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2.0 Weight Ratio: Weight Ratio Dispensing; Edit
SUMMARY: In the Weight Ratio Dispensing mode, the LabTec™ provides automated sample
weighing and sample dilution. With this operational mode, the LabTec™ must be connected to
an electronic, top-loading scale. The SETUP: Scale sub mode provides electronic scale options,
i.e. scales that can be interfaced with the LabTec™: Mettler, Ohaus, and Sartorius. The selected
scale is connected to Port S1. The LabTec™ also has provisions for printing / documenting your
dispensing data. The printer (P/N: 080-095) is connected to the LabTec™ via the Printer Port. Use
SETUP: Printer for setting up the printer communications parameters. Back pressure of any filter
in the system can be monitored by use of a SciPres
®
Pressure Sensor, enabling the pressure alarm
in SETUP: Press Sensor, and setting a user-defined limit.
When executing the Weight Ratio Dispensing mode, the LabTec™ will display “SCALE
INITIALIZATION / Please Wait”. While this message is being displayed, the LabTec™ checks the
scale communication. If scale communication fails the LabTec™ will display “SCALE ERROR /
Press any key”. Check the RS-232 cable connection as well as the communications parameters
in the scale. Also make sure the correct scale manufacturer is s e l e c t e d i n t h e S E T U P : S c a l e
submenu.
WGT FACTOR: Defines the weight ratio (multiplier) that is applied to the actual sample weight, as
determined by the scale, to arrive at the required diluent weight. For example, if the WGT FACTOR
is set at 9.00 (default value), and the actual sample weight is 10.0 grams, then the diluent target
weight is 90.0 grams resulting in a 10-fold sample dilution by weight.
SNIFFLE: The SNIFFLE function consists of a brief pump reversal to suck in the droplet that
typically hangs at the end of the dispensing tip. The length of time for the pump reversal is
user-selectable from 0 to 2.0 seconds. The SNIFFLE function is implemented at the end of
each dispensing cycle thereby avoiding carry-over between cycles and a cleaner dispensing
environment.
SLOW FACTOR: Defines the diluent weight that is dispensed slowly at the end of the dispensing
cycle. For example, if the diluent weight is 90.0 grams, then the SLOW FACTOR is selected to be
25.0 gm. When the LabTec™ initiates diluent dispensing, the first 65 gm. will be dispensed at a high
pump rate (e.g. 80% of max.), while the last 25 gm will be dispensed in a multiple step ramp down
of flow to avoid overshooting the diluent target weight. The SLOW FACTOR as well as the LabTec™
pump rate is user-selectable.
PUMP DIRECTION: Defines the rotation of the pump head; this parameter can be changed from
clock-wise (CW, default) to counter clock-wise (CCW).
PUMP RATE: Defines the relative pump speed (0% to 100% of max.) with which the diluent is being
dispensed. Typically, this parameter is set at 80% (default), however, a slower pump speed setting
is
advisable if excessive back-splashing should occur.
TIME DELAY: Not used in the Weight Ratio mode, should be set to 1.0 (default).
COUNT: Not used in the Weight Ratio Dispensing mode, should be set to 1 (default).
CONTAINER WEIGHT: Enter the weight of a standard container or bag, and it will automatically be
deducted from the total weight of container and sample to arrive at the sample weight. The pump
will then proceed to dispense the calculated diluent weight, skipping the “Press RUN When Sample
is in Vessel” step and the initial tare of the scale.
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