Xylem H-4161 - Manual (Page 8)

1-4 Introduction
H-4161
Figure 3 Example architecture with sixteen 4-20mA channels and a data logger
1.3 Initiate Measurements (Module Mode = 1)
Applications often arise where is it desired to connect a SDI-12 sensor directly to a 4-20mA input device
such as a PLC without the use of a data logger. When programmed to initiate measurements, the H-4161
sends 0M! (or 0M1 to 0M9) commands to the sensor attached to the auxSDI-12 port and collects the
measurement data. The data is scaled and used to update the H-4161's 4-20mA output.
The Initiate Measurement mode also provides support for a hybrid architecture employing both a data
logger and PLC. Both the primary and auxSDI-12 ports can be used. For example, the following
illustration shows a dam equipped with sixteen SDI-12 gate position sensors (inclinometers). Each gate
is equipped with a H-4161 module which initiates measurements and sends 4-20mA data to the PLC. All
16 channels make simultaneous measurements. The radial architecture provides near real-time gate
position data to the PLC. The system also has a data logger which periodically collects the gate position
and other data on a timed schedule. The data logger sends “aM!” measurement commands to each H-
4161 and collects the resulting data, channel-by-channel. The measurement data collected in response to
the “aM!” command will be the data from the most recent measurement made by the H-4161 to the
sensor on the auxSDI-12 port (no actual “measurement” is made). The H-4161 supports simultaneous
SDI-12 commands/responses on both the primary and auxSDI-12 ports. The data logger can collect gate
position data without disturbing any measurements currently in progress with the gate position sensors.
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