Work Item
ASTM WK86150
Revision of D445-21e2 Standard Test Method for Kinematic Viscosity of Transparent and Opaque Liquids (and Calculation of Dynamic Viscosity)
Rationale
At the December 2014 meeting of D02.07.A, Kevin Bly of ExxonMobil had proposed a revision to the definition of “Timing Devices” and the subsequent validation of these devices as defined in D445. The discussion centered on the methods requirement to periodically validate these timers. In particular, some users of automated viscometers were hung up on this requirement as no practical means existed for doing so. Some company QA auditors were forcing them to check the timers in their automated viscometers because of Annex A3. Originally, we had put this proposed revision on hold because D02.07.A was in the midst of putting forth several ballot items on D445 related to the large Grand Design Task Force.
Back when D445 originated (mid-1930’s) it was common for mechanically-wound spring stop watches to be used for viscosity measurement. Additionally, because manual glass viscometers were typically calibrated at one laboratory and used in another, the chances of using the same stop watch for both calibration and operation were very small. Additionally, manual viscometers, baths, and stopwatches need to all be verified because they could be interchangeably used in a laboratory. Therefore it makes good sense to have the timing device accuracy validated so as to reduce bias/error in the viscometer measurement.
In automated viscometers, digital microprocessor-controlled (relying on ultra-precise solid-state oscillators) timers are used which are inherently and significantly more accurate than the requirements stated in D445 Section 6.5. Additionally, the accuracy of such timers is embodied in the overall system calibration – performed using a series of CRM’s and where the same time base is used to both calibrate and operate the viscometer. Furthermore, none of the other automated viscosity methods under D02.07.A (D7042, D7279, D7945), where internal timers are employed as part of the measurement, require separate calibration/accuracy verifications.
Our proposed changes, developed over time with the assistance of the instrument manufacturers, leave the manual timer accuracy requirement unchanged. We are merely adding provisions for the digital (electronic) timers used in automated viscometers.
Work Item Status
Date Initiated: 04-28-2023
Technical Contact: C. Patrick Maggi
Item: 000
Ballot:
Status: