Choice of Dynamometer and Calibration
Choice of Measuring Range
The ring dynamometers are available with various methods in execution. Depending on the design the measurement range lasts from 50 N up to 200 kN.
The universal dynamometers are combination instruments for tensile or compressive forces. Drawbar eyes carry the tensile force whereas pressure seats take the compressive force. Alternative both forces can be connected via screw bolts. Other pure tensile and compression dynamometers are available as well.
The dynamometers are designed for specific ranges that may not be exceeded, not even temporarily by shock. Thus, if the measured force is not exactly known or you are not sure that the force is free of shocks, then the next strongest ring has to be chosen. For continuous (1 hour or longer) or permanent changing loads, only 80% of the maximum of measuring range may be used.
The calibration of the dynamometers with a maximum load up to 100 kN is done with force measuring equipment at Tiedemann. The accuracy of our calibration device is certified periodically by the measurement office of material testing of University Stuttgart. It is classified into the grade of quality 0.5 (highest possible accuracy) according to DIN 51220. Instruments with a higher load are calibrated by the University.
Therefore, it is traceable in all cases to the official comparison standard according to ISO 9000ff.
The determination of the calibration values (10 steady steps from zero to the maximum load) occurs according to the internal testing method following DIN 51301 (increasing and decreasing load and for indication for maximum load). The values are determined separately for each device and slightly corrected according to a compensation curve of minimal quadratic divergence (polynomial of degree 3). By this, incorrect values or irregularities in the dial indicator can be recognized before delivery. The calibration curve through the 10 given values is almost straight for tensile forces, but slightly curved for compressive force.
For analogue dynamometers a calibration table or a drawn scale for direct readable values is provided, for digital indicators the calibration is saved in the indicator. The indicator shows the values directly in N or kN.
The calibrated dynamometers must not be modified after delivery. If the drawbar eyes for tensile forces or the seats for compressive forces are turned or removed, the rigidity of the whole device will be changed. The calibration table and the maximum load are no longer valid.
Tensile forces must always be fed in with a bolt intended for the size of the device (dimension d). Thinner bolts will lead to deformation or breakage of the drawbar eye. As an alternative we offer special high strength steel shackles.
Compressive forces are preferably fed in by steel balls:
Repair and Calibration Services
According to DIN 51301, the testing certificate is valid for only 24 months. Therefore, it is recommended to recalibrate the device after this period.
Tiedemann will provide this calibration service. The performance of the dynamometer is examined before calibration. In case the dynamometer is from Tiedemann, damaged parts are replaced by new ones automatically. After recalibration, our company will deliver a practically new instrument.
If required Tiedemann would provide a test certificate showing the repair and calibration for dynamometers with a maximum load of 100 kN (necessary for quality control according ISO 9000ff.) Additionally and for dynamometers for higher forces, an official test certificate from the measurement office of material testing can be provided.