If the input applies to an ammeter, what is the sensitivity?
Ammeter sensitivity is the amount of current needed to cause a full scale reading of the ammeter.The ammeter is more sensitive to the amount of current.An ammeter with a maximum current reading of 1 ampere would have a sensitivity of less than 1 microampere, and would be more sensitive than an am meter with the same reading.The term "ammeter sensitivity" refers to the entire ammeter and not just the meter movement.An ammeter is more than just the meter movement.
If you have a meter movement with a sensitivity of 1 millimeter, you can connect it to a circuit and measure the currents.
10 volts are applied to two resistors at the same time.R1 and R2 are 10 and 1.11-ohm resistors, respectively.The voltage in parallel branches is the same.
The relationship between IR1 and IR2 remains the same.IR2 is nine times greater than IR1, and IR1 is one-tenth of the total current.
If R1 is replaced by a meter movement that has 10 ohms of resistance and a sensitivity of 10 amperes, the reading of the meter will represent one-tenth of a current in the circuit.The portion of the current from the meter movement that R2 diverts is called a ShUNT.A 10-ampere meter movement can measure current up to 100 amperes.The current can be read directly by adding a second scale to the meter.
The ammeter will be able to measure several different maximum current readings with the addition of several shunt resistors in the meter case.
Most meter movements have sensitivities between 5 and 1 microampere.The shunt an ammeter that uses a meter movement with a sensitivity of 100 microamperes is shown in Figure 1-22.
The ammeter has five ranges with a single ampere selected by a switch.
The ammeter will be able to measure several different maximum current readings with the addition of several shunt resistors in the meter case.
Most meter movements have sensitivities between 5 and 1 microampere.The shunt an ammeter that uses a meter movement with a sensitivity of 100 microamperes is shown in Figure 1-22.
The ammeter has five ranges with a single ampere selected by a switch.
The current will go through the meter movement if the switch is in the 100 microampere position.The current won't go through the resistors.The current being measured will have parallel paths of the meter movement and all the shunt resistors if the ammeter is switched to the 1 milliampere position.
Only a portion of the current will travel through the meter movement and the rest will go through a shunt resistors.The 10-milliampere position is when the meter is switched.Only the R1, R2, and R3 are used.Since the resistance of the shunting resistance is less than with R4 in the circuit, there will be less current going through the meter movement.The resistance decreases and more current goes through it.The meter movement will never have more than 100 microamperes of current through it if the current to be measured does not exceed the range chosen.
The transistors are made with close tolerances.That means that if a shunt resistor is selected with a resistance of.01 ohms, that's it.The actual resistance will not change by more than 1 percent.
To allow accurate measurement and protect a meter movement, it is important that the resistance of the shunt resistor is known very accurately.
Figure 1-22 shows an ammeter.The meter case has a switch that selects the shunt resistors.Internal shunts are used for limited current ranges.
Ammeters that use external shunts are used for higher current ranges.The internal and external shunts serve the same purpose.The circuit to be measured is connected to the external shunt in a series.A portion of the current goes through the ammeter.
The maximum current value that the ammeter will measure will be marked on each external shunt.The ammeter in Figure 1-23 uses external shunts and a d'Arsonval meter movement.Figure 1-23(A) shows the internal construction of the meter and how it is connected to the circuit being measured.Some typical external shunts are shown in Figure 1-23(C).