In AC siginal measurements??

Question

in an ac siginal how to measure the :
-amplitude
-Peak to Peak
-Periodic time
-Frequency
and what will happen if the frequecy get higher or lower??

Answer 1

You can measure all of these with an oscilloscope.

I will assume you know the basics of operating an oscilloscope.

Once you get your waveform displayed nicely on the screen, the Amplitude is the voltage (height) of the waveform, from top to bottom. Measure the height of the waveform, in divisions (most 'scopes have divisions of 1cm) and multiply that by the "Volts/div" or "Volts/cm" setting on the channel vertical knob. Check your probe, see if it is set on x1 or x10 compensation, if it is on x10, then multiply the resultant value by 10. This is the Amplitude of the waveform.

I was taught that Amplitude and Peak-to-Peak voltage were the same thing, in college Electronics Engineering courses.

The period (or periodic time) is determined by the time (width) of one complete cycle of the waveform; for example, from the center of one positive peak, to the center of the next positive peak. With the waveform displayed on the 'scope, measure the width (again in divisions) and multiply that by the "time/div" or "time/cm" or "sec/cm" value on the horizontal sweep knob. For most common AC signals, this will be a very small fraction of a second....Line voltage is .0167 sec or 16.7 milliseconds...audio signals get down to 0.00005 sec or 50 microseconds...AM Broadcast radio signals are centered on 0.000001 sec or 1 microsecond, and FM Broadcast radio signals are centered on 0.00000001 sec or 10 nanoseconds.

The frequency is the reciprocal of the periodic time. 1 / period (in seconds) = frequency, in hertz. 1,000 hertz is a kilohertz, 1,000,000 hertz is a megahertz, and 1,000,000,000 hertz is a gigahertz.

When the frequency gets higher or lower, amplitude and peak-to-peak voltage will remain the same. As the frequency gets lower, the period will get larger, and the waveform displayed on the 'scope will "stretch out" horizontaly. As the frequency gets higher, the period gets smaller and the waveform will "squeeze in" on the 'scope.

IF YOU DO NOT HAVE AN OSCILLOSCOPE, you can measure these values with a voltmeter, and a frequency counter.

Amplitude and Peak-to-Peak voltage are measured with a volt meter. Read the measured voltage on the display, and (because the display reads the RMS value of the voltage, rather than the peak-to-peak value) and multiply that value by 2.8.8 (which is the square root of 2, times 2). The resulting Voltage value is your Peak-to-Peak voltage, and Amplitude.

To get period and frequency with a frequency counter, feed the signal into the frequency counter, and read the frequency directly off of the display. Then 1 / freq (in hertz) = Periodic Time (in seconds).

Answer 2

Then as NASA measures all RF signals is in dBm . it is a little hard but is a real eng. tool. A signal of 30dBm is 1000 Milli watts.

Answer 3

you can measure this on cro.
so you need to learn how to use cro(cathode ray oscilloscope)
there you have various knobs for amplitude freq etc.