Commonwealth of Pennsylvania PA Test Method No. 418 Department of Transportation 5 Pages LABORATORY TESTING SECTION 1. SCOPE Method of Test for NUCLEAR GAUGE CALIBRATION and STANDARD COUNT VERIFICATION 1.1 This method of test covers the calibration and standard count verification of moisture/density nuclear gauges. 2. APPARATUS 2.1 Density Calibration 2.1.1 Nuclear gauge and accompanying accessories necessary for calibration. 2.1.2 Three Reference Calibration Blocks: Magnesium, Magnesium-Aluminum, and Aluminum. 2.2 Moisture Calibration 2.2.1 Nuclear gauge and accompanying accessories necessary for calibration. 2.2.2 One Reference Calibration Block for moisture. 2.3 Post Calibration Check 2.3.1 Nuclear gauge and accompanying accessories. 2.3.2 Magnesium, Magnesium-Aluminum, Aluminum, Granite, and Limestone calibration blocks. 3. GAUGE STANDARDIZATION PROCEDURE STANDARD COUNT 3.1 Prepare the Reference Calibration Standard Block by cleaning the block so that the block is free of dust and foreign matter. 3.2 Allow critical circuits to stabilize during a warm up period with the gauge in the safe position and the battery fully charged. Gauges require at least a five-minute warm up period. 3.3 Check the accuracy of the gauge timer by comparison with a stopwatch.
PTM No. 418 Page 2 3.3 If the gauge has not been standardized within the last three weeks, perform at least four new 4-minute standardization counts and enter into memory. Record the standard counts and check that they have been accurately entered into memory. If any of the new standard counts were not entered into memory, perform another standard count and enter into memory and record. A minimum of four new standard counts must be entered into memory. 3.4 Begin the standardization process by taking a standard count with the gauge on the reference standard block. The standardization shall take place at least 1.8 m (6 feet)6 feet from any building or structure, and a minimum of 9.1 m (30 feet)30 feet from any other radioactive source. The standardization shall take pplace reference standard block on any surface with a density of at least 1,601 kg/m 3 (100 lbs./cu ft.)100 pounds/cubic foot. Do not perform the standardization on truck beds, tailgates, etc. Begin the standardization process by taking a standard count with the gauge on the reference standard block. Place the source rod in the safe position and begin taking the four-minute standard count. The standard count passes if the count falls within the projected lower and upper limit density count range established for the specific date the standard count is performed. If there were no problems with the conditions under which the standard count was taken and the standard count passes, accept the new standard count into memory. If the standard count fails and there were no problems with the conditions under which the standard count was taken, do not accept the standard count. Perform at least four new 4-minute standardization counts and enter into memory. Record the standard counts and check that they have been accurately entered into memory. If any of the new standard counts were not entered into memory, perform another standard count and enter into memory and record. A minimum of four new standard counts must be entered into memory. Once the four new standard counts are in memory, perform an additional standard count. The additional standard count passes if the count falls within the projected lower and upper limit density count range established for the specific date the standard count is performed. If there were no problems with the conditions under which the standard count was taken and the standard count passes, accept the new standard count into memory. If the standard count does not pass, the gauge must be calibrated according to Section 4 of this PTM. Perform a second standard count. If the second standard count passes and there were no problems with the conditions under which the second standard count was taken, accept the new standard count and enter into memory. If the second standard count fails, erase all of the old standard counts. Four new sets of standard counts shall be taken and entered into memory. Record the standard counts. 3.5 If the gauge has not been standardized within the past three months, perform at least four new standardization checks. 3.63.5 If for any reason the measured density becomes suspect during the day's use, perform another standardization check.
4. GAUGE CALIBRATION PROCESS PTM No. 418 Page 3 4.1 Nuclear density gauges must be calibrated every twelve months. 4.14.2 Perform the statistical stability test (Stat Test) to validate the normal operation of the gauge, i.e. to check for erratic readings or readings that may indicate a problem with the gauge. Place the gauge on the reference standard block with the source rod in the safe position. Perform the Stat Test by using the Stat Test function on the gauge, taking twenty one minute counts. If the results of the Stat Test pass, print out the Stat Test results. If the results of the Stat Test fail, perform the Stat Test a second time. The ratio for the density and moisture results from the Stat Test shall range between 0.17 and 0.33. Values outside this range indicate a problem with the gauge. No further calibration under this procedure can occur if the values obtained by the Stat Test are outside the range of values mentioned above after the second Stat Test. If the results from the Stat Test fall within the range indicated but gauge readings continue to fluctuate from test to test, perform the Drift Test later in the procedure to determine the long-term drift of the gauge. Perform the Drift Test 3-4 hours after the Stat Test has been performed without turning the gage off in between the Stat and Drift Tests. 4.24.3 Place the gauge on the Magnesium block and put the source rod in the backscatter position. Take a 4-minute measurement. Record the count for both moisture and density. 4.34.4 With the gauge still on the Magnesium block align the source rod over the hole and adjust the source rod to 50 mm (2 )2-inch, 100 mm (4 )4-inch, 150 mm (6 )6-inch, 200 mm (8 )8-inch, and 250 mm (12 )12-inch depths and take 4-minute readings at each Record the density count for each 4.44.5 Place the gauge on the Magnesium/Aluminum block and align the source rod over the hole and take 4-minute readings at the backscatter position, at depths of 50 mm (2")2-inch, 100 mm (4")4-inch, 150 mm (6")6-inch, 200 mm (8")8-inch, and 250 mm (12 )12-inch. Record the density counts for each 4.54.6 Place the gauge on the Aluminum block and align the source rod over the hole and take 4-minute readings at the backscatter position, at depths of 50 mm (2")2-inch, 100 mm (4")4-inch, 150 mm (6")6-inch, 200 mm (8")8- inch, and 250 mm (12 )12-inch depths. Record the density counts for each 4.64.7 Place the gauge on the Magnesium/Poly block and with the gauge in the backscatter position. Take a 4-minute reading. Record the moisture count. 4.74.8 With the gauge still in the backscatter position and on the Magnesium/Poly block, place 4 shims under each corner of the gauge (simulates surface roughness) and take a 4-minute reading. Record the moisture count.
PTM No. 418 4.84.9 Without turning off the gauge from the time the Stat Test was taken, Page wait 4 3-4 hours after performing the Stat Test and start the Drift Test. Place the gauge on the reference standard block with the source rod in the safe position. Perform the Drift Test using the Drift Test function on the gauge by taking five 4 minute counts. If the Drift Test results pass, print out the Drift Test results. If the Drift Test results fail, perform the Drift Test a second time. If the Drift Test fails the second time, retake the Stat test. If the Stat test passes retake the Drift Test. If the Drift test fails again terminate the calibration process. 4.94.10Place all standard counts taken during the calibration process (Sections 4.2-4.7) into the Troxler software program to compute the individual calibration constants. 4.11 Type the individual calibration constants taken from the Troxler software program into the nuclear gauge under the calibration constants function. 4.104.12 Check the density of the Magnesium, Aluminum, and Magnesium/Aluminum Standard Blocks. All density values from the nuclear gauge after calibration shall be within 1 pound/cubic foot of the values on the side of the standard calibrated blocks.
This page left intentionally blank PTM No. 418 Page 5