Xylem 780 LIQUID SAMPLER - Manual (Page 5)

5
As shown in the diagram, the compressor starts when the
sampler is started. When starting, the valves are switched
out to put pressure on the sample glass, to remove any
previous sample. The purge time is determined by the
timer T1 (purge).
When time T1 has elapsed, the valves switch to create a
vacuum. The sample glass and the water will be pulled into
the sample glass, until the level electrodes are activated.
When the level electrodes have been activated, the valves
are switched over again, to put pressure on the sample
glass. Excess sample will be blown back in the sample
tube. Pressure continues until the time, determined by the
timer T2 has elapsed.
The outlet valve opens under pressure and the sample is
dropped into the sample container. The outlet valve
remains open for time T3 (purge).
It is possible to switch off the last purge by cutting off the
connection “Purge“ 2.
The sequence contains an alarm, which activates if the
sample does not contact the electrodes by a preset time
T4 (alarm). This alarm protects the sampler from continuous
cycles caused by blockage. However since the
compressor creates a 4 bar pressure, it is not very likely
that blockage will occur.
If the sampler does not succeed to activate the level
electrodes the second time before the time T4 has run out,
the sampler will stop and prevent further starts. To indicate
the alarm, the yellow alarm flashes and the alarm relay is
activated. To make the sampler start again, the alarm state
has to be reset by activating the “alarm” key.
Setting of sequence times Setting of sequence times Setting of sequence times Setting of sequence times Setting of sequence times
The sequence time is factory adjusted, to a total sample
time of approx. 2 minutes.
The 4 timers have the following time ranges:
Timer (function) Timer (function) Timer (function) Timer (function) Timer (function) Range Range Range Range Range Factory setting Factory setting Factory setting Factory setting Factory setting
Purge T 1: 30 - 150 sec 30 sec
Volume T 2: 30 - 150 sec 30 sec
adjustment
Outlet T 3: 30 - 150 sec 30 sec
(outlet)
Alarm T 4: 30 - 150 sec 60 sec
The sequence times are adjusted with the potentiometers
on the back of the control unit. To adjust the time, the
control unit must be removed. Switch off the sampler (ON/
OFF) key and unscrew the 4 screws, which hold the front
panel to the control panel. The control unit is integral with
the front panel. When the control unit has been removed
the sampler can be started again and the adjustment
made.
There are no dangerous voltages present at the control
unit, so it can be touched during operation. When the
desired adjustment has been made, depress (“ON/OFF”
key) to avoid short circuit during mounting, and the control
unit attachment.
External sequence External sequence External sequence External sequence External sequence
The sampler can be controlled externally, e.g. from a PLC.
When an external control is connected, it works in parallel
with the internal control, so that it is possible to select a
manual sample controlled by the internal system of the
sampler, at the same time as the external control.
The inputs are semi-conductor inputs as indicated at the
diagram.
The input signal should be not activated <0,5 V DC
Activated 5-24 V DC.