STEPPER MOTORS: THE BASICS

Found in both industrial and commercial settings as a result of their affordability, reliability, durable construction, and high torque at low speeds, stepper motors are brushless synchronous electric motors that work by converting digital pulses into mechanical rotation. Every revolution of a stepper motor consists of a division of steps and the motor is sent a pulse for each step. A stepper motor’s position can be controlled without feedback because stepper motors are able to take only one step at a time and each step is the same size. When pulse frequency increases to a certain point the step movement will turn into continuous rotation with the speed directly related to the frequency of pulses.

There are a number of reasons to use a stepper motor: 1) open-loop control simplifies the motor and makes control less expensive; 2) the motor’s rotation angle is directly proportional to the input pulse; 3) you need precise positioning and reliable repetition of movement; 4) stepper motors have wide operational ranges because the speed is commensurate to the input pulses’ frequency; 5) they have excellent response times with regard to starting, stopping, and reversing; 6) good stepper motors are accurate within three to five percent of a step; 7) when the windings are energized stepper motors have full torque at complete standstill and, when the load is coupled, you can achieve remarkably low speed synchronous rotation; and 8) because stepper motors don’t have contact brushes, they have an exceptionally high mean time between failure.

The three types of basic stepper motors are variable reluctance, permanent magnet, and hybrid — hybrids combine the strengths of variable reluctance and permanent magnet engines. Hybrid stepper motors have toothed stator poles, a permanent magnet rotor,typically  two hundred rotor teeth, and most hybrid motors rotate at under two degrees each step. As a result of their high static and dynamic torque and their ability to run at quite high step rates, hybrid stepper motors are commonly used in a number of different applications including computer disk drives, printers, machine tools, and much more.

Hopefully this brief overview helped you to understand a little bit more about the operation of stepper motors, their characteristics, and some common applications where stepper motors are employed.

USING SHUNTS IN CONJUNCTION WITH DIGITAL PANEL METERS

In the medical world a shunt is a means of diverting, e.g., blood from its typical path to another route. Shunts work in a similar manner in the realm of electronics, allowing current to bypass one point in a circuit and travel to another point.

An example of this would be Christmas lights. Because they are set in series, when one bulb fails the entire circuit goes out. Modern lights prevent this with shunts: each bulb has its own shunt in order to pass the current along, so to speak, when a filament fails.

Circuits are commonly tested for current, resistance, and voltage. Some devices — e.g. ammeters, voltmeters, and ohmmeters — individually measure these parameters. Other devices, like digital multimeters, can test several parameters at once. Digital panel meters are used to measure, display, and record a circuit’s current, resistance, and voltage; but because they are continually subjected to the parameters which they measure, they are prone to damage. However, using panel meters in conjunction with shunts mitigates the risk of damage.

When you combine shunts and panel meters you end up with shunt-resistive circuits which enable you to circumvent predetermined levels of current surrounding a piece of electronic testing equipment. Using a shunt and panel meter together (i.e., a shunt resistor) reduces the excess flow of current through your instruments and helps keep them better protected.

Moreover, combining a shunt and digital panel meter can extend the range of the shunt, which is known as a meter shunt. When you divide current between parallel shunt resistors you increase the range of an ammeter by adding another parallel resistor. Let’s say your meter can only read between zero and one milliamperes but your test requires full-scale detection of one hundred milliamperes. In this situation you can use a shunt to take on the difference between the detection capabilities of your meter and the desired level of full-scale detection. With regard to our example, your shunt would have to be able to handle the remaining current (i.e., ninety-nine milliamperes).

Shunts have myriad uses in electronics testing, but their chief utility comes from their ability to protect delicate equipment and boost the capabilities of panel meters, making shunts exceedingly useful for those who do serious electronic testing.

FUNCTION GENERATOR OVERVIEW

Sometimes a device will not properly respond to electrical impulses and other times a device won’t respond at all. In these situations a function generator is handy for diagnosing the problem. Function generators test the response of various circuits to electrical signals and impulses by releasing voltage patterns of differing frequencies and amplitudes, which are controlled by the operator of a function generator. Function generators are frequently used in conjunction with an oscilloscope, which displays electrical waveforms.

Waves

Function generators allow you to choose the shapes of the output which replicate several mathematical functions: a square wave moves abruptly from high to low voltage; a sine wave gently curves from from high to low voltage; triangle waves move from high to low at a fixed rate (i.e. diagonal lines); and sawtooth waves rise slowly and drop quickly.

Reason to Use a Function Generator

Function generators are a very easy and convenient means of testing electrical devices. You can use a function generator when a device or part of an electrical system malfunctions or stops functioning altogether. You test the device or system’s response to electrical activity by replicating its ordinary impulses using the function generator’s waveforms. When you send a device/system an electrical impulse like the one which it would usually have and the device/system either distorts or fails to accept the signal, you know that your device/system is defective.

Function generators are also used for measuring feedback from musical equipment — amplifiers, microphones, electric instruments, etc. — because the waveforms imitate situations when the device you’re testing will be affected by electricity, enabling you to draw conclusions as to what’s not working right.

Function Generator Use

The first step to using a function generator is (you guessed it) powering it on. Next you’ll connect your lead and ground to your oscilloscope in order to check the controls and make sure the generator is configured to use the waveform you need. After you have the waveform you want you’ll connect the signal lead to the device you want to test and the ground lead to the device’s ground (some devices have a negative lead; connect your ground lead to the negative lead in this case). After everything is set up you can then send impulses to your device. Not only can you control the waveform you send the device, you can also control the volume of the wave as well.

BENEFITS OF PC-BASED USB OSCILLOSCOPES

PC-based USB oscilloscopes, which display signal voltage as two-dimensional graphs and indicate amplitude distortions related to events and frequency, are used by hobbyists and professionals alike for testing hardware and research. Conventional oscilloscopes are typically stand-alone pieces of testing equipment that aren’t readily portable. PC-based oscilloscopes connect directly to your computer’s USB port and enable you to power the device, acquire and store data, and supply record evaluation; these features have given users more options and new techniques when using an oscilloscope.

PC-based oscilloscopes utilize your computer’s hardware — specifically its processor(s) — to display data on the computer’s screen and record that data on the computer’s hard drive or other storage devices. There are myriad modifications that can be done with PC-based oscilloscopes that aren’t practical for stand-alone oscilloscopes.

There are a wide variety of uses for PC-based oscilloscopes. Technicians use PC-based oscilloscopes as diagnostic tools for computer problems and maintenance work on all sorts of electrical equipment. PC-based oscilloscopes are also useful for everything from conducting electrocardiograms (medical professionals) to diagnosing issues with cars (automotive repair).

Modern computer processors are faster than they’ve ever been and their prices are dropping all the time — it’s no wonder that PC-based oscilloscopes are being used more often. In addition PC-based oscilloscopes can do everything that stand-alone units can but cost less and work with just about any computer. Old PCs are often significantly faster and more powerful than many stand-alone oscilloscopes that cost hundreds or even thousands of dollars, meaning that you can pull that ten-year-old computer out of storage, dust it off, and bring it back to life with an oscilloscope.

Furthermore data collected with a PC-based oscilloscope can be quickly and easily stored, shared, or exported as a result of a computer’s word processing and spreadsheet software, storage capacity, and networking capabilities. On top of that PC-based oscilloscopes offer better screen resolution and portability. It’s not hard to see why PC-based USB oscilloscopes have increased in popularity in recent years. Stand-alone oscilloscopes may soon be a thing of the past.

USB OSCILLOSCOPE OVERVIEW

USB oscilloscopes, which allow you to take measurements of electrical impulses and observe constantly varying signal voltages, operate via one of your computer’s USB ports. An oscilloscope measures all detected signals and displays a graph indicating precisely how much impulses change for a specific time period. You will notice several things regarding a single signal: the signal’s frequency, voltage, duration, and the level of alternating and direct current. While standard oscilloscopes are powered by direct electrical connections, USB oscilloscopes derive their operating power from linking to your computer by way of its USB port.

In the past oscilloscopes were used sparingly because of their power requirements, but recent technical developments have led to portable oscilloscopes that can be powered by plugging into a USB port, making these multipurpose tools — which are used in a variety of applications from basic electronics to advanced physics testing and experimentation by hobbyists and professionals alike — standard equipment in many classrooms and laboratories.

The invention of USB-powered oscilloscopes has enabled them to be used in a number of new ways. Because USB oscilloscopes can be powered by a laptop computer, they can be used nearly anywhere. USB oscilloscopes also have the added convenience of quickly and efficiently downloading information to the computer to which it is attached. Another benefit of USB oscilloscopes is that the information they collect is instantly displayed on your computer. As a result of the speed at which information is transmitted to a computer, its easy for all the data taken by an oscilloscope to be shared between several viewers on different computers, which is an advantage for specialists who want to quickly distribute data to colleagues elsewhere.

There are a wide variety of USB oscilloscopes available including basic oscilloscopes for less demanding testing applications and more sophisticated (and expensive) oscilloscopes that feature better specifications, additional capability, and excellent accuracy. This diversity in the USB oscilloscope market makes these powerful pieces of test equipment suitable and cost-effective for a variety of disciplines, including everything from basic production jobs to more technical tasks like research and product development.

USING THE RIGHT OSCILLOSCOPE PROBE

A piece of test equipment’s performance is always limited by its peripheral equipment, and the same holds true for digital storage oscilloscopes. Most people tend to focus on an oscilloscope’s specifications — especially considering that specifications generally determine price — but an oscilloscope probe’s performance is every bit as important. A substandard oscilloscope probe will impair the performance of even the very best oscilloscope.

You want your oscilloscope probe to provide a simple means of presenting the signal on a circuit board or whatever is being tested to the oscilloscope’s input. A standard oscilloscope probe will consists of a probe tip, length of shielded wire, and a compensation network.

Passive probes are the most common kind of oscilloscope probe and there are two noteworthy types of passive probes: X1 and X10. X1 probes present a signal as it exists to your oscilloscope. Ordinarily an oscilloscope’s input impedance is one megohm, but this impedance can load the device you’re testing and distort the waveform. Moreover, an X1’s tip capacitance can be as high as one hundred picofarads. To avoid these limitations and lessen the load on the circuit you’re testing an X10 probe can be used instead. Because an X10 probe has an input impedance of ten megohms and a tip capacitance of around ten picofarads, this type of probe will distort the waveform far less than an X1.

Active oscilloscope probes are another option when you need even greater levels of performance. These probes have very low levels of capacitance and significantly higher input impedances as a result of having an active element quite close to the oscilloscope probe’s tip.

Calibration

It’s very easy to simply plug your oscilloscope probe in and start taking measurements with your oscilloscope; however, your oscilloscope probe needs to be calibrated before you use it to make sure that its response is flat. Almost every oscilloscope has a built-in calibrator for this reason. The calibrator provides a square wave output, and the oscilloscope probe has a small preset adjustor. You connect the probe to the calibrator’s output and manipulate the present adjustor until the shape of the displayed waveform is perfectly square. When the oscilloscope probe’s high frequency response is down the edges of the square wave on the display will be rounded and, if the high frequency response is up, the probe’s wave will overshoot the edges.

This simple adjustment is imperative for ensuring that the oscilloscope probe performs perfectly.

Differences Between Digital and Analog Oscilloscopes

The oscilloscope has been a commonly used piece of testing equipment for over fifty years now and is used by TV technicians and aerospace engineers alike. Oscilloscopes are one of the most frequently used instruments in the field of electronics circuit design, testing, and troubleshooting because they have the ability to graphically depict the waveform, magnitude, and time base of electrical signals on its screen.

In addition it can be calibrated so that the magnitude and frequency can be observed with a great deal of accuracy. Most models also have more than one input, allowing for two or more signals to be observed at once. For these reasons oscilloscopes are invaluable to those seeking to observe the function and operation of electronic circuits in real time. Because electronic circuits operate in a decidedly non-visually way, an oscilloscope acts as a window into its operation.

Early oscilloscope designs were based on analog amplifier circuits which brought the signal’s amplitude to a level sufficient to drive the oscilloscope’s cathode ray tube’s deflection plates. An analog oscilloscope’s built-in sawtooth waveform moved the CRT’s beam from one side to the other and rapidly returned it for a consecutive scan, but these days it needs to be able to trigger at the exact moment of a digital event and it needs to be capable of showing what happens in other parts of the circuit when a digital event occurs (it may or may not be repetitive).

For this reason triggering systems capable of causing the oscilloscope to sweep exclusively at the instruction of the incoming pulse were developed. It was also commonly necessary to synch the horizontal sweep to the digital system’s clock frequency in order to show the digital switching events because timing was and is a high priority for those debugging a logic module.

It’s no wonder that digital oscilloscopes developed into a collection of of electronic circuits when you take into account all the functionality digital devices demanded. Digital oscilloscopes have quickly become very complex instruments that require some of the brightest minds in the digital electronics field for their design and to fine tune their performance characteristics as digital equipment — especially computers — become faster and more sophisticated.