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.
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.
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 .
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.
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.
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.
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.