MERRICK MC3 35.00.EX, Руководство по эксплуатации и обслуживанию, Страница: 8 / 69

SYSTEM OVERVIEW
A Weigh-Out batching system is designed to produce batches of material with a pre-
determined weight. A weigh hopper is placed on load cells, producing a signal
proportional to the weight of the hopper and its content. At the bottom, there is a variable
speed feeding device, such as a material screw or a vibrating pan. The MC³ controller
will run the feeding device in such a way that the weight reduction in the hopper
corresponds to the desired value (the setpoint). Typically the feeding device first runs fast
(Fast Feed) and then switches to a slower speed (Fine Feed), as the weight loss
approaches the setpoint.
When the weight of the hopper content reaches a pre-set low weight, called the Heel
Weight, the MC³ controller will call for the hopper to be filled, up to another pre-set
weight, called the Fill Weight. During the filling, no batching can take place, and the
feeding device is stopped. Typically, an automatic valve or feeding device is used to re-fill
the weigh hopper, under control of the MC³.
BATCHING CONTROL
Setpoint Signal Load Cell Signal
Setpoint Signal
Conditioning
Load Cell Signal
Conditioning
Setpoint Filter
Rate
Calculation
State Logic
Hopper
Parameters
Batch
Parameters
Feeder Speed
Demand Signal
Stability
Calculation
The MC³ 35.00.EX controller uses a self
correcting algorithm to optimize batch
accuracy and batch performance. There is
always a trade-off between the two, meaning
that that faster batching reduces batch
accuracy and vice versa.
Key parameters
Each of the function blocks above has one or more parameters associated with it. They
all have to be set properly for good batching control. Most of them can be set
automatically, by running Quick Setup (see page 28). Some of them can be continuously
updated by the controller itself, as a part of a self-adjusting scheme.
Load Cell Signal Conditioning
The weight signal conditioning block takes the Load Cell Signal as an input, passes it
through an A/D converter, called the HPAD, and produces a weight value as an output.
Parameters are:
Zero Weight
The weight of the hopper, feeding device etc when the hopper is
empty. Set by running a Zeroing Procedure (page 47). You can also
set it manually. See Zero Weight on page 28.
Scale Factor
A divisor to translate the load cell signal counts from the load cell A/D
converter, the HPAD, to usable engineering units, such as lb or kg.
Set by running a Material Calibration (page 48) Weight Procedure
35.00.EX O&M Manual 4