AEC Systems 
Agricultural Data Loggers and Controllers 
POB 234 
Delta Junction, AK 99737 
    
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Irrigation Monitor 
Model 915 
User's Manual
Introduction
What to Do First
Installing the Maintenance Program
Running the Maintenance Program
  Connecting to a PC
  Setting the Sample Interval
  Setting the Data Logger Clock
 Connecting the sensors
Setup Hardware
 Uploading Data
 Sensor Calibration
  Reading and calibrating the temperature sensor
 

Introduction

The #1000915 irrigation data logger is a portable device that can measure and record soil moisture tension, unattended, for  an entire growing season. You can bury the device below working depth  before field work starts in the spring, or after the  crop is planted .Three soil moisture sensors and a temperature probe attach to the data logger. You can place each sensor at  different depths to monitor the moisture through the soil profile, or spread them out at the same depth. The latter method is  great for monitoring drip irrigation, to determine the width of the subsurface wetting front. All you need to do is install the device and record the date and time you started the data logger,. then go about your regular farming chores. You have two options of retrieving data from the device.

You can opt to view all of the data at the end of the crop season only. With this method you don't have to leave the upload cable above ground. If you have a forage crop or a row crop, that needs a lot of cultivation, this will probably be the best method  to use to avoid damaging the upload cable. At the end of the season you upload all of the data to any PC, and compare the soil  moisture data with your irrigation schedule. As you study the changes in soil moisture compared to the time you irrigated you  can make adjustments to your irrigation schedule for the following year. If you keep daily weather records, you can factor that  into your irrigation decisions, too. The data is stored as a text file that is comma delimited, and can easily be imported into  a spreadsheet.

 The second method of retrieving data from the data logger is a few hours after each irrigation. This method is useful in a field  that needs to have very little machine work throughout the growing season. Fields of grain, row crops that need little  cultivation, and landscapes are ideal for this method. You can use a laptop PC, or special data retrieving device for this. In  addition to viewing the data in the field, you can store if for later use, too. Using this method you can make your irrigation  changes right away, and start saving money immediately.

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Setup of the Hardware

Caution: the electronics of the irrigation data logger are very sensitive to electrostatic discharge. Be extremely careful when handling the circuit board. I've found that touching a grounded item, like the case of a PC, before touching the circuit board helps. Also, make sure you place circuit board on an electrical insulator, wood or cardboard, when the batteries are installed.

 
Fig. 1  The first step is to route the sensor wires through the hole in the end cap of the PVC pipe. Leave enough wire on the inside of the cap to conveniently hook them up to the circuit board. After you attach them to the terminal strip you can adjust them to place the circuit board edge about an inch from the cap. If you're using the full set of sensors there should be five wires going through the hole. They are, the upload cable, three soil moisture leads, and the temperature sensor lead. 
 
 
Fig. 2 The second step is to attach the sensor leads to the terminal block on the circuit board. Place the terminal block end of the circuit board toward the end cap. Start with the temperature sensor lead. Look for the temp marking on the circuit board and use the two terminals at this marking. The temperature sensor leads must be installed with the black lead in the end terminal, near the edge of the board, which is the ground, and the red lead in the adjacent terminal. Do not worry about the length of the leads on the circuit board side of the end cap at this time. Just give yourself a lot of room to work. You'll adjust the lead length after all the connections are made. 
Fig. 3 You don't have to worry about the polarity of the moisture sensor leads. Hook them up to the set of terminals marked GYP0, GYP1, and GYP2. Be sure to double check all the leads for a good firm connection to the terminal block. Bend the leads toward the terminal block keeping them along the terminal block but not protruding over the board edge too much. 
 
Fig. 4. The third step is to hook up the upload cable to the circuit board. Make sure the connector latches into the modular jack, then push it all the way into the jack. Route the upload cable along the edge of the  circuit board opposite sensor leads. 
 
Fig. 5. The forth step is to adjust the leads and circuit board with the end cap. Pull the leads through the hole in the end cap until the circuit board is about one inch from the end cap. Dress the leads along circuit board making sure they're still held firmly in the terminal block. Pull on each sensor lead so that they form a neat bundle. 
 
Fig. 6. The fifth step is to seal the hole in the end cap. Make sure the cap is clean, and free of oil of grease. Any type of RTV sealant can be used. Make sure the sealer gets in between the sensor leads. Check the out side of the cap to be sure the sealant protrudes a little with the sensor leads. Build up a puddle about the size of a quarter around the leads to get a little extra adhesion. Let the sealant cure as stated in its instructions. 
 
Fig. 7. The sixth step is to install the batteries and start the data logging. Different power sources are available for the data logger. You can use a 9 volt battery, four AA cells, or 6 AA cells. You'll get about a month operation with the 9 volt battery, to over a year with the six cells .Install the cells in the battery holder Watch the polarity of the cells as you install them. The negative end of the cell goes against the spring in the holder.
Fig. 8. Make sure the switch on the circuit board is in the off position. The off position is with the handle of the switch toward the center of the circuit board. Attach the battery holder to the to the circuit board with the snap connector. 
 
Fig. 9. Fig. 10. 

The last step is placing the components into the pipe housing. Start with the battery holder. Make sure the power connector is secure. Keep the pipe fairly level and slide battery holder into the pipe as far as you can with your finger. Turn the on at this time. The on position on the switch is with the handle toward the outside edge of the board. Grab the circuit board by the edges on the terminal block end and use it to push the battery holder farther into the pipe. Continue sliding the circuit board into the pipe until it's flush with the open end. Then, gently stand the pipe on the closed end and slowly lower everything into it with the cap. See figure 11..Fig. 11.

Fig. 12. Push the end cap on the pipe as tight as you can. We have used it this way in test without any leakage. If you have a high water table you may want to apply a bead of RTV sealer around the edge of the cap and pipe. Caution: do not glue the cap to the pipe. If you bury the upload cable be sure to protect the plug from moisture. Wrap the plug in plastic and tape the plastic to the wire. 
 
 
 
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Connecting the Sensors to the Data Logger

 
   Fig. 22 The only sensor that is polarized is the temperature sensor. You must connect the red lead to the second terminal from the edge of the circuit board, and the black to the terminal closest to the edge of the circuit board. 

All of the other sensors can connect to either terminal pair that are on each side of the arrow points see figure 22 

GYP0 through GYP2 are read in columns 1 through 3 respectively, and TEMP is read in  column 4 of the upload program. 
 

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Configuring the Model 915 Data Logger

 
Before you use the model 915 data logger you must set the sampling interval. You set the sampling interval with a Microsoft Windows 95/98 compatible computer, with parallel printer port, special cable, and the PCPGMIRR maintenance program.

The maintenance program for the model 915 data logger is shipped with the unit. It comes on one 3 ˝ inch floppy disk. To install the program run the setup application on the diskette, and follow the on screen instructions.
 
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Installing the Maintenance Program

License: Even though the PCPGMIRR program is copyrighted there are no restrictions on how many copies of the program you can make. You can also use the program on as many computers, at the same time, as you want. For example, if you're using the data loggers in a class project, you can legally give each student a copy of the program.. However, you cannot sell these copies for more than the cost of making the copies.

When PCPGMIRR loads itself on a computer it installs a few support files. If you want to remove it from your computer be sure to use the uninstall utility in the ADD/REMOVE programs in the control panel. This way you'll get rid of the support files, too.

PCPGMIRR saves an upload in a comma delimited text file with the extension DAT. You can import this file into a spreadsheet program such as excel. We can design supplemental programs for the model 915 that allow you to view the data in various ways. Contact us if you are interested in these
.
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Connecting the Data Logger to the PC

Fig. 13. You can upload the data to any PC running Microsoft Windows. All you need is a cable for the PC end and a control box. Data are uploaded through the parallel printer port of the PC. On some systems you have to set the printer port to SPP mode, and use lpt1 as the port address. Check your computers manual for instructions on how to setup the printer port. 

To upload data from the data logger follow these steps. The special cable has a DB-25 male connector on one end and a six position telephone plug on the other. Connect this cable to the parallel printer port of a computer. 

Fig. 14.
 
 
 
 

Connect the other end of this cable to the ‘To PC' jack on the control box. Make sure the plug snaps into the jack and push it all the way in. 
 
 

Fig. 15. Make sure the Run/Upload switch on the control box is in the run position Connect the upload cable coming from the data logger to the other telephone jack on the control box. Make sure that the plug snaps in place and that it's pushed all the way into the jack. 
 
Fig. 16.   
 

When you're ready to upload the data flip the switch into the Upload position. Follow the instructions on the PC side to retrieve the data. 
 

Fig. 17.  

If you want to continue logging data without losing the previously contents of memory just place the Run/Upload switch in the Run position and unplug the cables. After uploading the data you may want to clear the data loggers memory and start new. To do so press the Reset button on the control box before placing the Run/Upload switch in the Run position. Hold the Reset button for about a second to make sure the data logger resets. Then place the Run/Upload switch in the Run position.

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Running the Data Logger Maintenance Program

 
After you've connected the data logger to the PC, turn on the power to the PC. When the system is booted run the PCPGMIRR program you'll get the screen shown below in figure 18. Before you can set the sampling interval you must click the upload button. You'll see a warning window telling you to make sure the upload/run switch is in the upload position, and to turn the data logger's power on. Do this. Click okay. A progress bar will appear to show you something is happening as the PC reads the memory in the data logger. Don't be concerned with the numbers uploaded at this time. They're the result of final testing of the data logger 
 
 
Fig. 18.
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Setting the sampling interval

When the program is done reading the memory , and the progress bar disappears,  you can proceed with setting the sampling interval. Click the Program button, and another window appears see figure 18.. The interval setting screen consist of four sections. In the upper left hand corner is the first section. You enter the interval between samples in the white window with the up and down arrows. You can't type into this window. The entry has to be made with the up/down arrows or the buttons to its right. We added the eight buttons in the next section, upper middle and upper right, for your convenience. Add as many combinations of the buttons and arrows presses that you like. There are limits to the sampling interval. The minimum sampling interval is 1 minute, and the maximum is 255 minutes, or 4 hours, 15 minutes. The lower right portion of the screen converts the sampling interval to days, hours, and, minutes that the data logger can run without a memory overflow. In the example shown above a sampling interval setting of 120 minutes will sample data for 85 days, 2 hours, and 0 minutes, without overwrites.
The lower left of the screen contains the control buttons. Clicking the program button writes the new interval into the data logger. Clicking Close or cancel will take you back to the opening window. However, close will warn you to make sure you pressed the program button in case you forgotten, but cancel will not show this warning. The new sampling interval will not take effect until you turn the data logger off and then on again. 
 
          Fig 19.
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Setting the Data Logger Clock

In order for us to keep the cost low, the clock that drives the sampling interval is temperature dependent. You can order your data logger with a crystal controlled clock that is very accurate, although at a high price.. We have found in our soils, and at the depth we bury the data logger, that the temperature doesn't change much. To test the variation due to temperature we ran a test in a refrigerator with a temperature of 36 °F. The sampling interval was set to 15 minutes at room temperature. In the refrigerator the actual sampling time decreased to 14.1 minutes. If you are concerned about the drift of the clock it's best that you calibrate it at the average temperature of operation.

During final testing the clock was set at room temperature. To change it click on the Adjust Time button on the sampling time interval screen, see figure 19. You'll see the screen in figure 19. You can use the instructions in the text box to set the time. Be sure to turn the data logger off and then on to activate the new time setting. If you don't have a logic probe or LED you can still adjust the time.  All you need to do this is a watch that displays seconds. First set the sampling interval to one minute. Start the data logger and note the time.
Figure 20.
Upload the data after 30 minutes If you have 30 data points displayed on the upper right of the screen, see figure 17, you're within ±2 seconds per minute. Of course, with the logic probe or LED you can set time right on.
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Uploading Data

You can upload data at any time. Figures  13141516 , and  17   in the hardware section show how to hook the computer to the data logger. After uploading you can reset the memory or continue saving data without writing over the previous data. If you want to just continue saving data in memory where you left off before uploading, then don't press the reset button on the control box. Just place the upload/run switch in the run position. To clear the memory and start from scratch press the reset button before switching to the run position. As soon as the switch is in the run position the logging process starts.

Be aware that while uploading the sampling interval clock is stopped. For short sampling intervals too many uploads can throw off the correlation with real time. Therefore, record the date and time each time you finish uploading and switch to run. For long sampling intervals, if you switch to upload just before pressing ok on the upload warning screen, and back to run as soon as the process bar disappears, you'll not have this problem.
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Sensor Calibration

We usually calibrate our sensors on the soil type we're using them. This is the most accurate way, especially if you have the water retention curves. After calibration, we make a table of data logger counts to gravimetric water content. We then use the soil survey data to get the water tension and inches of water. You can usually get the soil survey data from your NRCS office. You'll need a balance large enough to weigh a can gallon can of saturated soil with the sensors and data logger. The balance should have a resolution of at least a gram, but a tenth of a gram is better.

We graphed resistance to counts for those that don't have the equipment to calibrate their sensors, see figure 21. Please note that these are fixed resistors and will not have the same AC characteristics as the sensors in soil solution. If you need help with calibration please  contact  us.
 
Figure 21.

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Reading the Temperature Sensor

To convert the data logger temperature reading to degrees Celsius, subtract 140 from the reading and multiply the result by 1.95. The resolution of the temperature is 2 °C. For example, it the temperature reading, in column 4 of the upload program, is 145. Subtract 140 from this reading to get 5. Multiply the result, 5, by 1.95. The result is 9.75, or 10 °C.. If you calibrated the temperature sensor and found it 2 °C. high, subtract 2 from the 10 °C.. The real temperature is therefore 8 °C..

The output of the sensor is linear throughout its range -40 °C. to +100 ,°C. . The individual temperature sensors can be off by 4 °C. Because it's linear you can calibrate it at just one temperature and add or subtract the difference from the data logger reading. We've used crushed ice and water as a calibration point and found it works good at soil temperatures. Our high end data loggers do have temperature resolutions of 1 °C..
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