ISO 21612-2021 pdf free download – Road vehicles — Crosstalk determination for multi-axis load cell.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and lEC maintain terminological databases for use in standardization at the following addresses:—ISO online browsing platform: available at https://www.iso.org/obp
—IEC Electropedia: available at http://www.electropedia.org/
3.1
crosstalk
undesired measured output of a transverse channel under defined load on the calibrated axisNote 1 to entry: Crosstalk is alternatively known as transverse or cross sensitivity.
4 Field of application
The described measurement procedure refers to any multi-axis load cell.
The crosstalk value helps to check the transducer’s performance and to identify sources of error duringthe calibration process. Therefore, it is recommended to determine the load cell’s crosstalk valueduring the calibration. It could be an indicator for a wrong test setup (loading point, fixtures, channelallocation, overloading, etc.).
5Crosstalk determination
5.1Test setup requirements and general preconditions
Prior to determination of crosstalk values, the conditions as follows need to be maintained.
.The load cell calibration test setup follows the common standards for vehicle crash transducers forforces and moments.
The crosstalk value is only considered for the traceable calibration range, which is defined in thecalibration standard by a minimum and a maximum.
Manufacturer’s calibration fixtures or calibration fixtures which have been validated in regard tothe manufacturer’s fixture characteristics are utilised. While using a fixture for moment loading,
consider the force range limits specified by the load cell manufacturer for the neutral axis in whichthe eccentric force is applied.Avoid applying forces exceeding the manufacturer’slimits, for examplein order to reach the desired moment with a shorter moment arm.Inappropriate calibration fixturesor insufficiently defined calibration ranges can cause extrapolation errors.
Thedata acquisition(DAQ) and filter settings of all recorded channels followthe common calibrationstandards.
All force and momentchannels are measured duringthe calibration process ofeach axis.Allchannelsare to be offset corrected in unloaded condition prior to the calibration test.
一 For force loading the force is applied within the neutral axes of the load cell.
Considering material settling for better comparability it is necessary to apply the loading processsequence given by the manufacturer of the calibration fixture.
In order to keep accuracy and to prevent misalignment it should be avoided to exert torque withinthe mounting plane between load cell and fixture.This load case should be last in the sequence. Itcan cause rotation of the load cell within the fixture.Thus subsequently exerted loads can be shiftedfrom the intended load axis.
5.2Additional test information
ldentify the calibration range for each axis ( if different from the nominal range of the load cell).Identify the order of the loading sequence, e.g.Fx→My →Mz→Fy→Fn→Mx.
ldentify the loading force direction at the moment of calibration for the correct polarity of thecrosstalk value.
ldentify the typical sensitivity for each axis in order to select the appropriate gain settings for themeasurement. If the sensitivity is known(e.g.value from a former calibration existing in the data base),the known value can be used for the test setup.
5.3 Crosstalk determination
For a loading in discrete steps or a continuous loading procedure, the output voltages in [mV/V] of alltransverse channels need to be recorded.
After the calibration of all axes, the current sensitivities of these channels are known and can be usedfor the calculation of the crosstalk as percentage of the transducer axis’ calibration range.
For the force and moment channels,the transverse channels’ output voltage recorded in [mV/V](see NOTE 1) shall be converted to the physical dimension force or moment by applying the currentsensitivity determined from the calibration test before.
NOTE1 For digital sensors signal conditioning and A/D conversion moved into the sensor. The transduceritself is strain gage based and delivers an mV/V output. Digital sensors are covered if the transition from [mV/V]to [LSB] is validated.ISO 21612 pdf download.