Low Supply Pressure Shutdown
High Membrane Feed Pressure Shutdown
High Feed Water Temperature Shutdown
Low Salt Rejection Shutdown
Output or Transformer Overload
High Differential Pressure Shutdown (when using analog sensors)
High Permeate Pressure Shutdown (when using analog sensors)
High and Low Flow Recovery Shutdown (when using flow sensors)
All 24 VAC outputs are protected by positive temperature coefficient resistors
(polyfuses). The polyfuses interrupt the current to the AL250-V2 outputs should an
overload condition occur on an output. The polyfuses will reset when power is turned
off to the AL250-V2 and the fuse is allowed to cool. This eliminates the need for
replaceable fuses and prevents damage caused by the incorrect fuse being installed.
The primary side of the transformer in the AL250-V2 is also protected by a polyfuse.
The AL250-V2 will indicate an overload condition for each output. It will also indicate
an overload condition if the power to the AL250-V2 is interrupted within five seconds
after any of the six outputs have been activated. In this way, the AL250-V2 can
detect an overload in the transformer.
Inputs The AL250-V2 is equipped with the following inputs:
Conductivity Sensors: There are five inputs for each conductivity sensor, two for the
temperature detector (RTD), two for the electrodes in the conductivity cell,
and one for the cable shield. Inputs are available for both the feed and
product sensors. Sensors with cell constants of 0.01, 0.1, 1.0, and 10.0 may
be used. These cell constants provide a detection range of 1 uS/cm to
100,000 uS/cm. Only sensors with a 1000 ohm RTD will work with this
controller.
Pressure Sensors: There are four 4-20 mA inputs for pressure sensors monitoring
feed pressure, interstage pressure, reject pressure, and permeate pressure.
Differential pressures are calculated from feed pressure less interstage
pressure and interstage pressure less reject pressure. If not used, these
pressure inputs may be disabled in the settings menu.
Flow Sensors: There are three inputs for sinking pulse flow sensors. One sensor is
configured for feed or permeate flow, one sensor is configured for recycle
flow, and one sensor may be configured for either reject or permeate flow.
Percent recovery is calculated from feed and permeate flow. If not used,
these flow inputs may be disabled in the settings menu.
Low Pressure Switch: This is a dry contact that signals the system to shut down if the
pump suction (supply) pressure falls below the desired value. This is a
normally closed contact (when system is shut down). When a circuit is not
complete between the two terminals, the system will operate. If contact is
made between the two terminals, the system will shut down. An LED will
indicate when the system is in a state of low pressure shut down. The
system will attempt to restart every thirty seconds. The system will make up
to five attempts at restarting. The system must be able to run continuously
for thirty seconds without sensing low pressure. If the controller still senses
low pressure after the fifth restart, it will lock out and the alarm reset button
must be pressed to resume operation.
