Re: [Owfs-developers] Ocean Temperature

[Jan Kandziora]

Am 07.11.2015 um 10:26 schrieb Colin Law:
>>
>> When you connect the ground line to data-, you have a different current
>> on the common ground/data- line because the ground line also carries the
>> supply current. So there's no way the receiver can successfully
>> eliminate line noise. Instead, it picks up supply current noise. It just
>> doesn't work.
> 
> Does that argument hold in the case of parasitic power, where the data
> and common lines do carry the same current?
> 
Your argument is good as you have two data wires and no ground
connection in that case. The same when the slave circuits are powered by
local batteries.

*BUT* this only works when the host ground is *not connected* to earth,
not even by a noise filter. As soon it is, your circuit isn't symetrical
anymore as one of your two data wires (the "ground") is tighter coupled
to earth than the other, and subsequently picks up noise more eagerly.
Which destroys the loop's cancellation effect.

You can try to minimize that effect by mounting your twisted pair
(again) on a pole and avoid shielding at any cost.


Kind regards

Jan



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Re: [Owfs-developers] Ocean Temperature

[Martin Patzak (GMX)]

Peter,

we used to make our splices ourselves, to adapt them to our special 
needs and to avoid any connectors whatsoever.


In aggressive enviroment like seawater we would use stainless tubing to 
encase the splicing as well as to house the sensor itself.
Then we did fill the tube with 2 component epoxy and for faster and 
bubble-free curing we put this into an oven to cure for an hour or so at 
100 Celsius - but that depents on the epoxy you use


Cheers,

Martin


On 11/07/2015 02:37 AM, Peter Hollenbeck wrote:

I'll do as you suggest on the splice.
Thank you for your input.
Peter

On Fri, Nov 6, 2015 at 1:21 PM, Colin Reese > wrote:


You're going to need a waterproof butt splice of some sort. I
would probably solder, heat shrink, and epoxy. Cable should be
fine. Might as well double up conductors, could even use four
conductors for ground if you wanted.

C

On Fri, Nov 6, 2015 at 1:11 PM, Peter Hollenbeck
> wrote:

Ocean temperature at depth of about 5 feet.

On Fri, Nov 6, 2015 at 1:08 PM, Jan Kandziora > wrote:

Am 06.11.2015 um 21:24 schrieb Peter Hollenbeck:
> I ordered one of these:
> Waterproof DS18B20 Digital temperature sensor
>
> Where I want to measure is 170 feet
>
What do you want to measure? 170 feet seawater depth?

Kind regards

Jan


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Re: [Owfs-developers] Ocean Temperature (Colin Law)

[Loren Amelang]

On Sat, 7 Nov 2015 09:26:24 +
Colin Law clan...@gmail.com wrote:

>> Jan Kandziora j...@gmx.de wrote:
>> When you connect the ground line to data-, you have a different current
>> on the common ground/data- line because the ground line also carries the
>> supply current. So there's no way the receiver can successfully
>> eliminate line noise. Instead, it picks up supply current noise. It just
>> doesn't work.
> 
> Does that argument hold in the case of parasitic power, where the data
> and common lines do carry the same current?

And what about when you have an out-and-back path through the same CAT5, to 
maintain a single chain and avoid a "star" configuration? Or when you have 
other signals (relay coils!) in the same CAT5? I can't say I've tried the 
experiment of putting ground and data on different twisted pairs, but since I 
eliminated all the star branching from my (parasitic) bus (which always keeps 
data and ground on the same twisted pair) I can go for months of reading every 
ten seconds without a single error. Despite the total path now being much 
longer due to out-and-back. 
 
One other trick that seemed to help stop the last few rare errors on this long, 
perilous route was adding termination on the far end - a (reverse biased) 
1N5711 Schottky diode and a 1.5KE20A-T TVS in parallel. 

I know, separate cables for 1-wire would be better, but it seems no matter how 
much cable I pull around this house, there is never enough! 
 
| Loren Amelang | lo...@pacific.net |




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Re: [Owfs-developers] Ocean Temperature (Colin Law)

[George Hills]

> 
> And what about when you have an out-and-back path through the same CAT5, to 
> maintain a single chain and avoid a "star" configuration? Or when you have 
> other signals (relay coils!) in the same CAT5? I can't say I've tried the 
> experiment of putting ground and data on different twisted pairs, but since I 
> eliminated all the star branching from my (parasitic) bus (which always keeps 
> data and ground on the same twisted pair) I can go for months of reading 
> every ten seconds without a single error. Despite the total path now being 
> much longer due to out-and-back. 
> 
> One other trick that seemed to help stop the last few rare errors on this 
> long, perilous route was adding termination on the far end - a (reverse 
> biased) 1N5711 Schottky diode and a 1.5KE20A-T TVS in parallel. 
> 
> I know, separate cables for 1-wire would be better, but it seems no matter 
> how much cable I pull around this house, there is never enough! 

I have loads of star branching, but I provide power to every device. 

As I extend it, when it goes flakey, I just add another DS9490R and split off 
another section of bus.

Absolutely agree on there never being enough cable.

Cheers
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Re: [Owfs-developers] Ocean Temperature

[Colin Law]

On 7 November 2015 at 18:29, Jan Kandziora  wrote:
> Am 07.11.2015 um 17:24 schrieb Colin Law:
>>>
>>> *BUT* this only works when the host ground is *not connected* to earth,
>>> not even by a noise filter.
>>> As soon it is, your circuit isn't symetrical
>>> anymore as one of your two data wires (the "ground") is tighter coupled
>>> to earth than the other, and subsequently picks up noise more eagerly.
>>> Which destroys the loop's cancellation effect.
>>
>> Don't follow that.  We are talking about series mode inductive loop
>> pickup not common mode (or at least I am).  Provided it is only
>> earthed at one point (which should be the case for all 1-wire
>> circuits) I don't see it makes any difference to the series mode
>> pickup.  I am not an expert in this area by any means though so am
>> happy to be further educated.
>>
>
> My expert times in Kirchhoff exercises are a bit dated, too.
>
>   noise
>  -->
>__  +-+
>   1.5k pullup /  \ | |
> +-/\/\(+--+  |
> |  |  \__/|  |
>/|\ |  /  |
>   | | ||5v   -->  \ load |
>\|/ |   __ /  |
> |  v  /  \|  |
> +-+---(+--+  |
>   |   \__/ | |
>   |   ===   ===
>   || |
>   ++-+
>
>
> The cable capacitance on the ground wire directly shortens the noise
> source while the cable capacitance on the DQ wire only shortens the
> noise source through the pullup resistor.
>
> So for the same influx, the noise voltage on the ground line is much
> smaller than on the DQ line.

Hm, not sure.  With inductive loop pickup is it not right that the
noise is not relative to ground, but is around the loop, so it is not
trying to get to ground, just round the loop.  So I am not sure
whether capacitance to ground is relevant.

Colin

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Re: [Owfs-developers] Ocean Temperature

[Peter Hollenbeck]

The splice won't be immersed. Only the sensor and five feet of its cable.

On Fri, Nov 6, 2015 at 1:02 PM, George Hills  wrote:

> I ordered one of these:
>
> Waterproof DS18B20 Digital temperature sensor
>
>
> Where I want to measure is 170 feet from my RaspberryPi with 1wire
> interface.
> Is this the right wire to buy:
>
> http://cables4sure.com/200ft-cat5e-outdoor-above-ground-bulk-cable.html?gclid=CjwKEAiAvPGxBRCH3YCgpdbCtmYSJABqHRVwlNENYZipkhNh9ioFjIV8a1cDyfY1jV9WQePqMCBNwBoCZZTw_wcB
>
>
> It is OK for outdoors but if you plan to immerse it in saltwater I’m not
> sure how long it will last.
>
> I think my biggest concern would be the join between the sensor tails and
> the cat5, if the environment is that hostile.
>
> Cheers
>
>
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Re: [Owfs-developers] Ocean Temperature

[Jan Kandziora]

Am 07.11.2015 um 22:06 schrieb Colin Law:
> 
> Hm, not sure.  With inductive loop pickup is it not right that the
> noise is not relative to ground, but is around the loop, so it is not
> trying to get to ground, just round the loop.  So I am not sure
> whether capacitance to ground is relevant.
> 
The noise has a certain power which flows into these voltage sources. So
it's either high voltage at low current or high current at low voltage.

If and how much ground capacitance is relevant depends on the frequency
of the noise. R_c = 1/(2*pi*f*C), calculate for yourself. Given f=1MHz,
C=1nF, it's 160 Ohms. That's smaller than the 1.5kOhms of the pullup
resistor. The load resistance of the open circuit of a slave
(master,too) is very high for onewire, megaohms, so it doesn't matter
for the above calculation.

Kind regards

Jan

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Re: [Owfs-developers] Ocean Temperature

[Colin Law]

On 7 November 2015 at 15:18, Jan Kandziora  wrote:
> Am 07.11.2015 um 10:26 schrieb Colin Law:
>>>
>>> When you connect the ground line to data-, you have a different current
>>> on the common ground/data- line because the ground line also carries the
>>> supply current. So there's no way the receiver can successfully
>>> eliminate line noise. Instead, it picks up supply current noise. It just
>>> doesn't work.
>>
>> Does that argument hold in the case of parasitic power, where the data
>> and common lines do carry the same current?
>>
> Your argument is good as you have two data wires and no ground
> connection in that case. The same when the slave circuits are powered by
> local batteries.
>
> *BUT* this only works when the host ground is *not connected* to earth,
> not even by a noise filter.
> As soon it is, your circuit isn't symetrical
> anymore as one of your two data wires (the "ground") is tighter coupled
> to earth than the other, and subsequently picks up noise more eagerly.
> Which destroys the loop's cancellation effect.

Don't follow that.  We are talking about series mode inductive loop
pickup not common mode (or at least I am).  Provided it is only
earthed at one point (which should be the case for all 1-wire
circuits) I don't see it makes any difference to the series mode
pickup.  I am not an expert in this area by any means though so am
happy to be further educated.

Cheers

Colin

>
> You can try to minimize that effect by mounting your twisted pair
> (again) on a pole and avoid shielding at any cost.
>
>
> Kind regards
>
> Jan
>
>
>
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Re: [Owfs-developers] Ocean Temperature

[Colin Reese]

You're going to need a waterproof butt splice of some sort. I would
probably solder, heat shrink, and epoxy. Cable should be fine. Might as
well double up conductors, could even use four conductors for ground if you
wanted.

C

On Fri, Nov 6, 2015 at 1:11 PM, Peter Hollenbeck  wrote:

> Ocean temperature at depth of about 5 feet.
>
> On Fri, Nov 6, 2015 at 1:08 PM, Jan Kandziora  wrote:
>
>> Am 06.11.2015 um 21:24 schrieb Peter Hollenbeck:
>> > I ordered one of these:
>> > Waterproof DS18B20 Digital temperature sensor
>> >
>> > Where I want to measure is 170 feet
>> >
>> What do you want to measure? 170 feet seawater depth?
>>
>> Kind regards
>>
>> Jan
>>
>>
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>
>
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Re: [Owfs-developers] Ocean Temperature

[Jan Kandziora]

Am 06.11.2015 um 21:24 schrieb Peter Hollenbeck:
> I ordered one of these:
> Waterproof DS18B20 Digital temperature sensor
> 
> Where I want to measure is 170 feet
>
What do you want to measure? 170 feet seawater depth?

Kind regards

Jan

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Re: [Owfs-developers] Ocean Temperature

[Peter Hollenbeck]

Ocean temperature at depth of about 5 feet.

On Fri, Nov 6, 2015 at 1:08 PM, Jan Kandziora  wrote:

> Am 06.11.2015 um 21:24 schrieb Peter Hollenbeck:
> > I ordered one of these:
> > Waterproof DS18B20 Digital temperature sensor
> >
> > Where I want to measure is 170 feet
> >
> What do you want to measure? 170 feet seawater depth?
>
> Kind regards
>
> Jan
>
>
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Re: [Owfs-developers] Ocean Temperature

[Jan Kandziora]

Am 06.11.2015 um 22:11 schrieb Peter Hollenbeck:
> Ocean temperature at depth of about 5 feet.
> 
In that case your concerns should be:

* No flame retardants in the cable sheath. Because these are hygroscopic
so seawater will make the sheath crumble.
* UV resistance. Ground cable obviously has zero UV resistance. It's
built to resist pressure from gravel, ground movements and mice.
* No air inside the cable. Because if you have air inside the cable,
there's room for water in it, too, which makes your whole cable foul
away if you have a single spot which is not water-tight.



I'm concerned how many people think Cat5e is the most suitable cable for
onewire. It isn't. Onewire will work with any cable, the limitation is
cable capacitance, which is especially bad with twisted-pair, as Cat5e
offers. You gain no benefit from TP because onewire has asymetric drive.
Plus, the shield is ineffective when not properly *earthed* (not
grounded!), as it seldom is. In that case, the shield acts as an antenna
which picks up additional noise.

For onewire, unshielded telephone wire on a pole is better than Cat5e.


My suggestion is to use a 3x1.5mm² silicone cable intended for mains
voltage, as silicone doesn't need flame retardants, it is UV resistant
and hasn't got air inside the cable, as Cat5e has. If you need more
mechanical stability, try black PE sheated cable but take care for the
flame retardants and air.

Kind regards

Jan

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