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H-424ms – Xylem H-424MS V1.0 User Manual

Page 11

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H-424MS

Operation 1-3

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.