Measuring Torque: Guide, Methods, and Accuracy
Measuring torque means precisely capturing the rotational effect of a force about an axis and converting it into a reproducible measured value. Whether in quality assurance, on test benches, or in development: a correct torque measurement determines process reliability and product quality. This guide shows you step by step how to measure torque correctly, how to calculate it, which sources of error to avoid, and how to achieve high measurement accuracy. This practical expertise comes directly from ETH-messtechnik's in-house development and manufacturing.
Quick answer: Torque is measured by having a sensor capture the minimal deformation of a measuring body caused by the rotational force and convert it into a proportional electrical signal in newton meters (Nm).
Calculating Torque: The Basis of Every Measurement
Torque describes the rotational effect of a force acting at a distance from an axis of rotation. Physically, it is the product of force and lever arm:
formula: M = F · r
Here, M is the torque in newton meters (Nm), F is the applied force in newtons (N), and r is the perpendicular distance to the axis of rotation in meters (m).
Two calculation examples:
A force of 10 N acts perpendicularly on a lever at a distance of 0.5 m: M = 10 N · 0.5 m = 5 Nm.
- A wrench 0.3 m long, operated with 200 N: M = 200 N · 0.3 m = 60 Nm.
Since torque cannot be read directly on real components, it is determined indirectly via a physical effect, usually through the torsional deformation of a measuring body. This is precisely where metrological measurement comes into play.
Quick Overview: What Do You Use to Measure Torque?
Torque measurement uses sensors that convert torsional deformation into an electrical signal. The most common are sensors with strain gauges (SG); in addition, there are piezoelectric and magnetic methods. Which design (static or rotating) and which measuring principle is optimal for your application depends on the type of rotation, accuracy requirements, and dynamics.
To learn in detail which sensor types and measuring principles are available, see our overview page for torque sensors. This guide focuses on the correct measurement process.
Measuring Torque Correctly: Step-by-Step Guide
A reliable torque measurement follows a clear sequence. These six steps ensure reproducible results.
- Step 1: Define the measurement task. First, clarify what is to be measured: a static reaction torque or the torque on a rotating shaft? What measuring range (in Nm) is expected, and what accuracy is required? Also check whether additional measured variables such as rotational speed or angle of rotation need to be captured, and how high the rotational speed is in rotating applications.
- Step 2: Select the appropriate sensor. Choose a measuring range with sufficient overload reserve and a signal output that matches your evaluation setup (PLC, DAQ, display unit). The nominal value should match the expected load range in order to avoid over- and under-dimensioning. An overly coarse rating degrades resolution, while one that is too tight risks overload.
- Step 3: Install it mechanically correctly. Install the sensor into the force path without play and use suitable couplings to compensate for shaft misalignment and to keep out disruptive lateral, axial, and bending forces. Incorrect installation is the most common cause of inaccurate measured values.
- Step 4: Condition and connect the signal. Connect the sensor to the measuring amplifier or evaluation unit. Sensors with an integrated amplifier deliver an already conditioned, interference-proof signal and simplify the connection.
- Step 5: Set the zero point and measure. Perform a zero adjustment (tare) in the unloaded state. Then capture the measured values across the relevant load range, using a sufficiently high sampling rate for dynamic processes so that peak values are not lost.
- Step 6: Evaluate and document. Assess the results against your target values and document them. A validly calibrated sensor is the prerequisite for traceable results.
Measuring Statically or Dynamically: What Matters in the Process
Whether you measure statically or dynamically mainly changes the measurement process itself.
In static torque measurement, the shaft stands still or moves only over a limited angle of rotation. The measured value stabilizes, so very high precision can be achieved with steady signal averaging. What matters here is a cleanly set zero point and a torsion-free installation, since even small secondary forces can distort the result.
In dynamic torque measurement, the shaft rotates continuously, for example to capture power, efficiency, or load changes. Decisive for a correct result here are a sufficiently high sampling rate to capture rapid load peaks, as well as a torsionally stiff coupling. If the coupling is too soft, its torsional spring rate influences the resonances of the setup, and torsional vibrations arise that distort the measurement. In addition, soft couplings dampen the measured signal: torque peaks are compensated by elastic couplings and are therefore not represented correctly.
Practical tip: For highly dynamic measurements, the rule of thumb for coupling selection is "as torsionally stiff as possible," so that load peaks reach the signal undistorted.
Typical Sources of Error When Measuring Torque
Even highly accurate sensors deliver incorrect values if the measuring chain is not right. These sources of error occur most frequently in practice:
- Disruptive secondary forces: lateral, axial, and bending forces acting on the sensor without a suitable coupling.
- Shaft misalignment: alignment errors between drive and load that lead to deviations and mechanical stress.
- Incorrect dimensioning: a measuring range that is too large degrades resolution; one that is too small risks overload.
- Missing zero adjustment: an unset zero point distorts the entire measured value.
- Temperature influences: temperature changes without compensation affect the signal.
- Expired calibration: drift due to aging and use goes unnoticed.
- Sampling rate too low: with dynamic processes, peak values are not captured.
- Faulty signal connection: interference coupling with long, unshielded cables without a conditioned signal.
How to Achieve High Accuracy When Measuring
The accuracy of a torque measurement depends not only on the sensor but on the entire measuring chain. What is decisive is clean installation, a set zero point, appropriate sensor rating, and a valid, traceable calibration. Only a regularly calibrated sensor delivers traceable, documentable values.
How often calibration should be performed and what traceability means in detail is explained in the "Calibration and Traceability" section on our product page for torque sensors.
Measuring Torque with ETH-messtechnik: Our Service
As a manufacturer, we support you beyond the mere supply of sensors throughout the entire measurement task. This way, we ensure that you not only measure torque, but measure it correctly and reproducibly.
- Technical consulting by engineers: We work out the measurement task, design, and measuring range with you, directly from development, without a call center.
- We also develop and manufacture customer-specific special designs and complete torque testing facilities according to your needs and requirements.
- Customer-specific sensor design: measuring ranges from ±0.02 to 20,000 Nm, individual connections, flanges, and interfaces, as well as complete torque testing facilities.
- Calibration and recalibration: traceable calibration of your torque sensors with a calibration certificate.
- Support with integration: help with installation, coupling selection, and signal connection to PLC, DAQ, or evaluation unit.
- Made in Germany: development, production, and calibration from a single source in Gschwend.
Would you like to implement a torque measurement precisely? Talk to our engineers or request an individual quote. [
Frequently Asked Questions About Measuring Torque (FAQ)
How do you measure torque correctly?
Torque is measured with a sensor that captures the deformation of a measuring body caused by the rotational force and converts it into a signal in newton meters. Decisive for a correct result are a play-free installation with a suitable coupling, a set zero point, and a validly calibrated sensor.
How do you calculate torque?
Torque is calculated as the product of the applied force and the perpendicular lever arm to the axis of rotation: M = F · r. A force of 200 N on a lever of 0.3 m therefore produces 60 Nm.
In what unit is torque measured?
Torque is measured in newton meters (Nm).
What should be considered for static versus dynamic measuring?
For static measuring, what counts above all is a clean zero point and torsion-free installation. For dynamic measuring, a sufficiently high sampling rate and a torsionally stiff coupling are decisive in order to capture load peaks correctly and avoid torsional vibrations.
What are the most common errors when measuring torque?
The most common errors are disruptive secondary forces due to a missing coupling, shaft misalignment, an incorrectly dimensioned measuring range, a missing zero adjustment, and an expired calibration.
How do I achieve high measurement accuracy?
Through the right sensor design, play-free installation with a suitable coupling, a set zero point, and regular, traceable calibration. High-quality sensors can thus achieve an accuracy of up to 0.05% of full scale.
Why do I need a coupling to measure?
A coupling compensates for shaft misalignment and keeps disruptive lateral, axial, and bending forces away from the sensor. This prevents measurement errors and protects the sensor.