Torque measurement with strain gauge sensors converts the elastic deformation of a sensing element into a signal proportional to the applied torsional moment: it is the basis of digital torque meters for the inspection of tightening operations, closures and threaded couplings.
- Strain gauge transducer: deformation to electrical signal
- N·m units and submultiples: N·cm, kgf·cm, lb-in
- Peak / First Peak modes: capture of the peak value
- Accuracy down to ±0.3%: of reading or of full scale
- Memory and software: data acquisition and analysis
- Go/no-go comparator: pass/fail testing
- Certified calibration: NIST traceability
Torque (or torsional moment) is the product of a force and the arm at which it is applied, and is measured in newton meters (N·m) and its submultiples. Accurate measurement is essential wherever a tightening operation, a closure or a threaded coupling must meet a preset value: too low a torque does not guarantee the seal, too high a torque damages the component or prevents it from being opened.
In digital torque meters the torque is detected by a strain gauge transducer: the elastic deformation of the sensing element is converted into an electrical signal proportional to the applied torque. RODER offers this technology with the Shimpo cap torque meters (FG-7000TA, TNC, TNP).
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What torque is and how it is measured
Torque quantifies the action that tends to rotate a body about an axis. In industrial quality control the quantities of interest are typically the closing torque (tightening) and the opening torque (release) of caps, rings and threaded components. The measurement is made by applying the torque to the instrument, or by placing it between the tool and the workpiece, and reading the value on a digital display, with the option of storing the measurement, comparing it with tolerance thresholds and transferring it to a PC.
The strain gauge principle
The heart of the torque meter is a strain gauge torque transducer. Strain gauges applied to an elastic element detect its minute deformation when subjected to torsion: connected in a Wheatstone bridge configuration, they provide an electrical signal proportional to the applied torque, which the electronics convert, linearize and display. This principle guarantees high linearity, repeatability and long-term stability. On the FG-7000TA the transducer is external and is recognized automatically when connected to the display base; on the TNC and TNP bench models the sensor is built into the test structure.
Measuring mode
To suit different types of test, torque meters offer several operating modes. Track mode shows the reading in real time; Peak stores the maximum value reached during the test; First Peak records the first peak after a programmed decrease (useful for catching the opening “click” of a cap); modes such as Auto Peak, Auto First Peak and Double Peak (available on the TNC) automate and repeat the measurement. Preset mode, with programmable high and low thresholds, enables go/no-go pass/fail testing.
Accuracy, units and calibration
The accuracy of Shimpo torque meters is high: ±0.3% (FG-7000TA and TNC) or ±0.5% F.S. (TNP), with resolutions down to a thousandth of a N·m depending on the capacity. The selectable units of measurement include N·m, N·cm, kgf·cm and lb-in, according to the range. To ensure metrological traceability, the instruments can be supplied with a calibration certificate (NIST traceable as well). Correct periodic calibration is essential to keep the measurement valid for quality control purposes.
RODER torque meters
RODER distributes the Shimpo cap torque meters: the portable FG-7000TA with external transducer and adjustable clamp (1/5/10 N·m), the bench-top TNC up to 20 N·m with seven measuring modes and the bench-top TNP (50 N·cm to 10 N·m) with HI-GO-LO LED comparator. For the practical application to closure inspection see Inspection of cap tightening torque.
External or built-in transducer
There are two main architectures. In systems with an external transducer, such as the FG-7000TA, the torque sensor is separate from the display base and is recognized automatically on connection: this makes it quick to change sensor in order to cover different capacities and to place the cell where it is needed. In bench-top systems such as TNC and TNP the transducer is built into the test structure, with adjustable clamps that hold the specimen: a robust and repeatable solution, ideal for series testing in the laboratory or in production.
Measuring ranges, resolution and overload
The capacity of the instrument should be chosen according to the torque to be measured, working preferably in the upper part of the range in order to make the best use of the resolution. Shimpo torque meters cover from 50 N·cm up to 20 N·m depending on the model, with resolutions down to a thousandth of a N·m on the lower capacities. Overload protection (120 to 150% of full scale) protects the transducer from accidental stress, while the high sampling rate (up to 2000 Hz) makes it possible to capture fast transients accurately, such as the release click of a cap.
Data acquisition and software
Shimpo digital torque meters have internal memory (up to 1000 readings) and USB outputs and, on the models that provide it, RS-232, as well as a comparator output for integration into a quality system. The free software makes it possible to download the measurements, display them, plot their trend on a chart and calculate the statistical values (mean, maximum, minimum) directly in a spreadsheet, making documentation and traceability of the tests easier.
Frequently asked questions
Through a strain gauge transducer: strain gauges applied to an elastic element detect its deformation under torsion and, in a Wheatstone bridge configuration, provide a signal proportional to the torque, which the electronics display and store.
The closing torque is the torque needed to tighten the closure; the opening torque (or release torque) is the one needed to open it again. Both matter in guaranteeing the seal and the openability of the product.
Peak stores the maximum value of the test; First Peak records the first peak after a programmed decrease, useful for catching the opening click of a cap.
±0.3% (FG-7000TA and TNC) or ±0.5% F.S. (TNP), with selectable units N·m, N·cm, kgf·cm and lb-in and the option of a traceable calibration certificate.
Yes: they can be supplied with a calibration certificate, NIST traceable as well, and should be calibrated periodically to keep the measurement valid for quality control purposes.
Contacts & Information
Contact for general information : info@roder.it
Machine Vision Division of RODER : www.rodervision.com
RODER Instruments Division : www.innovacheck.com
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Note: Some images on this website have been intentionally generated using artificial intelligence (AI). This is because, for many applications and projects, photographs of the actual installation or system cannot be disclosed owing to confidentiality agreements, contractual clauses and non-disclosure agreements (NDAs).
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