Report Assignment BENP 2183 Electronic Instrumentations REPORT ASSIGNMENT 1.0 TITLE Design of basic shunt DC multirange ammeter using Permanent Magnet Moving Coil (PMMC) of I fsd = 100 µA for range of 0 − 100mA, 0 − 150mA and 300mA . 2.0 OBJECTIVES i. To design a basic shunt DC multirange ammeter using PMMC. ii. To understand the properties of a basic shunt DC multirange ammeter. iii. To calculate the current through a circuit measured by basic shunt DC multirange ammeter using PMMC. iv. 3.0 To measure the actual value internal resistance of PMMC. EQUIPMENTS/ MATERIALS NO. 4.0 EQUIPMENT UNIT/S 1 Resistor 2.2Ω 3 2 PMMC (micro-ammter) 1 3 4 ways switch 1 THEORY Meter A meter is any device built to accurately detect and display an electrical quantity in a form readable by a human being. Usually this "readable form" is visual: motion of a pointer on a scale, a series of lights arranged to form a "bar graph," or some sort of display composed of numerical figures. In the analysis and testing of circuits, there are meters designed to accurately measure the basic quantities of voltage, current, and resistance. The display mechanism of a meter is often referred to as a movement, borrowing from its mechanical nature to move a pointer along a scale so that a measured value may be read. The design of most mechanical movements is based on the principle of electromagnetism: that electric current through a conductor produces a magnetic field perpendicular to the axis of electron flow. The greater the electric current, the stronger 1 Report Assignment BENP 2183 Electronic Instrumentations the magnetic field produced. If the magnetic field formed by the conductor is allowed to interact with another magnetic field, a physical force will be generated between the two sources of fields. If one of these sources is free to move with respect to the other, it will do so as current is conducted through the wire, the motion which usually against the resistance of a spring being proportional to strength of current. However, practical electromagnetic meter movements can be made now where a pivoting wire coil is suspended in a strong magnetic field, shielded from the majority of outside influences. Such an instrument design is generally known as a permanentmagnet, moving coil, or PMMC movement: Figure 1: Construction of Permanent Magnet Moving Coil (PMMC) In the picture above, the meter movement "needle" is shown pointing somewhere around 35 percent of full-scale, zero being full to the left of the arc and full-scale being completely to the right of the arc. An increase in measured current will drive the needle to point further to the right and a decrease will cause the needle to drop back down toward its resting point on the left. The arc on the meter display is labeled with numbers to indicate the value of the quantity being measured, whatever that quantity is. 2 Report Assignment BENP 2183 Electronic Instrumentations Ammeter Figure 2: A Typical 0-1mA Ammeter Figure 3: D’Arsonval used in DC Ammeter circuit A meter designed to measure electrical current is popularly called an "ammeter" because the unit of measurement is "amps." The earliest design is the D'Arsonval galvanometer or moving coil ammeter. It uses magnetic deflection, where current passing through a coil causes the coil to move in a magnetic field. The voltage drop across the coil is kept to a minimum to minimize resistance across the ammeter in any circuit into which it is inserted. Besides that, moving iron ammeters use a piece or pieces of iron which move when acted upon by the electromagnetic force of a fixed coil of wire. This type of meter responds to both direct and alternating currents as opposed to the moving coil ammeter, which works on direct current only To measure larger currents, a resistor called a shunt is placed in parallel with the meter. Most of the current flows through the shunt, and only a small fraction flow through the meter. This allows the meter to measure large currents. Multi-Range Ammeter In practical terms, ammeters with a single range are not very useful. However there are some exceptions such as Marine meters-voltage, fuel, Power station meters (voltage, frequency) and automotive meters (ammeter, tachometer).All of which have one useful range. To make an ammeter to measure several ranges at once, one approach is to have a separate shunt resistor for each range and we can calculate each resistor value of the shunt. 3 Report Assignment BENP 2183 Electronic Instrumentations Figure 4: Several Range Meter Connections By referring to Figure 4, the position of the switch, one of R1 to R4 would be connected as a shunt across the meter. However, a problem may have with thus arrangement. At the point when the switch is moved from position 1 to position 2, the PMMC movement will be forced to pass a current that may be more than full scale deflection current, I fsd . This will most likely destroy the meter, or at best blow a fuse. Hence, to solve of this problem another ways of connection can be used. Those are a make-before-break switch and a Universal or Ayrton Shunt. The make-before-switch establishes contact with the next contact position before losing contact with the existing connection. In this manner, the shunt resistors are never removed from the circuit and the PMMC movement is always protected. Figure 5: The Make-Before-Switch Connection 4 Report Assignment BENP 2183 Electronic Instrumentations Figure 6: The Universal or Ayrton shunt of Multi-Range Ammeter As refer to Figure 5, the Universal or Ayrton shunt connection. The shunt resistors, R1, R2 and R3, are all in series and collectively in parallel to the meter movement. Thus, Rsh = R1 + R 2 + R3 If the input is connect to position 1, it can be say that Vsh = Vm I sh Rsh = I m Rm ( I − I m )( R1 + R 2 + R3) = I m Rm Where, Ish = shunt current for this position. If the input is connect to position 2, ( I − I m )( R 2 + R3) = I m ( Rm + R1) If the input is connect to position 3, ( I − I m )( R3) = I m ( Rm + R1 + R 2) Hence, by using substitution of equations the value of shunt resistors, R1, R2 and R3 can be calculated. Besides, this method is used for this project. 5.0 PROCEDURE 1. A basic shunt DC multirange ammeter was designed using PMMC of Ifsd=100µA for range of 0-100mA, 0-150mA and 0-300mA. 2. The designed circuit was tested by using Multisim. 3. The internal resistance, Rm for the micro-ammeter was measured by using DMM. 5 Report Assignment BENP 2183 Electronic Instrumentations 4. The designed circuit was constructed on a breadboard and the circuit was checked. 5. The observation and the finding were discussed. 6.0 RESULT Theoretical/ Calculation Result To design basic shunt DC multirange ammeter using PMMC, the Aryton Shunt or Universal Shunt was used. I SH I fsd = 100µA Figure 1: An Aryton Shunt design circuit Calculation for circuit in Figure 1 to provide an ammeter with a current range of 0 − 100mA, 0 − 150mA , 0 − 300mA and I fsd = 100 µA . Firstly, voltage across resistors R1, R2 and R3 parallel with the voltage Rm. Hence, VSH = VRm I SH RSH = I M RM But, I = I SH + I fsd ∴ I SH = I − I fsd For range 0 − 100 mA, (100 m − 100 µ )( R3 + R 2 + R1) = 100 µRm 6 Report Assignment BENP 2183 Electronic Instrumentations 99.9m( R3 + R 2 + R1) = 100 µRm -- (1) For range 0 − 150 mA, (150 m − 100 µ )( R 2 + R1) = 100 µRm 149 .9m( R 2 + R1) = 100 µ ( Rm + R3) -- (2) ( R 2 + R1) = 667 .11µ ( Rm + R3) -- (3) For range 0 − 300mA, (300m − 100 µ )( R1) = 100 µRm 299.9m( R1) = 100 µ ( Rm + R3 + R 2) R1 = 333 .44 µ ( Rm + R3 + R 2) -- (4) Substitute equation (3) into equation (1), 99.9m[R3 + 667.11µ ( Rm + R3)] = 100µRm 99.9m[R3 + 667.11µRm + 667.11µR3] = 100µRm 99.9mRm + 66.64µRm + 66.64µR3 = 100µRm 99.97mR3 = 33.36Rm R3 = 333.70 µRm -- (5) Substitute equation (3) and equation (4) into equation (2), 149.9m[R 2 + 333.44 µ ( Rm + R3 + R 2)] = 100 µ ( Rm + R3) R 2 + 333.44 µRm + 333.44 µR3 + 333.44 µR 2 = 667.11µ ( Rm + R3) R 2(1 + 333.44 µ ) + 333.44 µRm + 333.44 µ (333.7 µRm) = 667.11µ (333.7 µRm) R 2(1 + 333.44 µ ) = 333.82 µRm R 2 = 333 .71µRm -- (6) Substitute equation (5) and equation (6) into equation (4), R1 = 333.44 µ ( Rm + R3 + R 2) = 333.44 µ ( Rm + 333.70 µRm + 333.71µRm) = 333.44 µRm + 111.27 nRm + 111.27 nRm = 333.66 µRm Hence, the value of R3, R2 and R1 ∴ R3 = 333.70 µRm R 2 = 333.71µRm R1 = 333.66 µRm From the laboratory result, the Rm for the PMMC micro-ammeter is 6.72kΩ Ω Therefore, the value of R3, R2 and R1 7 Report Assignment BENP 2183 Electronic Instrumentations Simulation Result (i) A basic DC circuit of voltage source and resistor was constructed and measure by using multimeter in Multisim Software. Figure 2 Calculation by using mathematical method: By using Ohm’s Law, V = IR V R 12 = 1k = 12mA ( proved ) I calculated = 8 Report Assignment (ii) BENP 2183 Electronic Instrumentations A designed basic shunt DC Multirange ammeter and connected to a basic circuit as in Figure 1 was constructed by using Multisim Software. Figure 3 (iii) Internal resistance of ammeter was set to 6.72k Ω . Figure 4 9 Report Assignment BENP 2183 Electronic Instrumentations Due to set value of internal resistance, Rm=6.72k Ω hence the resistor’s value obtained and used in designed basic shunt DC Multirange ammeter was, R3 = 333.70 µRm = 333.70 µ (6.72k ) = 2.242Ω R 2 = 333.71µRm = 333.71µ (6.72k ) = 2.242Ω R1 = 333.66 µRm = 333.66 µ (6.72k ) = 2.242Ω (iv) A basic DC circuit was measured by using designed basic shunt DC Multirange ammeter of I fsd = 100 µA for range of 0 − 100mA . Range of 0 − 100mA on designed ammeter was selected to measure the current of DC circuit as connected. Measured current value from ammeter, I = 12.001µA . 10 Report Assignment BENP 2183 Electronic Instrumentations Hence, I dc circuit = I measured × I selected I fsd range Given, I fsd = 100 µA ∴ I dccircuit = 12.00 µ × 100m 100µ = 12.00mA = I calculated (v) A basic DC circuit was measured again by using designed basic shunt DC Multirange ammeter of I fsd = 100 µA for range of 0 − 150mA . Range of 0 − 150mA on designed ammeter was selected to measure the current of DC circuit as connected. Measured current value from ammeter, I = 7.815 µA . Hence, ∴ I dccircuit = 7.815µ × 150m 100 µ = 11.7225mA ≈ 12.0mA ≈ I calculated 11 Report Assignment (v) BENP 2183 Electronic Instrumentations A basic DC circuit was measured again by using designed basic shunt DC Multirange ammeter of I fsd = 100 µA for range of 300mA . Range of 300mA on designed ammeter was selected to measure the current of DC circuit as connected. Measured current value from ammeter, I = 3.916 µA . Hence, ∴ I dccircuit = 3.916 µ × 300m 100µ = 11.748mA ≈ 12.0mA ≈ I calculated Laboratory Result The internal resistance, Rm for the PMMC micro-ammeter is 6.72kΩ Ω Components Measured value Internal resistance, Rm 6.72kΩ Resistor 1kΩ 0.989kΩ 12 Report Assignment BENP 2183 Electronic Instrumentations Resistor 2.2Ω I m = I fsd = 2.2Ω IRSH Rm + RSH (100m)(6.6) 6.72k + 6.6 = 98.12 µ = The range 0 – 100mA Voltage,Vin Voltage,Vin Measured current,I Calculated value,Vo value,Vo % error (V) (µA) (V) (%) 10 10 10.08 0.80 11 11 11.09 0.81 12 12 12.10 0.83 13 13 13.10 0.76 14 14 14.11 0.79 15 15 15.12 0.80 16 16 16.13 0.81 17 17 17.13 0.76 18 18 18.14 0.78 19 19 19.15 0.79 20 20 20.16 0.80 13 Report Assignment BENP 2183 Electronic Instrumentations The range 0 – 15 150mA Voltage,Vin Voltage,Vin Measured Measured current,I Calculated value,Vo % error (V) (µA) (V) (%) 10 7.0 10.58 5.8 11 7.6 11.49 4.45 12 8.0 12.10 0.83 13 9.0 13.61 4.69 14 9.0 13.61 2.78 15 10.0 15.12 0.80 16 11.0 16.63 3.94 17 11.4 17.24 1.41 18 12.0 18.14 0.78 19 13.0 19.65 3.42 20 13.6 20.56 2.80 Voltage,Vin Voltage,Vin Measured current,I Calculated value,Vo % error (V) (µA) (V) (%) 10 3.6 10.88 8.80 11 4.0 12.09 9.91 12 4.0 12.09 0.75 13 4.4 13.3 2.31 The range 0 – 300mA 300mA 14 Report Assignment BENP 2183 Electronic Instrumentations 14 5.0 15.12 8.0 15 5.2 15.72 4.80 16 5.6 16.93 5.81 17 6.0 18.14 6.71 18 6.0 18.14 0.78 19 6.4 19.35 1.84 20 7.0 21.17 5.85 For range 0 – 100mA The calculation of the Vo, When Vin = 10V Vo = I I fsd x(range) xR4 10 µ x(100mA) x0.989k 98.12 µ = 10.08V = When Vin = 11V 11µ x(100mA)x0.989k 98.12 µ = 11.09V Vo = The calculation of the percentage error, When Vin = 10V, 15 Report Assignment %error =| BENP 2183 Electronic Instrumentations Yn − Xn | x100% Yn 10 − 10.08 | x100% 10 = 0.8% =| When Vin = 11V, %error =| 11 − 11.09 | x100% 11 = 0.81% For range 0 – 15 150mA The calculation of the Vo, When Vin = 10V Vo = I I fsd x(range) xR4 7µ x(150mA) x0.989k 98.12 µ = 10.58V = When Vin = 11V 7.6 µ x(150mA)x0.989k 98.12 µ = 11.49V Vo = The calculation of the percentage error, 16 Report Assignment BENP 2183 Electronic Instrumentations When Vin = 10V, %error =| Yn − Xn | x100% Yn 10 − 10.58 | x100% 10 = 5.8% =| When Vin = 11V, %error =| 11 − 11.49 | x100% 11 = 4.45% For range 0 – 300mA 300mA The calculation of the Vo, When Vin = 10V Vo = I I fsd x(range) xR4 3.6 µ x(300mA) x 0.989k 98.12 µ = 10.88V = When Vin = 11V 4.0 µ x(300mA)x0.989k 98.12 µ = 12.09V Vo = The calculation of the percentage error, 17 Report Assignment BENP 2183 Electronic Instrumentations When Vin = 10V, %error =| Yn − Xn | x100% Yn 10 − 10.88 | x100% 10 = 8.80% =| When Vin = 11V, %error =| 11 − 12.09 | x100% 11 = 9.91% 18 Report Assignment 7.0 BENP 2183 Electronic Instrumentations DISCUSSION/ ANALYSIS The shunt resistance was very small relative to the internal resistance of the micro-ammeter. A high voltage that passes through the shunt resistor may cause the resistor burnt. Therefore, no connection was made from the resistors directly to the high voltage supply. A resistor which has a high resistance is connected to the shunt resistor in parallel to avoid the burning of resistors occur. A Permanent Magnet Moving Coil (PMMC) was used to design an ammeter,. Before design the ammeter, internal resistance of the PMMC was measured to do the calculation. The PMMC galvanometer constitutes the basic movement of a dc ammeter. Since the coil winding of a basic movement is small and light, it can carry only very small currents. When large currents are to be measured, it is necessary to bypass a major part of the current through a resistance called a shunt. The shunt resistance used may consist of a length of constant temperature resistance wire within the case of instrument. The general requirements of a shunt are as follows. a. The temperature coefficient of the shunt and instrument should be low and nearly identical. b. The resistance of the shunt should not vary with time. c. It should carry the current without excessive temperature rise. d. It should have a low thermal emf. The current range of the dc ammeter may be further extended by a number of shunt and it is known as multirange ammeter. A switch can be connected in the circuit to choose the range desired. The switch used to connect in the circuit must be a low resistance and high current carrying capacity, since its contacts are in series with low resistance. To prevent the ammeter broken when in use, the highest current range was used to measure current first, then decrease the range until good upscale reading is obtained. When an ammeter was inserted in a circuit, it always increases the resistance of the circuit and reduces the current in the circuit. This effect was known as the ammeter insertion effects. To reduce the insertion effects, the resistance used to design the ammeter should be as low as possible. 8.0 CONCLUSION 19 Report Assignment BENP 2183 Electronic Instrumentations After doing this assignment, it is found that the ammeter was design by using a PMMC. Beside that, to measured a large current, the ammeter can be designed with a resistor connect parallel with the PMMC or known as shunt. In this assignment, a basic shunt DC multirange ammeter using PMMC was designed. Beside that, before design the ammeter, internal resistance of the PMMC was measured first. When designing the multirange ammeter, some requirements as shown in the discussion were considered, this is to make sure the ammeter that had designed have an accurate and a precise reading. The insertion effects which the ammeter will increases the resistance of the circuit when connected in the circuit thus decreases the current flow in the circuit also considered in the design. That is the resistor used to design the ammeter is the resistor with a low resistance. 9.0 REFERENCES Book Sources: i. Kalsi H.S., “Electronic Instrumentation”, Second Edition, Tata McGraw Hill, 2004. Internet Sources: i. Ammeter http://en.wikipedia.org/wiki/Ammeter ii. Ammeter Design http://www.allaboutcircuits.com/vol_1/chpt_8/2.html iii. Ammeter impact on measured circuit http://www.allaboutcircuits.com/vol_1/chpt_8/5.html iv. AMP[Shunt Ammeter Circuit http://home.cogeco.ca/~rpaisley4/CircuitIndex.html v. Construction of Voltmeter or Ammeter From a Galvanometer 20 Report Assignment BENP 2183 Electronic Instrumentations http://www.physics.purdue.edu/~clarkt/Courses/Physics271L/Exp4/ex p4.html vi. DC Ammeter http://tpub.com/content/neets/14188/css/14188_82.htm 21