We all know how important oscilloscopes are. They are used for analyzing and measuring wide range of electrical signals. Because of their higher precision and data storage capabilities digital storage oscilloscopes are used extensively. These scopes are used in field engineering, research and development, technical education, electronics and electrical system analysis and debugging. Current trends in microprocessor and digital signal processors technologies allowed these devices to crunch large amount of data, they are also pushing speed barrier to the extremes. Scopes are becoming smarter and smarter because of multi-core designs.
Entry level oscilloscopes christened the 1000 series oscilloscopes are good powerful oscilloscopes at affordable prices. These oscilloscopes are targeted to cater to the needs of technical education market segment. Priced in the range of $400 to $800, several major manufacturers have introduced their scopes for this segment. They have simplified user interface, which makes it easier to learn how to use them.
Tektronix introduced their TBS1000 series oscilloscopes in late 2012. In the same year, Agilent introduced its DSO1000 series oscilloscope. Two years earlier, Rigol launched its version – the DS1000E series. Let us consider the models which have a bandwidth of 100 MHz and two channels, and do a comparison. So, we will look at Agilent – DSO1102B, Rigol – DS1102E and Tektronix – TBS1102 models. How digital scopes work is beyond the scope of the current discussion and this can be addressed in a separate article if need be.
( You can virtually experience the TEKTRONIX TBS Scope at - http://tektronix.docircuits.com/ )
The key parameters to be seen while comparing oscilloscopes are: number of channels, bandwidth, sampling frequency, memory depth, triggering, rise time and cost. Let us understand these parameters one by one.
The rate at which an analog signal is sampled is called the sample frequency, the number of samples per second. If the sample frequency is higher it means that interval between two samples is shorter. Higher sample frequency allows the original signal can be reconstructed much better from the digital samples.
For any given sampling frequency number of samples acquired determines the record length or memory depth. For example, if your scope specification says that it’s memory depth is 2.5k points and it acquires samples at 1GS/s then is calculated as mentioned below.
Measurement duration = Memory depth / Sampling frequency
= 2.5k/1G = 2.5 usec
Memory depth is always proportional to sample frequency. So, deeper the memory, higher will be the sample rate. Higher sample rate increases the scope’s bandwidth. This is both an advantage as well as disadvantage. Having a sufficiently large memory allows you to measure the signal for higher duration in one go. However, having a higher memory depth points will make scope slow.
The trigger determines when the oscilloscope starts to acquire data and to display a waveform. When a trigger is set up properly, the oscilloscope converts unstable displays or blank screens into meaningful waveforms.
Typically, edge, pulse, video and alternate trigger types are provided by most of the vendors.
Edge trigger can be used Can be used with analog and digital circuits. An edge trigger occurs when the trigger input passes through a specified voltage level with the specified slope. Pulse trigger is used to find pulses with certain widths. Video trigger is used to trigger on fields or lines for standard video waveforms. Alternate trigger is used to trigger on non- synchronized signals.
DSO vendors offer automatic voltage and time measurements on channel data;
Voltage measurements include maximum voltage, minimum voltage, arithmetic mean, peak-to-peak voltage, peak voltage, true RMS voltage, overshoot and preshoot.
Time measurements include frequency, period, rise time, fall time, positive width, negative width, duty cycle so on and so forth.
USB device interface allows you to connect DSO to a desktop computer to upgrade on board firmware. This interface also allows you to connect DSO to a PictBridge compliant printer to print screen image directly. USB device interface provides another very useful feature of controlling DSO remotely by sending appropriate commands over the network.
USB host port allows you to take a copy of acquired data on to a USB mass storage device in a file format.
Other miscellaneous features provided are math operations such as addition, subtraction, multiplication and FFT on channels, simultaneous view of main and zoomed waveforms. Most of the vendors provide digital filters namely; LPF, HPF, BPF and BRF.
You can buy one of these directly from respective vendors, or you can also try element14 or RS component. The pricing remains the same even if you buy from distributors
Here is a comparison across various important specs;
|Specification||Agilent – DSO1102B||Rigol – DS1102E||Tektronix – TBS1102|
|Bandwidth||100 MHz||100 MHz||100 MHz|
|Sampling||1GS/s – 1 channel on500MS/s – 2 channels on||1GS/s – 1 channel on500MS/s – 2 channels on||1GS/s – 1 channel on500MS/s – 2 channels on|
|Memory Depth||16kpoints – 1 channel on8kpoints – 2 channels on||16kpoints – 1 channel on8kpoints – 2 channels on||2.5kpoints – 1 channel on1.25kpoints – 2 channels on|
|Trigger Modes||Edge, pulse width, video, and alternate||Edge, Pulse Width, Slope, Video, Alternate||Edge, Video, and Pulse Width|
|Automatic Measurements||22 voltage and time measurements and cursor measurement||22 voltage and time measurements and cursor measurement||16 voltage and time measurements and cursor measurements|
|Connectivity||USB device and host||USB device and host, RS232||USB device and host|
|Cost||1100 USD||399 USD||1100 USD|
Every DSO model is designed keeping certain applications or use-case scenarios in mind. You should choose a model which suits your application. Don’t get biased by the numbers, because bigger is not always better. So, be smart and choose your scope wisely.
For more information, visit the following links;
You can also visit the following link to virtually experience TBS1102