Instructions
The James Rebar Datascan™ is a rugged, precision instrument for inspection of reinforcing bars in concrete. It generates a magnetic field and measures changes in this field due to presence of magnetic material. The digital display records the distance from the bottom face of the probe to the bar. The meter in the probe enables quick and easy location of the bar or tendon.

The use of the instrument is not restricted to reinforcing bars; it can be used for detection of any magnetic material.

Typical applications include:

• location of tendons, tendon splices, and broken ends, etc., in prestressed concrete.
• location of pipes, conduit, flues, ducts, and manhole covers.

The unit also provides for automatic logging of depth in a plug-in module, and subsequent readout by a PC using an RS-232 interface. Since this unit measures something that cannot generally be seen, or otherwise conveniently measured, it is strongly recommended that use of the Datascan™ be practiced on simulated or known reinforced structures before using the instrument on site.

Location and measurement of individual, reasonably spaced rebars are straightforward.

However, when two or more parallel rebars lie within the field of the instrument, interpretation of the readings becomes more difficult. In extreme cases, depending on the geometry of the rebar system, it may only be possible to locate the center lines of the rebars. Then, an estimate of the depth or size can be made. This type of situation is often found in columns with heavy reinforcements.

NOTE: Probes are not interchangeable. Each probe is matched at the factory to the instrument.

TURN-ON PROCEDURE
1. Remove the instrument and probe from the carrying case. Plug in the probe connector.
2. Turn on the instrument by switching the on-off switch; allow about one minute for the battery output to stabilize.
3. Check battery voltage by depressing the BTY pushbutton.
OPERATING MODES
The unit has three operating modes:
TEST MODE. The unit comes on in the test mode where the reading of the internal, linear analog-to-digital converter is displayed. While in this mode the external memory used for logging readings can be accessed by way of the RS-232C interface.
COVER MODE. In the cover mode, the reading of A/D converter is translated into depth of cover for the selected bar or tendon size, and is displayed on the digital readout.
SIZE MODE. In this mode, the unit will accept two depth readings, with the second incremented by two inches using a spacer and will display an estimated diameter for the rebar.
ZERO. There are two pushbuttons; one on the probe and one on the panel of the instrument. Both perform the same function. To zero the unit, hold the probe so that it is at least 18” to 24” (45 to 60 cm) away from magnetic material.
METER ZERO. If the analog meter on the probe does not read zero, turn the zero adjustment knob on the probe to bring the pointer to zero – or just slightly above. If the meter is set below zero, an apparent insensitivity in meter indication will result.
DIGITAL DISPLAY ZERO. With the probe situated as above, press either of the zero buttons. This will make an entr into the internal computer of the ambient noise level and zero offset at the same time the zero pushbutton is depressed. This level will be automatically subtracted from succeeding readings, until button is pressed again, substituting a new reading.

The meter zone and the digital display zero do not affect one another; a zero error on the analog meter will have no effect on the accuracy of cover or size measurements.
COVER/SIZE. This pushbutton is alternate action and allows selection of either the cover or the size operating mode.
BATT. When this button is depressed, the digital display will show the battery voltage. A reading below 11.5 volts indicates need for battery recharge. Operating at a lower voltage may result in error.
E/M. This button is alternate action and allows either English (e) or metric (m) depth measurement selection. It does not affect bar diameter selection.
DIA. This allows for selection of diameter of bar or tendon for cover measurements. Successive depressions of this button will step you though the calibrated diameter ranges for English or metric rebars or the calibrated fractional ranges for tendons, depending on which has been selected.
STORE. There are two of these buttons, one on the probe and one on the instrument. Both perform the same function. If a memory module is installed, depressing either button will cause the cover reading on the digital display to be stored in the module, along with a sequence number: the first reading will be preceded by a 1, the second by a 2, etc. Sequence numbers are incremented automatically. If either button is pressed when a module is not installed, an error message will appear on the digital display. Otherwise, operation is not affected. In the Size Mode, pressing the Store pushbutton will command the unit to store the first reading for subsequent processing. Pressing the button a second time will command the unit to make a second reading, and based on a two inch increment in depth, to make an approximation of the bar diameter. See section on, “Estimation of Unknown Bar Diameter” for more information.
ENTER. This switch performs two functions depending on the operation mode. If it is depressed immediately after power-up, it will switch from the Test Mode to the Cover Mode and require that the unit be zeroed before continuing operation. If in the Cover Mode, it will switch to the Test Mode.
REBAR TENDON. This is an alternate action switch that allows selection of either type.
AUDIO. This too, is an alternate action switch that allows turning the audio output on or off.

BATTERY CHARGING
The rechargeable battery in the Datascan should not be totally discharged. 11.5 volts is the minimum voltage that the system should be allowed to reach. Turn off the Datascan when not in use. The battery system has three months of shelf life at 20° C. Store in a cool, dry place: recharge fully before use. Overcharged, totally discharged, or damaged batteries are not covered by manufacturer’s warranty.

The rebar Datascan is powered by a twelve volt, lead acid rechargeable battery. It will provide approximately 8 hours of operation between charges. The Datascan incorporates an external charger unit. This system will provide a full charge from a full discharge in 16 hours (overnight). To charge, first, plug in the cord with the phone plug on the charger to the phone jack on the rear of the Datascan. Then, plug in charger to the appropriate AC power source.

During charging, the charger becomes warm. This is normal, and no cause for concern. Overnight charging from full discharge is required to recover to full capacity. Avoid overcharge.

LOCATING POSITON OF REINFORCING BARS
Switch unit to the Test Mode by pressing the Enter pushbutton. Then zero the analog meter display and note the lowest number on the digital display. This number becomes the reference for that locality. Determining the location of primary and secondary reinforcing bars is accomplished by moving the probe along the surface of the concrete.

The needle of the meter in the probe will indicate a maximum deflection when the axis of the probe is parallel to, and directly over, the axis of a reinforcing bar, or group of bars.

The digital display will show a maximum count at the same time. For very small or very deep bars the digital display will exhibit greater sensitivity than the meter display, if passed very slowly over the area. Curves I, II, and III in Figure 2 indicate the meter deflection obtained with various distances between reinforcing bars, when probe is parallel to the bars. As noted above, the digital display will also show a maximum count in Test Mode. The variation in readings decreases as the number of bars increase and the distance between them is decreased. By observing the needle movement, the operator determines whether there is a single bar or several in the location.

MEASUREMENT OF CONCRETE COVER
To perform cover measurements with maximum reliability, digital zero must be set accurately, and checked frequently.
1. With the unit powered-up and zeroed, select cover measurements by pressing the Cover/Size button. Press the Dia button to select the bar diameter and the E/M button to select English or metric depth measurement display. If the exact diameter of the bar is unknown, a value may be assumed; any resulting error should be minimal.
2. Rezero the instrument. Then place the probe on the concrete at the chosen location. Align the probe so that the axis is parallel to-and directly over-the reinforcing bar. This is indicated by maximum deflection of the meter needle and maximum depth display on the readout.
3. Wait a few moments for the reading to stabilize on the digital display and read the depth. This value corresponds to the distance between the bottom surface of the probe and the top of the reinforcing bar closes to the surface (See fig. 3).
For a given depth, the reading will decrease with increasing bar cross sectional area and with decreasing steel strength. Reading variations because of the steel temper or strength are in the order of 5% for #5 and larger bars. Calibration of the Datascan is based on a “best fit” average for different bar strengths.

When examining a structure, the digital readout may indicate less than 1”, or the meter pointer may go offscale. This indicates that the concrete cover over the rebar is too thin to be read directly or that the surface of the probe is touching the tie rod. Should this happen, measurement can be made by interposing a non-magnetic shim of known thickness between the concrete surface and the probe. Then subtract the shim thickness form the reading.

Before attempting to measure the depth of concrete covering the reinforcing steel, it is advisable to determine whether the concrete itself contains any magnetic material. To do this, turn the instrument on and allow it to stabilize. Switch the instrument to the Test mode by pressing the Enter button. After zeroing the instrument, place the probe on the concrete at least 10” away from any rebar or other magnetic object. Note reading on display! If it flickers to more than a few counts above zero (the ambient noise level), the presence of magnetic material is indicated. See section on, “Correction for Magnetic Concrete” before proceeding.

EFFECT OF CLOSE PARALLEL BARS
Curves I, II, and III in Figure 2, illustrate the effect of bars parallel to one another, some distance below the surface of the concrete. Moving the probe parallel to the reinforcing bar axis will cause the depth reading to increase as the instrument passes over the space between the two bars – the amount of increase depending on their combined influence on the instrument.

The combined influence of two bars is negligible only when their axes are separate by at lease three times the thickness of the concrete cover. If the depth reading drops to 10” (25 cm) or greater when the probe is between two bars, their effect is minimal and can be ignored.

When two bars lie one above the other in a plane perpendicular to the concrete surface, with their axes parallel to the surface, the depth of cover reading will be substantially less, as indicated in curve I of Figure 2. While it is not possible to make a direct determination of the effect of the more distant bar, this phenomenon can be used to find the end of a splice. Whenever the reinforcing bars are close together, depth of cover indicated on the readout is slightly less than that indicated for a single bar (see curves II and III of Figure 2). To estimate the depth of cover, it is necessary to locate the position of each rebar in the area under examination. Use the following procedures to determine the correction factors:
1. Locate precisely the position of each rebar in the area being examined.
2. Consider each rebar parallel to the concrete surface and spaced more than four inches from the outside of the nearest adjacent bar, to be isolated. Now, read the cover depth for the bar size without correction.
3. When two bars are closely adjacent to each other in a plane parallel to the surface (Figure 4), set bar diameter (using the Dia button) to the bar diameter nearest to the sum of the diameter of the two bars.
Then read depth of cover from the display.
4. When tow bars are closely adjacent to each other in a plane that is perpendicular to the concrete surface (Figure 5) set bar diameter nearest to ¾ of the sum of the diameters of the bars and read cover as
above.
These procedures produce good estimates. If very precise measurements are required, the comparison method as discussed in the paragraph on page 12 should be used.

PERPENDICULAR ADJACENT BARS EFFECT
Always locate all of the elements of the reinforcing bar system before starting to measure the concrete cover. When the probe is placed above a bar, the presence of bars perpendicular to the axis of the probe will have less effect on the measurement of cover than that of parallel bars. The measured values will contain a small error. It is usually sufficient to compensate by reading depth of cover to be slightly more than the display indicates. However, the accuracy of measurement can be improved as follows:

If the perpendicular bars are underneath the bar being measured, the effect is negligible. There are no effects if the probe is not directly over the axis of the perpendicular bar.

If the perpendicular bars are above the bar being measured, three cases must be considered:
1. Bars spaced 14” (35 cm) or more between axes; Carry out the measurements without correction by placing the probe equidistant between the perpendicular bars (Figure 6, position A).
2. Bars spaced 7” to 14” (18 to 35 cm) between axes: Carry out measurements without correction by placing probe straddling one of the perpendicular bars (Figure 6, position B).
3. Bars spaced less than 7” (18 cm) between axes: Calculate the cover over the lower bar by adding the diameter of the reinforcing bar above it.
4. Hooks and hoops: When operating near hooks or other elements smaller in diameter than the main rebars, effect is negligible if they are under the bars. If they are above the main bars, eliminate effect by placing probe above the main elements and as far as practical from secondary elements.
5. Finally, if the spacing is such that it is not possible to avoid placing probe close to secondary elements, use the Comparison Method as explained in the following paragraph.

COMPARISON METHOD
This method consists of making an exact full-scale model of the reinforcing structure.
Switch the unit to the Test mode by pressing the Enter button, and zero the display. Then place the probe on work at the desired spot and note reading on the digital display. Take a second measurement on the model in the same manner, using shims until the digital readout is equal to the first reading.
When that position is found, the thickness of the concrete over the reinforcing bar is equal to the thickness of the shims, as long as the zero adjustment has not been altered.
Zero adjustment should be done before each measurement.
When other materials are to be measured for which the instrument has not been calibrated, a similar procedure may be used. For example, to measure the thickness of a refractory furnace lining, it is necessary to make a calibration chart. This can be done using a piece of steel plate or sheet of the sort used for the exterior of the furnace, about 18” square. Make sure that there is no other magnetic material near the probe.
Space the probe 1” (25 mm) from the center of the plate and note the reading on the display. Increase spacing in ½” (12 mm) increments, noting the reading for each new increment. Re-zero before each new increment. The resulting chart can be used to determine the lining thickness from the displayed reading. This same procedure can also be used, for example, for iron pipe, using an 18” (45 cm) length of pipe.

SIMPLIFICATIONS
The shape of some concrete structures allows for measurements to be made more easily than previously indicated. Consider the structure of Figure 7.
Simply by locating the bar axis on two faces of the concrete, the exact position of the bar is determined. Instrument zero in this case is not a factor.

CORRECITON FOR MAGNETIC CONCRETE
When the probe is placed on concrete containing magnetic materials, such as pozzolans, fly ash, etc., the display may show a depth measurement even without any reinforcing steel present. The metallic debris on the concrete surface will have the same effect and should be removed. The presence of magnetic material in concrete will affect the measurement of the concrete cover. The following allows automatic compensation for this.
Zero the instrument in the normal manner. Switch to the Test mode. Locate probe on the concrete where there is no reinforcing. (Move probe across surface of concrete and search for an area where there is no change in meter deflection). Mark area for future reference. Return to Cover mode and with the probe squarely on the concrete, press Zero button. This will store the reading caused by the magnetic material and automatically subtract it from subsequent readings. When re-zeroing the digital display, return probe to the marked area, to ensure consistency of readings.

ESTIMATION OF UNKNOWN BAR DIAMETER
When the bar diameter is unknown, size may be estimated using the following procedure. Switch to the Size mode. Carefully locate and mark the exact centerline of the bar. With the probe on this line, press the Store pushbutton. Using a 2” (50 mm) non-magnetic shim between the probe and concrete surface, again locate the probe exactly above the bar, and press the Store button. The internal computer will search the calibration tables for the bar size for which the change in coverage is approximately equal to the shim thickness.

Bar diameter estimation requires great care to achieve accurate results. Material variation of the steel bars and increase depth of cover negatively influence results.

Where the bar size is an important parameter, it is recommended that you confirm readings by drilling a small hole to the top of the bar, measure the hole depth and compare this with the Datascan cover reading using the estimated bar size.

Accuracy of bar size estimation decreases with depth of cover; depths below 8” (200 mm) are not recommended.

AUTOMATIC LOGGING
When a memory module is plugged into the memory socket, automatic logging of cover readings for rebars may be used. The Memory Module is a non-volatile random access memory having a capacity of 1000 readings.

With the probe located at the desired location, press the Store button on the probe. The digital display reading at this point will be stored in the Memory Module. A sequence number for the reading will also be stored. If the reading points are marked, numbered, and read in sequence, the readings will correlate with the physical structure.

Data are stored in conventional ASCII code. When data logging is completed, unit may be turned-off. The data will be retained for future readout using a personal computer.

Readout of the Memory Module can be done using the RS-232C interface. Plug the interface adapter into the Jack on the unit and into a serial interface port (typically COM 1) on the PC. The interface is configured for 4800 baud, no parity, 8 data bits, 1 stop bit.
Any conventional terminal program, such as KERMIT, PROCOMM, Q-MODEM, or the like may be used on the PC. Configure the terminal program, both display and save to diskette or other memory.

Transmit the command ‘M’ to the Rebar Datascan™; it will execute a non destructive RAM memory dump. When data transfer is complete, the Memory Module may be cleared for re-use by using the command ‘E’.

TENDON MEASUREMENTS
Following the procedures given above, the cover measurements for tendons may be made by pressing the Rebar/Tendon button. The Size measurement function for tendons is not available.

FAST SCAN FEATURE
Using the rebar similar to the ones in the structure, set the distance (cover) using nonmagnetic shims and adjust the manual analog meter Zero knob on the panel to the appropriate reference line on the analog meter.

When the cover is less than the value set, the meter needle will deflect above the set line;

when the cover is greater than the set value, the needle will deflect below the line. This feature is useful when scanning large areas, i.e. bridge decks.

NOTES ON DATASCAN USE
A common cause of error in measuring cover is that the instrument is not accurately zeroed on the analog meter. A small inaccuracy in zeroing amplifies to a large discrepancy in readings.

A second cause of discrepancy is due to differences in magnet permeability of the rebar from country to country and batch to batch. The magnetic permeability can vary with the grade of steel being used. We have calibrated the instrument using average metric rebar obtained from Europe. Should the rebar you are using have widely different magnetic properties than what we used for calibration, the following procedure can compensate for the differences.

Preparation for Developing a Calibration Curve
1 Using straight rebar sample about 1 m long and not badly pitted from rust.
2 Use rebar that is representative of the rebar that will be encountered in the structure.
3 Select an area or surface that is free of magnetic material, i.e. no nails or screws in a 2 square metric area. Prepare a number of wooden shims; a combination of which will give the range of cover readings desired, i.e. 3 cm, 4 cm, 5 cm thick with overall dimensions of 10 cm wide and 20 cm long.

Actual Procedure
A. Place the instrument in the magnetic free environment and turn-on and wait one minute for the instrument to stabilize.
B. Press Enter button, this puts instrument into its Test Mode.
C. Turn the zero adjustment knob on the probe to set zero on the analog meter – at this point the counter number on the LCD display should be 11050 or very close to that number.
D. Place rebar you are to calculate with on the metal-free area.
E. Put the 3 cm thick wooden shim on top of the rebar and place the probe on top of the shim making sure the centerline of the probe is over the center of the rebar. You may have to use pieces of cardboard to support the edges of the shim and ensure it is stabilized.
F. Take the count number.
G. Repeat E and F using increasing thickness of the shim.
When range of shims is completed, make a table and graph of the test count number vs. actual thickness of shim. Make a curve of best fit connecting up each point on the graph.