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As we know, that statistical process control (SPC) is an effective method of monitoring a process through the use of control charts. Statistical process control (SPC) involves using statistical techniques to measure and analyze the variation in processes.  Most often used for manufacturing processes, the intent of Statistical process control (SPC) is to monitor product quality and maintain processes to fixed targets.  Statistical quality control refers to using statistical techniques for measuring and improving the quality of processes and includes statistical process control in addition to other techniques, such as sampling plans, experimental design, variation reduction, process capability analysis, and process improvement plans.

Statistical process control is used to monitor the consistency of processes used to manufacture a product as designed.  It aims to get and keep processes under control. No matter how good or bad the design, That process control--SPC can ensure that the product is being manufactured as designed and intended. 

Thus, SPC will not improve a poorly designed product's reliability, but it can be used to maintain the consistency of how the product is made and, therefore, of the manufactured product itself and its as-designed reliability.

1. Discrete Process Control.

This form of process control is found in many manufacturing, motion and packaging applications. Robotic assembly, such as that found in automotive production, can be characterized as discrete process control. And most discrete manufacturing involves the production of discrete pieces of product, such as metal stamping.

2. Batch Process Control. 

Some applications require that specific quantities of raw materials be combined in specific ways for particular durations to produce an intermediate or end result. One example for such applications is the production of adhesives and glues, which generally require the mixing of raw materials in a heated vessel for a period of time to form a quantity of end product. Other important examples of this type are the production of food, beverages and medicine. Batch processes are generally used to produce a relatively low to intermediate quantity of product per year (a few pounds to millions of pounds). Batch process control are widely used here.

Statistical Process Control (SPC) is an effective method of monitoring a process through the use of control charts. Much of its power of Statistical Process Control (SPC) lies in the ability to monitor both process center and the variation about that center.

By collecting data from samples at various points within the process, variations in the process that may affect the quality of the end product or service can be detected and corrected, thus reducing waste as well as the likelihood that problems will be passed on to the customer. Statistical Process Control (SPC) has an emphasis on early detection and prevention of problems.

Below is an example to illustrate statistical process control.

A commonly used control device called a programmable logic controller (PLC), is used to read a set of digital and analog inputs, apply a set of logic statements, and generate a set of analog and digital outputs. For example, the room temperature would be an input to the programmable logic controller (PLC). The logical statements would compare the setpoint to the input temperature and determine whether more or less heating was necessary to keep the temperature constant. A programmable logic controller (PLC) output would then either open or close the hot water valve, an incremental amount, depending on whether more or less hot water was needed. Larger more complex systems can be controlled by a Distributed Control System (DCS) or SCADA system.

In practice, process control systems can be characterized as the following forms:

1. Discrete

2. Batch

3. Continuous