SRA – 100 8M
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Application
The filling level limit switch
SRA – 100 8M
is used, to evaluate one or two filling levels resp. limit levels in
electrically conductive liquids with a conductivity of minimum 0,125µS/cm resp. a resistance of maximum 8M
.
For the connection of level resp. measurement transducer in explosion hazardous areas, the device is equipped
with two intrinsically safe supply and signal circuits.
Function
Measuring principle
The signal circuit of the filling level limit switch is connected to the reference electrode or the metallic wall of the
container resp. pipe and to the measuring electrode.
The alternating voltage, that is generated by the integrated electronic is than applied either between the
electrode rods or between the electrode rods and the metallic wall of the container resp. pipe that is connected
to the metallic process connection, realizing the reference electrode.
Due to the use of a alternating voltage the corrosion at the electrode rod and the electrolytic decomposition of
the filling liquid is avoided.
As soon as the electrically conductive liquid makes a connection between the electrodes resp. between the
electrode and the metallic wall of the container resp. pipe, an alternating current flows, that causes a decrease
of the alternating voltage.
Signal evaluation
An evaluation circuit supervises this alternating voltage. A voltage drop is detected and the evaluation circuit
switches the relay resp. relays, depending on the set safety function.
The switching state of the relays is indicated at the front side of the device by two yellow LED’s.
Switching delay
In some applications it is necessary to compensate heavy signal fluctuations that may be produced by mixing
machines or at fill-in resp. emptying of containers, to avoid spurious switching actions.
Two switches at the front side of the device allows the configuration of a switching delay of 0,5 / 3 / 5 / 8 s.
This delay time effects both channels separately, at activation and deactivation of the filling level relays.
Sensitivity range
The device can be adjusted in the resistance range 1 to 8 M
. Within this range a fine adjustment can be
carried out by a trimmer at the front side of the device.
Configuration of the second output relay S2
The second output relay can be configured in two operation modes:
2nd filling level relay to electrode at CH1 (relay switches like filling level relay S1 – parallel mode)
Filling level relay to electrode at CH2 (two channel mode: CH1 to S1 / CH2 to S2)
