Recalibration; Quick Check; Full Check - Elcometer Protovale CoverMaster CM52 Operating Instructions Manual

6. RECALIBRATION

The CM52 CoverMaster is calibrated for ribbed high-tensile steel bars, since these are
the type most commonly used. Since the accuracy of cover measurements for bars
which are smooth and/or made from mild steel is generally within ±5%, recalibration for
those purposes is usually not necessary.
If it is necessary to recalibrate the instrument for other types of bars, or to demonstrate
compliance with a National Standard, the following procedures should be used.

6.1 Quick check

After zeroing the instrument in 'free air', place a length of ribbed high-tensile reinforcing
bar (at least 500mm long, with a diameter corresponding to the setting of the DIAM
control) on the white face of the search head. When the head is aligned correctly, the
indicated cover should be 30±2mm (typically ±1mm).

6.2 Full check

1. Prepare a set of spacers of non-magnetic material (eg plastic or wood) of known
thicknesses covering the range from 30mm to the maximum distance to be
checked.
2. Prepare a set of high-tensile steel bars covering the range of diameters to be
checked, and including T16. Bars used for calibration must be of high-tensile
steel if the calibration is to be valid for practical reinforced concrete. Each bar
must be at least 500mm long, and measurements must be made at the centre of
the bar.
3. Apart from the bar under test, the area must be metal-free; this includes any
other bars, wristwatch, rings or a metal belt buckle. Also the main unit must be
as far away from the search head as possible.
4. If the batteries have been recently charged, the instrument must have been left
on for at least one hour before making test measurements, and for at least two
hours before re-calibration to BS1881:204.
5. Systematically repeat the following steps 6 – 10 for the whole range of bar
diameters and cover depths to be measured.
6. Set DIAM to the size of bar to be measured.
7. Place the search head on a horizontal non-metallic support, black face upwards,
and place a spacer of the depth to be measured upon the head.
8. Set MODE to CALibrate and use the ZERO control to bring the display to .000
The zero must be re-checked after every cover reading.
9. Place the centre of the test bar on the spacer and carefully adjust it for maximum
signal as indicated by the digital display.
10. Set MODE to DEPth, and read and record the indicated cover.
30
v
.