MAGUIRE Weigh Scale Blender 4088 Installation Operation & Maintenance page 80

DISPENSE TIMING: (DATA line 3)
The second number is the number of milliseconds 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, 40, 50, 60 milliseconds, 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 20, you are operating in a range where 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 for the following.
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).
Additive, for example, is a percentage of the natural. In the example above, Natural is 1538.4 grams, so
additive, at 4 percent of Natural, is targeted to be 61.5 grams. In fact, if 62.8 were dispensed, the error would
be 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 and
material flow 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 (40, 50, 60 milliseconds) 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.
80