- Output voltage, current, and power
- Setting resolution and accuracy
- Ripple and noise
- Features and programmability
Oscilloscopes – What to look for
First, think about what you will use it for and where.
- Where will you use the scope (on the bench, at a customer’s site, under the hood of a car)?
- How many signals do you need to measure at once?
- What are the maximum and minimum amplitudes of signals that you need to measure?
- What is the highest frequency of signal you need to measure?
- Are your signals repetitive or single shot?
- Do you need to view signals in the frequency domain (spectrum analysis) as well as the time domain?
Bandwidth: You should look to purchase an oscilloscope with a bandwidth five times (5X) higher than the maximum frequency of the signal you need to measure. This ensures an accurate representation of the waveform. Unfortunately, high-bandwidth scopes are expensive, so you may need to compromise here.
Memory depth: Digital oscilloscopes store captured sample points in memory. The amount of memory the scope has determines how long it can store the signal before having to dump it. This can limit the effective sampling rate of the oscilloscope if there is insufficient memory. This is most apparent when zooming in on a signal.
Channels: Two channels let you compare a component’s input to its output. Four analogue channels let you compare more signals and provides more flexibility to combine channels mathematically, while 6 or 8 channels allows for either multiple bus analysis whilst simultaneously viewing voltage or current type signals in a power related environment.
Function and Signal Generators
A signal generator is a device that creates electronic signals, typically varying in voltage or current over a short period of time, with varying waveforms, or shapes, where the voltage increases or decreases at different rates as it reaches its peak value. There are many different types with many different applications. Function generators, arbitrary waveform generators, and vector signal generators are common types of specialized signal generators.
What is the difference between a Signal Generator and a Function Generator? - A Signal Generator is a fairly simple piece of kit that can produce basic waveforms for Electronic Design, Test and Repair projects, typically producing Sine, Square & Sawtooth waveforms with possibly some variation of those. A function generator is a more sophisticated instrument that can produce waveforms of multiple programmed design, used more in advanced development projects where simple waveforms can create limitations.
What is an Arbitrary Function Generator? - An arbitrary function generator is a combination of Signal and Function Generation -it has a pre-set list of waveforms or patterns to output, combined with being able to change the parameters of waveforms, such as frequency, the amplitude and offset, and add some basic forms of distortion or modulation.
Bench Digital Multimeters
As the most commonly used instruments on any design engineer’s bench, a digital multimeter (DMM) is utilised to make quick and simple voltage measurement or data log temperature measurements over time. From concept to prototype, turn-on, and debugging, all the way through testing and validation, the DMM is ever-present through the entire product cycle.
Bench v Handheld: In most cases, a typical benchtop DMM will have higher accuracy, better resolution, more sophisticated system programmability, and more advanced functionalities compared to a handheld DMM. Many technicians and electricians use handheld DMMs because of their portability and simple functions. Engineers and designers prefer benchtop DMMs for their accuracy and sophisticated measurement.
Digits, Accuracy & Resolution: The digits translate directly into counts that tell us about the resolution of the DMM. It’s not directly related to accuracy, which is a different specification. Accuracy tells us how close the measured value comes to the actual value being measured, typically defined as a range with a lower bound and upper bound.
Visualisation: By default, a DMM displays numeric data. Many advanced DMMs also offer sophisticated features like trend charts (value vs. time) and histograms, allowing for quick insight into the measurement.
Secondary Measurements: With the right architecture and design, some advanced DMMs can now display secondary measurements.
Simple DC Power Measurements: Power measurements are critical in many test applications. For those without a power meter, the DMM has traditionally been the instrument of choice to make such measurements. A true power measurement requires both voltage and current to be measured simultaneously.
Decade Boxes
While developing electrical and electronic circuits, decade boxes provide an invaluable degree of flexibility in analysis by enabling resistance and capacitance values to be selected and trialled without having to change components. Any resistance value from 1Ω to 11MΩ, or capacitance value from 100pF to over 4μF can be dialled up and selected. Decade boxes are ideal for demonstrating what changes in the relative value can make to the circuit under test.
Source Measurement Unit (SMU)
A development of the Digital Voltmeter and advanced Power Supply unit is to combine the two function into one unit, and produce a Source Measurement Unit SMU. It can produce exact voltage or current output, and simultaneously measure that output as it varies with DUT parameter changes; or voltage/current at other points in the circuit as required. It combines the features of a digital multimeter (DMM), power supply, true current source, electronic load and pulse generator, all into a single, synchronised instrument. SMUs are considered more useful than the combination of any of the other instruments, due to the simultaneous control and synchronised measurements.
