
Small Mouth: Models A, B, C – 8″ sq stand x 26-31″ high or Model D – 10″ sq stand x 42″ high
Small Mouth: Models A, B, C – 8″ sq stand x 26-31″ high or Model D – 10″ sq stand x 42″ high
Time to do something, when Batch Weighing Accuracy Performance does not meet Accuracy Requirements. Understanding the problem should the first thing on the to do list.
Sometimes accuracy problems are design issues and sometimes maintenance issues. If it worked before, you are lucky you only have a maintenance issue. If your system has trouble maintaining itself within tolerance, you may not be so lucky after all.
Closed Loop Control and every component all affect Closed Loop Control Performance.
1) Scale accuracy and
2) the response time it takes for the control system to sense the change accurately
3) and the response time it takes to control the flow to the scale all affect performance
Material is being fed between controlling devices and scale. The shorter the distance between the two improves Closed Loop Control response time. Controlling devices can be gates, valves, rotary valves, augers, conveyors, etc. A consistent head of material feeding these is important to maintain. The system is adjusted for a given amount of material to be delivered in a certain amount of time. When that material is not there at the scale, your system has to adjust on the fly. Production rates and product quality suffers.
An unknown factor affecting accuracy is the amount of material (in the air) between the controlling device and the scale. The material in the air the flow controlling device and the scale is always questionable when flow rate is not consistent. This problem can be minimized at the cost of production rates. So the question is; At what cost do you fix the inconsistency or live with lower productions rates or trade off to less accuracy?
Production Rates and Quality Control often seems at odds with each other. Tie that in with inconsistent feed to the weighing device and meeting set point becomes more difficult to achieve.
Most readers already have a n electro-mechanical system in place. Usually, mechanical fixes are harder to implement than electrical systems.
Batching systems compare setpoint to the scale readings. Material can be weighed in one of two ways.
Whether you are weighing through the scale or to the scale, material will not be accounted for in free fall. This becomes an assumption. This assumption can be most accurate the more we keep our flow constant. A constant head of material helps.
When flow is not constant and when slower production rates are acceptable, the batch control can be set to creep up to setpoint at slower feed rates by adding an additional set point or two. Auger, rotary valve and conveyor speeds can be slowed, gates can go into a chatter mode, gates can be positioned from completely open to half open to 10% open to closed.
The human element is always a factor. Everyone seems to have their recipe for the best operating procedure. Develop your best operating procedure taking all tradeoffs you have into consideration. Train your operator to use it consistently.
Net Weights vary…
Life is all about trade-offs. Educate yourself on the trade-offs and navigate to the best set of them for the job.
Clarence Richard, Instructor
Plant Operation Workshop Web-Based Training Provider http://clarencerichard.adobeconnect.com/workshopdemo
clarence@clarencerichard.com www.clarencerichard.com 952-939-6000
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