Xylem H-3342 - Manual (Page 7)

H-3342
Introduction 1-3
1.5 Using the Adjust Knob to Change SDI-12 Address
If the ‘Read’ button is held down while the H-3342 is being powered up, the display will show
the H-3342's current SDI-12 address. The SDI-12 address may be changed using the Adjust
screw. Turning the Adjust screw will change the address in the range of 0 to 9. When the Read
button is released, the new SDI-12 address is saved and the display switches to the normal stage
readout. To change the SDI-12 address again, the power must be disconnected and the special
power-up sequence repeated. The H-3342's address may also be changed with an extended SDI-
12 command (See Chapter 3).
1.6 4-20mA Output
The H-3342 has a 12-bit digital-to-analog converter (DAC), precision voltage reference and a 4-
20mA current transmitter. The SDI-12 and 4-20mA sections are isolated from each other with a
high voltage digital opto-coupler. The Stage is scaled into a 12-bit value and loaded into the
digital-to-analog converter to control the current transmitter.
The 4-20mA output is updated whenever a measurement is made. If no measurements are made,
the 4-20mA output becomes “stale”. For industrial applications where the H-3342 is connected to
a SCADA or PLC system and low-power is not of concern, the H-3342 can be programmed to
make continuous measurements. See Chapter 3 for details. The H-3342 comes from the factory
with the power mode set to the Sleep mode.
Note: When the H-3342 is first powered up, the output current is set to 4.0mA. It remains at
4.0mA until the first measurement sequence. The digital-to-analog converter is powered from
the loop side of the opto-isolator. If the loop power is disconnected or is applied after the SDI-12
side is powered up, the data in the digital-to-analog converter will be lost. When the loop power
is restored, the 4-20mA output will be at an unknown value. Once a fresh SDI-12 measurement
is made, the digital-to-analog converter will be loaded with new valid data.