YANBU INDUSTRIAL COLLEGE DEPARTMENT OF ELCTRICAL AND ELECTRONICS ENGINEERING TECHNOLOGY SEMESTER -2, 2019-20 (1441H) As a team analyze and answer the following 1) As part of an alarm system for overheating of liquid in container, a measurement system is required which will set off an alarm when the temperature rises above 40° πΆ. The liquid is normally at 30° πΆ. The output from the measurement system be a 1V. as an engineer suggest a possible measurement system. We first use an NTC thermistor sensor whose resistance temperature graph is shown below: We see that at 30 degree C, its resistance is 8260 ohms and at 40 degree C, the resistance is 5740 ohms. Thus, if we plan to use this in a Wheatstone bridge, the nominal resistance to be used for the other resistors are 8260ohms. We connect the thermistor in a Wheatstone bridge as follows: YANBU INDUSTRIAL COLLEGE DEPARTMENT OF ELCTRICAL AND ELECTRONICS ENGINEERING TECHNOLOGY SEMESTER -2, 2019-20 (1441H) While temperature is 30 C we want the bridge to be balanced. To balance the bridge Vc must Equal Vd so we have to do some calculations π 2 To determine VC, we use this equation π£πΆ = π 1 +π 2 × π£π 8260 While R1=R2=8260 ohms and Vs = 5v thus π£πΆ = 8260+8260 × 5 = 2.5π£ To determine VD, we use this equation π£π = π π 4 3 +π 4 × π£π 8260 While R4=R3=8260 ohms and Vs = 5v thus π£π = 8260+8260 × 5 = 2.5π£ πππ’π‘ = ππ − ππ = 2.5 − 2.5 = 0π£ When temperature rises to 40 C, we want the bridge to transduce the change in resistance into voltage. To determine the output of the bridge when temperature is equal to 40 C. We know when the temperature of NTC is 40 C the resistance is equal to 5740 ohms. so, we can calculate the following: π£πΆ = π π 2 1 +π 2 π£πΆ = × π£π and π£π = π π 4 3 +π 4 × π£π π 2 × π£π π 1 + π 2 8260 = 8260+8260 × 5π£ = 2.5π£ (πππ€ππ¦π ππππ π‘πππ‘) π 4 π£π = π + π × π£π 3 4 = 5740 × 5π£ = 2.05 (π£πππππ π€ππ‘β π‘πππππππ‘π’ππ ππ πππΆ) 8260 + 5740 Thus, when temperature is 40 C the output voltage can be determined as follows: πππ’π‘ = ππ − ππ = 2.5 − 2.05 = 0.45π£ But in this system the output must be equal to 1v we can use an instrumentational amplifier to amplify 0.45v to a 1v signal at output. YANBU INDUSTRIAL COLLEGE DEPARTMENT OF ELCTRICAL AND ELECTRONICS ENGINEERING TECHNOLOGY SEMESTER -2, 2019-20 (1441H) In instrumentational amplifier the gain formula can be found as: π΄π£ = π£ π£π 2 −π£1 Since we want Vo to be 1v we can determine what value of gain is required while V2 = Vc, V1= VD. So, π΄π£ = π£ π£π 2 −π£1 = 1π£ ππ−ππ 1π£ 1 = 2.5π£−2.05π£ = 0.45π£ = 2.2 so we can understand that to get output of 1v we have to design an instrumentational amplifier with 2.2 gain. With following equation, we can design the amplifier to amplify 0.45v input to 1v Signal. Vo 2π 1 π 3 π΄π£ = (1 + ( )) × ( ) π π¦ π 2 Put R3=R2=1k, R1=750 ohms then solve for Rg. 2(750) 1π 2.2 = (1 + ( )) × ( ) π π 1π π π = 1250 = 1.250π πβππ We get a gain of 2.2, and the output = 1V, when the temperature rises to 40-degree C. YANBU INDUSTRIAL COLLEGE DEPARTMENT OF ELCTRICAL AND ELECTRONICS ENGINEERING TECHNOLOGY SEMESTER -2, 2019-20 (1441H) 2) With drawing, write about variable differential transformer transducer, and how it can be used in displacement measurement using two differential transformers in a closed loop servo system provide your answer with a diagram. LVDT-Linear variable differential transformer β’ Used to measure Linear motion and Displacement. β’ Primary transducer of Displacement measurement. β’ Secondary transducer for force weight pressure. When there is no movement πΈπ1 = πΈπ2 πΈ0 = πΈπ1 − πΈπ2 = 0 When the core moves Right to left Left to Right πΈπ1 > πΈπ2 πΈπ1 < πΈπ2 πΈπ = +ππ πΈπ = −ππ The secondary transducer is connected in different mod 180π phase operation πΈ −πΈ π·ππ ππππ πππππ‘ = πΈπ2 +πΈπ2 π1 β’ β’ β’ β’ O/P Tells about the Displacement i.e. Right to Left / Left to Right. o/p of LVDT is Linear free from friction lessees low power consumption. Sensitivity of LVDT is due to exeat cancellation of secondary voltage π2 YANBU INDUSTRIAL COLLEGE DEPARTMENT OF ELCTRICAL AND ELECTRONICS ENGINEERING TECHNOLOGY SEMESTER -2, 2019-20 (1441H) A Servomotor is a rotary actuator or linear actuator that allows for precise control of angular or linear position, velocity and acceleration. The term servomotor is suitable for use in a closedloop control system. A Servomotor is a closed-loop servomechanism that uses position feedback to control. The input to its control is an analog signal or digital signal representing the position commanded for the output shaft. The motor is paired with some type of encoder to provide position and speed feedback. The device is controlled by a feedback signal generated by comparing output signal and reference input signal. Servo motor can be rotated from 0 to 180 degree, but it can go up to 210 degree, depending on the manufacturing. The LVDT is used to monitor the position of the moving bolster. It consists of three solenoid coils which are faced opposite to each other. The core is placed between the coils. The movement of the core which causes induced voltage to change. The change in voltage will cause the changes in movement of bolster. It can operate up to high temperature of 12000 F. The operating voltage for the LVDT is 24 V DC. It is mainly used in the servo motor for the position feedback control. We use BALLUFF LVDT for this operation. It can withstand up to 850F.The over voltage protection is possible and also it will record the default reading when it is turned off suddenly. The LVDT is connected with help of the 8-pin female connector. Figure 4 Architecture of the system Figure 5 Construction of LVDT
