ASTM E1079-16,Standard Practice for Calibration of Transmission Densitometers.
ASTM E1079-16 covers the calibration of transmission densitometers used to perform radiographic film density measurements (see Note 1).
5. Apparatus
5.1 Apparatus should consist of the following:
5.1.1 A calbrated step tablet covering the density rangeused in production radiographs shall be used. The step tablet may be a NIST X-ray Step Tablet,or alternately a step tablet from another supplier that is traceable to the NIST steptablet in the range provided by NIST certification. The steptablet shall have at least five step densities, which cover the density range that is used for production radiographs. A calibration certificate shall be provided with the step tablet indicating the tablet ID and recorded values for each step density.
6. Calibration
6. 1 Full-scale linearity calibration should be performed at least every 90 days during use as follows:
6.1.1 Use the manufacturer’s recommended warm-up time to stabilize circuitry before starting the calibration procedure or the periodic verification checks described in Section 7. Adjust the “0” reading of the densitometer after the warm-up period.