ANNEX(Mandatory Information)A1. CAL

ANNEX
(Mandatory Information)
A1. CALIBRATION OF APPARATUS


A1.1 Calibration tests shall be performed in accordance with the following procedures as applicable to the meter type being employed.
A1.2 Calibration of the Calibration Vessel—Determine accurately the weight of water, w, required to fill the calibration vessel, using a scale accurate to 0.1 % of the weight of the vessel filled with water. This step shall be performed for Type A and B meters.
A1.3 Calibration of the Measuring Bowl—Determine the weight of water, W, required to fill the measuring bowl, using a scale accurate to 0.1 % of the weight of the bowl filled with water. Slide a glass plate carefully over the flange of the bowl in a manner to ensure that the bowl is completely filled with water. A thin film of cup grease smeared on the flange of the
bowl will make a watertight joint between the glass plate and the top of the bowl. This step shall be performed for Type A and B meters.
A1.4 Effective Volume of the Calibration Vessel, R—The constant R represents the effective volume of the calibration vessel expressed as a percentage of the volume of the measur-ing bowl.
A1.4.1 For meter Types A, calculate R as follows (Note A1.1):
R = 0.98 w/W (A1.1)
where:
w = weight of water required to fill the calibration vessel, and
W = weight of water required to fill the measuring bowl.
NOTE A1.1—The factor 0.98 is used to correct for the reduction in the volume of air in the calibration vessel when it is compressed by a depth of water equal to the depth of the measuring bowl. This factor is approximately 0.98 for an 8-in. (203-mm) deep measuring bowl at sea level. Its value decreases to approximately 0.975 at 5000 ft (1524 m) above sea level and 0.970 at 13 000 ft (3962 m) above sea level. The value of this constant will decrease by about 0.01 for each 4-in. (102-mm) increase in bowl depth. The depth of the measuring bowl and atmospheric pressure do not affect the effective volume of the calibration vessel for meter Types B.
A1.4.2 For meter Types B calculate R as follows (Note A1.1):
R = w/W (A1.2)
A1.5 Determination of, or Check of, Allowance for Expan-sion Factor, D:
A1.5.1 For meter assemblies of Type A determine the expansion factor, D (Note A1.2) by filling the apparatus with water only (making certain that all entrapped air has been removed and the water level is exactly on the zero mark (Note A1.3) and applying an air pressure approximately equal to the operating pressure, P, determined by the calibration test described in A1.7. The amount the water column lowers will be the equivalent expansion factor, D, for that particular apparatus and pressure (Note A1.5).
NOTE A1.2—Although the bowl, cover, and clamping mechanism of the apparatus must of necessity be sturdily constructed so that it will be pressure-tight, the application of internal pressure will result in a small increase in volume. This expansion will not affect the test results because, with the procedure described in Sections 6 and 8, the amount of expansion is the same for the test for air in concrete as for the test for aggregate correction factor on combined fine and coarse aggregates, and is thereby automatically cancelled. However, it does enter into the calibration test to determine the air pressure to be used in testing fresh concrete.
NOTE A1.3—The water columns on some meters of Type-A design are marked with an initial water level and a zero mark, the difference between the two marks being the allowance for the expansion factor. This allowance should be checked in the same manner as for meters not so marked and in such a case, the expansion factor should be omitted in computing the calibration readings in A1.7.
NOTE A1.4—It will be sufficiently accurate for this purpose to use an approximate value for P determined by making a preliminary calibration test as described in A1.7 except that an approximate value for the calibration factor, K, should be used. For this test K = 0.98R which is the same as Eq A1.2 except that the expansion reading, D, as yet unknown, is assumed to be zero.
A1.5.2 For meters of Type B design, the allowance for the expansion factor, D, is included in the difference between the initial pressure indicated on the pressure gage and the zero percent mark on the air-content scale on the pressure gage. This allowance shall be checked by filling the apparatus with water (making certain that all entrapped air has been removed), pumping air into the air chamber until the gage hand is stabilized at the indicated initial pressure line, and then releasing the air to the measuring bowl (Note A1.5). If the initial pressure line is correctly positioned, the gage should read zero percent. The initial pressure line shall be adjusted if two or more determinations show the same variation from zero percent and the test repeated to check the adjusted initial pressure line.
NOTE A1.5—This procedure may be accomplished in conjunction with the calibration test