Special purpose oscilloscopes
Electronic measuring instruments
Special Purpose Oscilloscopes
In the previous chapter, we discussed the cathode ray oscilloscope (CRO), which is a basic oscilloscope . We will get special purpose oscilloscopes just by adding a few more blocks to the base oscilloscope as needed.
These are the special purpose oscilloscopes .
- Dual-beam oscilloscope
- Dual-trace oscilloscope
- Digital storage oscilloscope
Now let's talk about these special purpose oscilloscopes one by one.
The oscilloscope, which displays two voltage waveforms, is called a dual-beam oscilloscope. Its functional diagram is illustrated in the figure below.
As shown in the figure above, the cathode ray tube of the dual beam oscilloscope consists of two sets of platesvertical deflection and a set of horizontal deflection plates.
The combination of the following blocks is called a channel .
- Pre-amplifier and attenuator
- Delay line
- Vertical amplifier
- One set of Vertical Deflection Plates
There are two channels in the dual beam oscilloscope. So, we can apply the two signals, namely A and B as input to channel A and channel B respectively. We can choose any of these four signals as trigger input to the trigger circuit using a switch. These are the input signals A and B, the external signal (Ext) and the line input.
This oscilloscope will produce two vertically deflected beams, because there are two pairs of vertical deflection plates. In this oscilloscope, the blocks which are useful for deflecting the beam in the horizontal direction are communs for both input signals. Finally, this oscilloscope will output both input signals simultaneously on the CRT screen.
Dual Tr Oscilloscope ace
The Oscilloscope, which produces two traces on its screen, is called a Dual Trace Oscilloscope. Its functional diagram is illustrated in the figure below.
As shown in the figure above, the CRT of the double-trace oscilloscope consists of a set of vertical deflection plates and another set of horizontal deflection plates. channel consists of four blocks, i.e. pre-amplifier and attenuator, delay line, vertical amplifier and vertical deflection plates.
In the diagram above, the first two blocks are present separately in the two channels. The last two blocks are common to both channels. Therefore, with the help of an electronic switch , we can connect the output of lidelay gne of a specific channel to a vertical amplifier.
We can choose any of these four signals as the trigger input for the trigger circuit by using a switch. These are the input signals A and B, the external signal (Ext) and the line input.
This oscilloscope uses the same electron beam to deflect input signals A and B vertically using an electronic switch, and produces two traces . the blocks which deflect the beam horizontally are common to both input signals.
Digital storage oscilloscope
The oscilloscope, which stores the waveform digitally, is called a digital storage oscilloscope. The block diagram of the (digital) storage oscilloscope is below -
Additional blocks required for digital data storage are added to a basic oscilloscope toconvert it to a digital storage oscilloscope. The blocks required for digital data storage are located between the preamplifier and attenuator and the vertical amplifier in the digital storage oscilloscope. These are Sample and Hold circuit, analog-to-digital converter (ADC), memory, and digital-to-analog converter.
Control logic controls the first three blocks by sending
The digital storage oscilloscope stores data in digital form before displaying it. the waveform on the screen. While the basic oscilloscope does not have this functionality.