Maguire Products Weigh Scale Blender WSB, Operation & Maintenance Manual

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M A G U I R E P R O D U C T S , I N C .
Edition: August 6, 2014
68
W E I G H S C A L E B L E N D E R
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The second number is the number of interrupts calculated to dispense the material. If these times are consistent but the weight of
the first dispense varies, then the material does not flow well, or consistently. Another possibility is excessive vibration or
interference with the weigh bin.
Excess vibration, particularly on small dispenses, may cause incorrect weight readings even though the weight dispensed was, in
fact, correct.
If the timing number is very small, 10, 20, 30 interrupts, perhaps this is asking too much from a slide valve. Very short times mean
you want small amounts, but are using a high rate dispense valve to do the job. An auger, a vertical valve, a horizontal valve with a
flow restrictor, or a smaller valve would help to improve accuracy and control.
If the timing number is below 5, you are operating in a range were it is difficult for the blender to perform well.
The LAG time parameter adds time to every dispense. This is to compensate for the time at the beginning of a dispense when the
solenoid valve shifts and air pressure builds, before the valve starts to move. LAG times are always set slightly longer then the
necessary minimum. If a calculated dispense time is very short, the Lag time that is added, while small, may interfere with
accuracy, and cause an over dispense.
PERCENTAGE ERRORS
: (DATA line 1)
When looking at errors of percentage of color or additive dispensed, look further.
1. First, look for indications of "retries". Retries are evidence of a problem that will also cause percentage errors.
When FIRST time dispense, (DATA line 3), does not equal FINAL dispense, (DATA line 1), one or more retries have
occurred. This means the hopper ran out of material, or the flow rate is so erratic that the first dispense was short for no
good reason. Parameters _RT and _RP determine what shortage error is necessary to force a retry.
Inconsistent loading resulting in large variations in hopper material level can cause retries.
Excessive vibration can also cause bad weight readings, which can cause unwarranted retries. If the BAILOUT line is
printing occasionally, then vibration is most likely causing this. Increasing the BAILOUT parameter should fix this.
A LAG time set too high may cause retries to overshoot their mark resulting in over dispensing.
2. Second, look at ACTUAL weight dispensed (DATA line 1).
Color, for example, is a percentage of the natural. In the example above, Natural is 1908.3 grams, so color, at 4 percent
of Natural, is targeted to be 76.3 grams. In fact, 77.6 were dispensed. The error is 1.3 grams, well within the expected
accuracy of a 1” auger feeder.
The actual GRAM error of a dispense is more meaningful then the percentage error. Mechanical devices are not perfect.
The most we can expect from them is to operate within a reasonable range of accuracy. This range is better defined by
an error expressed in grams, rather them percentage.
3. Third, look at the dispense TIME (DATA line 3).
Very short times (10, 20, 30 interrupts) indicate dispense devices not well matched to the task. Accuracy on a
percentage basis, cycle to cycle, will suffer. This may very well be acceptable as long as overall usage percentages are
still accurate.
BAILOUT: (line 4)
If bailouts occur, vibration is usually the cause and these bailouts may be causing other problems. Raise the value of the BAL
parameter to 200 or 300 grams to reduce or eliminate unnecessary bailouts.
Vibration may also cause throughput rates to suffer due to the added time required to obtain acceptable weight readings.
Increase the WDF parameter to 2 or 3 grams, (WDF 00003) or (WDF 00030), or more if necessary.