Conducting an ACCA survey and an ACVG Survey

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Conducting an ACCA Survey

An Alternating Current, Current Attenuation, (ACCA) survey measures the attenuation of the transmitted 4Hz signal to establish the pattern of current loss.
The results can be used to; establish the condition of the pipeline coating, locate faults, or find shorts caused by contact with other metal objects.
Having used the pinpointing method  Locate_&_pinpoint_the_pipe to ensure you are directly above the correct pipeline, it is now possible to take measurements of the 4Hz signal.

Procedure:

1. Use the peak response reading and compass direction to ensure you are directly above the pipeline.
2. Sit the receiver on the ground, keeping it upright and very still.
3. Press and holdthe key for approximately one second. Upon release a live 4Hz reading is displayed on the bottom right of the screen. It is normal for this reading to fluctuate within a couple of mA.
However, a widely fluctuating reading may indicate interference and it may be better to move along the pipeline to take the measurement.
4. The reading can be stored by pressing theor rejected by pressing thekey. The PCMx can store up to 10,000 readings and the log number of the stored reading will be shown on the display.
5. Continue taking readings in this way along the length of the pipeline you wish to survey.
6. For best results, readings should be taken at intervals of equal distance.

NOTE: If Bluetooth is switched on, the PCMx receiver will automatically attempt to send the reading via Bluetooth to a paired device. If the PCMx has not been paired,a BT error code will be displayed. If it is intended to only save the reading internally within the PCMx receiver,switch the BT-PC setting in the DATA menu to OFF.

Temporary measurements

In some situations, it can be difficult to view the display when taking a measurement.
A temporary measurement can be taken for review before committing the record to memory. Take the measurement as detailed above, but instead of pressing the save or delete key, press the antenna key. The measurement will be held on screen for review. To save the measurement, press .

Review and Overwrite Measurement Logs

Saved readings within the PCMx can be reviewed or overwritten. To view a saved result, press to enter the system menu and select VIEW. The last saved result will be displayed.

To view other logs, use the orkeys to step through.

To overwrite a saved result, select the result log and press .

Once a new measurement is taken, press thekey to overwrite the selected reading. The log number that was overwritten will be displayed and the receiver will revert to storing new measurements at the end of the current records.

Conducting an ACVG Survey

An Alternating Current Voltage Gradient, (ACVG), survey measures the leakage current in the vicinity of the pipeline to assess the coating condition, and pinpoint coating defects. An advantage of this survey method is that it can be done on a route parallel to the pipe. For example, it may be done on a pavement or grass verge parallel to a pipe running below a road surface. It requires the use of an A-Frame in addition to the PCMx receiver and transmitter.

 Procedure:

  1. Connect the transmitter to the pipeline and ground using the procedure described previously.
  2. Set the PCMx transmitter to either ELCD or LFCD mode.
  3. Connect the A-frame to the PCMx receiver via the accessory socket, and turn on the receiver.
  4. The PCMx will automatically choose ACVG mode and an A-frame symbol will be displayed.
  5. Choose an appropriate starting point for your survey. If a suspected fault location has been identified from a previous ACCA survey, begin the survey approximately 60 feet, (20meters) from the suspected fault.
  6. Place the A-frame spikes in the ground above, or parallel with, the pipe. Position the green spike forwards and the red spike towards the transmitter connection point.
  7. If no fault is apparent, the arrows will flicker on and off and the dB readings will be erratic. When a fault is present, the Fault Find, (FF) arrows will display the fault direction and the dB readings will be stable. The dB reading will increase as the A-Frame is positioned closer to the fault.
  8. Follow the pipeline pushing the A-Frame spikes into the ground at regular intervals and checking for FF arrows.
  9. Move in the direction of the arrows. Find the point at which the arrows change direction. If the A-frame has been positioned directly above the pipe, the fault location will be directly below the A-Frame at this point.
  10. If the measurements have been taken to the side of the pipe line, rotate the A-Frame 90° so that the green spike points towards the pipeline. Move back and forth across the pipeline to locate the fault in this direction, the intersection point will be directly over the fault.

 Conducting survey types simultaneously

The PCMx allows users to conduct both an ACCA and an ACVG survey simultaneously. By collecting the data in one pass of the pipeline, rather that two, survey time can be reduced significantly.

Procedure:

1. Connect the transmitter to the pipeline and ground using the procedure described previously.
2. Set the PCMx transmitter to either ELCD or LFCD mode.
3. Connect the A-frame to the PCMx receiver via the accessory socket, and turn on the receiver.
4. The PCMx will automatically select ACVG mode and an A-frame symbol will be displayed.
5. Match the mode of the receiver to the transmitter by repeated presses of thekey.
6. Begin your survey by following the procedures given above for conducting an ACVG survey. The display will show locate information (Peak-PLUS mode) and FF information.
7. To take a 4Hz current reading, follow steps 2 through 6 of the procedures given above for conducting an ACCA survey.

 

 

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