Measurement Bench. Accessories. Power supply. Wave form generator. Multimetre. Oscilloscope. Dr. L.Scucchia

Transcription

1 Measurement Bench Accessories Power supply Wave form generator Multimetre Oscilloscope

2 OSCILLOSCOPE

3 Oscilloscope (1) The oscilloscope allows to display a voltage (vertical axis - Y axis) versus time (horizontal axis - X axis). The oscilloscope can also display two voltages on both the axes (XY mode). The quantities shown on the screen are voltages. To facilitate reading of the magnitudes, on the screen there is a grid consisting of some horizontal and vertical divisions. The oscilloscopes in the laboratory are DSO3202A and MSO-X 3012T by Keysight (ex Agilent). DSO stands for Digital Storage Oscilloscope MSO stands for Mixed Signal Oscilloscope A digital oscilloscope uses an analog-to-digital converter (ADC) to convert the measured voltage into digital information. The digitized data are stored in a channel memory

4 Oscilloscope (2) Input BNC + Attenuator Amplifier ADC - DC Offset Coupling DC Level + - Comp signal Logic Channel Memory Timebase System Display DSP Yellow = Channel specific blocks Blue = System blocks DSO Block Diagram CPU System

5 Oscilloscope (3) A probe feeds the input signal into the oscilloscope where the attenuator and the amplifier are used to compensate for input levels for various voltage per division settings. The trace position is adjusted changing the DC Offset. Input BNC + Attenuator Amplifier ADC - DC Offset Coupling DC Level + - Comp signal Logic Channel Memory Timebase System Display DSP Yellow = Channel specific blocks Blue = System blocks DSO Block Diagram CPU System

6 Oscilloscope (4) The ADC provides a discrete form of the signal: in the time domain (sampling) and in the amplitude domain (quantization). The ADC converter operates continuously at the maximum sampling frequency. Input BNC + Attenuator Amplifier ADC - DC Offset Coupling DC Level + - Comp signal Logic Channel Memory Timebase System Display DSP Yellow = Channel specific blocks Blue = System blocks DSO Block Diagram CPU System

7 Oscilloscope (5) The memory is organized as a circular buffer. The write pointer advances at the rate of the ADC. write pointer Input BNC + Attenuator Amplifier ADC - DC Offset Coupling DC Level + - Comp signal Logic Channel Memory Timebase System Display DSP Yellow = Channel specific blocks Blue = System blocks DSO Block Diagram CPU System

8 Oscilloscope (6) The trigger signal, through the timebase system, causes the start of the reading cycle of the channel memory write pointer read pointer Input BNC + Attenuator Amplifier ADC - DC Offset Coupling DC Level + - Comp signal Logic Channel Memory Timebase System Display DSP Yellow = Channel specific blocks Blue = System blocks DSO Block Diagram CPU System

9 Oscilloscope (7) The trigger event defines a reading interval. The trigger determines when captured data are stored and displayed. On the display the result is a signal portion preceding and following the trigger event read pointer level 0 k n-1

10 Oscilloscope (8) problems (different trigger events) Two or more trace on the display. A trace in movement on the display read pointers level 0 k n-1 0 k n-1 0 k n-1

11 Oscilloscope (9) Newer DSOs use custom DSPs to quickly process data and then send waveform data into display memory. Input BNC + Attenuator Amplifier ADC - DC Offset Coupling DC Level + - Comp signal Logic Channel Memory Timebase System Display DSP Yellow = Channel specific blocks Blue = System blocks DSO Block Diagram CPU System

12 Oscilloscope (10) Sampling Theory The Nyquist sampling theorem states that for a limited bandwidth signal with maximum frequency f MAX, in order to reconstruct the sampled signal without aliasing, sampling frequency f S must satisfy this equation: f MAX f S /2 Nyquist frequency (f N ) Aliasing Aliasing occurs when signals are under-sampled (f MAX >f S /2). Aliasing is the signal distortion caused by low frequencies falsely reconstructed from an insufficient number of sample points.

13 Oscilloscope (11) Attenuation Oscilloscope Bandwidth and Sample Rate (1) For the sampling theory the required sample rate is f S = 2f BW assuming there are no frequency components above f MAX (f BW ) and it requires a system with an ideal brick-wall frequency response. 0 db f BW = f s /2 Frequency

14 Oscilloscope (12) Oscilloscope Bandwidth and Sample Rate (2) All oscilloscopes exhibit a low-pass frequency response typically called a Gaussian response. A Gaussian frequency response closely approximates a single-pole low-pass filter. As the frequency of an input signal increases, the Oscilloscope will begin to attenuate the input signal and then begin to make inaccurate measurements. The frequency at which a sine wave input signal is attenuated by -3dB is the oscilloscope bandwidth. But -3 db of attenuation is equivalent to approximately -30% attenuation (considering the formula 20 Log(Vo/Vi)).

15 Oscilloscope (13) Oscilloscope Bandwidth and Sample Rate (3) On the other hand, digital signals have frequency components above the fundamental frequency (square waves are made up of sine waves at the fundamental frequency and an infinite number of odd harmonics), and typically oscilloscopes (with 500MHz bandwidths and below) have a Gaussian frequency response. So, in practice, the oscilloscope sample rate should be four or more times its bandwidth: f S 4f BW. This way, there is less aliasing, and aliased frequency components have a greater amount of attenuation. f BW f s /4 Frequency

16 Oscilloscope (14) Example This slide shows two different bandwidth oscilloscopes capturing the same 100 MHz square waveform. The first oscilloscope has f BW =f Max =100MHz The second oscilloscope has f BW =5f Max =500MHz, it is able to capture up to the fifth harmonic with minimal attenuation. Input = 100-MHz Digital Clock Response using a 100-MHz BW scope Response using a 500-MHz BW scope

17 Oscilloscope (15) Oscilloscope Rise Time The oscilloscope rise time is the fastest edge speed the oscilloscope can produce and not the fastest edge speed that it can accurately measure. Closely related to an oscilloscope bandwidth specification is its rise time specification. Bandwidth Rise time Oscilloscopes with a Gaussian-type frequency response have rise time 0.35/f BW With rise time obtained from 10% to 90% of the V top.

18 Oscilloscope (17) Memory Depth and Sample Rate o For an oscilloscope's analog-to-digital converter there is a maximum sample rate. o The memory point number (memory depth) of an oscilloscope is fixed. o The actual sample rate is determined by the time of the acquisition (related to the oscilloscope horizontal time/div scale). Actual sample rate = memory depth/ acquisition time Storing 50μs of data in memory points, the actual sample rate is 1 GSa/s. Storing 50ms of data in memory points, the actual sample rate is 1 MSa/s. The actual sample rate is displayed in the summary box in the right-side information area. Oscilloscope achieves the actual sample rate decimating the unneed samples. 50 ms Sample rate = 1 MSa/s points

19 Oscilloscope Sample Rate Oscilloscope Bandwidth Memory Depth Oscilloscope Bandwidth Rise Time Actual Sample Rate

20 Oscilloscope (18) DSO3202A (Agilent) 200-MHz Bandwidth 2 analog channels 1 GSa/s sample rate MSO-X 3012T (Keysigth) 100 MHz Bandwidth 2 analog +16 digital channels 5 GSa/s sample rate

21 Oscilloscope DSO3202A (Agilent) 200-MHz Bandwidth 2 analog channels 1 GSa/s sample rate Vertical controls MENU ON/OFF Measure controls Horizontal Controls Run controls Waveform controls Entry knob Menù controls controls Power switch Display Menu defined buttons Inputs Compensation terminals

22 Oscilloscope DSO3202A (Agilent) Display

23 Oscilloscope MSO-X 3012T (Keysight) Vertical controls Entry knob controls Horizontal Controls Run controls Auto Scale Measure controls Waveform Keys File Keys Digital channel Power switch Inputs Softkeys Compensation terminals Analog channel Inputs Tool Keys

24 Oscilloscope (20) MSO-X 3012T (Keysight) Display

25 Oscilloscope (21) Softkeys The functions of these keys change based upon the menus shown on the display directly above the keys. MSO-X 3012T DSO3202A The Back/Up key moves up in the softkey menu hierarchy. At the top of the hierarchy, the key turns the menus off, and oscilloscope information is shown instead. Entry knob It is used to select items from menus and to change values. The function of the Entry knob changes based upon the current menu and softkey selections. The curved arrow symbol next the entry knob illuminates whenever the entry knob can be used to select a value. When the Entry knob symbol appears on a softkey, you can use the Entry knob, to select values. Often, rotating the Entry knob is enough to make a selection. Sometimes, you can push the Entry knob to enable or disable a selection. Pushing the Entry knob also makes popup menus disappear.

26 Oscilloscope (22) Low Frequency Compensation 1. Set the Probe menu attenuation to 10X. 2. Attach the probe tip to the probe compensation connector. 3. Press the Autoscale front panel button. 4. If the waveform is not rectangular you must compensate. 5. Through a nonmetallic tool adjust the screw located near the probe up to get a signal perfectly compensated. High Frequency Compensation 1. Using the BNC adapter, connect the probe to a square wave generator. 2. Set the square wave generator to a frequency of 1 MHz and an amplitudeof 1 Vp-p. 3. Press the Autoscale front panel button. 4. If the waveform does not appear like the Correctly Compensated waveform shown in figure, then adjust the 2 high frequency compensation adjustments on the probe for the flattest square wave possible.

27 Oscilloscope (23) Vertical controls [1] and [2] analog channel on/off keys: these keys permit to switch a channel on or off, or to access a channel menu in the softkeys. There is one channel on/of for each analog channel. Vertical scale knobs: for each channel there is a knob marked with. Use these knobs to change the vertical sensitivity (gain) of each analog channel. Vertical position knobs: use these knobs to change the channel vertical position on the display. sensitivity (gain) of each analog channel. DSO3202A MSO-X 3012T MSO-X 3012T Mathematical operations are activated by pressing Math. The waveforms may be stored using the menu Ref.

28 Oscilloscope (24) Vertical controls: menu in the softkeys DSO3202A Channel Coupling Control Bandwidth Limit Control Probe Attenuation Control Invert Control Digital Filter Controls MSO-X 3012T To specify channel coupling To specify channel input impedance To specify bandwidth limiting To change the vertical scale knob's coarse/fine adjustment setting To invert a waveform Setting Analog Channel Probe Options

29 Oscilloscope (25) MSO-X 3012T When AC coupling is chosen, you cannot select 50Ω mode. This is done to prevent damage to the oscilloscope. AC coupling places a 10 Hz high-pass filter in series with the input waveform that removes any DC offset voltage from the waveform.

30 Oscilloscope (26) DSO3202A Connection control - pushing the button to the right of Coupling you can choose between three possible connections: AC for a connection via capacitor (display the AC component) DC for a direct connection (display full signal) GND for the check of the reference level (ground voltage) Bandwidth Limit Control - allows to remove, from the waveform examined, the high frequency components not relevant to the measurement made. Press the key corresponding to BW Limit function is activated (ON) and all components at frequencies greater than 20 MHz are rejected.

31 Oscilloscope (27) DSO3202A Control probe attenuation - Allows you to specify the attenuation on the probe selected. The probe attenuation control changes the attenuation factor for the probe. The attenuation factor changes the vertical scaling of the oscilloscope so that the measurement results reflect the actual voltage levels at the probe tip. Invert control - The invert control inverts the displayed waveform with respect to the ground level. Digital filter controls - Pressing the Digital Filter menu key displays the Filter Controls. The filter controls set the digital filter used to filter the sampled waveform data. The types of filters that are available are shown in the table.

32 Oscilloscope (28) Horizontal controls The oscilloscopes permit to fix only one value of time per division for all waveforms. Horizontal scale knob: it is marked with the symbol and permit to adjust the time/div (sweep speed) setting. Horizontal position knob: turn the knob marked to see through the waveform data horizontally. DSO3202A MSO-X 3012T The menu associated with the time base is activated by pressing: [Main/Delayed] (DSO3202A), [Horiz] and Zoom key (MSO-X 3012T).

33 Oscilloscope (29) Horizontal controls MSO-X 3012T You can see the captured waveform before the trigger or after the trigger. If you pan through the waveform when the oscilloscope is stopped (not in Run mode) then you are looking at the waveform data from the last acquisition taken. [Horiz] key: press this key to open the Horizontal Menu where you can select XY and Roll modes, enable or disable Zoom, enable or disable horizontal time/division fine adjustment, and select the trigger time reference point. Zoom key : Press the zoom key to split the oscilloscope display into Normal and Zoom sections without opening the Horizontal Menu. [Search] key Lets you search for events in the acquired data. [Navigate] keys Press these keys to navigate through captured data via time, search events, or segmented memory acquisition.

34 Oscilloscope (30) Horizontal controls MSO-X 3012T The figure shows the Horizontal menù obtained pressing the [Horiz] key. To change the horizontal time mode (Normal, XY, or Roll) To display the zoomed time base To change the horizontal scale knob's coarse/fine adjustment setting To position the time reference (left, center, right)

35 Oscilloscope (31) Horizontal controls DSO3202A With Delayed command you can enable or disable delayed sweep mode. In this mode, the screen is divided into two parts, the upper part shows the original waveform while the lower part shows an enlarged view. The enlarged portion is called the delayed sweep window. and the monopole of scale and horizontal position control the relevant parameters of the waveform. The key for Time Base allows you to choose the format TY and XY. In XY format, the vertical displacement of the trace on the screen depends on the signal on channel 1 while the horizontal deviation depends on the signal on channel 2. In XY format many as the functions are not supported.

36 Oscilloscope (32) Horizontal controls MSO-X 3012T The Trig-Offset button allows you to relocate the center of the track displayed on the screen. The holdoff time is the period of waiting before starting a new trigger to change the duration of this interval is sufficient to press the key next to Holdoff and adjust the time using the knob added. Pressing the Reset holdoff the holdoff time is set to its minimum value of 100ns.

37 Oscilloscope (33) controls DSO3202A Level: it changes the voltage level of the trigger signal. Force: it forces the acquisition. 50%: voltage level of the trigger signal is set equal to the average value. Ext Trig: external trigger. Mode/Coupling: menu is activated. Mode Edge, Pulse e Video (metods) Source CH1, CH2, ext, Slope Sweep Auto, Normal Coupling AC, DC, LFrejet e HFrejet

38 Oscilloscope (34) controls MSO-X 3012T These controls determine how the oscilloscope triggers to capture data. Adjusting the Level Forcing a Edge then Edge Pulse Width Pattern OR Rise/Fall Time Nth Edge Burst Runt Setup and Hold Video Serial Zone Qualified menù

39 Oscilloscope (35) controls MSO-X 3012T You can adjust the trigger level for a selected analog channel by turning the Level knob or using the touchscreen. The [Force ] key causes a trigger (on anything) and displays the acquisition. The [] key displays the trigger menu: Press the softkey, and use the Entry knob to select Edge. Select the trigger source (Analog channel, Digital channel, External, Line, WaveGen, WaveGen Mod (FSK/FM)) Press the Slope softkey and select: Rising, Falling, Alternating and Either edges.

40 Oscilloscopio (26) Waveform Keys DSO3202A Acquire Controlls Mode: Normal, Average, Peak_detect Sampling methods:real time, Equ time Averages: Sequence: Display Controls Type: Grid: Persist: Clear: Vectors, Dots Infinite, OFF Menù Display: 1s,2s,5s Screen: Normal,Invert The Average mode allows to remove random noise from the waveforms thus improving the accuracy of the measurement. To avoid aliasing is useful acquiring type Peak Detect. Real time is recommended to observe non-periodic signals. Equ-time allows to visualize high frequency signals better. The command Sequence allows to record the waveform input from the channel 1 or 2, with a depth of acquisition of 1000 frames. Pressing the Display button the corresponding menu is shown where you can specify the display characteristics of the track and the grid.

41 Oscilloscopio (27) DSO3202A (Agilent) Real-time sampling In the real-time sampling mode, single waveforms are sampled at same intervals. The digitizer works at maximum speed to acquire as many points as possible in one sweep, and the 3000 Series oscilloscopes provide sampling rates up to 1 GSa/s. In real-time sampling the trigger event happens on a particular feature of the waveform (amplitude). In this type of data acquisition, the sample rate of the ADC determines the sample spacing and the number of points that will be displayed. Equivalent time Sampling The input signal is only sampled once per trigger. At the next triggered, a small delay is added and another sample is taken. The number of samples determines the necessary number of cycles to reproduce the waveform.

42 Oscilloscope (42) Waveform keys MSO-X 3012T [Acquire] key: lets you select Normal, Peak Detect, Averaging, or High Resolution acquisition modes and use segmented memory [Display] key: lets you access the menu where you can enable persistence, clear the display, and adjust the display grid (graticule) intensity. [Touch] key: press this key to disable/enable the touchscreen.

43 Oscilloscope (43) MSO-X 3012T To select the acquisition mode: 1 Press the [Acquire] key on the front panel. 2 In the Acquire Menu, press the Acq Mode softkey; then, turn the Entry knob to select the acquisition mode. The Infinii Vision oscilloscopes have the following acquisition modes: Normal at slower (greater) time/div settings, normal decimation occurs, and there is no averaging. Use this mode for most waveforms. Peak Detect at slower (greater) time/div settings, the maximum and minimum samples in the effective sample period are stored. Use this mode for displaying narrow pulses that occur infrequently. Averaging this mode permit to average multiple acquisitions together to reduce noise and increase vertical resolution (at all time/div settings). Averaging requires a stable trigger. High Resolution at slower time/div settings, all samples in the effective sample period are averaged and the average value is stored. Use this mode for reducing random noise. In MSO-X 3012T model you can use only the Realtime sampling. The Equivalent time sampling option is present in MSO-X 3102T, MSO-X 3104T model.

44 Oscilloscope (41) Run Control keys When the [Run/Stop] key is green, the oscilloscope is acquiring data (is running) when trigger conditions are met. To stop acquiring data, press [Run/Stop]. When the [Run/Stop] key is red, data acquisition is stopped. To start acquiring data, press [Run/Stop]. To capture and display a single acquisition (whether the oscilloscope is running or stopped), press [Single]. The [Single] key is yellow until the oscilloscope triggers. DSO3202A MSO-X 3012T

45 Oscilloscope (36) DSO3202A Autoscale Control The Autoscale key is used to retrieve and set automatically the oscilloscope controls necessary for a good display of the waveform at the input. Save and Recall Controlls Save/Recall: Waveforms, Setups Default Setup Waveform: 1-10 Setup: 1-10 Load Save Utility Controlls Mask Test: Menù I/OSetup Menù Language: English,.. Sound:, System Info Self-Cal Self-Test

46 Oscilloscope (45) Autoscale Control MSO-X 3012T Tools keys : [Utility] key the utility Menu, which lets you configure the oscilloscope's I/O settings, use the file explorer, set preferences, access the service menu, and choose other options. [Quick Action] key Press this key to perform the selected quick action: measure all snapshot, print, save, recall, freeze display, and more. [Wave Gen] key Press this key to access waveform generator functions. [Analyze] key To access analysis features like: - Measurement threshold setting. - level setting. - Video trigger automatic set up and display. - Counter (DVMCTR). - Digital voltmeter (DVMCTR) - Mask testing - The DSOX3PWR power measurement and analysis application. File keys [Save/Recall] key: it is used to save or recall a waveform or setup. [Print] key: it opens the Print Configuration Menu so you can print the displayed waveforms.

47 Oscilloscope (28) Measure Controls DSO3202A Meas Sourcee: Voltage: Time Clear Display All: CH1, CH2 Vpp,Vmax, Vmin, Vavg,... Freq, Period, OFF, ON Cursor Manual: Menù Track: Menù Auto Measure: Menù Meas button on the front panel activates the automatic measurement system, in particular this enables oscilloscope to perform 20 different measures including: Vpp, Vmax, Vmin, Vamp, Vavg, Vrms, Freq, Period, risetime and Fall Time. The Cursor button on the front panel activates the menu corresponding to the measures concerning the marker. There are three modes: Manual, Track and Auto Measure. Manual, the screen shows two parallel cursors that can be moved on the track in order to obtain the measures of voltage or of time desired. The values corresponding to the cursors are shown in the upper part of the screen. Track, two sliders are automatically activated that can be adjusted using the added knob. Auto Measure, available when the measurement system is automatically activated, the oscilloscope displays the cursor in relation to the latest measures used.

48 Oscilloscope (44) Measure controls MSO-X 3012T The measure controls consist of: Cursors knob: Push this knob to select cursors from a popup menu. Then, after the popup menu closes (either by timeout or by pushing the knob again), rotate the knob to adjust the selected cursor position. [Cursors] key: Press this key to open a menu that lets you select the cursors mode and source. [Meas] key: Press this key to access a set of predefined measurements.

49 Oscilloscope (29) DSO3202A (Agilent) Voltage measurements: Vpp Vmax Vmin Vavg Vamp Vtop Vbase Vrms Overshoot Preshoot (Peak-to-Peak Voltage) (Maximum Voltage) (Minimum Voltage) (Average Voltage) (Amplitude Voltage = Vtop - Vbase) (Top Voltage) (Base Voltage) (True Root-Mean-Square Voltage) (Measure the overshoot voltage in percent (Vmax-Vtop)/Vamp. Overshoot is a waveform distortion which follows a major edge transition) (Measure the preshoot voltage in percent (Vmin-Vbase)/Vamp,. Preshoot is a waveform distortion which precedes a major edge transition)

50 Oscilloscopio (30) 3202A (Agilent) Time Measurements: Frequency Period Rise Time Fall Time +Width -Width +Duty -Duty Delay 1 2 Delay 1 2

51 Left display side Left display side Oscilloscope (31) DSO3202A (Agilent) Delay 1-2, rising edges Delay 1-2, falling edges Dt a 50% Channel 1 Channel 1 Dt a 50% 50% Channel 2 50% Channel 2 t 1 t 2 Delay From channel 1 to channel 2 rising edges ( t 2 -t 1 ) t 1 t 2 Delay From channel 1 to channel 2 Falling edges ( = t 2 -t 1 ) t 2 -t 1 =Dt a >0

52 Left display side Oscilloscope (32) DSO3202A (Agilent) Delay 1-2, rising edges 50% Dt a Channel 1 t 2 -t 1 =-Dt b <0 Dt a =T-Dt b >0 50% 50% Channel 2 t 2 t 1 Delay From channel 1 to channel 2 rising edges ( = t2-t1)

53 Oscilloscope (29) DSO3202A (Agilent) The math functions control allows the selection of the math functions add, subtract, multiply, and FFT (Fast Fourier Transform) for CH1 and CH2. The mathematical result can be measured visually and also using the cursor controls. The FFT math function mathematically converts a time-domain waveform into its frequency components. The FFT of a waveform that has a DC component or offset can cause incorrect FFT waveform magnitude values. To minimize the DC component, choose AC Coupling on the source waveform. To reduce random noise and aliasing components in repetitive or single-shot waveforms, set the oscilloscope acquisition mode to averaging. To display FFT waveforms with a large dynamic range, use the dbvrms scale. The dbvrms scale displays component magnitudes using a log scale.

54 Oscilloscope (30) DSO3202A (Agilent) Selecting an FFT Window FFT based measurements are subject to errors from an effect known as leakage. This effect occurs when the FFT is computed from of a block of data which is not periodic. To correct this problem appropriate windowing functions must be applied. The window is shaped so that it is exactly zero at the beginning and end of the data block and has some special shape in between. For the 3202A there are 4 FFT windows. Each window has trade-offs between frequency resolution and amplitude accuracy. Your source waveform characteristics along with your measurement priorities help determine which window to use.