Rate of Change by Weight (ROC)
Typically deployed in two manufacturing areas: MAKE (batching and blending) and PACK (filling and dispensing). Rate of change (ROC) is normally used to measure the rate at which material enters or leaves a weigh hopper. It may be used in either “gain in weight” or “loss in weight” applications.
ROC is a weight change over time. For example, if material is being taken off the scale the ROC will display a negative value; if material is being added onto the scale the ROC will display a positive value. If no material is being taken on/off the scale, the ROC value will be ZERO.
The value is dependent on the time constant selected, for example lbs/min, lbs/hour, etc. The ROC value is used by a PLC to control the rate at which a feed is being executed e.g., feed 1000 lbs of material at 100 lb/min.