Xylem H-3531 FlashLite - Manual (Page 22)

2-10 Installation
H-3531
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-3531
FlashLite™ is connected to a SCADA or PLC system instead of a SDI-12 data logger, the
H-3531 FlashLite™ can be programmed to automatically make continuous measurements.
To program the H-3531 FlashLite™ to make continuous measurements, issue an extended
SDI-12 command and set or use the RS-232 menu interface. See chapter 4 and 5 for
details. This setting can be made at the factory if requested.
Note: When the H-3531 FlashLite™ 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 is loaded with new valid data.
2.8.3.1 Programming the 4-20mA Output Range
The H-3531 FlashLite™ scales the current Stage data to drive the 4-20mA output.
The 4-20mA_Hi and 4-20mA_Lo settings control how the Stage data is processed.
The 4-20mA_Lo should be set to the desired Stage corresponding to a 4.00mA
output. The 4-20mA_Hi should be set to the desired Stage corresponding to a
20.00mA output. See chapter 4 and 5 for more details.
2.9 Testing
Before installing the H-3531 FlashLite™ in your field location, you may wish to first test the
sensor and data logger in your shop or lab. This allows you to become familiar with H-3531
FlashLite™ and the data logger in a controlled environment. The H-3531 FlashLite™ can be
tested with a pressure standard or water filled standpipe. However, for this test to work correctly,
the standpipe must be connected to the chassis ground of the data recorder. The wire establishes
a ground connection between the water and the data logger. Water and other conductive objects
isolated by a plastic bucket or table surface pick up AC noise from nearby lighting and power
lines. The AC noise is coupled by the water to the stainless diaphragm in the pressure sensor. If
a plastic or non-conductive tube is used to connect to the pressure source to the H-3531
FlashLite™, the sensor will be electrically isolated from the water media. The AC noise may
affect the pressure measurement due to large voltages between the water media and the sensor
(data logger) ground. This precaution is not necessary for field installations because surface water
and ground water are not isolated from earth ground.