Endress+Hauser Prosonic S FMU90, Description, Page: 51 / 216

The "flow" menu
51
3.2 The "backwater" submenu
3.2.1 Basics
The flow measurement can be impaired by backwater on the downstream side or by dirt within the
flume. The backwater and dirt detection function can detect these errors and ensure that the
Prosonic S reacts appropriately.
Two sensors are required for backwater and dirt detection. The first sensor is mounted above the
upstream water, the second above the downstream water. The Prosonic S evaluates the ratio of the
downstream level h
2
and the upstream level h
1
.
Backwater detection
Backwater is detected if the ratio h
2
/h
1
exceeds a critical value (typically 0,8 for Venturi flumes).
In this case, the flow is continuously reduced to 0. An alarm relay can be configured which indicates
the backwater alarm.
Dirt detection
Dirt within the flume is detected if the ratio h
2
/h
1
falls below a critical value (typically 0,1). An
alarm relay can be configured which indicates the dirt alarm.
L00-FMU90xxx-19-00-00-yy-033
(a): Upstream sensor;(b): Downstream sensor
3.2.2 The "basic setup" submenu
"backwater sensor selection"
"input"
Use this parameter to allocate the downstream sensor to the channel.
The available options depend on the instrument version and the connected sensors.
"sensor selection"
Use this parameter to specify the type of the connected ultrasonic sensor.
Prosonic S
(a)
(b)
Q
h
1
h
2
⇒
backw. sensor sel. F1304
input:
sensor selection:
detected: