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4.2 Open Channe l Flow Measurement
•
For ultimate accuracy, install the sensor as close as possible above the expected maximum water level (see minimum measuring range).
•
Install the device in a place defined by the characteristics of the metering channel along the longitudinal axis of the flume or weir. In case of Parshall
flumes supplied by NIVELCO the location of the sensor is marked.
•
In some cases foam may develop on the surface. Make sure that the surface, opposite to the sensor remain free of foam for proper sound reflection.
•
From the point of view of measurement accuracy the length of the channel sections preceding and following the measuring flume and their method of
joining to the measuring channel section are of critical importance.
•
Despite of the most careful installation, the accuracy of flow metering will be lower than that of specified for the distance measurement. It will be
determined by the features of the flume or weir applied.
4.3 Electrical Con nection
•
After removal of the cover of the housing and taking out the
display module (if any), the screw terminals can be accessed.
Suggested cable core cross section 0.5 ... 1.5 mm
•
The unit has to be grounded by the inner or outer grounding
screw. For practical purposes units with plastic housing has to
be grounded by the outer grounding screw.
•
The unit may be damaged by electrostatic discharge (EDS),
via its terminal, thus apply the precautions commonly used to
avoid electrostatic discharge e.g. by touching a properly
grounded point before removing the cover of the enclosure.
•
After connecting the cable and unit programmed proper
sealing and closing should be ensured.
4.4 Loop Curent C hecking
After removing the cover (and the Display Module if there is any) the actual loop current can be measured with an accuracy of 0.5% by connecting an
ampermeter (in the range of 200 mV) to the points indicated on the drawing above
SE/SG-300 series two-wire compact ultrasonic level transmitters
2
1/2" NPT
4mA
20mA
4...20mA
Pg 16
Pg 16
Grounding
Loop current
checking point
4 ... 20 mA
and
Power Supply
(HART)
I- I+
1/2" NPT
9
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