MIT-SCAN-T2 Operation Guide

MIT-SCAN-T2 Operation Guide The MIT SCAN-T2 Device - Overview The MIT (Magnetic Imaging Technology) Scan-T2 system (Figure 1) is a commercially availa...
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MIT-SCAN-T2 Operation Guide The MIT SCAN-T2 Device - Overview The MIT (Magnetic Imaging Technology) Scan-T2 system (Figure 1) is a commercially available equipment that uses magnetic tomography to detect locations of steel discs placed on the base prior to paving and hence interpret the constructed thickness of the pavement in question. The system consists of the following components. A. B. C.

A handheld Sensor Unit A battery charging system Magnetic zinc or aluminum coated steel reflector discs.

Figure 1 The MIT-SCAN-T2 sensor unit

Figure 2 Stainless steel reflector discs of 70 mm and 300 mm diameter The device can measure pavement thicknesses up to 460 mm (18 inches) with a stated accuracy of ±(0.5% of measured thickness in mm + 1 mm) which is as small as ±3.3 mm for the maximum thickness of 460 mm (18 inches).

Principle of Operation The MIT-SCAN-T2 relies on a field generating unit that emits a weak, pulsating magnetic signal and a sensor unit that detects a transient magnetic response signal induced in the metal reflector discs placed on the base during construction. The principles of tomography are then used to determine the depths of the discs and therefore thickness of pavement. The entire sequence of operation consists of three steps: 1. Secure placement of metal reflector discs on the base layer surface prior to placement of the surface layer whose thickness is to be measured 2. Construction of the surface layer whose thickness is to be measured 3. Using the MIT-SCAN-T2 to locate the metal reflector discs and obtain the layer thickness.

Steps of Operation 1. Placement of metal reflector discs a. Select the metal reflector disc to be placed based on the designed pavement thickness as per Table 1 below. Table 1 Disc selection guide Design Pavement Thickness 0 to 180 mm (0 to 7.1 in) 181 to 450 mm (7.1 to 17.7 in)

Disc Diameter 70 mm (2.7 in) 300 mm (11.8 in)

b. Select and mark random, but representative, locations throughout the section to be paved where the discs will be placed. These sites should be properly documented as to be easily located after the surface placement. c. Care should be taken to ensure that the disc locations selected are far enough away from other metallic and magnetic objects, as so stated in Table 2 and Figure 3, as not to influence the scanning/detection that will be undertaken after placement of the pavement. d. Additionally, other requirements such as maneuvering space further restrict the area under the proposed slab where the reflector discs can be placed. Consider the example of a 12 ft. x 12 ft. JPCP slab shown in Figure 4. e. Place the reflector discs at the selected locations and secure them using PK nails at least 50 mm (2 in) long for granular bases. A nail gun may be used when securing the discs to CTB or asphalt layers (Figure 5). The length of nail gun anchors and the shot load may vary based on the hardness of the base layer. f. Make sure that a mark is placed in the surrounding area to facilitate easy location of the discs after the surface layer has been constructed (Figure 6). Table 2 Clearance distances for operation of MIT-SCAN-T2 sensor unit Interference type Parked cars Moving traffic Other reflector discs (edge-to-edge) Construction equipment Guardrails and other safety features

Minimum clearance from sensor unit 2 m (6.6 ft) 1 m (3.3 ft) 0.5 m (1.7 ft) 4 m (13 ft) 1 m (3.3 ft)

Reflector disc 0.5 m (1.7 ft) Other reflector discs, keys, coins, etc. 1 m (3.3 ft) Moving traffic, safety features 2 m (6.6 ft) Parked cars 4 m (6.6 ft) Construction equipment, heavy machinery Figure 3 Clearance distances required during measurement

Min. 520 mm (1.7 ft)

Dowel bars Tie bars Min. 520 mm (1.7 ft) ~ 1,525 mm (5 ft)

Place reflector disc in shaded area. Recommended placement area is lightly shaded

Proposed concrete slab 12 ft x 12 ft

~ 1,525 mm (5 ft)

Figure 4 Example of reflector disc placement location selection for a 12ft x 12ft JPCP slab

Figure 5 Securing a 300 mm metal reflector disc using a nail gun on ATB on CA-210

Figure 6 Place an identifying mark on the shoulder or other features to help locate the disc after paving

2. Thickness measurement a. Once the pavement layer, whose thickness is to be measured, has been constructed, scanning may be commenced. b. Assemble the MIT-SCAN-T2 device by sliding the ‘slad’ into the slot of the handle unit containing the keypad-display of the sensor unit as shown in Figure 7. The handle can slide in only one way.

Slad Slot

Close

Open

Figure 7 Assembling the MIT-SCAN-T2 for operation c. Turn on the unit by pressing and holding the ‘Search’ (button below the holding handle) and ‘Measure’ (button on top of the holding handle) buttons simultaneously.

d. Check the battery condition and insure an adequate charge by pressing the‘C’ key followed by ‘B’ key on the keypad. Press the ‘F’ key twice to return to the main menu. Charge the battery as necessary.

e. Warm up the sensors by running the ‘search function’ (press and hold the ‘Search’ button on the holding handle for about 5 minutes). This is an important step to ensure the accuracy of measurement. Note that in the event of ‘no activity’ the unit will turn itself off after 1 minute. f. When the unit is ready, input the type of reflector disc used by pressing the ‘A’ key followed by ‘D’ key on the keypad. Scroll down and select the calibration file as per Table 3. Table 3 Selection of calibration file for measurement Diameter of Stainless Steel Disc Used Calibration File to be Selected 70 mm (2.7 in) MIT-R07 300 mm (11.8 in) MIT-R30 g. Press the ‘F’ key to return to the main menu. If desired, input the site information by pressing the ‘B’ key and follow the menus. This is not required for measurements. The unit is now ready to be used to locate discs. h. Locate the approximate position of the disc to be measured using the ‘Search’ function (press and hold the ‘Search’ button on the bottom of the holding handle while searching). i. Once the disc is located, place the sensor unit about 300 mm (12 in) away from the approximate location of the edge of the disc and start the measurement by pressing the ‘Measure’ button on top of the holding handle. The supplied earphone may be attached to the port on the handle to enable audible indication of the disc during any phase of the search or measurement operations. j. Guide the sensor unit on its wheels at a slow and steady rate over the disc for a distance of about 1.5 m (5 ft) until the unit ‘beeps’ to indicate that measurement is complete. During the measurement, the LCD display will show the strength of the signals detected by each of the four sensors of the sensor unit. If the earphone was connected, a high pitched sound will indicate a higher strength signal being detected

k. Save the data to memory when prompted or repeat the measurement if desired.

l. To verify the measurement, a repeat measurement may be carried out on the disc in a different direction from the one used before. This is a recommended step. m. Before proceeding to the next disc, press the ‘A’ key to increment (record) the station number or the number ‘9’ to decrement (remove) the station number to be recorded in the data files. n. When all measurements are complete, turn off the unit by pressing the ‘E’ key from most menu screens. 3. Transferring the data to a PC a. On a PC, install the SCAN-T software provided on the supplied CD-ROM. b. Connect the MIT-SCAN-T2 unit to the PC using the supplied data cable and then turn on the unit. c. On the bottom left corner of the software window, select the port on the computer to which the unit is connected and press the button labeled ‘Daten-Trasfer’. All data stored in the memory of the MIT-SCAN-T2 is imported in the window. d. Click on the button labeled ‘Datei schreiben’ to store the imported data into a file on the PC.

e. Provide a name and location for the data file when prompted, then click on the button labeled ‘Beenden’ on the bottom right corner of the software window to exit the program.

Figure 8 The SCAN-T software window on a PC before importing data from the sensor unit 4. Interpreting and analysis the imported data a. Open the data file created by the SCAN-T software in Microsoft Excel. The data is stored in the format shown in

b. Table 4 and Figure 9. Note that Columns 7 and 8 are general identification parameters as input by the operator during measurement. These are not required to be input and may show default values if not input by the operator.

Column 1 Serial No.

Table 4 Format of data stored in file by SCAN-T software Column Column Column Column Column Column 2 3 4 5 6 7 Date Time Station Measure Reflector Layer d depth disc type identifier (mm)

Column 8 Side identifier

Figure 9 The output of SCAN-T software opened in Microsoft Excel The data is now available for analysis as required.