Setting Up the XP3000 for Your Application 4-6
8 Check aspirate/dispense.
Send the command [IA3000OA0R] to aspirate a full syringe stroke (3000 steps)
from input and dispense it to output. Successful execution will move the syringe
plunger to position “3000” then back to “0,” then it will return a “Ready” status.
Possible errors:
Error 9 (plunger overload). The stepper motor is unable to move the syringe
plunger, probably because of excessive backpressure caused by excessive
flowrate, narrow tubing I.D., or valve or tubing blockage. Note whether the error
occurred during aspiration or dispensing. To differentiate between blockage and
flowrate limitation, reduce syringe plunger speed by sending the command
[S12IA3000OA0R]. Repeat with decreasing plunger speed (increase “S_” value)
until the pump aspirates and dispenses successfully.
9 Set start velocity and top velocity.
The XP 3000 plunger speed can be controlled from 1.2 seconds per stroke to 20
minutes per stroke (top speed) using the [S] command. (The [V] command allows a
slightly larger speed range.) As a general rule, aspiration should be slow (to avoid
cavitation) and dispense fast (to promote breakoff). Since cavitation and breakoff
will affect both accuracy and precision, velocity settings may be optimized
separately for aspiration and dispense.
Using aspirate/dispense commands, set start velocity [v] and top velocity [V] to meet
application throughput goals.
a)
Send the command [v50IA3000OA0R]. Repeat with increasing start velocity
(increase “v_” value) to find the maximum value.
b)
Send the command [vxVxIA3000OA0R] to set top velocity equal to start
velocity (
x). Repeat with increasing top velocity (increase “V_” value) to the
maximum value that does not overload the plunger or cause cavitation.
Now optimize start velocity and top velocity for dispensing using a similar
approach.
10 Set cutoff velocity and slope.
Using aspirate/dispense commands, set slope [L] and cutoff velocity [c] to attain
reproducible breakoff. Note that cutoff velocity controls only dispensing.
To optimize the slope, send the command [v
xVyL14IA3000OA0R]. Repeat with
modified slope (“L_” value) to achieve the overall time suited to your application
without plunger overload.
To optimize the cutoff velocity, start with the maximum cutoff velocity allowed for
your application (the lower of 2700Hz or the top velocity). Send the command
[cxIA3000OA0R] and monitor the dispense for plunger overload or any splattering
of the fluid dispensed outside of the dispense vessel. If any of these conditions
occurs, lower the cutoff velocity until the pump can dispense the fluid with clean
breakoff.
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