Appendix 1: First Drop Compensation; Appendix 1-1: Background; Appendix 1-2: Calculating First Drop Compensation - Graco Advanjet Diaphragm-Jet HV-2000 Setup And Operation

Appendix 1: First Drop Compensation

Appendix 1-1:
Many viscous fluids are thixotropic and their viscosity decreases with motion. This is
often referred to as shear thinning. When dispensing a thixotropic fluid, the very first
drop ejected is often smaller than subsequent drops if the jet has been idle for some
time.
Traditionally, operators dispense a few ―wasted drops‖ in a blank area of the substrate
to get the dispensing material into a shear-thinning condition. Although this technique is
a good idea because it gets rid of the first drop problem altogether, it wastes time and
fluid. The Advanjet HV-2000C has a better solution.
Appendix 1-2:
To compensate for small first drops, the HV-2000C offers two jetting parameters:
Refill + and Refill ++. The first drop compensation process is based on the following:
Elapse Time = Idle time of the jet since the last dispense
Extended Timeout = Time entered in the Recipes Menu/Adjust Refill Time
If Elapse Time < Extended Timeout, then Refill Time = Refill + T
If Elapse Time > Extended Timeout, then Refill Time = Refill + T
Examples: For a time-cure material, the fluid could be slightly thickening if it sits idle for
a long time, especially if the fluid is being actively heated. Suppose Extended Timeout is
set at 20 seconds. The first drop refill time will equal (Refill +T*), where the value of T*
depends on how long the jet has been idle.
If Elapse Time < 20 sec (Extended Timeout), then T* = T
If Elapse Time ≥ 20 sec (Extended Timeout), then T* = T
Lines: For the first drop of all the lines, Refill Time = Refill + T
have a Refill Time without any compensation if multiple drops are specified.
Individual Drops: For individual drops, Refill Time = Refill + T
individual drops with an Elapse Time of less than 20 seconds, the compensation is
always applied.
3A5856A
Background
Calculating First Drop Compensation
+
T = First Drop Compensation
++
T = Extended Drop Compensation
for first drop ―msec after YY seconds‖
Advanjet HV-2000C Jet Controller Setup and Operation
+
++
+
++
++
. Subsequent drops will
+
. When dispensing
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