29.11.2019
When carrying out fatigue tests, the connected signal conditioning electronics must also be calibrated. One way of doing such a calibration is described in the international standard ISO 4965-2. The first part of the standard deals with the associated test systems. At PTB, a calibration of such a measuring amplifier has now been performed for the first time for a customer. The calibration comprises a test with static and dynamic signals. The reference for the calibration is the dynamic bridge standard of PTB. It is particularly suited to this application as it can generate static and dynamic signals and can, thus, carry out all investigations with just one instrument and within a comparatively short period of time.
The standard ISO 4965-2 [1] describes a conformity assessment of the signal conditioning and display electronics during fatigue tests. The customer would like to offer such an accredited service. The characterization of the measuring amplifier required for this purpose was carried out at PTB.
The conformity assessment of the electronics is carried out in two parts, first with static and then with dynamic excitation signals. In the dynamic investigation, the measuring amplifier to be investigated is excited once with sinusoidal signals which are superimposed by static signals and then, additionally, with higher-frequency distortions which superimpose both the sinusoidal and the static signals. The sinusoidal, undistorted excitation signals are shown in Figure 1.
Fig. 1: Dynamic signals for amplifier calibration according to ISO 4965-2.
PTB’s dynamic bridge standard [2,3] is particularly suited to these investigations because it can generate static and dynamic signals. The signals with superimposed static and dynamic components which are required for the dynamic investigations can be programmed and generated directly. The measurement uncertainties of the dynamic bridge standard are clearly below the measurement uncertainties that are required by the standard.
For the conformity test, the signal recorded by the amplifier (under the same conditions as in the later tests) is compared with the generated signal form. The same software that is used later in the application is used to record the data. The limit values which must be complied with for the deviations are defined in the standard. As is usual with conformity tests, the result plus the expanded measurement uncertainty of the dynamic bridge standard must lie within the required limits of the standard [4].
The evaluation of the data was carried out independently of the recording (which can be undertaken in different ways, depending on the customer) with the GNU Octave open source software. Currently, the inclusion of these investigations according to ISO 4965-2 in the service catalogue of Department 1 is under preparation.
Literature:
[1] ISO/TC 164/SC 5, “ISO 4965-2:2012, Metallic Materials –Dynamic Force Calibration for Uni-axial Fatigue Testing – Part 2: Dynamic Calibration Device (DCD) instrumentation”, International Organization for Standardization, Genf, Schweiz, 2012.
[2] M. F. Beug, H. Moser, G. Ramm, Dynamic Bridge Standard for Strain Gauge Bridge Amplifier Calibration,in Proc. of 2012 Conference on Precision Electromagnetic Measurements (CPEM), pp. 568-569, Washington D.C., USA, 2012. 
DOI:10.1109/CPEM.2012.6251056
[3] L. Klaus, M. F. Beug, Th. Bruns, Setup for the Dynamic Calibration of Bridge Amplifiers from DC up to 10 kHz, ACTA IMEKO, 8:19, 2019,ISSN: 2221-870X, DOI:10.21014/acta_imeko.v8i1.657
[4] BIPM, IEC, IFCC, ILAC, ISO, IUPAC, IUPAP and OIML – Joint Committee for Guides in Metrology (JCGM), “Evaluation of measurement data — The role of measurement uncertainty in conformity assessment”, JCGM 106:2012, Sèvres, Frankreich, 2012
Contact:
Leonard Klaus, FB 1.7, AG 1.73, E-Mail: 
leonard.klaus(at)ptb.de