Wilkerson Instrument DR1920 Operating Manual

SYSTEM CONSIDERATIONS

The intent of the DR1920 is to provide
protection from an overflow. To this end,
the DR1920 should be made as
independent of the normal working level
control system as possible.

Pushing the AUX Alarm switch until Pump
1 starts and then releasing it will exercise
Timer 1, Timer 2, and Pump 1. The pump
should stop when Timer 2 reaches its set
time.

DR1920

DUPLEX LIFT STATION

BACK-UP PUMP

CONTROLLER

DESCRIPTION

The DR1920 Back-Up Pump Control is a
compact DIN rail mounted unit used to monitor
a backup level alarm in a tank or wet well
and start up to two pumps when a high
alarm switch closes. The unit is used as a
backup to normal tank / well level controls
and is wired to the High-High Alarm switch
to prevent overflows in situations where
the primary level control system fails.

When the level switch in the tank or well
closes, the DR1920 closes a relay that starts
Pump 1 and starts an internal Timer 1. When
Timer 1 reaches its set time, and the level
alarm switch is still closed, Pump 2 is
started. Pump 1 and Pump 2 will run until
the level alarm switch opens. When the
level switch contact opens, Timer 2 is
started and both pumps continue to run until
Timer 2 reaches its set time.

If the alarm switch opens during the Timer 1
interval, Timer 2 is started when the switch
opens. Pump 2 is not started and Pump 1
will run until Timer 2 reaches its set time.

The DR1920 also has provisions to alarm
on a switch opening.

ALARM SWITCH MONITOR

The DR1920 monitors the open or closed
status of a switch contact that is already
wired into a control system. This switch
may have any of several voltages that are
used to control the pump system. In addition,
if the primary control system fails, the normal
voltages may not be present.

The DR1920 is wired across the alarm
switch contacts and uses a unique circuit
that measures the impedance present
between the switch contacts. When the
DR1920 senses a low impedance, it begins
its control function, regardless of any
absence or presence of voltage across the
switch contacts. This feature allows the
DR1920 to be wired in parallel across the
switch contacts without regard to the
existing control system, permitting simple
installation in existing systems. For
situations where the existing wiring
prevents this circuit from being used, an
isolated contact must be provided. A second
input, which requires an isolated contact or
open collector transistor is also provided.

A Reset input is provided to stop the pumps
and reset the timers. It requires a contact
closure or open collector transistor.

Since the Back Up Pump Control is used
only when there is a problem with the
primary control, the digital alarm inputs, as
well as the reset inputs, are provided to
allow the periodic exercising of the system
to verify functionality.

The Alarm Input of the DR1920 should be
wired directly across the contacts that
sense an emergency high level condition.
If this is done, the only requirements for
the DR1920 to be able to prevent the
overflow is that it has primary power, the
pumps can be started and the alarm switch
closes as it should.

Because the DR1920 is only used for an
emergency, it should be tested periodically
to insure it is performing properly. A
manual momentary pushbutton switch can
be wired to the AUX Alarm Input and
another can be wired to the RESET input
to perform this testing.

SPECIFICATIONS

Alarm Inputs:

Impedance Input - NO or NC switch
contact. Switch can be wired to other
devices and still be monitored by the
DR1920. To sense an “open” switch,
the impedance across the switch must
be 1500 ohms or greater at 20 KHz. To
sense a “closed” switch, the impedance
across the switch must be less than
500 ohms at 20 KHz. Will work with
switch wired in series with 120VAC
relays or in series with 12 or 24V DC
relays. See Figure 2.

Auxiliary Input - Isolated switch or Open
collector NPN transistor

Internal jumper may be selected for
“Open” or “Close” to alarm. Jumper
affects both inputs.

Reset Input:

Stops pumps and reset timers
Requires isolated contact closure or
open collector NPN transistor

Outputs:

Pump Control Relays - Two NO 10A
(Form A) relay contacts

Pushing the AUX Alarm switch and holding
it until Pump 1 and Pump 2 are running and
then releasing it exercises Timer 1, Timer
2, Pump 1 and Pump 2. Since Timer 2
was tested in the first test, the Reset
switch can be pushed to reset the timers
and stop the pumps.

This testing can be performed by a PLC if
due consideration is given to the tank level
when testing is started and the potential
problems that could occur if the PLC fails
in a mode that creates a constant Alarm
input or constant Reset input.

Discrete Outputs - Individual optically
isolated NPN transistors conduct for
Pump 1 and Pump 2 run.
Sink or source - 30 mA

Timers:

Timer 1 - Pump 2 start delay.
Adjustable 2 to 126 seconds (2.1
minutes) in 2 second increments

Timer 2 - Pump(s) Run Time
(after alarm switch opens)
Adjustable 5 to 1,275 seconds (21.25
minutes) in 5 second increments

Timers are set with binary coded DIP
switches inside the enclosure

Indicators:

LED Indicators for -

Pump 1, Green OFF, Red RUN
Pump 2, Green OFF, Red RUN

Power:

85/250 VAC ±10% 50/60 Hz, 2 VA

1 2

WIRING

DR1920

WARRANTY

The DR1920 carries a limited 3 year warranty
from the date of shipment. In the event of a
failure due to defective material or
workmanship, the unit will be repaired or
replaced at no charge. Repairs will take
place at the Wilkerson Instrument Company
factory. In no event shall Wilkerson Instrument
Company's responsibility exceed the original
purchase price of the covered product.

The product covered by this warranty is
warranted to perform to it's original
specifications as published by Wilkerson
Instrument Company. There is no warranty
of merchantability or fitness for a particular
purpose. This warranty excludes liability for
any consequential damage that may
accompany or follow a covered defect or
failure. The warranty excludes damage
from improper use, abuse, or operation
contrary to instructions provided by
Wilkerson Instrument Company.

MOUNTING

The module mounts on a standard H-35 DIN
rail. A spring latch holds it in place. The
module is demounted by using a screw
driver to release the latch. The latch is
accessible at the bottom of the module.

The ALARM input is designed to monitor the status of switch contacts that may already be
in use. The ALARM input senses the impedance it sees across the switch contacts and
when this impedance drops below 500 ohms at 20 KHz, the DR1920 senses an alarm
condition.

If the "Alarm On Open" mode has been selected, then the alarm switch is normally closed
and an impedance higher than 1500 ohms at 20 KHz must be seen by the DR1920, when
the switch opens, for an alarm condition to be sensed.

This unique circuit allows the DR1920 to be wired across most contacts that are already
in use.

The circuit drawings below show how the DR1920 can be used to monitor contacts that are
used to switch an AC relay and a DC relay with built in transient supressor diode and LED
status indicator.

Figure 1

Figure 2

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CASE DIMENSIONS INCHES [mm]

Specifications Are Subject To Change Without Notice. © 2007 Wilkerson Instrument Co., Inc. DWG#W103854 3/07

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