ASTM D6786 Test Method for Particle Count in Mineral Insulating Oil
ASTM D6786 Standard Test Method for Particle Count in Mineral Insulating Oil Using Automatic Optical Particle Counters
10. Calibration
10.1 Calibration of the instrument shall be with a NIST-traceable calibration fluid in accordance with ISO 11171.
10.2 Calibrate the instrument annually, unless experience justifies longer or shorter intervals.
10.3 Interim calibration checks should be made regularly by using a particle count standard fluid prepared using the procedures of ISO 11171. The check values should be within 10 % of the standard values.
11. Procedure
11.1 If necessary, wipe the outside of the sample bottle with a clean lint-free towel.
11.2 If other tests are to be run on the same sample, shake the sample bottle as described in 11.3 and transfer a specimen for particle count to another particle-clean bottle. Do this before running any other tests in order to avoid contamination.
11.3 Agitate the sample bottle vigorously for 30-60 s to redistribute particles, the length of time depending on the effectiveness of the method of agitation. Use hand shaking or a mechanical shaker. Do not use a magnetic stir bar or any other device that comes in contact with the oil. Do not use an ultrasonic bath as this may break up the large particles.
11.4 Allow a few seconds for gas bubbles to escape or apply vacuum to the bottle until bubbles dissipate.
11.5 Immediately analyze the sample with the automatic particle counter according to the manufacturer's operating instructions. Usually the analyzer is flushed with a specimen of the oil prior to testing. After the initial flush, 2-3 runs on each sample are recommended.
11.6 When particle count runs are finished, flush the instrument with particle-clean solvent or particle-clean oil in accordance with the instrument manufacturer's recommendations.
