1. Explain why a DMM must be connected in parallel with a resistor in order to m

Question

1. Explain why a DMM must be connected in parallel with a resistor in order to measure the voltage across it while a DMM must be connected in series with a resistor in order to measure the current through it.

2. With your DMM set as an ohmmeter, explain why you can’t measure the value of a resistor when it is already connected in a circuit.

3. With respect to sinusoidal signals, explain the difference between the way we normally define “Amplitude” and the “Amplitude” setting on the VirtualBench function generator and the “Amplitude” measurement on the VirtualBench oscilloscope.

4. The waveform on an oscilloscope is measured by converting an analog signal into digital levels by an analog-to-digital converter (ADC). Since only finite numbers of levels are available to represent the signal, there is a quantization error of at least 1 Least Significant Bit (LSB) which is the minimum detectable voltage change - also known as resolution. Discuss how the measurement accuracy could be affected by the resolution of an oscilloscope. Also discuss briefly how you would choose a proper vertical scale for a waveform of known amplitude V to get most accurate measurements.

5. Based on your observations in Experiment 6, derive an expression for an appropriate oscilloscope time scale (horizontal scale) for a waveform of frequency ‘f ‘, so that only two complete waveforms are seen on the oscilloscope screen. Hint: Time period (T) of a waveform is the time required to complete one cycle and is the inverse of frequency (f).

Explanation / Answer

1)  An ammeter measures current, a voltmeter measures the potential difference (voltage) between two points, and an ohmmeter measures resistance. A multimetercombines these functions, and possibly some additional ones as well, into a single instrument.

To measure current, the circuit must be broken to allow the ammeter to be connected in series. All the current flowing in the circuit(or resistance) must pass through the ammeter. Meters are not supposed to alter the behaviour of the circuit, or at least not significantly, and it follows that an ammeter must have a very LOW resistance.

To measure potential difference (voltage), the circuit is not changed: the voltmeter is connected in parallel. This time, you do not need to break the circuit. The voltmeter is connected in parallel between the two points where the measurement is to be made. Since the voltmeter provides a parallel pathway, it should take as little current as possible. In other words, a voltmeter should have a very HIGH resistance.

2) An ohmmeter does not function with a circuit connected to a power supply. If you want to measure the resistance of a particular component, you must take it out of the circuit altogether and test it separately. Ohmmeters work by passing a small current through the component and measuring the voltage produced. If you try this with the component connected into a circuit with a power supply, the most likely result is that the meter will be damaged. Most multimeters have a fuse to help protect against misuse.

3) Amplitude of a sinusoidal signal: The distance between the farthest point of a wave and the equilibrium point or medium.

“Amplitude” setting on the VirtualBench function generator: When we vary the amplitude at the command of VirtualBench generator function, the amplitude (definition above) of the output signal is changed.

“Amplitude” measurement on the VirtualBench oscilloscope: The amplitude will be measured from the horizontal axis at 0 V to the maximum height and is calculated based on the scale factor (in V/div) of commanding amplitudes. The V / div vertical axis defines the amplitude that has the oscilospoio.

4)

In an oscilloscope two types of controls that are used as controllers that adjust the input signal and allow consequently measured on the screen and so you can see the shape of the signal measured by the oscilloscope there basically, it called technical way you can say that the oscilloscope serves to observe the signal measured.

To measure it can be compared to the Cartesian plane.

The first control regulates the X (horizontal) axis and appreciates fractions of time (seconds, milliseconds, microseconds, etc., depending on the resolution of the device). The second regulates the Y axis (vertical) controlling the input voltage (in volts, millivolts, microvolts, etc., depending on the resolution of the device).

The value of known amplitude between the number of divisions (V / div) horinzonteles having the oscilloscope screen from the center line of the oscilloscope is divided. It is placed in the Control veltical the equal value of V / div or immediate superior.

5) For the selection of the horizontal control for two full wave forms seen on the screen of the oscilloscope, the period of the function (1 / f) = T is obtained, where "T" is the period and the "f" is the known frequency of the wave. The period is then multiplied by 2 and divided into between the amount of vertical diviciones have the oscilloscope screen, horizontal control knob is placed on the value obtained or immediate superior.

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