Appendix B - Pump Control from a PLC
Application
Application
Application Note
Note
Note 1
1
1 --- Flow
Flow
Flow Mode
Mode
Mode vs.
vs.
vs. Pressure
Pressure
Pressure Mode
Mode
Mode
In the majority of applications it is desirable to
always run in flow mode and allow the back pressure
regulator to control the line pressure. This ensures
that the material velocity is always at the target for
particulate suspension.
• To determine whether or not the pump can be run
exclusively in flow mode, test with the maximum
flow demand, open up all robot drops and spray
guns and so on. Then check the pump outlet
pressure to see if the BPR can maintain it. If so,
then pressure mode is not needed.
•
If the BPR cannot hold the fluid pressure during
peak material demand times, then it will be
necessary to run pressure mode during production.
In this mode the pump will speed up to match
demand and hold the target pressure. It will also
slow down automatically to maintain pressure
when the demand drops.
Use of this mode likely means switching back and
forth between pressure mode and flow mode;
pressure mode during production and flow mode in
off production. See the following application note
for considerations in this scenario.
Application
Application
Application Note
Note
Note 2
2
2 --- Pump
Pump
Pump Setpoint
Setpoint
Setpoint transitions
transitions
transitions
For applications where the flow rate and pressure
settings are being changed periodically, such as
during off production times, it is important to consider
the following:
• When the pump is in pressure mode, it will come to
a complete stop at any time if the back pressure in
the line is equal to or above the pressure setpoint
of the pump.
• Viscosity changes throughout time can increase
the back pressure in the line, such that when it is
time to switch from flow mode (off production) to
pressure mode, the pump will not move, because
a new, higher, pressure set point is needed to
overcome the increased back pressure.
• We recommend reading the active pressure or
force before switching to pressure mode and using
that for the new pressure setpoint - Read from
register 404103 if the motor is operating without a
pressure sensor (ie. Force/% mode).
• Read from register 404104 if the motor is
controlling from pressure sensor 1 or register
404105 for pressure sensor 2 - For applications
with a pneumatic BPR, the profile BPR setpoint
can be used to manage the system through the
Graco BPR controller kit (24V001).
• In off production flow mode, register 405107
(405X07 for profile X) can be set to 0 (%) to fully
open the BPR This allows the target flow rate to
flow with reduced pressure, and therefore lower
energy consumption For example:
Using profile 1, while in off production the pump
is set in flow mode (register 405106 = 1) with a
flow rate target setting of 8 gallons/minute (30
liters/minute) (register 405104 = 80) and the profile
maximum pressure setting was left at the system
default. Before switching to pressure mode, save
the value of the current pressure from register
404104 (The motor is controlling to the feedback
provided by pressure sensor 1) and use that value
as the new setting for the pressure target in register
405101. Then set the mode register (405106) to
0 (pressure mode)
Note: Using only profile 1 (4 are available) allows
you to control the pump with fewer registers mapped.
However, to configure multiple profiles, then the
above scenario can be applied where 405X01 is the
pressure target for profile X, 405X04 is the flow rate
target for profile X and so on for the other profile
variables.
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