Troubleshooting

Below is a presentation of the most common problems, together with our suggestions on how to improve the result of the check, if it is not related to a damaged probe. For the troubleshooting to be fully effective, a “before” probe check to compare your suspicious probe check against is a good starting point. If you have older data files with good scattering conditions, this should come in handy. If not, use the examples above.

Boundary interference: The sample volume should be centered around 50 mm and the curve should look more Gaussian than the above. Suggestion: Try using a deeper bucket.

Multiple echoes from the bottom reflecting off the surface can also appear in the probe check data. These will typically be at roughly integer multiples of the actual distance to the bottom. Depending on the acoustic path length, an echo closer to the actual boundary position may be the result.

When a side-looking Vectrino probe is placed close to the bottom, the two receivers slanted at 45° may see interference from the bottom. If you see interference in beam 3 and beam 4, try moving the probe upwards a bit in the water column.

Boundary interference: If there are any obstructions in the beam path, the result may look like this.

Little scattering material/low power: The curve showing the sampling volume is “too low” in terms of counts. If the scattering level is sufficient, increase the output power.

Too little scattering material or power level too low.

Bent receiver arm: Please look at the location (range) of the peak in amplitude on the probe check for each receiver. If it is significantly shifted closer or further away, that’s usually an indication of a bent receiver arm. In the figure below, the red and blue curves (representing beam 1 and beam 2) are not aligned with the other two curves. In this case, beam 2 was bent a bit out, beam 1 a bit in.

Check to confirm: Gently place the probe on a flat surface and confirm that all beams touch the surface at the same time. A bent receiver arm will change the calibration since the receiver arm geometry has changed. If there are only minor changes, then you may not notice much difference, but it will introduce a bias to the measurements. Contact Nortek for further guidance.

Bent receiver arms: The curves presenting data for beam 1 and beam 2 are not aligned with the expected curves.

Saturated signal: The probe check should have a nice peak around the sampling volume and not plateau at any point. Try lowering the power level and see whether the result improves.

 

Saturated signal: The curve flattens at the peak. (The peak around 340 mm from the probe is the bottom.)

Problem with one of the receivers: The red beam is not functioning properly – the curve for this receiver is not aligned with the other three. Check to see whether there is something blocking it, or contact Nortek for further guidance.

Problem with receiver on beam 2.

Problem with the transmitter: Note that this probe is submerged (you will get a similar result when running a probe check in air). The transmitter is not functioning properly. Check to see whether there is something blocking it, or contact Nortek for further guidance.

Problem with transmitter: Either blocked or not functioning.

Grounding (Vectrino: loose grounding wire): The noise floor is varying around 50 counts. Tests in laboratory tanks can sometimes lead to grounding problems that show up as elevated noise levels, but only after the instrument is submerged in water. You will not automatically see the increased noise level in your data if your signal from the water is above the noise, but the increased noise level could look like signal. Suggestion: First check that the grounding wire between the probe and the electronics on the Vectrino is connected (you will need to remove the probe to check this). Second, you may be able to reduce your problems by coiling your cable into a tight bundle and raising the cable above the floor (i.e. placing it on a chair). 

Vector: One way to determine the noise level in the tank is to collect with the transmitter out of the water but the receiver arms in the water. The signal you now see is noise only. Grounding problems will disappear when you disconnect the Vector from the computer and from the external power supply. Collecting data to the internal recorder using batteries can be an option to remove possible grounding problems in indoor environments.

 

Grounding: Keep in mind that grounding problems occur around man-made structures, and are not normally a problem in the field.

Sharp peak around 30 mm (relevant for the Vector): This is just electronic noise that has no influence on the current measurements. There is nothing wrong with the instrument.

Sharp peak in the beginning of the plot.

Scaling: The graph grows beyond the screen. Solution: Right-click inside the graph and select “Scaling” to adjust the range of the Y-axis.

The scaling of the axis can be adjusted in the software.

Test yourself: What is the problem here?

A number of different issues are appearing in the probe check. If you encounter anything similar, try to rule out one potential issue at a time.

 

Do you want to plot the .pck (probe check data) in Matlab? Try making a code like the following:

load pdata.pck
 d= pdata;
 i=(18:512);
 j=512+(18:512);
 plot(d(i,2),d(i,3:6)),grid,title('Distance data')
 plot(d(j,2),d(j,3:6)),grid,title('Probe check data')