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

Page 10

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1-2 Operation

H-424MS

Normally the H-424MS operates as a transparent SDI-12 to SDI-12 bridge. However, in order to

wake the remote end of the link from sleep the master H-424MS can be addressed itself as a

“sensor”. The H-424MS comes from the factory with its address set to “0". When the master H-

424MS detects address 0 it responds as a SDI-12 sensor and does not pass the command to the

remote site(s). Issuing the “0M!” command causes the H-424MS to perform a wakeup sequence

to the remote sites. The timing is controlled by two timers; a Wakeup and an Inactivity timer.

The settings of these programable timers is stored in EEPROM within the H-424MS;

Power Save Operating Sequence

1. The data recorder first issues a “0M!” command to the master H-424MS module.

2. The master H-424MS responds to the command as a pseudo “sensor”, and reports the

measurement will take a fixed period of time to complete. The reported time is determined by

the Wakeup Interval time setting + 1 seconds.

3. The master H-424MS transmits wakeup nulls every 40usec during the “measurement”.

4. Remote H-424MS modules periodically wakeup and check for inbound messages. The

wakeup is initiated by a low power circuit controlled by the Wakeup Interval setting.

5. If an inbound message is detected while awake, the remote module remains awake for a

period set by the Inactivity Timer.

6. At the completion of the “0M!” command, both the master and slave H-424MS modules are

awake and can service a SDI-12 command. At this point the data logger issues measurement

or other commands to the actual remote sensors.

7. If no additional commands are sent by the data logger, both master and remote modules

resume their low power sleep mode after their respective Inactivity Timers run down.

1.3 Setting the Jumpers

The H-424MS circuit board has three push-on jumpers which must be properly set. Each jumper

is a 3-pin stake-pin header with two possible positions. The jumpers can be accessed by opening

the front cover of the enclosure.

Jumper Function

Options

Description

J2

Mode

Master/Slave Selects either Master or Slave operation

J3

Power Save

On/Off

Enables or disables the power save feature

J6

Loopback Test On/Off

Enables or disables the loopback test mode

All H-424MS's in the installation MUST have the same power-save jumper selection. Leave the

Loopback Test jumper in the OFF position for normal operation.