Data Sheet

Application notes for 72.01 and 72.11
Applications
The main application for these relays is for the sensing and control of the
level of conductive liquids.
Selectable options allow for this control to be achieved either through
a filling operation or through an emptying operation, and in either case
“positive logic” is used.
Level control can be achieved around a single level- using 2 electrodes, or
between Minimum and Maximum levels- using 3 electrodes.
Additionally, the 72.01, with its adjustable sensitivity setting, can be ideal
for monitoring the conductivity of liquids.
Positive safety logic
These relays work according to the principle that it is the closure of
a normally open output contact that will be used to control the pump,
both in filling and emptying applications. Consequently, in the event of
a failure of the supply local to the relay, the filling or emptying will cease.
This is generally considered to be the safest option.
Overrunning of tank on filling
Care must be exercised to ensure that the tank cannot overrun. Factors
that have to be considered are the pump performance, the rate of
discharge from the tank, the position of the single level electrode (or
maximum electrode), and the run-on time delay. Keeping the time delay to
a minimum will minimise the possibility of tank overrun, but will increase
the installed switching rate.
Prevent dry running of pump on emptying
Care must be exercised to ensure that the pump cannot run dry. Similar
considerations must be given as outlined above. In particular, keeping the
run-on time delay to a minimum will minimise the risk, but again, it will
increase the installed switching rate.
Run-on time
In commercial and light industrial applications the use of a short Run-on
time delay is more appropriate, due to the relatively small size of tanks and
the consequential need to react quickly to the change in level. Larger scale
industrial applications involving larger tanks and powerful pumps must
avoid a frequent switching cycle, and the use of the 72.01 set for the longer
Run-on time of 7seconds is suggested.
Note that the short run-on time will always achieve closer control to the
desired level(s), but at the cost of more frequent switching.
Electrical life of the output contact
The electrical life of the output contact will be enhanced where a larger
distance between the Max. and Min. electrodes (3-electrode control) can
be realised. A smaller distance, or level control to a single level (2-electrode
control), will result in more frequent switching and therefore a shorter
electrical life for the contacts. Similarly, the long run-on time will enhance,
and the short time will reduce, electrical life.
Pump control
Small single-phase pumps within the kW (0.55kW- 230VAC) rating stated
may be driven directly by the level relay output contact. However, where
very frequent switching is envisaged, it is better to “slave” a higher power
relay or contactor to drive the pump motor. Large pumps (singlephase and
three-phase) will of course require an interposing contactor.
Water leakage and condensation in oil lubrication systems
To detect condensed water vapour or water leakage within lubricating
systems, monitor by sensors connected to B1- B3 (Function E or ES, Z1-
Z2 linked). Condensed water vapour has low conductivity, therefore
choose monitoring relay type 72.01.8.240.0002 with sensitivity range of
(5…450)kΩ and sensor type 072.11.
Floor flooding control
To detect floor water due to spills or flooding, monitor using sensors
connected to B1 - B3 (Function E or ES, Z1 - Z2 linked).
Choose monitoring relay type 72.01.8.240.0000 or 72.11.8.240.0000,
together with floor water sensor type 072.11.
Electrodes and cable lengths
Normally 2 electrodes or 3 electrodes will be required for control about
a single level, or control between Min. and Max. levels, respectively.
However, if the tank is made of conductive material it is possible to use
this as the common electrode, B3, if electrical connection can be made
to it.
The maximum permitted length of cable between the electrode and the
relays is 200m, for a cable not exceeding 100nF/km.
A maximum of 2 relays and associated electrodes can be employed in the
same tank- if two different levels need monitoring.
Note: It is permitted to make direct electrical connection between
terminals B1-B3, and B2-B3, (without using electrodes/liquid), but in this
case it is not possible to set up the sensitivity.
Electrode choice
The choice of electrodes may depend on the liquid being monitored.
Standard electrodes 072.01.06 and 072.51 are suitable for many
applications but some liquids may be corrosive for example, and may
therefore require custom made electrodes- but these can usually be used
with the 72.01 and 72.11 relays.
On site commissioning
To confirm the suitability of the relay sensitivity to the resistance
between electrodes it is suggested that the following checks are made.
For convenience it is suggested that the fill function and the shortest
run-on time are selected.
Commissioning
Follow these setting-up instructions to achieve correct operation:
72.01
Select the function “FS” (Filling and Short delay of 0.5s), and set the
sensitivity control to 5kΩ. Ensure that all electrodes are immersed in
the liquid - expect the output relay to be ON. Then, slowly rotate the
sensitivity control in the 150kΩ direction until the level relay switches
OFF (internal output relay will switch OFF and red LED will switch slowly
flash).
(If the level relay does not switch OFF then, either the electrodes are not
immersed, or the liquid has too high impedance or the distance between
electrodes is too long).
Finally, select the filling or emptying function as required, run in real time
and confirm that the level relay works as required.
72.11
Select the Filling function “F”, (Z1- Z2 open). Ensure that all electrodes
are immersed in the liquid, but leave electrode B3 disconnected - output
relay should be ON. Connect electrode B3, and the level relay should
switch OFF (internal output relay will switch OFF and red LED will switch
slowly flash).
(If the level relay does not switch OFF then, either the electrodes are not
immersed, or the liquid has too high impedance or the distance between
electrodes is too long.)
Finally, select the filling or emptying function as required, run in real time
and confirm that the level relay works as required.
14
IV-2018，www.findernet.com
E
72 SERIES
Monitoring relays
72
SERIES