Xylem H-424MS V1.1 - Manual (Page 7)

1.4 Programming Your Data Recorder
You must prepare your data recorder to receive and record SDI-12 data from the sensors
attached to the data recorder. Since data recorders differ widely, refer to your recorder
manufacturer's directions.
If you are not using the H-424MS power save feature (power save jumpers are set to OFF), no
additional programming of the data recorder is needed. The SDI-12 radio link will operate
transparent to the data recorder’s operation. Do not set the address of any remote sensor to “0".
If you are using the H-424MS power save feature (power save jumpers set to ON), you will need
to program your data recorder to collect one data value from the local H-424MS with a “0M!”
command. The H-424MS's address can be changed if necessary (see Chapter 2). The dummy data
value collected can be discarded. The data recorder must make this “measurement” BEFORE
attempting to access any sensor located on the remote end of the radio bridge. The purpose of this
pseudo measurement is to allow built-in time to wake the remote sites from sleep. The H-424MS
will send a normal service request at the completion of the “measurement”.
Your data logger allows you to select which SDI-12 addresses which will be logged, but certain
models do not allow the address sequence to be specified. Often the logger will start at the lowest
selected address and automatically sequence to increasing addresses. You must change the
address of your sensors or of the H-424MS such that the H-424MS's “pseudo” sensor is always
accessed first. The H-424MS comes from the factory with its address set to “0" which will work
for most installations.
1.5 Programming the H-424MS Power Save Settings
When the power save option is not selected, the radios are continually powered, normally in a
receive mode drawing 135mA. In order to reduce the power draw use the power save mode. If
the power save option is selected, the radios are normally turned off, reducing the standby power
draw to 0.5mA. Periodically the slave H-424MS wakes up from the low power mode, turns the
radio on and listens for messages from the master. The Wake Interval value determines how
often this occurs. The default Wake Interval is 15 seconds. The slave listens for 170ms, if no
messages are found it returns to the sleep condition. The Wake Interval setting determines the
average current draw, for this example the slave draws 0.5mA for 15 seconds and 135mA for
170ms. A shorter Wake Interval setting allows faster completion of the “0M!” command at the
cost of higher average current drain.
The master H-424MS remains in the 0.5mA low power mode until the data logger issues a break.
After receiving the “0M!” command the radio is turned on, requiring 135mA. If no SDI-12
activity is detected over a period of time controlled by the Inactivity Timer setting, the radio is
turned off and the master resumes it’s 0.5mA low power mode. The default Inactivity Timer is 30
seconds.
H-424MS
Operation 1-3