IT paper
Project Plan and Design
This project is about planning, designing, and reporting a Multimeter which can measure Current (Ammeter) and Voltage (Voltmeter) in a circuit.
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Analog instrument
Current
In the coil
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The galvanometer is called an analog instrument. Its basic units are a pair of magnetic poles, north and south. In between the poles a current carrying coil is placed. The coil is held by a pivot and a spring. If current passes through the coil the coil will produce a magnetic field which interacts with the existing magnetic field because of north and south poles. Because of interaction the coil will exert a force. Since the coil is held by the spring it will act against the spring. If the spring is force is less than the coil force the coil will rotate around the pivot. The movement is circular instead of linear due to the design arrangement. A needle which is attached to the coil will also rotate. Spring that restores the pointer when current is removed. We can calibrate a scale so that the amount of rotation can be measured as the amount of current that is flowing. So, we can measure the current.
Ammeter design from the galvanometer
- The specification of a certain meter movement requires 0.001 Amps, or one milliampere of current, for full scale deflection of the needle. The ohmic resistance of the meter movement coil is 100 ohms. Calculate the shunt resistor design values (Technical data) for a meter that will measure four different ranges. The ranges are as follows: 0-1 mA, 0-10 mA, 0-50 mA, and 0-100 mA.
- mA means milliampere.
- ohmic resistance means simply resistance.
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Step 1 and 2 (0-10 mA)
The meter will require a shunt with a resistance value of 11.1 ohms for the 0-10 mA scale
Given
Calculate/Find:
- Voltage Drop across the Meter
- Current you would like to bypass
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There are three images in this slide. The first one, left side, is the galvanometer that shows its specification. The second one, top right, is a calculation. The calculation is as follows.
Voltage over current is resistance. Voltage is 0.1 Volts. Because 0.001, which is current in Amps, times 100 is 0.1. Note 1 mA equals 0.001 Amps. Given that, the galvanometer is to be redesigned by inserting a resistance so that it can handle higher current which is 10 mA. Applying Ohm’s law, we have the resistance value to be 11.1 Ohms. Because 0.1 Volts over 0.009 Amps is 11.1 Ohms. 0.009 Amps is due to the reason that the maximum current we would like to measure is 10 mA. And the meter can only allow 1 mA, so we have to channel the 10 minus 1 equals 9 mA which is 0.009 Amps through another path called shunt resistor. The value of the shunt resistor is calculated as 11.1 Ohms.
The third one, bottom right, shows the same galvanometer with additional shunt resistance connected in parallel to the galvanometer. It now can handle 10 mA of current. This is step-2 of the design process.
Step 3 (0-50 mA)
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There is one image in this slide. This is step three of our design. In this design, we need a meter which will be able to measure the current up to 50 mA. What would be the value of the shunt resistance? You can use the Ohm’s Law again.
Voltage over current is resistance. Voltage is 0.1 Volts. Because 0.001, which is current in Amps, times 100 is 0.1. Note 1 mA equals 0.001 Amps. Given that, the galvanometer is to be redesigned by inserting a resistance so that it can handle higher current which is 50 mA. Applying Ohm’s law, we have the resistance value to be 2.04 Ohms. Because 0.1 Volt over 0.049 Amps is 2.04 Ohms. 0.049 Amps is due to the reason that the maximum current we would like to measure is 50 mA. And the meter can only allow 1 mA, so, we have to channel the 50 minus 1 equals 49 mA which is 0.049 Amps through another path called shunt resistor. The value of the shunt resistor is calculated as 2.04 Ohms.
The image shows that how a basic original galvanometer with additional shunt resistance connected in parallel can increase the measuring range. It now can handle 50 mA of current.
Step 4 (0-100 mA)
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There is one image in this slide. This is step four of our design. In this design, we need a meter which will be able to measure the current up to 100 mA. What would be the value of the shunt resistance? You can use the Ohm’s Law again.
Voltage over current is resistance. Voltage is 0.1 Volts. Because 0.001, which is current in Amps, times 100 is 0.1. Note 1 mA equals 0.001 Amps. Given that, the galvanometer is to be redesigned by inserting a resistance, so that it can handle higher current values which is 100 mA. By applying Ohm’s law, we have the resistance value to be 1.01 Ohms, this time. Because 0.1 Volt over 0.099 Amps is 1.01 Ohms. 0.099 Amps is due to the reason that the maximum current we would like to measure is 100 mA. And the meter can only allow 1 mA, so, we have to channel the 100 minus 1 equals 99 mA which is 0.099 Amps through another path called shunt resistor. The value of the shunt resistor is calculated as 1.01 Ohms.
The image shows that how a basic original galvanometer with additional shunt resistance connected in parallel can increase the measuring range. It now can handle 100 mA of current.
The final design
0-1 mA, 0-10 mA, 0-50 mA, and 0-100 mA.
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There is one image in this slide. It shows the basic galvanometer with two terminals. The galvanometer is shunted with three parallel pathes containing three calculated values of the shunt resistances such as 11.1 ohms, 2,04 ohms, and 1.01 ohms in order to measure the corrent values within the range 0-10 mA, 0-50 mA, and 0-100 mA, respectively.
Designing a voltmeter from the basic galvanometer
- The specification of a certain meter movement requires 0.001 Amps, or one milliampere of current, for full scale deflection of the needle. The ohmic resistance of the meter movement coil is 100 ohms. Calculate the series resistor design values (Technical data) for a meter that will measure four different ranges of voltages. The ranges are as follows: 0-1 V, 0-10 V, 0-100 V, and 0-500 V.
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Step 1 with 1 V
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Remember that no more than 0.1 volt is allowed across the meter coil at any time. So, we need a resistor that will cause a voltage drop of 0.9 V. It must be placed in series with meter if the meter is to measure one volt. This resistor is sometimes referred to as the multiplier resister, Rm. Also, the meter only allows 0.001 A current for full scale deflection. This is the highest current allowed in the coil circuit. The multiplier resister must produce a 0.9 V drop when 0.001 A flows through it.
Now, the multiplier resistor, Rm equals to 900 ohms. Because 0.9 volts over 0.001 ampere is 900.
Step 2 (Convert to 10 Volts range)
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Remember that no more than 0.1 volt is allowed across the meter coil at any time. This time we want out meter should handle 10 volts. Right? So, we need a resistor that will cause a voltage drop of 9.9 V. This resistor must be placed in series with meter if the meter is to measure 10 volts. This resistor is sometimes referred to as the multiplier resister, Rm. Also, the meter only allows 0.001 A current for full scale deflection. This is the highest current allowed in the coil circuit. The multiplier resister must produce a 9.9 V drop when 0.001 A flows through it.
Now, the multiplier resistor, Rm equals to 9900 Ohms. Because 9.9 volts over 0.001 ampere is 9900.
Step 3(Convert to 100 Volts range)
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Remember that no more than 0.1 volt is allowed across the meter coil at any time. This time we want out meter should handle 100 volts. Right? So, we need a resistor that will cause a voltage drop of 99.9 V. This resistor must be placed in series with meter if the meter is to measure 100 volts. This resistor is sometimes referred to as the multiplier resister, Rm. Also, the meter only allows 0.001 A current for full scale deflection. This is the highest current allowed in the coil circuit. The multiplier resister must produce a 99.9 V drop when 0.001 A flows through it.
Now, the multiplier resistor, Rm equals to 99,000 Ohms. Because 99.9 volts over 0.001 ampere is 99,000.
Step 4 (Convert to 500 Volts range)
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Internal circuit of a typical voltmeter
R = 100Ω
0
100
0
500
0-1
900Ω
9.9 kΩ
99.9 kΩ
499.9 kΩ
0-10
0-100
0-500
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Remember that no more than 0.1 volt is allowed across the meter coil at any time. This time we want out meter should handle 500 volts. Right? So, we need a resistor that will cause a voltage drop of 499.9 V. This resistor must be placed in series with meter if the meter is to measure 500 volts. This resistor is sometimes referred to as the multiplier resister, Rm. Also, the meter only allows 0.001 A current for full scale deflection. This is the highest current allowed in the coil circuit. The multiplier resister must produce a 499.9 V drop when 0.001 A flows through it.
Now, the multiplier resistor, Rm equals to 499,900 Ohms. Because 499.9 volts over 0.001 ampere is 499,900.