System Setup

Drawbacks

SDI-12’s major advantage of allowing users to connect up to 62 sensors to one logger port also comes with one major drawback.  If one sensor on the line fails, the entire line of sensors will fail without indicating which of the sensors is faulty. SDI-12 users must be prepared for periodic system downtime. If loss of all data for any period of time will jeopardize your study, SDI-12 is a bad fit for you. Visit the Decagon website for more appropriate environmental monitoring systems.

However, if your study can handle brief time periods without data, keep reading.

Addressing Each Sensor

Before hooking up to 62 sensors into one data logger port, you must give each sensor a distinct address that the data logger will use to communicate with the sensor.  Imagine a classroom full of students and one teacher.  If  each student has a different name, the teacher can call on a specific student using their name.  This is how SDI-12 works: assigned addresses allow the sensors to share a port but be queried individually.

The sensor address can be any of the following:

  • A number between  0-9

  • A lower case letter between a-z

  • An upper case letter between A-Z

If two or more sensors on the same communication line have the same address, the logger will receive no data when  that specific address is queried, so it is a good idea to label each sensor as you set the  addresses.

Data Organization

Once each sensor is addressed, figure out where each addressed sensor will be installed in your study.  At minimum, we suggest making a map of your study site showing sensor locations and a spreadsheet containing your sensor addresses and notes.  SDI-12 logger data consists of only the sensor address followed by that sensor’s data, so you will want to have clear address and location information in your project notes.

How Can I Get 62 Wires into One Logger Port?

If you’ve ever tried to stick multiple wires into a small data logger port, you’ve probably found that you can squish about four wires into the port before there is no more room. In order to successfully connect up to 62 sensors to one logger port, you’ll need a sensor bus. There are some rudimentary solutions available, but typically the best solution is to build one yourself.  A bad bus is the main cause of  SDI-12 network failures, so take some time to do it right–you’ll thank yourself later.

Logger Programming

Once all of your sensors are addressed and connected to a logger, you’ll need to program your logger to know what information to ask your sensors for, and when it should ask for it. Using an example program as a starting point can make the programming process considerably easier, but you should expect to spend a significant amount of time on this step.