Question: What current is required for full scale deflection of a galvanometer having a current sensitivity of 50 micro-amperes per scale division? The meter has exactly 50 divisions on either side of the mid-scale index.
Answer:
There are two possible interpretations of the problem. One has a meter having a mid-scale index value of zero, a maximum positive current reading, and a maximum negative current reading.
To solve for the maximum positive value of current that will cause full scale deflection, simply multiply the current sensitivity by the number of divisions. In this case, 50 micro-amperes per scale division multiplied by 50 divisions will give 2500 micro-amperes or 2.5 mA.
The other interpretation is that a meter can read from zero to a maximum positive value of current, and that there are 100 divisions in between these two extremes. In this case, 50 micro-amperes per scale division multiplied by 100 divisions will give 5000 micro-amperes or 5 mA.
Showing posts with label Ammeter. Show all posts
Showing posts with label Ammeter. Show all posts
Saturday, May 19, 2012
How to create a wattmeter
Question: What type of basic meters can be configured as a wattmeter?
Answer:
A wattmeter measures power. Since power is the product of voltage and current, if we have a voltmeter and an ammeter available, these basic meters can be configured to measure power. The ammeter will be connected in series to the circuit element while the voltmeter is connected in parallel to the circuit element.
Answer:
A wattmeter measures power. Since power is the product of voltage and current, if we have a voltmeter and an ammeter available, these basic meters can be configured to measure power. The ammeter will be connected in series to the circuit element while the voltmeter is connected in parallel to the circuit element.
Why an ammeter has low resistance
Question: Why is it necessary that an ammeter be a low resistance instrument?
Answer:
Since an ammeter is connected in series to a circuit element, it should have a low resistance to avoid adding to the resistance of the circuit element. This prevents deviations in the value of the current being measured and ensures an accurate meter reading.
Answer:
Since an ammeter is connected in series to a circuit element, it should have a low resistance to avoid adding to the resistance of the circuit element. This prevents deviations in the value of the current being measured and ensures an accurate meter reading.
Use of a Shunt Resistor
Question: What device is used to extend the range of a DC ammeter and how is it connected to the basic meter?
Answer:
A resistor connected in parallel or shunt to the ammeter can be used to extend the ammeter's range.
Meter Movement
Question: Describe the type of movement used in analog meters
Answer:
The D'Arsonval movement is a DC moving coil-type movement commonly used in voltmeters, ammeters and ohm meters. An electromagnetic core is suspended between the poles of a permanent magnet as seen in the image below.
In an ammeter, current passes through the coils of the electromagnet (current path not shown in the figure). This current produces a magnetic field that opposes the magnetic field already set up by the permanent magnet in the figure. The stronger the current, the stronger the magnetic field, and the larger the pointer deflection. If current is no longer flowing, the upper and lower control springs will bring back the pointer to its default position for a zero current reading.
Answer:
The D'Arsonval movement is a DC moving coil-type movement commonly used in voltmeters, ammeters and ohm meters. An electromagnetic core is suspended between the poles of a permanent magnet as seen in the image below.
In an ammeter, current passes through the coils of the electromagnet (current path not shown in the figure). This current produces a magnetic field that opposes the magnetic field already set up by the permanent magnet in the figure. The stronger the current, the stronger the magnetic field, and the larger the pointer deflection. If current is no longer flowing, the upper and lower control springs will bring back the pointer to its default position for a zero current reading.
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