10 Inspirational Graphics About Ultrasonic Hatch Cover Tightness Test

These days, direct current (or DC) electric motors are used in a wide range of applications, such as the moving windows and seats in your car. Because of the concealed nature of these motors, it can be highly difficult to complete any repairs or maintenance on them without having to pull whatever it is powering apart. This is why, once you have managed to get to your DC electric motor, you should always give it a quick check to see whether it has gone "bad" and needs to be replaced. ™

Begin by removing the DC motor from its mount, ensuring that you have also removed any source of electric power that could accidentally cause it to begin turning. You may need to follow the manufacturer's instructions to do this, as some motors are very much wedged into position and could pose a risk of electrocution.

Next, you can test the electric motor's continuity (or connection) by attaching it to a volt ohmmeter. Ensure that the meter is in the "ohms" position, then place the red and black leads into its connections (the red lead should be attached to the "ohms" and the black lead to the "common" point). Test that the meter is working properly by touching these two leads together - the screen should read zero ohms (or full continuity).

To test your DC motor, touch the leads of the ohmmeter to the leads of the motor. The meter's screen should indicate a low resistance (somewhere between 10 and 30 ohms), but if it reads an infinite ohms or an open circuit you should rotate the end shaft of the motor. The ohmmeter should give different readings as this shaft is rotated (which is an indication that the electric motor itself is good, but that there is a problem with the electrical circuit. If the meter is still reading as an open circuit, the conducting brushes may have gone "bad".

Use a screwdriver to remove the brushes from the end of the electric motor (you can find them under the plastic end caps at the opposite end of the motor to the drive shaft). Carefully inspect the brushes for any sign of cracks or breaks in the surface - the area of the brush that sits against the conductor or commutator should be smooth and curved. If there are any broken wires or springs, the motor will fail. If the brushes appear fine, then the problem may be with the commutator.

Take the screwdriver again and use it to remove the rear end cap of the DC electric motor (by removing the two screws that run the motor's length). Inspect the plates that comprise the commutator assembly - there should be an opening between each. If you notice any broken wires or burnt varnish, the commutator has failed and its damaged parts will need to be replaced.

A rebound hammer is primarily used to assess the uniformity of concrete strength within a structure and to localize areas of inferior quality.

When using a rebound hammer to estimate in-situ compressive strength, the reference curves provided by the manufacturer must be used with some caution. The correlation between rebound number and compressive strength is very much dependent on the concrete mixture under test. In order to obtain an estimate of in-situ compressive strength using a rebound hammer in accordance with major standards, a calibration is necessary. The recommended method is to correlate the rebound hammer measurements with destructive tests made on core samples, or cubes/cylinders made from the same concrete mixture as that used in the structure.

Please refer to the following standards and guidelines for details of the requirements for creating such a correlation curve: EN 13791 (Europe), ASTM C805, ACI 228.1R-03 (North America), JGJ T23-2001 (China).

The resulting data is used either to shift a reference conversion curve or to define a custom curve for that particular mix. Typically the curve is defined to provide a safety margin to take into account the various factors that may affect the in-situ tests. EN 13791 recommends the use of a lower 10th percentile curve. This means that 90% of the Ultrasonic Hatch Cover Tightness Test data pairs lie above the curve and only 10% lie below.

Carbonation forms a hardened layer on the surface and as this layer increases it can lead to a significant over-estimation (possibly as high as 50 %) of the compressive strength of the underlying concrete when measuring with a rebound hammer. Either the carbonated layer must be removed before rebound testing, or the rebound test should be carried out before and after removal of the carbonated layer using a grinding machine over a surface area of about 120 mm diameter. This allows a correction factor to be considered (sometimes referred to as a "time coefficient").