Position-specific sensors

Before the performance of the loading we have to apply 5 up to 12 sensors, according their size, on the cylindrical part of the drums and after a short check of the required sensitivity and the wave propagation the pneumatic pressure test monitored by AE can be performed. The selection of the sensors and their positions was performed earlier in pre-tests under the postulate, that the complete cylinder can be tested with the same sensitivity, reliability and that furthermore the localisation accuracy of defects in the on-line- and the post analysis is sufficient for the required purpose. For the flat eovers, which will be tested by specific sensors, the geometrical shape is so complicated, that we perform in this case only a defect determination with a kind of zone-location. 

In harsh operational conditions environmental factors can affect the performance of DP which can lead to loss of the position control abiUty. For a Mobile Offshore Drilling Unit (MODU), loss of position without safe disconnection could result in critical damage not only to the well, but also to the subsea equipment. For an Offshore Support Vessel (OSV), loss of position could lead to colhsion with the nearby installation during operation or to damage to the subsea fadhties. In order to increase the safety and reliabiUty of a DP system, it is important to identify and quantify all influence factors and the way that they can affect the DP performance. For example bad weather condition is an effective factor on the position reference sensor or the local position reference system. Such operational conditions can vary from place to place and may have a dynamic nature in a specific location. Moreover, it is important to investigate safe recovery back to position, safe disconnection and reconnection when the loss of position is outside the safe operational range. 

In addition to this information, specific sensors may be used in conjunction with DIGISAFE XME. These sensors ate most often used for calculations of speed and train position. There ate two kinds of sensors ... 

The specific test was made into a specialized bunker of one partner of the CIAPES program. All the vessel was covered by AE sensors to locate witli accuracy AE sources. The corrosion defect was situated on the bottom of the vessel. The service pressure of the vessel was 8 bars, so the vessel was first submitted to a proof test at 12 bars. During this test, the pressure was increased with load holds in order to verify the assessment criteria. After the first hold at 4 bars, a cluster was located at the position of the defect. The number of events located in this cluster increased during all the test (figure 1). 

The procedures of experiments were the following [15, 26]. After deposition of a specific quantity of silver on substrate the heating of a tray with silver was turned off, the shutter 7 was opened and the sensor was positioned opposite to the substrate in such a manner that the surface of the sensor was parallel to the surface of substrate. In these experiments we detected an irreversible donor signal of the sensor which can be related to adsorption silver atoms on the sensor made of a zinc oxide film. It is known [27] that silver atoms are donors of electrons. Note that the signals of the sensor were observed only when the sensor was positioned in front of a substrate. There were no signals detected in any other arrangement between sensor and substrate. 

The instrumentation details must be specific in the same way as the other pieces of equipment. The accuracy, range, and type of the various sensors must be specified. The position of the sensors, sampling ports, and control devices must be indicated on the PIDs. The type of controller must be specified as, for example, on-off, proportional, proportional integral, and derivative, etc. As usual, standard items should be selected whenever possible. 

The readout device is a translator like the sensor. It translates the electrical signal produced by the signal processor to something the analyst can understand. This can be a number on a digital display, the position of a needle on a meter, a computer monitor display, etc. The readout device is not specific to the measurement. It can take the signal from any signal processor and display it. 

---