Measurements and Controls

Microprocessor Control System | Microprocessor and Microcontroller

microprocessor are essential for many of the products we use every day such as TVs cars, radio, home appliance, and computers.  microprocessor based controls also called microcontrollers. microcontroller is a digital integrated circuits which serves as a heart of many modern control applications.

microprocessor and microcontrollers are similar but the architecture of the both differs in the applications domains. microprocessor are employed for high speed applications such as desktop and laptop computers whereas the microcontroller are employed in automations and control applications such as microwave ovens, automatic washing machines, dish washers, engine management system, DVD players etc.

Sequential Control System | Washing Machine System Basic Operation

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.).

Displacement And Dimensional Measurements In Metrology | Mechanical Linear Measuring Instruments

Linear Dimensional Measurements In Metrology

Dimensional measurements in metrology is the science and technology of measurement. It involves the measurement of length, width, height, depth and other features on a three-dimensional object. The purpose of dimensional metrology is to ensure that objects are manufactured to the correct specifications. This is done by comparing the dimensions of an object with the design specifications.

Measurement of length, diameter, height and thickness of an object are commonly needed in connection with the production and assembly of machine parts, and testing of materials, components and structures. Dimensional measurements refer to the determination of the size of the object, while, displacement measurement implies movement of a point from one position to another.

It’s important to get dimensions correct when producing products. This is where dimensional measurement in metrology comes in. In metrology, the term “dimension” refers to a measure of length, width, height, or depth. There are three main types of dimension measurements: linear, angular, and volumetric. Linear measurements are distances between two points, while angular measurements are angles formed by two intersecting lines. Volumetric measurements are the sizes of three-dimensional objects. There

Linear Displacement Measurement Devices

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The limitation of human senses in providing exact quantitative information of a physical variable and phenomenon led to the development of aids or devices called instruments. Instruments can sense and indicate the value of a variable and can also manipulate and control it.

Length measurement standards are available as line comparison standards (e.g., scales and tapes) and as end comparison standards (e.g., gauge blocks, slip gauges).

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The primary error in the above devices is due to thermal expansion or contraction of the scale or of gauge blocks. But, when the gauge block and the work piece are of like materials and are at the same temperature there will be no error in measurement due to temperature.

No measurement can be made with perfect accuracy. An instrument when subjected to the same input repeatedly may not indicate the same output. Response of an instrument, when given an input in an increasing order then in decreasing order, may not be the same. Response of an instrument may change with time and also with changes in environmental conditions.

Dimensional Measuring Instruments

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Classification of Dimensional Measurements in Metrology

These devices are generally classified as

  1. low resolution (0.25 mm),
  2. medium resolution (2.5 * 10-3 mm),
  3. high resolution (2.5 * 10-5 mm) and
  4. super resolution devices,

Various Devices for Linear Dimensional Measurements in Metrology

which include various forms of interferometers. Various devices commonly used are:

  • Steel Rules
  • Vernier caliper’s
  • Micrometers
  • Dial Gauge
  • Indicators
  • Gauge Blocks

Non contact Displacement Sensors

In addition to above devices, optical methods used are, microscopes, telescope and optical flats with a monochromatic source of light and working on the principle of interference of light. Pneumatic comparators find frequent industrial applications for dimensional measurements.

Further the measured value of the input used for control purposes. E.g., switching off an oven when a particular temperature is attained. The measured input may sometimes require processing by a computer for a meaningful interpretation. Data processors and controllers may also form a part of the display devices.

There are two types of display devices used for this purposes. One is analog type devices where a relative displacement or movement of a pointer on a scale, or a spot of light on a scale indicates the value of measured variable. The second is the digital type devices where the measured value indicated by digits or directly as a number. Presently wrist watches often have both analog and digital displays.

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For choosing a suitable instrument for the measurement of a particular quantity, the starting point is the specification of the performance characteristics required e.g., range, resolution, sensitivity, accuracy etc. Dynamic response characteristics become important when quantity to be measured is time dependent.