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Rev. May 2001 GraviMaster-FGB-M05 (S) Page 13
Gravimetric Blender
2.7.6 Dispensing
Dispensing of the different components will start after the calculation of the related weights.
The components are dispensed in the order as defi ned in the recipe (gravimetric only). In
volumetric mode all components are dispensed at the same time.
Every mechanical valve has a reaction time. The controller uses the ‘Hardware Reaction
Time’ to calculate the time which the dispense valve must be activated. The ‘Hardware
Reaction Time’ is the maximum active time of the valve when no material is dispensed. The
controller uses a pulse of 5ms in the following algorithm:
OpenTime = Weight [g] / dipenseSpeed [g/s]
OpenPulses = (OpenTime [s] / 0.005 [s]) + HardwareReactionTime [Puls]
After every dispense cycle the weight is measured. The weight bin must be stable before
the weight can be measured, therefore a time delay is inserted between dispense and
measuring. When the controller starts measuring the signal must be stable for at least 1 sec.
(signal within the ‘Weighbin-variationband’)
After measuring the weight of the fi rst dispense some calculations can be done, and with
the results parameters can be changed. Result is a more accurate next dispense. After the
fi rst dispense of a material one of the following situation occurs:
Dispense is correct
The difference between calculated- and measured weight is less then the dispense accuracy.
In this case extra dispense tries of this material are not necessary.
Dispense not correct (too little)
The difference between calculated- and measured weight is more than the dispense
accuracy but there is less dispensed (measured) than calculated. In this case the controller
reacts according to the chosen ‘alarm-type’. The following ‘alarm-types’ are possible:
IGNORE No extra dispense-tries. Relations within the recipe will corrected by
re-calculations.
WARNING The controller tries to reach the dispense-accuracy by extra dispenses. The
extra dispenses are limited by the parameter ‘dispenseTry’. When after a
maximum number of dispense tries, the accuracy is not reached the controller
sends a warning only to the user (= The controller continues with the next
material).
ERROR The reaction of the controller is equal to ‘WARNING’ only an error is sent
to the user when the accuracy is not reached. Now the controller waits for a
confi rmation (enter) to initiate new dispense tries of the same material. This
process goes on until the dispense accuracy is reached.