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When the spray gun is triggered, the two components are
introduced into the integrator chamber one at a time (see
Fig. 2). Their entry into the chamber is controlled by a
dispense valve for each component. The volume count-
ers monitor the exact quantities being dispensed, and
send electrical pulses to the controller. The controller
monitors these pulses and turns the dispense valves on
or off accordingly (based on the preselected number of
counts entered on the front panel).
The following is a typical ratio cycle:
First, the component A dispense valve opens, and
the fluid begins to flow into the integrator chamber.
When the correct quantity has been dispensed
(based on the volume counter input), the dispense
valve closes.
Next, the component B dispense valve opens. The
fluid begins to flow into the integrator chamber and is
lined up proportionately with the previously-dis-
pensed component A sample. When the correct
quantity has been dispensed, the component B dis-
pense valve closes.
The process repeats itself as long as the spray gun is
triggered. When the trigger is released, the unit
idles; it will continue where it left off when the gun is
triggered again.
If the spray gun is triggered, but the number of counts (of
a component) shown on the SETPOINT selector isn't
reached within a specified time, the system stops and an
alarm indicator lights. By the same token, if the number
of counts is exceeded by more than a tolerance which
has been set on a TOLERANCE selector, the system
also stops, an indicator lights, and an overrun alarm is in-
dicated.
On leaving the mixing block, the components are pre-
mixed in an integrator and then given a homogeneous
blending as they pass through a static mixer tube. Output
from the mixer tube to the spray gun is controlled by a
fluid pressure regulator, if desired.
The two components continue to be alternately fed into
the mixing block as long as the gun is triggered. When
the trigger is released, the system idles. Operation can
also be stopped at any time by pressing the STOP button
or shutting OFF the ON/OFF switch on the control panel.
If the machine stops because of an excessive overrun,
the operator must press STOP to clear the program.
Pressing START will then restart the cycle at the same
count where it stopped. If the problem still exists, the unit
will again shut down.
Adaptive Overrun Correction
The actual volume of fluid dispensed each cycle can vary
slightly from the settings on the SETPOINT selectors.
However, the system monitors this variance and com-
pensates on the next cycle. For example, if the selector
for a component is set at 100, but 103 volume parts are
actually dispensed on the first cycle, then the system will
aim for 97 parts on the next cycle.
Whenever the fluid overrun is greater than the TOLER-
ANCE setting, an indicator on the control panel flashes
and the system stops.
Manual Mode
When the MAN button on the control panel is pressed,
the system alternately dispenses three cycles of each
component and then stops. The manual mode is not
"adaptive" – the TOLERANCE selectors are doubled, the
system does not monitor small variances from the SET-
POINT selections (but the "system monitors" explained
below are operative), and the alarm function does not
work.
External Controllers
The PrecisionMix is designed so that several of the con-
trol panel functions can easily be duplicated using exter-
nal contactors. Refer to the electrical diagram on page
21 for information on connecting remote start and stop
controls, or an external flushing control.
System Monitors
Time Control. Two timers in the rear of the control box,
one for component A and one for B, monitor the run time
of the corresponding component's portion of the dispens-
ing cycle. The timer is activated from an air flow switch
contact which monitors air flow to the spray gun indicat-
ing "gun on." The timer resets at the end of the material
dispense cycle. The timers can be adjusted between 00
and 99 seconds. The system shuts down and an indicator
lights if the "gun on" time exceeds the timer setting for
that dispense.
To turn off the time control monitoring, set the timer(s) at
"00".
NOTE: Setting the timers to "00" will cause you to lose
the underrun feature (see Troubleshooting).
Volume Control. The machine mixes best if the integra-
tor fills with 30 - 50 cc of fluid (120 - 200 [Total of A and B]
on the SETPOINT selectors). If the A and B selectors are
set so that their sum is greater than 200, the system
stops and the overrun and underrun indicators flash alter-
nately.
Impulse Control. This control will detect a failure of a
flow meter sensor and shut the system down.
Watchdog Control. The system also monitors all data
that is controlled by its microprocessor, and shuts down if
anything (such as an electrical power surge) causes the
computer program to be interrupted.
System Flushing
The PrecisionMix can be manually flushed with a com-
patible solvent and with air, as described in the Operation
section, or the flushing system can be tied to an automat-
ic control system. The ON/OFF switch must be OFF to
operate the pneumatic solvent and air flush buttons, un-
less automated.
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