CM-20 Applications
The
CM-20 can execute predefined control functions independently from SCADA
communications These control functions (or applications) are available at
this time:
Application #1
I/O Expander with Watchdog Output
One
or more CM-20 units is polled by your RTU via a 2-wire RS485 line and/or via
it’s RS232 port. Radio keying is available in the RS232 port.
Twelve
digital statuses as well as cycle counts (On to Off transitions) and elapsed
time accumulators for these inputs are available from each unit.
The cycle count and elapsed time accumulators retain their values even
when power is lost to the CM-20 or when your RTU receives a new download.
Four
digital outputs are available in each CM-20 for control by your RTU.
These outputs can drive DC relays or optically isolated relays.
A
watchdog output is provided on each CM-20.
This output toggles continuously until communications have failed for a
preset interval. By connecting this
output to an optional watchdog relay you can switch to a local control mode
automatically if telemetry fails.
Application
#2
Adjustable Frequency Drive Interface with Local Float Backup
This
configuration is useful for multiple pump applications such as those often used
in sewage lift stations. One CM-20 unit is connected to each adjustable frequency drive. A master controller using the 2-wire RS485 line coordinates
all units.
For
each pump, the CM-20 interfaces to the H-O-A selector switch, check valve limit
switch, drive status and fault contacts, and independent high and low floats.
For certain AFD’s, the RS232 port can monitor additional drive data.
Under
normal operation the CM-20 starts and stops the drive based on commands from the
master controller. If the high or
low limit floats are activated, the CM-20 will switch to backup mode after a
configurable delay. Once in backup
mode the CM-20 controls the pump in a constant speed mode independently of the
master controller.
In
all modes the CM-20 enforces parameters such as minimum on and off times, and
generates faults including check valve fail and flow fail.
A reset button wired to the CM-20 is used to clear faults and to reset
from backup mode.
If
control power for each CM-20 and it’s related input devices is derived from
its respective drive, each pump can operate in manual and backup modes totally
independent of the other drives as well as the master control system.
Application
#3
Duplex Pump Station Monitor with Local Float Backup
This
configuration is useful for small duplex pumping panels.
One CM-20 unit monitors the status of both pumps and various alarm
inputs. A SCADA master station
collects alarm and status information from multiple CM-20 locations.
The
CM-20 will generate “Pump Fail” alarms if the local control system calls for
a pump and it doesn’t run.
By
connecting a high float to the CM-20 it can provide a simple backup system.
If the float goes up for a configurable time delay, the CM-20 will start
pumps in “backup mode” bypassing the main system.
The pumps run until the float drops again and an additional delay is
satisfied.
As
with other configurations, pump cycles and run-times are saved through power
outages and downloads.
Application
#4
Service Pump Controller
This
configuration is useful for service pumps used in water distribution systems.
One CM-20 unit controls each service pump and it’s valve controls.
In automatic mode a master RTU communicates via the RS485 line to the CM-20’s
providing start/stop control and monitoring statuses
Upon
a call to start from the master RTU or the HAND operator the CM-20:
·
Energizes the pump starter and waits for pressure
to develop at the pump discharge.
·
After pressure is sensed, the CM-20 energizes the
valve open solenoid and waits for full-open status to be detected.
Upon
a call to stop from the master RTU or the HAND operator the CM-20:
·
De-energizes the valve control solenoid and waits
for the valve full-closed position to be detected.
·
Waits an additional short delay, then de-energizes
the pump starter.
The
CM-20 will generate alarms if the sequence of operations doesn’t occur as
expected. Minimum ON and OFF times,
as well as maximum starts per hour are enforced both in manual and automatic
modes. Pump cycles and run-times
are saved through power outages and downloads.
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