Nasa Target Echo electrical interference

[greggron]

'Berserk' - when the motor is on the reading seems to generate random numbers in quick succession changing every fraction of a second or so. The instrument reads absolutely fine when the motor is not on both stationary and at hull speed in calm water and a chop. The effect is seen when the motor is idling as well as driving.

Since the last thread, I have fitted a suppressor to the motor - no change. so it looks like I'm going to have to do more investigations.

The transducer is through hull, it is as far from the motor as I can get it on a 22footer.

Keep the suggestions coming please - all are helpful

Thank you

 

[lenseman]

VicS is spot on as usual with his suggestion in Message Number 14 above.

You don't want or need to trek down to anywhere to try and buy a component which might or might not work, let alone know where to fit it?

To flesh out what Vic said, you need to run the Echo Sounder from an independent power supply. This will immediately tell you if the interference is getting into the NASA via the air (radiated) or whether it is getting into the NASA via the power supply leads (conducted). It might even be getting into the NASA unit via mechanical, through some form of induced cavitation!

Your 1µF 16/25vDC working capacitor, which you intend to buy from an auto factors, might only be suitable of the interference is conducted. On the other hand, if the interference is radiated, then a more suitable capacitor might be in the region of a few nano-Farads or even ferrite beads suitably placed. You could be wasting your time, effort and money if you just purchase large capacitors before conducting a simple test with a battery which you should be able to lay your hands on even if you use the one from your car or a motorbike.

This is my field of expertise and if you need any further help, PM me or give me a ring. I can always come over with a Spectrum Analyser and Oscilloscope and check out the DC supply leads whilst I am still in south-east England.

 

[cimo]

I was watching star trek last night. That Spock and his probability estimates - perhaps we could take a leaf out here.

I pulled out one of these Nasa display driver boxes last week. It was located in an engine compartment. Alot of condensation on the circuit board plus heavy corrosion on the screw terminals. I gave it a good alochol rub on the workbench, powered it up and it's still working - well - on the bench at least.

from gregs last post, I'm begining to suspect the display driver is at fault. Hes got an outboard, so the driver is unlikely? to be mounted close to the engine - and therefore I'd least suspect radiated noise. (I'm sure the spark plug is changed as per owner manual recommendations). Also, given that nothing was changed prior to the problem, when things were sweet?, its perhaps more probable a corroded or poor electrical connection, exasperated by vibrations through the hull when the engine is running.

A complete electrical connection break/remake from transducer-to-driver-to-display could well be enough to resolve. If hull vibration is evident, remove the driver box from its mounts and check the display with engine running. Of course, electrical connections from alternator-to-battery-to-display driver box need to be checked yet.

Please let us know any outcome greg? - going by other posts, problems with these Nasa units don't appear to be uncommon?

rgds
c