ISO 6789-2:2017 pdf download – Assembly tools for screws and nuts —Hand torque tools — Part 2: Requirements for calibration and determination of measurement uncertainty.
The mean value of the measurement series Is calculated using Formula L4 with n = 10.
6.2.3.3 Variation due to geometric effects of the interface between the output drive of the torque tool and the calibration system, b
Hexagon and square drive interfaces between the output drive of the torque tool and the calibration system have an Influence since they can potentially run out of true and if not used In the same orientation each time, they can cause variation of reading.
The interface between the output drive of the torque tool and the calibration system shall be identified and documented.
The Following method Is described for the determination of the variation due to the drive interface. This value may be determined statistically for a sufficient number of specimens (at least 10) of a model of tool and its determination does not need to be repeated each time for future calibrations olthis model.
The tool shall be positioned on the calibration system according to ISO 6789-1:2017,6.5, and subjected to live preloadings at the lower limit value of the measurement range. Tm10.
The torqLle tool is removed from the calibration system and the drive interface is rotated by 60°
(hexagonal drive output) or 900 (square drive output). Ten measurements are recorded for each of at
least four positions distributed evenly over 3600. at the lower limit value of the measurement range.
Tmin, without changing the load application point.
The variation due to the Influence of the drive Interface Is calculated using Eormulaj6j:
The mean value of the measurement series is calculated using Furmulat4) with n 10.
6.2.4 Variation due to the variation of the force loading point, b1
Most torque wrenches have some variation in torque observed depending on the exact force loading point on the handle. This does apply to both indicating and setting wrenches, but not to torque screwdrivers of either type. For torque screwdrivers, the value of b1 shall be set to zero.
Where the loading point is not marked on the torque tool and no manufacturer information is available. the dinwnsion from the axis of rotation to the loading point used shall be documented.
The following method is described for the determination of the force loading point variation, b1. This value may be determined statistically for a sufficient number of specimens (at least 10) of a model of tool and its determination does not need to be repeated each time for future calibrations of this model.
The tool shall be positioned on the calibration system according to ISO 6789-1:2017, 6.5, and subjected to five preloadings at the lower limit value of the measurement range, Tm10.
Ten measurements are then recorded for each of two positions with changed force loading point, at the lower limit value of the measurement range, Tm. The two force loading points shall be 10mm on either side of the centre of the hand hold position or the marked loading point.
8 Calibration certificate
Calibration certificates in accordance with this document shall comply with ISO/IEC 17025 and contain at least the following additional information:
a) statement that it is a certificate of calibration En accordance with this document;
b) identification (type and serial number) of the torque tool;
c) where an interchangeable element has been used with the tool, the effective length or dimension of that interchangeable element shall be recorded;
d) specified torque range or fixed torque value of the torque tool;
e) identification (type and serial number) of the measurement device where the calibration has not been performed by a laboratory meeting the requirements of ISO/IEC 17025;
1) direction(s) of operation;
g) all values recorded during calibration (see ISO 6789.1:2017.6.5);
h) for all tools except setting tools Type II Class B, C, E and F. the mean value, X,., at each calibration point;
I) for setting tools Type II Class B.C.E and F, the nominal torque and mean value, Xr;
fl relative expanded uncertainty of the torque tool. W, for the mean value at each calibration point; k relative measurement uncertainty interval, W’, at each calibration point.