Raymarine ST 40 speed transducer malfunction

catmandoo

catmandoo

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In actual fact it is not the speed function that is misbehaving but the temperature indication in that sea temperatures shown are too high.

Has any one had experience of this problem ? I understand this is one bit that you can't correct by calibration . Hence do I have to get a new transducer . Is there a simple means of fault checking ? /forums/images/graemlins/confused.gif
 
I ask myself a special question when confronted by 'problems' like this. The question takes the form 'Do really need <insert problem>?' so in this case it would be 'do I really need to know the temperature of the sea?'. The answer may be yes occasionally but do you need it to be always available at the push of a button. I think probably not.
 
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I ask myself a special question when confronted by 'problems' like this. The question takes the form 'Do really need <insert problem>?' so in this case it would be 'do I really need to know the temperature of the sea?'. The answer may be yes occasionally but do you need it to be always available at the push of a button. I think probably not.

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Not sure that your question is so special . Its not the temperature that is the concern it is the implication that something is wrong and may ultimately get worse . My more relevant special question is that I want to know why it is not reading properly . It consists of a piece of electronics embedded in plastic with a cable comprising several wires . Is there a short somewhere that might ultimately affect the log which I am most certainly interested in
 
In the ST60 there is a user calibration for Temp because the depth reading depends on knowing the correct temperature. I don't have an ST40 but am sure there will also be a calibration. Otherwise ring Raymarine and ask.
 
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In the ST60 there is a user calibration for Temp because the depth reading depends on knowing the correct temperature. I don't have an ST40 but am sure there will also be a calibration. Otherwise ring Raymarine and ask.

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Funny that on the ST40 the speed instrument measures depth . presume this is because depth might be through hull measurement and data passed to depth via cross talk .

I have emailed Raymarine because their manual makes no mention but though someone on this forum might have come across this problem before
 
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Its not the temperature that is the concern it is the implication that something is wrong and may ultimately get worse . My more relevant special question is that I want to know why it is not reading properly . It consists of a piece of electronics embedded in plastic with a cable comprising several wires . Is there a short somewhere that might ultimately affect the log which I am most certainly interested in

[/ QUOTE ]Firstly, don't worry that a malfunction in the temperature sensing may affect your log - it won't. The speed/log and temperature systems in the transducer are quite separate.

The temperature sensor is a simple thermistor. These usually have a nominal resistance of 10K ohms at 25 degC. The thermistor is connected across the brown and white wires. If the instrument is showing the water temperature (even if incorrect), it suggests that the thermistor is OK. The reading error is likely to be in the instrument itself, which can't be user-calibrated.

Check that the brown & white wires are securely connected to the instrument, and that the wires aren't corroded. I suppose you could measure the resistance of the thermistor by disconnecting the brown & white wires and putting a meter on them. With a water temperature of say 4 degC, you should see around 26K ohms resistance. If your ST40 is showing a higher water temperature than it should, you could perhaps add resistance to the circuit to reduce the reading. For what it's worth, few instruments seem to show water temperature correctly.

But, to answer your main concern, the speed/log system won't be affected.
 
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