About Engineering & Plastic Technology

 INTRODUCTION Position indicating device is used to provide remote indication of position, such as indication of the open or shut condition of a valves. THERE ARE FOUR TYPES OF POSITION INDICATORS Limit switches Reed switches Potentiometer LVDT Limit and Reed switches act as ON/OFF indications to provide open and closed indication and control function. Reed switches can aslo be used to provide an incremental-position indication. Potentiometer and LVDT position indicators provide an accurate indications, such as the position of a rod throughout its travel. LIMIT SWITCHES Limit switch is a mechanical device, which can be used to determine the physical position of any part to provide full  open or full shunt indication. Many limit switch are the push button variety which gives ON/OFF corresponding to the valve position. Example : An extension of a valve shaft mechanically trips a limit switch as it moves from open to shunt or shunt to open. When the valve extension comes in cont...

  THERMOCOUPLE WORKING PRINCIPLE OF THERMOCOUPLE Thermocouple is a temperature measuring device constructed of two dissimilar metal wires joined at one end. When one end of each wire is connected to a measuring instrument the thermocouple becomes a sensitive and highly accurate measuring device. Thermocouple may be constructed of several different combinations of materials. The performance of a thermocouple material is generally determined by using that material with platinum, The measuring junction is normally formed at the bottom of the thermocouple housing. In a typical thermocouple, the leads are encased in a rigid metal sheath. CONSTRUCTION OF THERMOCOUPLE The most important factor to be considered when selecting a pair of materials is the thermoelectric difference between the two materials. A significant difference between the two materials will result in better thermocouple performance. Constantan is excellent for temperature up to 2000℉. Nickel/Nickel-Molybdenum sometimes r...

TOPICS COVERED  INTRODUCTION  CONTROL SYSTEM IN POLYMER PROCESSING CONTROL SYSTEM INPUT/OUTPUT TYPES OF CONTROL SYSTEM  AUTOMATIC CONTROL SYSTEM PROCESS VARIABLES  FUNCTION OF AUTOMATIC CONTROL SYSTEM ELEMENTS OF AUTOMATIC CONTROL SYSTEM INTRODUCTION Control system  is a set of integerated elements whose fuction is to monitor the process variables to maintain within desired range of values. CONTROL SYSTEM IN POLYMER PROCESSING Control system is a device or set of devices used to manage the functioning of polymer moulding machine. Control system of plastic processing machine is considered as its "brain" because the functioning of a machine depends upon efficiency of its control system. CONTROL SYSTEM OUTPUT Control system output is the actual response obtained from a control system NOTE:- A Control system may have more than one input or output. TYPES OF CONTROL SYSTEM  Open loop control system Closed loop control system OPEN LOOP CONTROL SYSTEM In an Open lo...

 INTRODUCTION An orifice is a small opening of any cross-section (such as circular, triangular, rectangular etc.) on the side or at the bottom of a tank through which a fluid is flowing. It is used to measure rate of flow of fluid  Thickness of orifice in direction of flow is very small in comparison to its other dimensions. i.e Orifice has a sharp edge so that there is an contact with fluid and consequently minimum friction resistance at its sides. If sharp edge is not provided the flow will depend on thickness of orifice and roughness of its boundary too. The rate of flow of fluid through orifice depend on shape, size and form of orifice. CLASSIFICATION OF ORIFICE A) On the basis of cross sectional area Circular orifice  Triangular orifice Rectangular orifice Square orifice B) According to size  Small orifice - If head of liquid (H) >5 Times depth of orifice Large orifice - H< 5d C) According to shape of edge Sharp edge orifice  Bell mounted D) According...