Analog Storage Oscilloscope : Block Diagram, Working & Its Applications

An oscilloscope is a type of laboratory instrument that is generally used to display single or repetitive waveforms on display. These waveforms can be analyzed for different properties like frequency, amplitude, rise time, distortion, time interval, etc. Oscilloscopes are used in different fields of industries like engineering, medicine, science, telecommunication, automotive industry, etc. In an oscilloscope, there are two techniques utilized to store signals; analog & digital storage. Analog storage is capable of higher speeds, although it is less versatile as compared to digital storage. This article discusses an overview of an analog storage oscilloscope – working & its applications.

What is Analog Storage Oscilloscope?

An analog storage oscilloscope is one kind of oscilloscope, used to store waveforms for visualization later. These types of oscilloscopes were very simple in terms of their performance, and they were very costly, so commonly used for only specialist applications. These oscilloscopes utilize a special CRT (cathode ray tube) by a long persistence facility. These CRTs had the capability to vary the persistence, however, if extremely bright traces were held above long time periods, then there is a chance of burning the trace permanently on the display. So these displays are required to be used with care.

Working of Analog Storage Oscilloscope

Analog storage oscilloscopes work by using a special CRT with long persistence ability. A special CRT by an arrangement is used to store charge within the display area where the electron beam had struck, thus allowing the fluorescence to stay for much longer than normal displays.

This oscilloscope simply works by applying a voltage directly being measured to an electron beam that moves across the screen of the oscilloscope. The beam is directed at a phosphor-coated screen, which glows when struck by the beam. The beam is then deflected by the signal, tracing the waveform on the screen.The voltage will deflect the beam up & down proportionally for tracing the waveform on the display. So this provides an immediate waveform picture.

Specifications

The specifications of an analog storage oscilloscope include the following.

• The dimension or size is approximate: 305(W) x 135(H) x 365(D)mm.
• The input impedance is 1 M Ohm.
• The trigger mode is AUTO/TV-V/ NORM/TV-H.
• X Y Phase Difference is below or equivalent to 3 degrees, DC – 50KHz.
• The selection of Polarity is + or -.
• Triggering with high sensitivity is equivalent to 1mV/division.
• Incremental magnification functions of the Ch1 channel for clearer inspection.
• It has a TV synchronous separation circuit to display a steady TV signal.
• CRT is a 6-inch rectangular shape screen with an inside graticule, 8 x10 div where 1 div = 1cm.
• The mode of the display is CH1, CH2, ADD, ALT, and CHOP.
• Rise time is ≤ 8.8ns.
• The input voltage maximum is 250V ≤ 1KHz.
• Input coupling is AC, DC, and GND.
• Accuracy is ± 3%.
• The trigger source is CH1, CH2, VERT, LINE, and EXT.
• Sensitivity & frequency is 20Hz ~ 60MHz.
• Waveform calibration is 1KH ± 20% frequency and 0.5V ± 10% voltage.
• Power supply is 220V / 110V ± 10% ; 50/60Hz.
• Its weight is 9Kg approximately.

Analog Storage Oscilloscope Block Diagram

An Analog storage oscilloscope block diagram is shown below which uses a CRT. The type of CRT used in this oscilloscope is electrostatic instead of magnetic deflection because it provides much faster electron stream control and allows analog oscilloscopes to attain very high-frequency operation. The analog oscilloscope includes a number of circuit blocks and it is capable of providing stable incoming waveform images.

Signal Inputs

There is a range of controls associated with the signal input or Y-axis on the display. In many cases, signals will be superimposed in a DC bias. So, it is necessary to connect a capacitor in series through the input to make sure that the DC is blocked. When a capacitor is utilized, choosing the AC option will signify that low-frequency signals may be restricted.

Y Attenuator

Y attenuator is used to make sure that the signals are presented to the Y amplifier at the required level or not.

Y Amplifier:

The Y amplifier in the oscilloscope simply provides the amplification to provide the output. This amplifier is mainly linear because this will decide the oscilloscope’s accuracy.

Y Deflection Circuit:

When the amplified signal from the y amplifier is given to the Y deflection circuit then it provides to the CRT plates at the required levels. The deflection used on the CRT is Electrostatic because this provides the high-speed deflection which is required for this oscilloscope.

Trigger Circuitry:

The trigger system is used to ensure that a stable waveform is exhibited on the display or not. It is required to set the ramp signal to start at a similar point on every cycle of the incoming signal to be checked. In this manner, a similar point on the waveform will be shown at a similar position on the display.

In the above block diagram, a signal is received from the Y amplifier’s output and it is given to one more conditioning amplifier. After that, it is passed through a Schmitt trigger circuit which provides single switch points when the waveform increases & decreases. The necessary sense is chosen for the trigger so that the trigger point can take place on either the increasing or decreasing edges of the waveform that can be selected before being given to the ramp circuit, wherever the trigger signal gives the start point for the ramp.

From an external source, it is also feasible to utilize a signal. So this can be a very suitable feature because it may be required to get the trigger from another source apart from the incoming signal.

Blanking Amplifier

A blanking amplifier is utilized to clean the screen throughout this fly-back phase. It only takes the reset element of the ramp to produce a pulse that is given to the grid of the CRT. This reduces the electron flow & efficiently blanks the display for this period.

Ramp Generator (Time Base)

The time base control is one of the essential controls on the analog storage oscilloscope. This will have a vast difference in speed & will be adjusted in time for each division on the scope CRT. Selecting the correct timebase speed to display the particular waveform required is essential.

The operation of this analog storage oscilloscope is; it uses the CRT to display signals in both horizontal and vertical axes. Typically the vertical axis is the instant incoming voltage value and the horizontal axis is the ramp waveform.

When the voltage of the ramp waveform increases, the trace moves across the display in a horizontal direction. Once it arrives at the screen end, the waveform comes back to zero & the trace goes back to the beginning. By using this approach, the horizontal axis corresponds to time whereas the vertical axis corresponds to amplitude. So in this manner, the common plots of waveforms can be displayed on the CRT.

Digital Storage Oscilloscope Vs Analog Storage Oscilloscope

The difference between digital storage oscilloscope and analog storage oscilloscope includes the following.

Advantages and Disadvantages

The advantages of analog storage oscilloscope include the following.

• Analog storage oscilloscopes are normally very less expensive.
• These oscilloscopes are capable of providing a good range of performance for many laboratory & service situations.
• These oscilloscopes provide accurate performances, especially for laboratory exercises.
• These oscilloscopes do not require Microprocessor, ADC, or acquisition memory for measurement.

The disadvantages of analog storage oscilloscopes include the following.

• Does not offer additional features as compared to digital oscilloscopes
• These devices are not suitable for analyzing higher-frequency sharp-rise-time transients within electronic circuits.
• These oscilloscopes are not simple to operate, so you need to have hands-on training.

Applications

The applications of analog storage oscilloscopes include the following.

• It displays single-shot & long-period waveforms.
• The analog oscilloscope is used to provide stable incoming waveform images.
• These types of oscilloscopes are extensively used for real-time observation of events that happen simply once.
• It is used to display very low-frequency signals.
• These oscilloscopes are mainly used where the time of display on the screen is too short to check the signals to be measured.
• This oscilloscope is used to map & display the signal’s constant variable input voltages by using an electron beam.

Q: What is the maximum frequency that can be measured by an analog storage oscilloscope?

A: The maximum frequency that can be measured by an analog storage oscilloscope is generally in the range of a few megahertz to tens of megahertz.

Q: What are the advantages of using an analog storage oscilloscope over a digital storage oscilloscope?

A: An analog storage oscilloscope is able to capture and display complex waveforms with high resolution, display multiple waveforms at the same time, and store the waveform for a period of time after the signal is no longer present. Additionally, analog storage oscilloscopes are generally less expensive than digital storage oscilloscopes.

Q: How does the storage CRT work in an analog storage oscilloscope?

A: The storage CRT in an analog storage oscilloscope is able to hold the image of the waveform on the screen for a period of time after the signal is no longer present. This allows the user to analyze the waveform even if the signal is no longer present.

Q: What are the different types of triggers available in an analog storage oscilloscope?

A: The types of triggers available in an analog storage oscilloscope include edge trigger, pulse width trigger, and video trigger.

Q: How does an analog storage oscilloscope display multiple waveforms at the same time?

A: An analog storage oscilloscope can display multiple waveforms at the same time by using a technique called “dual-beam” or “dual-trace” which uses two electron beams to display two signals simultaneously.

Q: How does an analog storage oscilloscope compare to a digital storage oscilloscope in terms of durability?

A: An analog storage oscilloscope is less durable than a digital storage oscilloscope due to its use of a cathode ray tube, which is fragile and can easily be damaged.

Q: What is the typical lifespan of the cathode ray tube in an analog storage oscilloscope?

A: The typical lifespan of the cathode ray tube in an analog storage oscilloscope is around 10,000 to 15,000 hours of operation.

Q: Can an analog storage oscilloscope be used to measure low-frequency signals?

A: Yes, an analog storage oscilloscope can be used to measure low-frequency signals, but it may require the use of an external low-pass filter.

Q: What are the common types of probes used with an analog storage oscilloscope?

A: The common types of probes used with an analog storage oscilloscope include passive probes, active probes, and differential probes.

Thus, this is an overview of analog storage oscilloscope – working with applications. In an analog storage oscilloscope, there are many controls that allow the instrument to display the signal precisely in the required way like Focus control, intensity control, signal inputs, time base, trigger, etc. Here is a question for you, what is a digital storage oscilloscope?