ST50 - How is Sea Temperature Measured?

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mrrovis

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After our boat went back in the water in March, I noticed that the sea temperature readings on the ST50 display were only 3 to 5 degC (I know it's cold in Scottish waters but not that bad). It's not a particularly important piece of data but it's starting to get at me and could indicate the start of a bigger problem. The manual says virtually nothing about temperature measurement or calibration. Does anyone know how the ST50 measures sea temperature, is there a separate transducer somewhere or does it use a cleverer method to calculate it? I would say it's reading about 7 deg under. Also any suggestions re fixing the problem would be appreciated.
 
Interesting. We've got ST60 instruments and I've never understood the high temperatures that show on the display. Certainly a damned sight warmer than the reality, that's for sure!!

Don't have the manuals to hand so does anyone know how to calibrate the thing? /forums/images/graemlins/confused.gif /forums/images/graemlins/smile.gif
 
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Don't have the manuals to hand so does anyone know how to calibrate the thing

[/ QUOTE ] Oh yes you do!

All the ST50 manuals are HERE

and the ST60 manuals HERE

No excuses now /forums/images/graemlins/grin.gif get reading /forums/images/graemlins/smile.gif
 
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No excuses now /forums/images/graemlins/grin.gif get reading /forums/images/graemlins/smile.gif

[/ QUOTE ]

Thanks Vic!! /forums/images/graemlins/smirk.gif /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif
 
Thanks for the links to the manuals, this enabled me to double check but they are the same as the ones I have on the boat and say nothing about temperature measuement, transducers or calibration. Temperature is only mentioned in the ST50 Speed manual so perhaps it's built into the paddle wheel.
 
Although I don't think it will do you much good! There is no mention of temperature in the ST 50 manuals that I can see. There is, however in the ST60 tridata, but all it tells you is how to select celcius or fahrenheit.

Would like to know the answer myself as I think mine under reads.
 
The temperature is measured by a thermistor in the paddle wheel transducer. For ST50/60 there should be 5 wires, IIRC it is the brown/white combination for temp. The others are speed. As I found the hard way, if the thermistor is broken or not connected then the ST60 Tridata will only function as a slave unless a resistor is put across its terminals, (I'm not sure if this applies to the speed inst. ). I sail in Scottish waters permanently at 27 deg. C
 
It's a temperature sensitive resistor in the paddle wheel housing.

In a previous thread, Iangrant said:
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There is no calibration adjustment for the Temperature in the ST50 Speed. To see if there is a fault with the transducer assembly, do following test;

Disconnect the transducer cable from the display head and locate pins 1 and 2. You do this by facing the plug end of the instrument cable with the reference notch at six o'clock position, Pin 1 is at 7 o'clock and pin 2 is at 10 o'clock position. With the instrument powered on, place a 10Kohm resistor between Pin 1 and Pin 2. The display should give a reading of 25 degrees Centigrade.

If this is the case then assume the instrument is functioning correctly and the temperature error is due to a faulty transducer or cabling.

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and <<edit>> earlybird said: (but he's just said it again /forums/images/graemlins/smile.gif )

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Agreed, the ST60 does have a temp calibration function, but, interestingly, another difference is that the ST60 speed needs to "see" a temperature sender otherwise it thinks that it is a slave unit and will only display seatalk speed rather than direct transducer data. This caused me a lot of frutration when I fitted an ST60 unit, a Tridata, to an old ST50 paddlewheel with a defunct temp. sender. The agent didn't know this but a forumite did. The solution was to fit a resistor across the instrument terminals. I now sail in seas that never fall below 27 deg.!

[/ QUOTE ]

Original thread from February here

Altavista found it, but I knew it was there!

Andy
 
Thanks Earlybird and Misterg, that was really helpful and gives me something to go on. I've looked at a typical (non linear) curve for a 10kohm (25degC) thermistor and this shows that a poor connection of around 5kohm would cause a 10degC sea temperature to be displayed as 5degC. I'll check this when I next go up to our boat in a couple of weeks time and will post my findings.

A bad connection would therefore not be the cause of Jerryrat's high readings but it seems that the ST60 can be calibrated.
 
[ QUOTE ]
A bad connection would therefore not be the cause of Jerryrat's high readings but it seems that the ST60 can be calibrated.

[/ QUOTE ]

Hi mrrovis!

Yes, thanks to Vic (saving me waiting till I get to the boat) I see the temperature can be calibrated, something I've never bothered with on mine. Looks like you have to hang over the side with a thermometer, measure the actual water temp then nip down to the cabin and enter the correct figure!

Ah well,another job for the weekend - if I can find a thermometer! /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif
 
I have ST60 and the temperature has always been wrong despite calibration. The agent could not or would not do anything about it saying it may be a software problem. I finally discovered that it reads correctly when the log is not running but then reads 50deg as soon as we reach 3knots or so. I thought I was the only one with the problem.
 
Hi JohnP!

[ QUOTE ]
I have ST60 and the temperature has always been wrong despite calibration. The agent could not or would not do anything about it saying it may be a software problem. I finally discovered that it reads correctly when the log is not running but then reads 50deg as soon as we reach 3knots or so. I thought I was the only one with the problem.

[/ QUOTE ]

Aha!! I think you may have solved the problem for me then. I did calibrate the temperature after I first installed the units (albeit using a very cheap thermometer) but it never read anything like an accurate figure.

I'll nip down to the boat this weekend and see what it reads before the log starts turning.

Thanks for the idea!
 
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