DIARY #18
DATA FLOWING IN EL YUNQUE
July 23-24th, 2000
At 13:11 on Monday, July 24th, Biological
Science Researchers in Puerto Rico began to benefit directly
from our installation of Wireless in the El Yunque Rain Forest.
Data began to flow from a Campbell CR10X
Data Logger on the top of a 120 foot Weather measuring 'El Verde'
tower near the El Verde Research Center down into a Windows
98 computer running Campbell's PCW208 software in the computer
room of the center.
Prior to this technological advance, all
weather and environmental data collection from the El Verde
Tower - which, by scientific necessity needs to be high enough
to clear the forest tree top canopy - required a researcher
or assistant to go into the field at least weekly, climb up
the tower, and bring back at least the memory module of the
data logger, attach it to a computer in the Center, download
the data, then eventually return the memory module to the logger
on the tower to capture more data. A labor intensive method,
which carries with it certain disadvantages. Namely, that the
data is available, and then only locally, as frequently as someone
carries out the manual retrieval chore from each deployed data
logger. When the loggers are deployed into difficult-to-reach,
or time-consuming-to-reach locations, the number of such deployed
data loggers is limited. And there is no way that a really distant
researcher - such as those associated with the El Verde LTER
whose sponsoring universities or agencies who are in the Continental
US - can retrieve the data from deployed loggers, other than
through personnel who are in Puerto Rico.
Additionally, and less obvious, is the fact
that if a researcher responsible for a data logger wants to
revise the program running in the data logger - adding new sensors,
or changing the frequency of data collection from existing sensors
(such as during extreme weather events) - the logger itself
must be brought down, taken off line, the new program loaded
in and tested, then put back into its original location. During
which period no field data is being collected.
Wireless retrieval opens the door to real-time,
or anytime, data retrieval, updating or change to the data logger's
software, and more timely monitoring of the performance of the
logger and its sensors. Broken sensors can be detected more
quickly. For it becomes possible to check the logged data much
more frequently - even multiple times a day if desired, rather
than the weekly or biweekly cycles normally used.
The El Verde Tower Radio Installation
It would have been very easy, and quick,
to simply install one $1,700 Freewave data radio on the high
El Verde Tower and another inside the El Verde Research Center,
optimized their antennas for communications with each other
through the rain forest vegetation in between, and simply 'dedicated'
the pair to the data retrieval task from one CR10X data logger.
But the El Yunque LTER is more complex than
that, with at least two more distant and somewhat difficult-to-reach
weather towers in the forest - Bisley, and Pico del Este. And
with more than one research center - the El Verde Center with
the University of Puerto Rico researchers, and the Sabana Work
Center with National Forest Service researcher, to connect up,
eventually. And many other potential data collection sites to
consider.
Thus, from the beginning, the wireless network
architecture for El Yunque was designed to permit the continued
expansion with the fewest number, and most strategically placed,
radio installations.
So, as originally designed, we decided to
put the 'Master' Freewave DRG115R point to multi-point radio
in the computer room of El Verde Center and initially connect
it to the most accessible - to researchers - Windows 98 machine,
running the basic Campbell PCW208 data collection software.
Then a second radio - a DRG115W (weather
proof) - running in the newer dual 'Slave-Repeater' mode was
put on the closest data logger equipped Weather Tower, there
at El Verde. The dual slave-repeater mode permitted that radio
not only to repeat and pass any traffic between the Master -
which is so far beneath the forest canopy that it cannot be
expected to connect with distant radios - but also to send and
receive data through its RS232 serial port - the CR10X data
logger on the same tower.
Then, counting on the signal strength of
the 'back plane' of the El Verde Tower radio to be strong enough
to reach the Center building and go through its walls to the
Master radio, we mounted a directional 10dB Yagi antenna on
the tower, pointing to the very summit of El Yunque Peak, with
which we would have to maintain a good connection if all traffic
from even more remote sites, and the other two towers, were
to reach the Master radio and computers in the El Verde Center.
By Monday, the 24th, the second day of this
trip, the installation on El Verde Tower was completed, and
we successfully connected with the CR10X from the Windows machine
in the Center using only a 0 dB short 8 inch omni antenna on
the Master DRG115R radio.
The installation included other changes to
what had been on the Tower previous to our arrival. Before us,
there was a small 12 volt battery, with no recharging links,
in the Campbell waterproof box on the tower, along with the
CR10X, the Memory Module. And the lines out of the box only
ran to the sensors. One weakness of that was that the battery
eventually ran down before it was swapped out by the staff -
and in one case, died, leaving only data in the memory module,
but stopping its collecting, dumping the program, and requiring
a reinstallation. We saw the consequences of that, as the first
time the wirelessly connected data logger met the PC through
the PCW208 software, it showed a wrong date for the data logger.
Which one click of the mouse corrected - updating the data logger
date/time.
So we decided to put everything, including
our most robust 35 amp hour West Marine Gel Cell battery, the
DRG115W radio, and the interface, inside the same box with the
CR10X data logger and memory module. And to switch over the
data logger to the larger battery, which would be then recharged
continuously by the Sieman's Solar Panel, which we mounted on
the tower. Then we fed the antenna cable from the radio out
of the box to the Yagi antenna, pointed up the mountain, and
the power cable from the battery to the solar panel. The following
picture shows the box on the tower, with all the components
in it - data logger, memory module, battery, radio, interface,
and cables, before it was tidied up, and closed.
There was one other important thing we had
to do, before the system worked.
The Campbell Data Loggers use a hybrid configuration
on their DB9 I/O connections coming out of the CR10/21/23X series.
One pin on the I/O is only 5 volts, rather than the RS232 Standard
12 volts on Pins 2 and 3. As a consequence, if one directly
plugs the Freewave Radio RS232 DB9 signal into the Data Logger
DB9 port, damage can result to the data logger. So it is necessary
to insert a Campbell SC932 '9 Pin to RS232 - DCE Interface'
($175) device between them. (It is also possible to use the
Campbell Optical Isolator SC32A ($145) which must be used to
directly connect their Memory modules to the serial port on
PCs running the PCW208 software. For the same 'difference in
voltage' reasons. But that then requires a Null Adapter also
to be put inline. Another cost, another point of possible failure.)
So the hard wired link is as thus;
CR10X I/O - Ribbon Serial
Cable - SC932 - Serial cable - DRG115 Radio
At the Computer end, the DRG115 radio simply
connects out its standard DB9 female serial port into the standard
male DB9 port on most computers. The radios have to be set up
for 9,600 baud I/O both at the Data Logger end, and at the PCW208
computer software end if a CR10X is used, for it only communicates
at 9,600 baud. (CR23Xs can be set faster)
When all this was done, the wireless link
was essentially this;
PCw/PCW208 -Serial- DRG115R
-(wireless)- DRG115W -Serial -CR10X Logger
The radio at the PC running Win98 and PCW208
looks essentially like this - the radio in front of the computer
for illustration. Normally it simply lies beside the computer,
with a wall plug transformer, and an RS232 modem cable running
into the PC chassis.
Because the spread spectrum wireless signal
was strong enough to reach all parts of the El Verde Research
Center building, all it would take to download the data to/from
any other Windows software (95 or 98) machine in the building
is to carry the radio, serial cable, and power supply to the
vicinity of the other machine, which has to be running the PC208
Campbell Software, and plug in. Thus the wireless solution also
permits close-by mobile access to the remote data logger from
any PC. Although - and this is VERY important to note - only
by one person at a time. More on that later.
First Practical Test Session
Below is a picture of the upper right portion
of the running PCW208 software screen. The absolute proof that
all the links are there, the wiring and wireless configurations
are correct, and the software can properly 'talk to' the Data
Logger - is to click on the 'Connect' Icon on the PCW208 Software.
If, after only a few seconds, the screen looks like the view
below - with the PC Date Time displayed, AND the Data Logger
Date Time displayed - and the 'Connect' icon (two little plug
images - link, then you ARE connected, wirelessly. And all other
things that the software permits are possible. Access to the
Logger Data, to the Module Data, download the running program,
or upload a new compiled Edlog program.
Or, as the below picture illustrates, correcting
the Data Logger time/date to match what the PC says it is. The
picture below was taken immediately after the very first 'connect'
via wireless. It shows the data logger off by one day from the
PC clock. (Caused, as stated before, by a battery failure).
All it took after the picture was taken was a mouse click on
the 'Set Datalogger Clk' icon, and the clock was updated on
the data logger on the tower - by wireless.
After several tests - we deemed the wireless
connection reliable and operational.
There is a point to understand. Even if
the wireless connection fails for some reason, no data is lost
in the logger, which can still be fetched manually. In the case
of El Yunque LTER, all the Memory Modules are programmed to
'loop' so that they do not have to be periodically cleared of
all data. The newest data in simply pushes the oldest data out.
And the period of retrieval - manual or wirelessly - is set
to be sure the data collected between downloads is less than
the memory capacity which can be held. Several months worth
in some cases, where the sensors are set to collect more infrequently.
However, with wireless, rather than manual, downloads, the data
loggers could be set to log much more data (more frequent reads),
since it is easy and fast to download them wirelessly - like
several times a day if desirable.
First Practical Operational
Use
When Dr. Jill Thompson, who customarily
climbs the El Verde Tower to retrieve the memory module, load
the data into her PC, write it to floppy disk, for manual forwarding
to Dr. Doug Shaefer at the Ecological Institute in San Juan,
came in from the field late in the afternoon - hot and dripping
from the humidity, we invited her to cool down by sitting in
front of the Window98 machine with PC208 software running on
it, attached to the DRG115R, which we had tested.
Instantly she 'connected' changed the clock
correctly with a mouse click, and then, because she knows the
Data Logger and its data being collected, simply ordered the
machine to download all the data since it was last manually
done. Here she is at the first session.
Then, rather thrilled at the ease, speed,
and reliability of the session she ran a series of instant graphing
sessions again the data just captured wirelessly from a distant
site. This picture shows the Window98 software in background,
the 'Connect' and configuration screen of the PCW208 Software,
then lines of just-downloaded data, and finally, the data's
representation graphically, over time.
If you look closely in the lower right corner
of the screen, you will see that the two 'plug' icons, indicating
being connected, or not (separate), are connected at this moment.
I.e. Dr. Thompson is connected, real-time, to the Data Logger
on the Tower.
Needless to say, tired from a day in the
field, she appreciated the value of the wireless connection.
(Though she jokingly observed that climbing the tower is good
exercise). She demonstrated the data and its handling to graduate
students who were there with her.
All we must now wait for is an Internet link
from El Verde Field Research Station, to the Tropical Ecology
Institute offices, 15 miles away, for Dr. Shaefer to be able
to fetch the same data, for himself, and not wait on a floppy
disk to be transported to him. But that will have to await other
connections.
