Trouble calibrating depth sounder

[colemj]

We have an Airmar 520-PLD depth sounder connected to our TZTL12F. I cannot seem to calibrate its depth to read accurately. It is in the hull, so I would like to make the depth read 2.5' more than it naturally reads, so the depth displayed is the actual depth from the water surface.

In the sounder menu, there is an adjustment for this. When I put in 2.5' in the transducer draft, the depth displayed jumps much more than 2.5'. For example, if the depth is reading 10' naturally, setting the transducer depth to 2.5' will make the depth read 18'.

By playing around, I found that a setting of 0.8' came close, but not accurate (the transducer is definitely 2.5' below the water surface).

However, while the PGN output for the depth says it has been changed, the display on the TZT continues to read the natural depth. When the TZT is cycled off/on, the depth returns to natural depth and will not keep the transducer depth adjustment.

More concerning, is that playing around with the transducer depth often causes the TZT to crash and just turn itself off. This is also happening randomly, and I will start a different thread on it. But messing with the transducer settings definitely will cause the problem.

Any suggestions? Both the TZT and the 520-PLD are new, and this is the first time we have it out in use.

 

[C-Bass]

Good morning Colemj,

Thank you for your inquiry.

Couple of questions, what is the software version of the unit that your are using?

Please confirm the following values:

Sounder Menu: Transducer Draft?
Initial Settings: External Transducer Draft?
Initial Settings: Keel Draft?
Initial Settings: Depth Display

Kind Regards,
C-Bass

 

[colemj]

The software is version 6.21

Sounder menu: Transducer draft = 0.8
Initial menu: Ext. transducer draft = 2.5
Keel draft = 4.0
Depth display = under sea level

I tried playing around with these values and get the same results - wild swings in shown depth on other instruments, no change in depth shown on TZT2, rebooting does not keep the settings.

 

[colemj]

Wait. It is working correctly again now.

I found that the external displays showing the depth data had unusual calibration values. It seems they take the depth calibration from the TZT2. For whatever reason, these got the wrong numbers in them recently, and the depth started reading incorrectly. Clearing all calibration data from the instruments and the TZT2, and starting over, seemed to do it.

Thanks!