Government Girls’ Polytechnic, Bilaspur Name of the Lab:Electrical&Electronic Measurement Lab Practical: Instrumentation & Process Control Lab Class : 5th Semester ( ET&T ) Teachers Assessment: 10

End Semester Examination: 30

EXPERIMENT NO 1 OBJECTIVE : Displacement measurement using LVDT MATERIAL REQUIRED : LVDT, MULTIMETER, CONNECTING WIRE

.

THEORY : Linear displacement is movement in one direction along a single axis. A position or linear displacement sensor is a device whose output signal represents the distance an object has traveled from a reference point. Linear variable differential transformers (LVDT) are used to measure displacement. LVDTs operate on the principle of a transformer. As shown in Figure 2, an LVDT consists of a coil assembly and a core. The coil assembly is typically mounted to a stationary form, while the core is secured to the object whose position is being measured. The coil assembly consists of three coils of wire wound on the hollow form. A core of permeable material can slide freely through the center of the form. The inner coil is the primary, which is excited by an AC source as shown. Magnetic flux produced by the primary is coupled to the two secondary coils, inducing an AC voltage in each coil 1. Connect the circuit according to the diagram. 2. Switch on power supply. 3. The core is initially brought to null position. 4. First turn the nut in the in the clock wise direction i.e. from left of null position and take respective reading in the voltmeter. 5. Now turn the nut in the anti clockwise direction i.e. from right of null position and again take respective reading from voltmeter. 6. Plot the graph from observation taken.

CIRCUIT DIAGRAM :

Instrumentation & Process Control Lab Manual:5th semester(ET&T)

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General LVDT Assembly

Proportionally Linear LVDT Response to Core Displacement


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Cross-Sectional View of LVDT Core and Windings OBSERVATION TABLE :

SR NO

DISPLACEMENT (MICROMETER)

DISPLACEMENT

ANALOG O/P

READING(mm)

1. 2.

RESULT: The graph is plotted between displacement and voltage. PRECAUTIONS : 1. handle all equipment with care. 2. Make connection according to circuit diagram. 3. Take readings carefully. 4. The connections should be tight.


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EXPERIMENT NO 2 OBJECTIVE : Weight measurement using strain gauge bridge

MATERIAL REQUIRED : Strain cantilever kit, multimeter, connecting wires.

THEORY : A strain gage is a sensor whose resistance varies with applied force; It converts force, pressure, tension, weight, etc., into a change in electrical resistance which can then be measured.When external forces are applied to a stationary object, stress and strain are the result. Stress is defined as the object's internal resisting forces, and strain is defined as the displacement and deformation that occur. The strain gage is one of the most important tools of the electrical measurement technique applied to the measurement of mechanical quantities. As their name indicates, they are used for the measurement of strain. As a technical term "strain" consists of tensile and compressive strain, distinguished by a positive or negative sign. Thus, strain gages can be used to pick up expansion as well as contraction. The strain of a body is always caused by an external influence or an internal effect. Strain might be caused by forces, pressures, moments, heat, structural changes of the material and the like. If certain conditions are fulfilled, the amount or the value of the influencing quantity can be derived from the measured strain value. In experimental stress analysis this feature is widely used. Experimental stress analysis uses the strain values measured on the surface of a specimen, or structural part, to state the stress in the material and also to predict its safety and endurance. Special transducers can be designed for the measurement of forces or other derived quantities, e.g., moments, pressures, accelerations, displacements, vibrations and others. The transducer generally contains a pressure sensitive diaphragm with strain gages bonded to it. 1.Connect the strain cantilever in the experimental kit. 2.Switch on power supply. 3.Give some time to stabilize the instrument. 4.Balance the cantilever bridge by corresponding zero. 5.Set the gain of the cantilever by SPAN , turn the trim point. 6.Now apply the weight at the cantilever beam and take readings.

CIRCUIT DIAGRAM :


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Wheatstone Bridge Circuit Schematic

Typical metal-foil strain gages

OBSERVATION TABLE : SR NO

WEIGHT

DISPLAY READING

ANALOG O/P(v)

SIGNAL(mv)

RESULT : Weight can be measured by using strain guage. Piezoelectric effect is studied with the help of strain guage. PRECAUTIONS : 1.handle all equipment with care. 2.Make connection according to circuit diagram. 3.Take readings carefully. 4.The connections should be tight.


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EXPERIMENT NO 3& 4 OBJECTIVE : Speed measurement of motor using magnetic proximity switch. Speed measurement of motor using photo electric pickup transducer.

MATERIALS REQUIRED : DC motor, proximity switch, connecting wire CRO. THEORY : : Protocontrol make Proximity Switches that serve as a basic block of automation. Find application for Position - Speed - Direction - Revolution -Liner Speed measurement. We are proximity switches manufacturer and also offering sensing solutions for all applications. You specify the requirement and we will help you to select suitable sensor from more than 2600 varieties we have. Every proximity sensor switches are designed for industrial application. An electronic speed control or ESC is an electronic circuit with the purpose to vary an electric motor's speed, its direction and possibly also to act as a dynamic brake. Asks are often used on electrically-powered radio controlled models.An ESC can be a stand-alone unit which plugs into the receiver's throttle control channel or incorporated into the receiver itself, as is the case in most toy-grade R/C vehicles. Some R/C manufacturers that install proprietary hobby-grade electronics in their entry-level vehicles, vessels or aircraft use onboard electronics that combine the two on a single circuit board.

1.Connect the circuit according to the diagram and switch on power supply. 2. Adjust the speed of dc motor by the knob and wait until the motor the maximum speed at the corresponding knob position. 3. measure the frequency from the output wave of CRO. 4.Find speed of motor by given formula.

CIRCUIT DIAGRAM :


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OBSERVATION TABLE : SR NO

RPM SENSOR

DISPLAY READING

1. 2.

RESULT : The speed of dc motor is calculated by piezoelectric pick up and the piezoelectric effect is studied. Speed of sensor =(frequency *diameter disc)/No of segments D=56.5 S=60

PRECAUTIONS : 1.handle all equipment with care. 2.Make connection according to circuit diagram. 3.Take readings carefully. 4.The connections should be tight.


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EXPERIMENT NO 5

OBJECTIVE : Temperature measurement using Thermocouple. MATERIAL REQUIRED :Thermocouple kit, water, thermometer, ice, heating arrangement.

THEORY : thermocouple is a junction between two different metals that produces a voltage related to a temperature difference. Thermocouples are a widely used type of temperature sensor for measurement and control and can also be used to convert heat into electric power. They are inexpensive and interchangeable, are supplied fitted with standard connectors, and can measure a wide range of temperatures. The main limitation is accuracy: system errors of less than one degree Celsius (C) can be difficult to achieve. Any junction of dissimilar metals will produce an electric potential related to temperature. Thermocouples for practical measurement of temperature are junctions of specific alloys which have a predictable and repeatable relationship between temperature and voltage. Different alloys are used for different temperature ranges. Properties such as resistance to corrosion may also be important when choosing a type of thermocouple. Where the measurement point is far from the measuring instrument, the intermediate connection can be made by extension wires which are less costly than the materials used to make the sensor. Thermocouples are usually standardized against a reference temperature of 0 degrees Celsius; practical instruments use electronic methods of cold-junction compensation to adjust for varying temperature at the instrument terminals. Electronic instruments can also compensate for the varying characteristics of the thermocouple, and so improve the precision and accuracy of measurements. Thermocouples are widely used in science and industry; applications include temperature measurement for kilns, gas turbine exhaust, diesel engines, and other industrial processes. In 1821, the German–Estonian physicist Thomas Johann See beck discovered that when any conductor is subjected to a thermal gradient, it will generate a voltage. This is now known as the thermoelectric effect or See beck effect. Any attempt to measure this voltage necessarily involves connecting another conductor to the "hot" end. This additional conductor will then also experience the temperature gradient, and develop a voltage of its own which will oppose the original. Fortunately, the magnitude of the effect depends on the metal in use. Using a dissimilar metal to complete the circuit creates a circuit in which the two legs generate different voltages, leaving a small difference in voltage available for measurement. That difference increases with temperature, and is between 1 and 70 microvolt’s per degree Celsius (µV/°C) for standard metal combinations. The voltage is not generated at the junction of the two metals of the thermocouple but rather along that portion of the length of the two dissimilar metals that is subjected to a temperature gradient. Because both lengths of dissimilar metals experience the same temperature gradient, the end result is a measurement of the temperature at the thermocouple junction. 1.Connect the main power cord at the input main socket. 2.Switch on the power supply red LED will glow..


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3.Connect the thermocouple sensor at pin the terminal. 4.Keep the thermocouple in boiling water and adjust the display ranging 100 by knob

CIRCUIT DIAGRAM :

OBSERVATION TABLE :

SR NO

TEMPERATURE

1.

TEMP WITH ICE POINT

2.

TEMP WITH BOILING POINT


DISPLAY READING(mV)

9

RESULT :The temperature can be measured using thermocouple.

PRECAUTIONS :

1.handle all equipment with care. 2.Make connection according to circuit diagram. 3.Take readings carefully. 4.The connections should be tight.


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EXPERIMENT NO 6 OBJECTIVE : Temperature measurement using resistance temperature detector MATERIAL REQUIRED : Resistance temperature detector kit, ice, water, thermometer, heating arrangement.

THEORY : Resistance temperature detectors (RTDs) operate on the principle of changes in the electrical resistance of pure metals and are characterized by a linear positive change in resistance with temperature. Typical elements used for RTDs include nickel (Ni) and copper (Cu), but platinum (Pt) is by far the most common because of its wide temperature range, accuracy, and stability. RTDs are popular because of their excellent stability, and exhibit the most linear signal with respect to temperature of any electronic temperature sensor. They are generally more expensive than alternatives, however, because of the careful construction and use of platinum. RTDs are also characterized by a slow response time and low sensitivity, and because they require current excitation, they can be prone to self-heating. RTDs are commonly categorized by their nominal resistance at 0 oC. Typical nominal resistance values for platinum thin-film RTDs include 100 W and 1000 W. The relationship between resistance and temperature is very linear and follows the equation o

2

3

For < 0 C RT = R0 [ 1 + aT + bT + cT (T - 100) ] o 2 For > 0 C RT = R0 [ 1 + aT + bT ] Where RT = resistance at temperature T R0 = nominal resistance a, b, and c are constants used to scale the RTD o

The most common RTD is the platinum thin-film with an a of 0.385%/ C and is specified per DIN EN 60751. The a value depends on the grade of platinum used, and also commonly o o include 0.3911%/ C and 0.3926%/ C. The a value defines the sensitivity of the metallic element, but is normally used to distinguish between resistance/temperature curves of various RTDs. 1.Connect the main power cord at the input main socket. 2.Switch on the power supply red LED will glow.. 3.Connect the RTD sensor at pin the terminal. 4.Keep the RTD in boiling water and adjust the display ranging 100 by knob.


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CIRCUIT DIAGRAM :

OBSERVATION TABLE :

SR NO

TEMPERATURE

1.

TEMP WITH ICE POINT

2.


DISPLAY READING(mV)

RESULT : We have measured the temperature with RTD.Change in temperature give electrical output.


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PRECAUTIONS : 1.Handle all equipment with care. 2.Make connection according to circuit diagram. 3.Take readings carefully. 4.The connections should be tight.


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EXPERIMENT NO 7 OBJECTIVE : Temparature measurement using thermistor. MATERIALS REQUIRED : Thermistor kit, ice, water,thermometer, heating arrangement. THEORY : Like the RTD, the thermistor is also a temperature sensitive resistor. While the thermocouple is the most versatile temperature transducer and the PRTD is the most stable, the word that best describes the thermistor is sensitive. Of the three major categories of sensors,the thermistor exhibits by far the largest parameter change with temperature.Thermistors are generally composed of semiconductor materials. Although positive temperature coefficient units are available, most thermistors have a negative temperature coefficient (TC); that is, their resistance decreases with increasing temperature. The negative T.C. can be as large as several percent per degree Celsius, allowing the thermistor circuit to detect minute changes in temperature which could not be observed with an RTD or thermocouple circuit. The price we pay for this increased sensitivity is loss of linearity. The thermistor is an extremely non-linear upon process parameters. Consequently, manufacturers have not standardized thermistor curves to the extent that RTD and thermocouple curves have been standardized. 1.Connect the main power cord at the input main socket. 2.Switch on the power supply red LED will glow.. 3.Connect the thermistor at pin the terminal. 4.Keep the thermistor in boiling water and adjust the display ranging 100 by knob.

CIRCUIT DIAGRAM :


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OBSERVATION TABLE :

SR NO

TEMPERATURE

1.

TEMP WITH ICE POINT

2.


DISPLAY READING(mV)

RESULT : We have measured the temperature with RTD.Change in temperature give electrical output.


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EXPERIMENT NO 8

OBJECTIVE : Performance of piezo electric transducers

MATERIAL REQUIRED : Rochhele Salt, quartz, CRO

THEORY : Piezoelectricity from the Greek word "piezo" means pressure electricity. Certain crystalline substances generate electric charges under mechanical stress and conversely experience a mechanical strain in the presence of an electric field. The piezoelectric effect describes a situation where the transducing material senses input mechanical vibrations and produces a charge at the frequency of the vibration. An AC voltage causes the piezoelectric material to vibrate in an oscillatory fashion at the same frequency as the input current. Quartz is the best known single crystal material with piezoelectric properties. Strong piezoelectric effects can be induced in materials with an ABO3, Perovskite crystalline structure. 'A' denotes a large divalent metal ion such as lead and 'B' denotes a smaller tetravalent ion such as titanium or zirconium. For any crystal to exhibit the piezoelectric effect, its structure must have no center of symmetry. Either a tensile or compressive stress applied to the crystal alters the separation between positive and negative charge sights in the cell causing a net polarization at the surface of the crystal. The polarization varies directly with the applied stress and is direction dependent so that compressive and tensile stresses will result in electric fields of opposite voltages. 1. Connect the circuit according to diagram. 2. Switch on power supply. 3. Plot thr graph according to the reading taken.

CIRCUIT DIAGRAM :


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RESULT : The performance of the piezoelectric transducer have been studied.

PRECAUTIONS : 1.Connect the circuit according to the diagram. 2. The connection should be tight.


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EXPERIMENT NO 9

OBJECTIVE : Displacement measurement with help of light dependent resistor

MATERIAL REQUIRED : LDR kit, connecting wire, multimeter.

THEORY : photoresistor, light dependent resistor (LDR) or cium sulfide (CdS) cell is a

resistor whose resistance decreases with increasing incident light intensity. It can also be referred to as a photoconductor. A photoresistor is made of a high resistance semiconductor. If light falling on the device is of high enough frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electron (and its hole partner) conduct electricity, thereby lowering resistance. A photoelectric device can be either intrinsic or extrinsic. An intrinsic semiconductor has its own charge carriers and is not an efficient semiconductor, e.g. silicon. In intrinsic devices the only available electrons are in the valence band, and hence the photon must have enough energy to excite the electron across the entire bandgap. Extrinsic devices have impurities, also called dopants, added whose ground state energy is closer to the conduction band; since the electrons do not have as far to jump, lower energy photons (i.e., longer wavelengths and lower frequencies) are sufficient to trigger the device. If a sample of silicon has some of its atoms replaced by phosphorus atoms (impurities), there will be extra electrons available for conduction. This is an example of an extrinsic semiconductor. The sensitivity of a photodetector is the relationship between the light falling on the device and the resulting output signal. In the case of a photocell, one is dealing with the relationship between theincident light and the corresponding resistance of the cell. Like the human eye, the relative sensitivity of a photoconductive cell is dependent on the wavelength (color) of the incident light. Each photoconductor material type has its own unique spectral response curve or plot of the relative response of the photocell versus wavelength of light

1. Connect the circuit as shown and note all connection should be proper and tight. 2.Switch on the lamp and place the lamp such that light falls on LDR. 3. Move the direction of lamp and the variations in R.Make sure the movement is low.


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CIRCUIT DIAGRAM :

OBSERVATION TABLE : Sr no

Lux meter

Display reading

1. 2.


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RESULT : The resistance of LDR decreases with increase in intensity.



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EXPERIMENT NO 10

OBJECTIVE : Displacement measurement using inductive pick up transducer MATERIAL REQUIRED :Variable inductance kit, multimeter, connecting wires.

THEORY : The variable inductive transducer works on the same principle as LVDT.It consists of core of ferromagnetic material.The displacement to be measured is applied to ferromagnetic target.This target do not have any physical with the core on which it is mounted.The core and target are separated by air gap.The displacement of the target allows the change in output voltage which results in change of resistance of air gap. n Inductor is a ive component used in electronic circuits. It stores energy in the form of magnetic field.

1. Connect the circuit according ti the diagram and make sure all connections are tight. 2. Set the variable inductance knob to zero position and see that there should not be any error. 3. Now rotate the knob from zero and note the reading of multimeter. 4. Repeat the step 3 atleast 5 times. 5. Make a graph between voltage and displacement carefully.

CIRCUIT DIAGRAM :


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The graph below shows the output voltage/position characteristics.

RESULT : The graph is plotted between displacement and voltage.

PRECAUTIONS :



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EXPERIMENT NO 11

OBJECTIVE : Pressure measurement using load cell

MATERIAL REQUIRED : Load cell, pressure guage,

THEORY : . A load cell is a transducer which converts force into a measurable electrical output. Although there are many varieties of load cells, strain gage based load cells are the most commonly used type. A load cell is a transducer that is used to convert a force into electrical signal. This conversion is indirect and happens in two stages. Through a mechanical arrangement, the force being sensed deforms a strain gauge. The strain gauge converts the deformation (strain) to electrical signals. A load cell usually consists of four strain gauges in a Wheatstone bridge configuration. Load cells of one strain gauge (quarter bridge) or two strain gauges (half bridge) are also available. The electrical signal output is typically in the order of a few millivolts and requires amplification by an instrumentation amplifier before it can be used. The output of the transducer is plugged into an algorithm to calculate the force applied to the transducer

CIRCUIT DIAGRAM :


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RESULT : Pressure is measured using load cell. PRECAUTIONS : 1.handle all equipment with care. 2.Make connection according to circuit diagram. 3.Take readings carefully. 4.The connections should be tight.


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EXPERIMENT NO 12

OBJECTIVE : Liquid level measurement using capacitive type transducer

MATERIAL REQUIRED : capacitive type transducer,

THEORY : The capacitance between two conductive surfaces varies with three major factors: •

The overlapping area(A) of those two surfaces

•

The distance between them(d)

•

The dielectric constant(εo & εr) of the material in between the surfaces.

If two out of three of these variables can be fixed (stabilized) and the third allowed to vary, then any measurement of capacitance between the surfaces will be solely indicative of changes in that third variable.The value of capacitance is determined by: (a) The area of the plates (b) The distance between the plates (c) The type of dielectric between the plates Some transducers work by making one of the capacitor plates movable, either in such a way as to vary the overlapping area or the distance between the plates. Other transducers work by moving a dielectric material in and out between two fixed plates: Capacitive transducers can be classified as : 1. Variable capacitive transducer 2. Differential capacitive transducer Variable capacitive transducer varies according to: (a) Area of overlap, (b) Distance between plates, (c) Amount of dielectric between plates. Transducers with greater sensitivity and immunity to changes in other variables can be obtained by way of differential design. Differential capacitive transducer varies capacitance ratio by changing: (a) Area of overlap (b) Distance between plates (c) Dielectric between plates.


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The differential devices shown above have three wire connections rather than two: one wire for each of the “end” plates and one for the “common” plate. As the capacitance between one of the “end” plates and the “common” plate changes, the capacitance between the other “end” plate and the “common” plate is such to change in the opposite direction.This kind of transducer lends itself very well to implementation in a bridge circuit.

CIRCUIT DIAGRAM :

RESULT :The height of liquid is calculated using capacitive transducer.



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EXPERIMENT NO 13, 14,&15

OBJECTIVE : Proportionate mode of control ,Proportionate + integral type control And Proportionate + integral + derivative control

MATERIAL REQUIRED : controller with proportional,,PI and PID control. THEORY : A proportional–integral–derivative controller (PID controller) is a generic control loop mechanism (controller) widely used in industrial control systems – a PID is the most commonly used controller. A PID controller calculates an "error" value as the difference between a measured process variable and a desired setpoint. The controller attempts to minimize the error by adjusting the process control inputs. The PID controller calculation (algorithm) involves three separate constant parameters, and is accordingly sometimes called three-term control: the proportional, the integral and derivative values, denoted P, I, and D. Heuristically, these values can be interpreted in of time: P depends on the present error, I on the accumulation of past errors, and D is a prediction of [1] future errors, based on current rate of change. The weighted sum of these three actions is used to adjust the process via a control element such as the position of a control valve or the power supply of a heating element. [2]

In the absence of knowledge of the underlying process, a PID controller is the best controller. By tuning the three parameters in the PID controller algorithm, the controller can provide control action designed for specific process requirements. The response of the controller can be described in of the responsiveness of the controller to an error, the degree to which the controller overshoots the setpoint and the degree of system oscillation. Note that the use of the PID algorithm for control does not guarantee optimal control of the system or system stability. Some applications may require using only one or two actions to provide the appropriate system control. This is achieved by setting the other parameters to zero. A PID controller will be called a PI, PD, P or I controller in the absence of the respective control actions. PI controllers are fairly common, since derivative action is sensitive to measurement noise, whereas the absence of an integral term may prevent the system from reaching its target value due to the control action.

Control loop basics A familiar example of a control loop is the action taken when adjusting hot and cold faucet valves to maintain the faucet water at the desired temperature. This typically involves the mixing of two process streams, the hot and cold water. The person touches the water to sense or measure its temperature. Based on this they perform a control action to adjust the hot and cold water valves until the process temperature stabilizes at the desired value. Sensing water temperature is analogous to taking a measurement of the process value or process variable (PV). The desired temperature is called the setpoint (SP). The input to the


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process (the water valve position) is called the manipulated variable (MV). The difference between the temperature measurement and the setpoint is the error (e) and quantifies whether the water is too hot or too cold and by how much. After measuring the temperature (PV), and then calculating the error, the controller decides when to change the tap position (MV) and by how much. When the controller first turns the valve on, it may turn the hot valve only slightly if warm water is desired, or it may open the valve all the way if very hot water is desired. This is an example of a simple proportional control. In the event that hot water does not arrive quickly, the controller may try to speed-up the process by opening up the hot water valve more-and-more as time goes by. This is an example of an integral control. Making a change that is too large when the error is small is equivalent to a high gain controller and will lead to overshoot. If the controller were to repeatedly make changes that were too large and repeatedly overshoot the target, the output would oscillate around the setpoint in either a constant, growing, or decaying sinusoid. If the oscillations increase with time then the system is unstable, whereas if they decrease the system is stable. If the oscillations remain at a constant magnitude the system is marginally stable. In the interest of achieving a gradual convergence at the desired temperature (SP), the controller may wish to damp the anticipated future oscillations. So in order to compensate for this effect, the controller may elect to temper their adjustments. This can be thought of as a derivative control method. If a controller starts from a stable state at zero error (PV = SP), then further changes by the controller will be in response to changes in other measured or unmeasured inputs to the process that impact on the process, and hence on the PV. Variables that impact on the process other than the MV are known as disturbances. Generally controllers are used to reject disturbances and/or implement setpoint changes. Changes in feedwater temperature constitute a disturbance to the faucet temperature control process. In theory, a controller can be used to control any process which has a measurable output (PV), a known ideal value for that output (SP) and an input to the process (MV) that will affect the relevant PV. Controllers are used in industry to regulate temperature, pressure, flow rate, chemical composition, speed and practically every other variable for which a measurement exists. PID controller theory This section describes the parallel or non-interacting form of the PID controller. For other forms please see the section "Alternative nomenclature and PID forms". The PID control scheme is named after its three correcting , whose sum constitutes the manipulated variable (MV). Hence:

Where Pout, Iout, and Dout are the contributions to the output from the PID controller from each of the three , as defined below. Proportional term


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The proportional term (sometimes called gain) makes a change to the output that is proportional to the current error value. The proportional response can be adjusted by multiplying the error by a constant Kp, called the proportional gain. The proportional term is given by: where Pout: Proportional term of output Kp: Proportional gain, a tuning parameter SP: Setpoint, the desired value PV: Process value (or process variable), the measured value e: Error = SP − PV t: Time or instantaneous time (the present) A high proportional gain results in a large change in the output for a given change in the error. If the proportional gain is too high, the system can become unstable (see the section on loop tuning). In contrast, a small gain results in a small output response to a large input error, and a less responsive (or sensitive) controller. If the proportional gain is too low, the control action may be too small when responding to system disturbances.A pure proportional controller will not always settle at its target value, but may retain a steady-state error. Specifically, the process gain - drift in the absence of control, such as cooling of a furnace towards room temperature, biases a pure proportional controller. If the process gain is down, as in cooling, then the bias will be below the set point, hence the term "droop".Droop is proportional to process gain and inversely proportional to proportional gain. Specifically the steady-state error is given by: e = G / Kp Droop is an inherent defect of purely proportional control. Droop may be mitigated by adding a compensating bias term (setting the setpoint above the true desired value), or corrected by adding an integration term (in a PI or PID controller), which effectively computes a bias adaptively. Despite droop, both tuning theory and industrial practice indicate that it is the proportional term that should contribute the bulk of the output change. Plot of PV vs time, for three values of Ki (Kp and Kd held constant) The contribution from the integral term (sometimes called reset) is proportional to both the magnitude of the error and the duration of the error. Summing the instantaneous error over time (integrating the error) gives the accumulated offset that should have been corrected previously. The accumulated error is then multiplied by the integral gain and added to the controller output. The magnitude of the contribution of the integral term to the overall control action is determined by the integral gain, Ki. The integral term is given by:where


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Iout: Integral term of output Ki: Integral gain, a tuning parameter SP: Setpoint, the desired value PV: Process value (or process variable), the measured value e: Error = SP − PV t: Time or instantaneous time (the present) τ: a dummy integration variable The integral term (when added to the proportional term) accelerates the movement of the process towards setpoint and eliminates the residual steady-state error that occurs with a proportional only controller. However, since the integral term is responding to accumulated errors from the past, it can cause the present value to overshoot the setpoint value (cross over the setpoint and then create a deviation in the other direction). For further notes regarding integral gain tuning and controller stability, see the section on loop tuning. The derivative term is given by: Where Dout: Derivative term of output Kd: Derivative gain, a tuning parameter SP: Setpoint, the desired value PV: Process value (or process variable), the measured value e: Error = SP − PV t: Time or instantaneous time (the present) The derivative term slows the rate of change of the controller output and this effect is most noticeable close to the controller setpoint. Hence, derivative control is used to reduce the magnitude of the overshoot produced by the integral component and improve the combined controller-process stability. However, differentiation of a signal amplifies noise and thus this term in the controller is highly sensitive to noise in the error term, and can cause a process to become unstable if the noise and the derivative gain are sufficiently large. Hence an approximation to a differentiator with a limited bandwidth is more commonly used. Such a circuit is known as a Phase-Lead compensator.: where the tuning parameters are: Proportional gain, Kp Larger values typically mean faster response since the larger the error, the larger the proportional term compensation. An excessively large proportional gain will lead to process instability and oscillation. Integral gain, Ki


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Larger values imply steady state errors are eliminated more quickly. The trade-off is larger overshoot: any negative error integrated during transient response must be integrated away by positive error before reaching steady state. Derivative gain, Kd Larger values decrease overshoot, but slow down transient response and may lead to instability due to signal noise amplification in the differentiation of the error

CIRCUIT DIAGRAM :

A block diagram of a PID controller

Plot of PV vs time, for three values of Ki (Kp and Kd held constant)

RESULT: The controller as proportional, proportional derivative and proportional,integral and derivative control is studied.


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PRECAUTIONS :



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EXPERIMENT NO 16 OBJECTIVE : Performance of data acquisition system. MATERIAL REQUIRED : data acquisition system.

THEORY : Data acquisition is the process of sampling signals that measure real world physical conditions and converting the resulting samples into digital numeric values that can be manipulated by a computer. Data acquisition systems (abbreviated with the acronym DAS or DAQ) typically convert analog waveforms into digital values for processing. The components of data acquisition systems include: • • •

Sensors that convert physical parameters to electrical signals. Signal conditioning circuitry to convert sensor signals into a form that can be converted to digital values. Analog-to-digital converters, which convert conditioned sensor signals to digital values. Data acquisition applications are controlled by software programs developed using various general purpose programming languages such as BASIC, C, Fortran, Java, Lisp, Pascal. COMEDI is an open source API (application program Interface) used by applications to access and control the data acquisition hardware. Using COMEDI allows the same programs to run on different operating systems, like Linux and Windows. Specialized software tools used for building large-scale data acquisition systems include EPICS. Graphical programming environments include ladder logic, Visual C++, Visual Basic, MATLAB and LabVIEW. Data acquisition begins with the physical phenomenon or physical property to be measured. Examples of this include temperature, light intensity, gas pressure, fluid flow, and force. Regardless of the type of physical property to be measured, the physical state that is to be measured must first be transformed into a unified form that can be sampled by a data acquisition system. The task of performing such transformations falls on devices called sensors. A sensor, which is a type of transducer, is a device that converts a physical property into a corresponding electrical signal (e.g., a voltage or current) or, in many cases, into a corresponding electrical characteristic (e.g., resistance or capacitance) that can easily be converted to electrical signal. Signal conditioning may be necessary if the signal from the transducer is not suitable for the DAQ hardware being used. The signal may need to be amplified, filtered or demodulated. Various other examples of signal conditioning might be bridge completion, providing current or voltage excitation to the sensor, isolation, linearization. For transmission purposes, single ended analog


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signals, which are more susceptible to noise can be converted to differential signals. Once digitized, the signal can be encoded to reduce and correct transmission errors. DAQ hardware DAQ hardware is what usually interfaces between the signal and a PC. It could be in the form of modules that can be connected to the computer's ports (parallel, serial, USB, etc.) or cards connected to slots (S-100 bus, AppleBus, ISA, MCA, PCI, PCI-E, etc.) in the mother board. Usually the space on the back of a PCI card is too small for all the connections needed, so an external breakout box is required. The cable between this box and the PC can be expensive The ability of a data acquisition system to measure differing properties depends on having sensors that are suited to detect the various properties to be measured. There are specific sensors for many different applications. DAQ systems also employ various signal conditioning techniques to adequately modify various different electrical signals into voltage that can then be digitized using an Analog-to-digital converter (ADC). Signals Signals may be digital (also called logic signals sometimes) or analog depending on the transducer used. due to the many wires, and the required shielding. DAQ cards often contain multiple components (multiplexer, ADC, DAC, TTL-IO, high speed timers, RAM). These are accessible via a bus by a microcontroller, which can run small programs. A controller is more flexible than a hard wired logic, yet cheaper than a U so that it is permissible to block it with simple polling loops. For example: Waiting for a trigger, starting the ADC, looking up the time, waiting for the ADC to finish, move value to RAM, switch multiplexer, get TTL input, let DAC proceed with voltage ramp. Many times reconfigurable logic is used to achieve high speed for specific tasks and digital signal processors are used after the data has been acquired to obtain some results. The fixed connection with the PC allows for comfortable compilation and debugging. Using an external housing a modular design with slots in a bus can grow with the needs of the . Not all DAQ hardware has to run permanently connected to a PC, for example intelligent standalone loggers and oscilloscopes, which can be operated from a PC, yet they can operate completely independent of the PC. DAQ software DAQ software is needed in order for the DAQ hardware to work with a PC. The device driver performs low-level writes and reads on the hardware, while exposing a standard API for developing applications. A standard API such as COMEDI allows the same applications to run on different operating systems, e.g. a application that runs on Windows will also run on Linux and BSD.

CIRCUIT DIAGRAM :


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RESULT : Performance of data acquisition system is studied. PRECAUTIONS : 1.handle all equipment with care. 2.Make connection according to circuit diagram. 3.Take readings carefully. 4.The connections should be tight.


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Overview 4q3b3c

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