Calibration: If a known input is given to the measurement system the output deviates from the given input, the corrections are made in the instrument and then the output is measured. This process is called “Calibration”. Sensitivity: Sensitivity is the ratio of change in the output signal to the change in the input signal. Readability: Refers to the ease with
Errors in Measurement : Error = Measured Value – True Value Em = Vm – Vt 1. Absolute Error : True absolute error : = Result of measurement – True Value Apparent Absolute error : = Result of measurement – Arithmetic Value 2. Relative error : It is defined as the results of the absolute error and the
It is defined as the probability that a given system will perform it’s function adequately for it’s specified period of lifetime under specified operating conditions. Common measures are : 1. Failure rate. 2. Mean time between failures(MTBF) 3. Survival percentage. Failure Rate: Rate which components of population fail. R(t)=Ns(t)/Nf(t) Where, Ns(t)- No. of components that survived during time ’t’ Nf(t)
MEASUREMENTS: A Measurement is the outcome of an opinion formed by observers about some physical quantity. CLASSIFICATION OF MEASUREMENTS: Standards – ( Reproduce the value of given quantity ) Fixed Gauges – (Check Dimensions) Measuring Instruments – (Determine the measured value) NEEDS FOR MEASUREMENT: 1. To Determine the true dimensions of a part. 2. To increase our knowledge and understanding
In many situation, various operations of a plant or process take place in a particular order. A sequential control system involve the sequential execution of well- defined operations that are performed in a prescribed order. Each operations or activity is called step. Each step may be an open or closed loop continues process or even a sequential sub- process. For example, while using automatic camera, the various basic steps in a sequence are switch on, battery check, auto- focus the image, auto flash on/off, taking the image, saving the image and then switching off the camera.
Each step of the prescribed sequence usually requires a switching of the equipment configuration and it may be triggered by time or an event(push of a button, completion of early task etc.).
An automatic control system is a pre-set closed loop control system that requires no operator action. Most of the closed-loop control systems are automatic in nature. It assumes that the process remains in the normal range for the control system. Various applications of automatic control systems are explained below.
