Process Variables

Process is defined as the changing or refining of raw materials that pass through or remain in a liquid, gaseous, or slurry state to create end products. The methods used to control process variables while manufacturing a product is referred as process control. oil and gas, cement, power e.t.c are examples of process industries. Process variable is a condition of process fluid (liquid or gas) that can change the manufacturing process in some way. Common process variables are listed below 

1. Pressure

2. Flow

3. Level

4. Temperature

5. Density

6. PH

Pressure : It is defined as force applied per unit area. P= F/A where, F = force and A = area. Units of pressure are bar, pascal, psi, tor, atm, kg / cm2, lb / in2.

1 Pa = 1N/ m2

1 psi = 1 lb/in2 (English unit) = 6,894 Pascal

1 Torr = 133.322 pascal

1 bar= 100000 pascal

1 atm= 101325 pascal

Flow : it is defined as volume per unit of time at specified temperature and pressure. Units of flow are kg / hr, litter / min, gallon / min, m3 / hr, Nm3 / hr.

Level : The height of a liquid or powder represented in meter ,mm, cm or percentage.

Temperature : It is an objective comparative measure of hot or cold. Units are Degree Centigrade, Degree Fahrenheit, Degree Kelvin, Degree Rankin.




Fahrenheit [°F] = [°C] × 9⁄5 + 32

Kelvin [K] = [°C] + 273.15

Rankine [°R] = ([°C] + 273.15) × 9⁄5

Delisle [°De] = (100 − [°C]) × 3⁄2

Newton [°N] = [°C] × 33⁄100

Reaumur [°Re] = [°C] × 4⁄5

Density : It is mass per unit volume. unit of density is kg/m3

PH : is a numeric scale used to specify the acidity or alkalinity of an aqueous solution. It is the negative of the logarithm to base 10 of the activity of the hydrogen ion. Solutions with a pH less than 7 are acidic and solutions with a pH greater than seven are alkaline or basic.

See Also :

level measurement: direct methods level measurement using hydrostatic pressure ultra sonic level measurement indirect methods for level measurement

Radiation Level Detection

The radiation type level measuring device operates on the principle that radiation can be blocked by any substance to a limited degree. This degree of blockage is measured and translated to indicate level.

The system itself consists of a radiation source, a detector, a conversion circuit, and an indicator. The source and detector are situated above and below the substance to be measured. As the level of the substance increases, the amount of radiation blocked increases. Therefore, the amount of radiation received by the detector decreases. This received radiation is translated into an electrical signal by the converter and sent to the indicator. A typical radiation type level measuring system is shown in Figure

radiation level detector

see also

level measurement using hydrostatic pressure ultra sonic level measurement indirect methods for level measurement level measurement: direct methods difference between sensor and transducer

Ultra Sonic Level Measurement

This type of instrument uses “time of flight” principle. An ultrasonic level measuring device uses reflected sound to determine the height of a substance in a vessel. The time required for a sound wave to be transmitted, reflected, and returned to the device may be translated directly into a level indication. A high frequency sound signal is used for this purpose, normally in the range of 20KHZ to 200KHZ.

The timing circuit of the device is started when the transmitter sends out the sound wave. It is stopped when the receiver detects the return of the reflected signal. The device is calibrated in an empty vessel; therefore, as the level in the vessel increases, the time required for the reflected signal to return decreases.

Although this principle is very accurate and used in many industries, it is not widely used as an indicator in power plants. The device is generally fragile and affected greatly by outside forces. Because of this, it requires frequent calibration to maintain its accuracy. It is, however, used to some extent as a level switch. A typical example is illustrated in Figure .

ultrasonic level measurement

see also

level measurement using hydrostatic pressure indirect methods for level measurement level measurement: direct methods difference between sensor and transducer

Water Level measurement using hydrostatic Pressure

Water Level measurement using static Pressure

The pressure at any point below the surface of a liquid and the level of water in height are related directly. Simply, the pressure at any point below the liquid surface is a measure of liquid level. Level measuring instruments using static pressure utilize this principle.

Static pressure type level instruments are normally only applied to open vessels, because they depend entirely on the static head. Any change in pressure on the surface of the liquid would affect the calibration, because it would cause a change of static head pressure. The pressure and Level relation can be summarized using the equation

h=P/ρg

Indirect Methods for Level Measurement

In case of indirect method or inferential method, levels are measured in terms of other parameters like pressure. Measuring instrument will be calibrated in terms of level. As discussed previously, direct reading level devices are normally for local indication only. When remote indication like in the control room or a control signal is required, an indirect measurement device must be used. There are different types of indirect level-measurement devices like differential pressure, static pressure, ultrasonic, and radiation level measuring instruments. Some are discussed below.

 Differential pressure level measurement

This type of instrument measures the differential pressure resulting from two columns of liquids with unequal height. The height of one column will be always constant and that of the other will be variable. A typical example of this type would be the steam drum water level measuring device, similar to the one shown in Figure.

Level measurement

In industries, Liquid levels are measured either directly or indirectly. In direct method level can be measured by using indicators such as dipsticks, floats, and gauge glasses. Where as in indirect method, it is measured using static or differential pressure instruments. Normally Direct measurements are used only for local indication, meanwhile Indirect measurements are used to provide both remote indication and a control signal.

Direct method

Direct methods are used only for monitoring or getting indications locally. Even though in industries, it is used for various reasons on many types of substances. There are different types of instruments for this purposes. Some of them are discussed below. 

Speaking aid for dumb - a simple project

ABSTRACT

      Speaking aid for dumb convert the gestures used by the dumb persons to sound. When a dumb person communicates using gestures, corresponding sounds will be heard through speaker. This will help the dumb people communicate with normal people who do not understand their gestures. LED-LDR networks are used for sensing the gestures. A flexible tube is placed between LED and LDR for passing the light. The LED-LDR network is placed on a glove worn by the dumb person. According to the finger bending, LDR resistance varies. The output of the sensor is converted to voltage and interfaced to   a LABVIEW through Arduino. The corresponding prerecorded sounds are played through loud speakers. This work produced sound for the gestures for the numbers 0 to 9 for which it was designed.

Purpose of motor drive

      Generally in industrial, commercial and utility applications electric motors are used to transform electrical energy into mechanical energy. The motors may be a part of mechanical systems such as mixer, conveyor, pump e.t.c. In many such cases, the speed of the system is determined by its mechanical design and loading. So, it is necessary to control the speed of motor for controlling the speed of system. The speed of motor is mainly controlled by using suitable electronic drive equipment, normally referred as variable speed drives. So the drives are used to

•   Increase the efficiency of a process
•   Provide accurate motor speed
•   Control motor torque
•   Enable the motor to run at a range of speeds
•   Automate and optimize a process                                                                                               

The above listed features help to improve the efficiency and quality of process run by motors.

What is the difference between sensor and transducer

The difference between sensors and transducers is one of the most confusing and ever discussed question among instrumentation students. the reason behind rising such confusion is that, both sensors and transducers are highly related and some people use these as synonyms. here i would like to explore some definitions and differences explained by experts.

the below explanation is by john wiley & sons in “Sensors and Signal Conditioning, 2nd. Ed.”:

“A transducer is a device that converts a signal from one physical form to a corresponding signal having a different physical form. Therefore, it is an energy converter. This means that the input signal always has energy or power, i.e. signals consist of two component quantities whose product has energy or power dimension. But in measurement systems, one of the two components of the measured signal is usually so small that it is negligible, and thus only the remaining component is measured.

AUTOMATIC PICK AND PLACE ROBOT

AUTOMATIC PICK AND PLACE ROBOT
{implemented based on below paper}

With the help of machine vision we identify the object and remove the noise in it. Visual servoing is used to control the trajectory of the robot toward the object in the image. After that we want to pick the object and return to the starting position for placing it.  We use Arduino, H bridge and motors for controlling the robot. This is the block diagram for automatic pick and place robot using camera. This contains mainly eight blocks as shown in Fig

block diagram for automatic pick and place robot

Ratio Based Distance Measurement for Automatic Pick and Place Robot

   Ratio Based Distance Measurement for Automatic Pick and Place Robot.

K.M.I.Yasar Arafath, Adeep Shafi, Adnan Aboobacker, Asha K V, Muhammed Mousoof  K, Rashida P P

kmiyasar@mesce.ac.in,adeepshafi@gmail.com,muhammedmousoofk@gmail.com,

ashakandanakam@gmail.com, rashrashida11@gmail.com

Abstract— Automatic pick and place robots have wide applications especially in the field of agriculture, industry, etc. The most important part in the pick and place robots is the calculation of distance between the object and the observer. Since cameras are becoming an integral part of the robot, this work uses a camera for the measurement of the distance. The previous works in this field either uses external hardware in addition to camera in order to measure the distance or has knowledge regarding the size of the object. This also makes the work useful in cases where measuring instruments cannot be used. This work uses a ratio based distance measurement method for calculating the distance between the observer and the object. The camera on the robot takes the picture of the object and calculates the pixel height. Then the robot moves a known distance towards the object and again calculates the pixel height of the object by capturing a new image. The actual distance to the object is calculated using the ratio of the pixel heights and the known distance moved by the robot. Then robot moves the measured distance, picks the object and places the object at the starting position. The MATLAB is used as the processing software and Arduino Uno is interfaced with MATLAB to control the robotic actions.