Graco ProMix PD2K Operation page 60

Operation Using a Programmable Logic Controller (PLC)
Flow Control Control System System
Flow Flow Control System
Overview Overview Overview
Flow control is an optional feature that precisely
regulates the flow of material to an automatic spay
device, to help ensure adequate coverage and avoid
sags or runs in the finish coat. The ProMix PD2K
system can control fluid flow by directly controlling
the proportioning pumps. The pumps accurately
dispense a fixed volume of fluid during each stroke.
For this reason, the flow rate of a given pump is
directly proportional to the velocity of the pump. As
long as the gun is open and the system is stable, flow
control is the most effective method for controlling
flow rate.
The flow control system relies on two main inputs for
controlling flow rate: Gun Trigger and Control Set
NOTE: NOTE: NOTE: These These inputs These inputs are inputs
Point.
recommends recommends recommends that that that users users wire users
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Alternatively these two inputs can be
driven by the network communications, but latency
could be an issue for systems requiring precise
timing.
See System Screen 4, page
configuring these options for 'Discrete' or 'Network'.
NOTE: Flow control cannot be selected with a
NOTE: NOTE:
manual gun system.
Normal Flow Flow Control Control
Normal Normal Flow Control
The ProMix PD2K will directly control the speed of
the pump(s) to the programmed flow control set point
to maintain accurate flow rate and ratio. The flow
control set point is set by Network Communications
or the Discrete Input.
The system is considered to be stable when the
pressure readings do not fluctuate and the flow rate
is maintained. While the system is considered stable
it will store ("learn") the associated pump pressures
to a table that is used if the gun trigger signal is lost
or removed.
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Pressure Control Pressure Pressure
When the gun trigger signal is removed the system
automatically switches to pressure control mode to
avoid over pressurizing the fluid lines and to allow
smooth transition to flow control if the gun trigger
signal returns. It also works to maintain a consistent
flow rate even though it has transitioned to pressure
control mode if the gun trigger signal is inadvertently
lost.
Gun Gun On/Off Gun On/Off Prediction On/Off
The pressure table also is used to predict if the gun
has been turned on or off (without a change to the
gun trigger input). The flow control system continually
monitors the desired outlet pressure compared to the
the the
actual outlet pressure. If the actual pressure remains
50% or 50 psi higher than the desired pressure,
whichever is larger, for longer than 10 msec, then
the system predicts that the gun trigger has been
released. If the actual pressure drops below the
desired pressure longer than 10 msec, then the
system predicts that the gun has been triggered.
The gun on/off prediction is used in the flow control
algorithm to prevent the fluid pressure from becoming
too high or too low due to a system disturbance. For
example, if a gun off prediction occurs while the gun
trigger input is high, the system will begin to control
to the pressure value last stored in the pressure table
for the current flow set point.
System System Startup System
The pressure table is reset for every mix cycle, or
after a power cycle of the ProMix PD2K controller.
This issue is not significant because the system
generally is able to recalculate new pressure table
values within a few seconds (depending on the
stability of the fluid system).
Control Control
Prediction Prediction
Startup and Startup and Defaults and Defaults Defaults
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