5.3 Functions
General functionality
The 3UG4501 lling level monitoring relays and the connectable 2‑pole or 3‑pole 3UG3207-..
probes are used to monitor the lling levels of electrically conductive liquids.
Monitoring
The working principle of the 3UG4501 lling level monitoring relay is based on measurement of
the electrical resistance of the liquid between the probes (minimum and maximum level) or the
reference potential (conductive measurement principle). The output relay changes its switching
state if the measured value is below the sensitivity set on the front. The probes (e.g. 3UG3207‑..)
are powered with alternating current (AC measured current) to exclude electrolysis phenomena
in the liquid.
Note
The lling level monitoring relays do not have active monitoring of probe defects or probe
conductor defects. Therefore when selecting the probes and routing the cable, make sure that
this source of error is precluded. For example, use stable bow probes if wire electrodes are in
danger of being broken.
Depending on their design, the 3UG4501 lling level monitoring relays are powered with a
24 V AC/DC or 24 to 240 V AC/DC rated control supply voltage through terminals A1+ / A2-. When
the rated control supply voltage is applied, the green LED next to the coil symbol on the device
cover lights up.
Note
On the 3UG4501‑.AA30 devices with 24 V AC / DC versions, as a common reference for the AC
probe voltage at terminals Min and Max, terminal M must not be connected to terminals A1 / A2
of the device or grounded!
On the 3UG4501‑.AW30 24 to 240 V AC / DC versions, terminals M, Min, and Max are electrically
isolated from terminals A1 and A2 of the rated control supply voltage!
Note
The specied voltages represent the absolute thresholds.
Tripping delay
Tripping can be delayed by 0.5 to 10 s to avoid tripping the switching function too early when
the level has not quite been reached (e.g. wave motion or foaming of the liquid).
The switching states of the output relay are given below in the section entitled "Function
diagrams."
3UG4501 lling level monitoring relay
5.3 Functions
SIRIUS 3UG4 / 3RR2 monitoring relay
Equipment Manual, 07/2021, NEB927043002000/RS-AD/005 73
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