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AutoJet® Spray Controller Regulation Modes
The
Model 2250 AutoJet Spray Controller has 8 built-in regulation modes
which allow for control of a wide variety of applications.
Open
Loop Batch Control (View
Demonstration)
This regulation mode is used to quickly switch between different
combinations of pressure settings. Up to 16 different sets of
parameters, or batches, can be set. Each set of separately controlled
parameters consists of
- Liquid
pressure
- Atomizing
air pressure, and
- Fan
air pressure
Each
pressure setting is constant and only one set of parameters may
be used at a time. Switching between batches can be accomplished
either manually or automatically using electronic inputs.
Open
Loop Pressure
Used for spraying at a constant fluid pressure. The fluid
pressure is a set point, programmed by the operator. The
Model 2250 AutoJet Spray Controller maintains this pressure electronically
using I/P converters and liquid pressure regulators.
Open
Loop Flow
Used for spraying at a constant flow rate. The flow rate
is a set point, programmed by the operator. The spray controller
calculates the necessary fluid pressure needed to maintain the desired
flow rate and adjusts the system accordingly.
Open
Loop Flow PWM (Pulse Width Modulation)
Pulse Width Modulation -- typically used with electric spray guns
-- involves rapidly turning a spray gun on and off. Like OL Flow,
this regulation mode is used for spraying at a constant flow
rate. However, OL Flow PWM sprays at constant fluid pressure
as well. In order to achieve this, the Model 2250 AutoJet Spray
Controller varies the duty cycle. For more information on PWM, click
here.
Closed
Loop Flow
Very similar to OL Flow, this mode is also used for spraying at
a constant flow rate. The spray controller varies the fluid
pressure in order to achieve this. Additionally, it makes use of
a flow or pressure sensor in order to gauge how accurately it holds
this flow. Thus, CL Flow uses feedback to constantly check that
it is operating as specified and is able to compensate for nozzle
wear and pressure drops in piping while holding much stricter tolerances
than OL Flow.
Open
Loop Speed (View
Demonstration)
Used for spraying at a constant application rate for conveyor
applications. The desired application rate is programmed in
by the operator. A tachometer located on the line tells the AutoJet
Spray Controller how fast the line is moving and adjusts the fluid
pressure so that the appropriate amount of fluid is applied for
the speed at which the line is running.
Open
Loop Speed PWM
Similar to OL Speed, this regulation mode maintains a constant
application rate with the notable difference that the process
is achieved using a single constant fluid pressure. The Model
2250 AutoJet Spray Controller adjusts the duty cycle in order to
maintain the application rate. For more information on PWM, click
here.
Closed
Loop Temperature (View
Demonstration)
This regulation mode is used to spray fluid so that a constant
temperature is maintained and is used in applications such as
gas cooling. The desired temperature is specified by the operator
and the spray controller, using a temperature sensor, constantly
adjusts the fluid pressure. This closed loop regulation mode is
capable of holding very tight tolerances.
How Pulse Width Modulation works
Pulse
width modulated flow control involves switching the spray gun on
and off repeatedly at a controlled rate, called the modulating
frequency. The modulating frequency is the number of times the
gun is switched on in one second, and is measured in Hertz (Hz).
If
a spray gun is switched on 10 times per second, the modulating frequency
is 10 Hz. The time from when the gun turns on to the next time the
gun turns on is called the period, in this case, 1/10th of
a second.
Within
a single period, the gun is switched on, then off. The time that
the gun is on divided by the total time of the period gives a percentage
called the duty cycle. For example, if the period is 0.10
seconds, and the gun is on half that time, the duty cycle is 50%.
For the same period, if the gun is on for 0.08 seconds, the duty
cycle is 80%. So at a 80% duty cycle, the flow will theoretically
be 80% of the maximum flow rate at a given pressure for the nozzle.
Using PWM, the flow rate for a spray application can be easily controlled.
Another
advantage of PWM is the extremely high flow turndown ratio that
can be achieved at a single pressure (up to 10:1 or more, depending
on the the regulating frequency and spray gun used).
Finally,
the Model 2250 AutoJet Spray Controller can also utilize a signal
from a pressure transducer to automatically compensate for variable
supply pressures by adjusting the duty cycle to maintain a constant
flow rate.
Note:
Pulse width modulation results in striping of the spray which is
not appropriate for all applications.
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