used for detailed recording of the torque curve, for example in engines, can be set to measuring rates of up to 1,000 measurements per second if required.

Storage of measured values and interfaces in the torque measuring device
In some applications, the tachometer must be used to record many values in a short time, which are required for later evaluation. The evaluation is made easier if the torque meter has a large internal memory and an interface for data transfer such as RS-232 or USB. Some devices also offer storage options on removable media such as MicroSD cards. Torque meters can also be equipped with an alarm output.

Evaluation software for torque meters
Project-related storage and evaluation of the measured values can be facilitated by the software that imports the values recorded by the torque measuring device. Some torque meters are delivered with the evaluation software as standard. After the measured values have been transferred to this software, the relevant values can usually be retrieved from the graphical representation of the torque curve quicker than from the tables. Previously defined lower and upper limit values are marked in the diagram as horizontal lines of different colours, so that they can be easily recognized if they are exceeded or the values fall down. Below the graph you can see, among other things, the number of measurements as well as the smallest and the largest measured value.