Where to Find Guest Blogging Opportunities on Ultrasonic Hatch Cover Tightness Test
The components of aerospace ultrasonic test equipment.
PC-based and external components make up an aerospace ultrasonic test system. Each of these components has features and considerations when put together to build custom flexible ultrasonic test equipment.
Assembling Ultrasonic Immersion Test Equipment.
Ultrasonic test equipment can take several forms, but the most common type of ATE is immersion test equipment. Squirter systems are the commonest used for aerospace composite material inspection and complex geometry composite parts. To achieve effective acoustical impedance matching between the couplant and the composite component or titanium plate that is the subject of the test (unit under test), and to achieve free range over the entire surface of the UUT, many test systems use an immersion tank filled with water. This equipment uses one or more ultrasonic transducers, which are More help moved over the surface of the UUT. It receives echoes from the surfaces. This process is repeated many times a second with one pulse and subsequent echoes. Application software sets up the test and presentation. Motion control moves the ultrasonic transducers. The signal from the ultrasonic transducer is amplified and filtered before it is sent back to the PC. The waveform is converted from voltage to bits using an analog-to-digital converter. The application software handles the data.
The scale of immersion test equipment can vary enormously in aerospace including, for example, anything up to 17 axis scanning bridges. Acoustic microscopes use high ultrasonic frequencies and high resolution scanning units.
Ultrasonic Transducers
Ultrasonic transducers are built around piezoelectric ceramics that vibrate at ultrasonic frequencies. Piezoelectric ceramics in ultrasonic transducers used in field service are commonly contact sensors, and are contoured to the surface to be inspected. Standard Immersion Ultrasonic Transducers works on the principal that in ultrasonics, the voltage amplitude is proportional to the amount of energy echoed by the flaw. In immersion testing, the ultrasonic wave must travel through water before arriving at the UUT. If the distance is known, a trigger delay can be implemented to minimize the amount of unnecessary data that is recorded and stored. There is a trade-off between resolution, speed, channel count, data throughput, and cost. However, the technology is evolving and many of these trade-offs will become insignificant with respect to cost.
Motion Control and switching
Most automated ultrasonic test systems use motion control to gather multiple data points with one transducer. For instance, acquiring B- or C-scans requires movement of the ultrasonic sensor
over the UUT surface to create a surface map.
As for switching, in ultrasound applications that have one digitizer and pulser/receiver for multiple ultrasonic sensors, switching is required to route the signals properly. This is used for equipment like acoustic microscopes that use arrays of sensors to create images. Arrays of ultrasonic sensors are common in aerospace NDT applications because the sound energy can be steered in multiple directions without moving the sensor array. Multitransducer applications are also common when speed of test is an issue.
Application software
One of the main trends in non-destructive testing, and ultrasonic test equipment, in particular, is full test automation. ATE includes not only data collection and presentation automation but also pass/fail
automation. Setting pass/fail templates increases statistical accuracy and eliminates much of the subjectivity that is commonly found with NDT.
As a former employee and current owner of an industrial generator rental company and electrician with 15 years of generator troubleshooting experience, I've had many situations where the engine powering the genset is running great, but the generator isn't producing any electricity. There are plenty of articles on the internet explaining how to flash the field in order to re-magnetize the generator, but this one will go a step further and also explain how artificially exciting a generator can aid in narrowing down the cause of the failure.
A WORD OF CAUTION...
Just because you don't see any volts on your panel meter doesn't mean that you won't be electrocuted. Remember, the panel meter can be flawed, check it with a hand held multimeter. Secondly, flashing a field results in a build up of magnetism within the generator. Over time of inactivity, the magnetism may dissipate entirely and flashing the field "refills" the missing magnetism. It is, however, entirely possible that the reason for the generator losing output isn't related to a lack of residual magnetism in the generator. If this is the case, then there will be a voltage present that is lower than the rated output voltage, but definitely enough to cause a painful electrocution.
CHECK THIS BEFORE YOU FLASH THE FIELD...
Use a multimeter to check if there is any voltage present at all. If there is, then it's a good indication that the problem is not within the generator.
Shut the machine off and locate the voltage regulator. You'll find 2 wires marked F+ and F-. Pay close attention to where each is and remove them. Put your multimeter on "Ohms" and measure the resistance across them and write down the result. Unfortunately each manufacturer has different values as normal, but 0 and infinite ohms are two bad news signs that you'll require the services of a generator rewind shop. If you have ohms, leave the wires off and keep reading.
HOW TO FLASH THE FIELD...
Ideally you'll have a variable DC supply available. If not, use a 9V battery, or even a car battery and carefully hook up the [+ to F+] and the [- to F-].
Start the engine, and keep it at low idle if possible. You should instantly notice a voltage is present. As you increase engine RPM, you'll notice the voltage will increase. Do not go beyond rated voltage. Keep the machine running for 30 seconds and shut off the engine.
Re-connect the F+ and F- to their original location. Now start the engine and see if you have volts.
I STILL DON'T HAVE ANY VOLTS...
By flashing the field and bringing the machine up to proper voltage, you've effectively ruled out any problems within the generator's main windings (the most expensive repair).
You should now focus on the AVR (automatic voltage regulator), a fuse in line with the AVR, or a wire or switch that supplies the AVR. Do "tug testing" of wires, visually inspect everything that you can. If nothing wrong is found, contact the manufacturer of the generator and find out what the ohms of the field should be and compare it to what you found earlier.
