Author Topic: Installed Davis Soil station: 4 moisture/temp probes  (Read 167 times)

dfw_pilot

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Installed Davis Soil station: 4 moisture/temp probes
« on: April 04, 2017, 05:10:40 AM »
I've had the soil station for over a year now, but finally got around to installing the 2nd, 3rd, and 4th, soil moisture and soil temp probes. It was a long, hot process, but I'm glad to have them installed. I trenched about 100 feet, and don't think I'll do that again anytime soon.

I finished this project so that I could accurately water my lawn here in Dallas where water is expensive, but also so I could water properly, by not putting out too much. Too much water makes the grass roots stay shallow, which in turn, hurts the plant during drought and periods of heat stress. I didn't bury them like a crop farmer would, but instead placed them 5" down, near the root zone, in four places in my yard. I bought some 18-8 sprinkler wire, soldered the probe leads to that wire, then did a heat shrink over the connection. So far, all is working perfectly. I share this because even after a call to Davis, they couldn't tell me what type of wire to buy for the soil probes (surprise). They recommend shielded, but good luck finding that in an affordable option. I didn't run the wires near anything electrical, and all has worked well with the 18-8. If you do this in the future, I can recommend using what I used.

The nice thing about irrigation wire is that it's color coded, so all eight wires were easy to keep straight as to which one went to which probe. I essentially placed the soil station in the middle of the four points where the probes were buried, and then had four probes on one side (two temps and two moisture) run back to the station from one direction and the same from the other direction. 18-8 is 18 gauge wire with 8 strands inside it. Each probe has two leads, so two moisture and two temp gauges will work on one line of 18-8. By running two 18-8 wires into the soil station from two directions, I was able to have 8 probes (16 wires) all feed properly into the station.

Places like WU only broadcast the soil temp and moisture level from the #1 labeled probe, but my WeatherCat website lists all four. I had to use two graphs as WC only allows three inputs per graph. I wonder if there is a way to have the graphs use only 1 temp graph and 1 moisture graph instead of one graph per input? Anyway, the graphs can be found here on the Lawn section and Graph section of my website. A hot linked graphic below:



Finally, for the expense of the Soil station unit, I'm surprised at how cheap and low quality the connection points are. It has cheap, breakable plastic pins you push in to open the "teeth" that grab the wire. One broke on me in the process. It needs to utilize posts or screws, like even the cheapest irrigation controllers use, so it is more solid, and not prone to breaking. If you get a soil station, be very careful about installing the wires into the unit. You've been warned.
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Weatheraardvark

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Re: Installed Davis Soil station: 4 moisture/temp probes
« Reply #1 on: April 04, 2017, 05:54:05 AM »
Having killed several of these stations myself (I have a fully populated station),  I too wondered about it.  I had an idea of getting a screw terminal, putting in the leads to the terminal block and screwing it in, but never really got to the part where I got  a different case for the terminal block and doing it.   I really have no idea why Davis has those crappy plastic push items, unless they figure you will never change the sensors.  and the sensors do wear out over time.   

Right now I have one tab dead and one of the sensor wires leaning up against the pinch clamp.   If it ever stops raining, and dries out, I will replace the transmitter. 

Weathercat does a nice job with the sensors.
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Felix

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Re: Installed Davis Soil station: 4 moisture/temp probes
« Reply #2 on: April 04, 2017, 10:52:46 AM »
@"If you get a soil station, be very careful about installing the wires into the unit. You've been warned."

I also have a station with four moisture sensors and four temp probes associated with the the moisture sensors.

The system has been remarkably reliable, this is the fifth year and (knock on wood) the only thing I've done is to replace the backup battery as preventive maintenance. I must be incredibly lucky concerning the plastic connectors, I didn't break any despite the *really* difficult job of getting eight connector wires (four moisture probes, four temp sensors) into bottom of the wireless transmitter box through the small holee.




dfw_pilot

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Agreed
« Reply #3 on: April 04, 2017, 01:29:05 PM »
Completely agree. Once the wires are in, it should last just fine. But, if you have to take a few out and rearrange or put a few wires in more than once, I think you are living on borrowed time.
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Blicj11

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Re: Installed Davis Soil station: 4 moisture/temp probes
« Reply #4 on: April 04, 2017, 05:44:39 PM »
Interesting discussion and good observations. Thanks for sharing.
Blick


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Re: Installed Davis Soil station: 4 moisture/temp probes
« Reply #5 on: April 04, 2017, 11:49:15 PM »
Interesting discussion and good observations. Thanks for sharing.

X2!!

Edouard

Felix

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Re: Installed Davis Soil station: 4 moisture/temp probes
« Reply #6 on: April 05, 2017, 02:24:38 PM »

DFW_pilot, unlike your set-up, my soil moisture sensors are only in two open-sun locations...one contains sensors (and the associated temp probes) at the 2.5- and 5-inch levels and the other (within 20 feet) contains sensors buried at the 8- and 16-inch levels.


The soil is clay loam with a mowed fescue overcover.


It's really quite interesting to watch the speed at which the 2.5- and 5-inch sensors respond to rainfall. For example, it takes a gully washer of a rain (over an inch in under four hours) to see any significant movement of that 5-inch sensor in under 6 hours. In fact, for the typical slow quarter- to half-inch of rainfall, it'll be over 12 hours before the centibar reading starts reflecting what happened a mere five inches above.


Of course, the moisture sensor at the 2.5-inch level responds quicker but there's still a fair amount of lag and response smoothing.


My assumption would be that the more silt in the soil, the quicker the response.


I was originally going to use those sensor outputs to control my lawn sprinklers in real time, but that proved unworkable because of the inherent lag. Now I just use the centibars of moisture at the 2.5-inch level to decide when I need to consider watering; but quite frankly, after living here for many years, I can tell just from the look and feel of the grass when I need to irrigate and a good estimate of for how long in each zone.



wurzelmac

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Re: Installed Davis Soil station: 4 moisture/temp probes
« Reply #7 on: April 05, 2017, 03:21:51 PM »
I second Blicj11, very interesting. Gives me a nice look at what all is possible with VP and its extensions! Thanks for sharing, too!
Reinhard


dfw_pilot

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Irrigation
« Reply #8 on: April 06, 2017, 03:11:58 AM »
I was originally going to use those sensor outputs to control my lawn sprinklers in real time, but that proved unworkable because of the inherent lag.

After a soil test, I found I have over 50% clay! It takes a lot of water to get it wet, but once it is, it holds the moisture and nutrients very well (unlike a sandy soil). I have a Rachio irrigation controller and its magic is great. It especially helps me control the moisture and irrigation while I'm away on a long trip. It's too much to ask the wife to check the grass with four little ones running around. I totally agree that usually, just walking on your grass will tell you when it is thirsty. I'm part of a lawn forum that is fun to chat about grass and lawns.

I'll only add that I think the lag isn't a big deal for irrigation purposes. The main goal is to water deeply and infrequently. A long soak is better than short sips twice a week. With that in mind, you set your irrigation to run long enough to get 1 inch of water. This can be done by buying three or four short rain gauges and set them around each zone. If you water that zone for 30 minutes and get 1/4 inch, you know that zone needs two hours of watering to get an inch. I'll bet that most soils, with one inch of rain, will be soaked within 12 hours. Then, when your soil gets into the 20-40 range, you know it's time to water again. On my Lawn Page, I have a range of centibars vs soil type for when it's time to water. The beauty of it is that you no longer care about errors in a formula (E/T) or how much rain you got, you just water when the sensors say to. In this regard, a cheap manual irrigation controller becomes just as smart as one like the Rachio!

All the best,

dfw
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