As an incremental encoder rotates it produces two square wave outputs A and B; together these signals create an incremental encoder’s quadrature output. For most encoders these square waves A and B are 90 degrees out of phase. By observing the changing states of the A and B outputs the encoder’s direction can be determined.
Typical encoder square wave outputs A and B(Image source: CUI Devices)
However, to determine the distance an encoder has traveled, or at what speed it is rotating, more information is required. To calculate this information it is important to know the encoder’s resolution. Resolution can be thought of as the encoder’s granularity, or put simply, how many pieces of the pie the encoder is divided into for one revolution.
CUI Devices uses the term PPR, or Pulses per Revolution, to represent encoder resolution. PPR describes the number of high pulses an encoder will have on either of its square wave outputs A or B over a single revolution. While CUI Devices does not use PPR to represent Periods per Revolution, it would still technically be accurate as the duty cycle of our standard offering of incremental encoders is 50%. Once resolution is known it can be used to calculate how many mechanical degrees each pulse and period is equal to.
Once an encoder’s PPR is known, mechanical degrees for each pulse can be determined(Image source: CUI Devices)
With that being said, the term PPR is not ubiquitous throughout the motion control industry. Although CUI Devices uses PPR for all of our encoder products, many companies will often use the terms PPR, CPR, LPR or resolution interchangeably with conflicting definitions.
CPR most commonly stands for Counts per Revolution, and refers to the number of quadrature decoded states that exist between the two outputs A and B. With both outputs A and B switching between high and low, there exists 2 bits of information represented as 4 distinct states. The term quadrature decoding describes the method of using both outputs A and B together to count each state change. This results in 4 times the amount of counts that exist for each pulse or period. Therefore, the CPR of an encoder is the encoder’s PPR multiplied by 4. It should also be noted that some encoder manufacturers use the CPR acronym to mean Cycles per Revolution. Cycles per Revolution refers to the full electrical cycles or periods on any one of the encoder outputs and is equivalent to Pulses per Revolution. With both Counts per Revolution and Cycles per Revolution using the same CPR acronym, but differing by a factor of 4, this can understandably cause some confusion and one must be careful to understand how the resolution is being defined.
How to compare typical datasheet waveform drawings and figures (Image source: CUI Devices)
Lines Per Revolution (LPR)
LPR, or Lines per Revolution, is another term that is equivalent to PPR. The line refers to the bars etched or printed onto an optical encoder’s disk. Each line on an optical encoder disk would represent a low pulse on the output as they have a one-to-one relationship.
Because resolution is defined differently across the industry, it is important to get the numbers into the same format when comparing products from different encoder manufacturers. This is best done by viewing waveforms or timing diagrams on the datasheet and if possible calculating the pulse width in degrees or arcminutes.
This content originated from BUD Industries blog. The original version of this blog can also be viewed here.
If you have specific application requirements, or cannot find a standard electronic enclosure to meet your exact needs, you may need to work with an electronic enclosure manufacturer to create a custom enclosure for your project.
Here are some key points that will help make your custom enclosure project go more smoothly.
Start with an idea of the type of enclosure you need. (See guide below.)
If you need a custom dimension or other structural change, look to a stock enclosure for inspiration.
Customizing a stock enclosure usually saves time and money.
A fully custom enclosure gives you freedom to design exactly what the application requires.
Metal enclosures are the most cost effective to create from scratch.
Enclosures made of plastic or fiberglass require completely new tooling that may be costly, so custom molded enclosures are best in high quantity.
What is the Difference Between a Modified Enclosure and a Custom Enclosure?
There’s no reason to invest in a custom electronic enclosure if you can modify a stock enclosure to meet your application’s requirements. Nevertheless, the decision isn’t always easy. The information below will help you weigh the benefits and drawbacks of each approach. You may even discover a few surprises.
Custom Electronic Enclosures
A custom electronic enclosure is defined as being completely developed from scratch and is mostly used when a suitable solution cannot be found off the shelf. This allows for a very specific visual look of the enclosure as well as exactly meeting the needed dimensions and functionality.
Bud can help with the electronic enclosure design and creation of a from-scratch enclosure, starting by understanding the application, then working with CAD tools to arrive at an ideal enclosure design. There is a lot to keep in mind, such as allowing space for cabling, planning how PCBs will be mounted, the location of power supplies, tolerances and drafting angles, and heat dissipation. Our experience can help prevent costly design mistakes.
More often the inspiration for a custom enclosure is a standard product. A designer may like a particular electronic enclosure box but need it in different dimensions or need a hinged cover on a stock enclosure that is available with only a screw-down cover. A common request is a special formulation of plastic, such as adding UV protection to an enclosure that was designed for use indoors. Basing a custom design on a standard enclosure provides a fast and cost-effective solution, because much of the engineering has already been worked out.
In addition to supplying custom-molded plastic enclosures, Bud can fabricate custom metal racks and sheet metal enclosures. Our factory has the machinery and skilled workers needed to form and weld almost any design of steel or aluminum enclosure. Making custom industrial enclosures in steel and aluminum is more popular than in other materials because tooling costs are relatively low.
The closer to a manufacturer’s standard enclosure the custom enclosure can be, then the more cost-effective it can be. A good example is a custom server rack we developed for an internet service company that had a specific assembly, weight load, and seismic needs. We used a standard Bud rack, slightly changed several dimensions, and upgraded it with extra welds, different gauge steel, and doors that were removable in a specific way that met the application’s needs. We performed seismic tests for them, simulating their equipment installed. The end product was a totally custom rack that still used many of the standard Bud design and production techniques.
Custom plastic or die-cast aluminum enclosures with dimensional changes are often significantly more expensive, as tooling costs can be quite high. The benefit of a new tool is that it is easy to design-in special features such as additional mounting bosses, wall-mounting provisions, card guides, as well as cutouts and holes that make the enclosure a turnkey unit. If the quantities are significant, the tooling charges are easily amortized, and so will allow for a unique looking product or one that meets the specific customer need. We have done this for several end-products offered by a wi-fi provider who had specific needs to make the box attractively mesh with the surroundings and contain easy installation features.
Other customizations for a plastic enclosure might include changing the plastic to allow for different colors, added UV protection, or flammability protection. If a standard size box is chosen, sometimes these changes will not require new tooling, which makes it a very reasonable shift.
Extruded aluminum enclosures typically have a fixed height and width but can readily be varied by depth. Changes in the fixed dimensions will require a new tool, although extrusion tooling is often not expensive.
Modified Enclosures
No conversation about custom enclosures is complete without discussing modified enclosures. A modified enclosure is a standard, off-the-shelf enclosure that can have features or functions added to it, using proper machinery or tools. The most common modifications are made to enclosures by cutting holes, slots, or cutouts. Most enclosures must be modified because they need to allow for input or output of power or data such as with front panel custom cut-outs for displays, switches, buttons, or signal wires… at minimum an opening for a power cable.
Some of these changes are functional, such as a special gasket that provides EMI protection. Some of these changes are cosmetic, such as digital printing and special colors intended to make the end product stand out in the marketplace.
Not really a modification, but along the same lines, is pre-assembly. Racks can be shipped with customer-specified configurations of accessories such as shelves, fan trays, cable organizers, and chassis. Electronic enclosures can be pre-assembled with accessories such as standoffs, internal panels, and vents. Bud will even drop ship such enclosures directly to your CM, streamlining the supply chain, simplifying installation, and saving time.
With a modified enclosure, the basic enclosure—its structure—does not change. Because there are so many families of enclosures, in so many sizes and shapes, usually design engineers can select a standard enclosure that will do the job with minor modifications. Bud offers around 3,000 different models of enclosures.
Starting with a stock enclosure is obviously more cost effective and much faster than ordering a custom enclosure that must go through an entire design, manufacturing, and shipping cycle. Many injection-molded enclosures are made in Asia, which lengthens the delivery time by several weeks or longer. In contrast, about 93% of Bud’s inventory is available for same-day delivery.
Ratings are another consideration. It’s easier to get a UL NEMA rating on a modified enclosure if the original box is NEMA rated.
Many of the electronic products that consumers touch are housed in enclosures that we don’t notice are actually stock enclosures. Enclosures used for medical devices, industrial tablet PCs, and hand-held remote controls come in so many variations that people don’t notice the enclosure is not custom. This is especially true of enclosures that are printed with logos and carry branded colors.
Considerations of Custom Electronic Enclosures
The decision to create a custom enclosure needs to consider the timeline. It takes time to develop detailed CAD drawings, to acquire or modify tooling, and to meet any certifications. A UL rating can take up to six months to obtain and longer if design changes are needed.
Another consideration is quantity. If tooling for a custom plastic enclosure costs $15-$60 thousand, then running only 100 pieces may not be economical. If instead the run is 100,000 pieces, then customization may be worth the cost because the enclosure can be designed to speed assembly, simplify maintenance of the end product, and match the look of the brand.
Even when customizing an off-the-shelf enclosure, experience matters. For example, welding on a lock or a hinge may change the tolerances of the enclosure. Also, there are minimum clearances for cutouts and mounts, such as the distance from an edge or corner. The impact of design changes must be understood so PCBs, cables, and other components fit as expected. Having Bud as an experienced partner will help assure success.
If you are truly starting from a blank sheet of paper, then the first decision to make about your enclosure is, what kind of enclosure do I need? Enclosures come in a variety of types, styles and materials. Look at the websites of enclosure suppliers to get an idea of what’s available.
Start by asking the basic questions.
Where will your design be used? What environmental threats should be considered?
How strong does the enclosure need to be?
Does the application require portability (lightweight)?
How will the enclosure be mounted?
Will internal heat be an issue?
What kind of access will be required in the field?
Are there indicators or displays that need to be read?
The answers to these questions will lead you to select a particular style and material.
Sheet metal electrical enclosures. (Aluminum and steel.) Pros: Metal dissipates heat. Strong. Easy to customize. RF shielding. Cons: Steel may corrode. Limitations in appearance, generally boxy.
Plastic electronic enclosures. Molded plastic permits any shape and texture. Popular for NEMA and IP rated enclosures. Clear covers are available with some models. Corrosion resistant.
Fiberglass electronic enclosures. Similar to plastic but stronger. Tighter dimensional tolerances. Lighter and less costly than stainless steel. High impact strength and has superior working temperatures. Chemical resistant.
Die cast aluminum electronic enclosures. Cost-effective protection. Metal dissipates heat the best. RF shielding. Strength and durability. Good for grounding.
Extruded aluminum electronic enclosures. Plastic end caps. Attractive and cost-effective, aluminum dissipates heat. Available with IR panels. Ideal for housing single PCBs.
Of course, if you need a cabinet or rack, then the only option is steel.
After you have selected the type of enclosure and its material, the next step is to determine the dimensions. Typically, engineers choose the smallest enclosure possible that will still accommodate their components and printed circuit boards. Engineers should properly plan the location of power components and signal wires. After you submit your CAD file or requirements to your custom enclosure supplier, then issues such as tolerances, mounting, and drafting angles are considered. Then the supplier will send you a CAD drawing for final approval.
Expert Advice
We hope the information in this guide to custom enclosures is helpful. To get specific advice or a quote on your next project, contact the Bud Industries experts at saleseast@budind.com or reach out to them on the Budind.com website’s chat.
The design of medical electronic equipment seems like a straightforward task, until you get into the details. Remember, as you know, this type of equipment is used in situations that range from home health care to surgical suites. Products used in the medical arena must perform, must be reliable, and must be effective, since they are frequently part of a life-saving process.
Many types of medical electronic equipment incorporate some type of alarm to indicate patient problems, equipment failure, or power interruption. In most cases these alarms are either audible or visual, but research has shown that audible signals can provide a strong sensory cue to establish the awareness of a situation. Simply stated, we can shut our eyes to block out the visual, but turning off our ears is a bit more difficult.
The number of alarms used on the equipment in a medical setting, as well as the amount of new medical electronic equipment being developed is also growing rapidly worldwide. The problem is, ongoing surveys of healthcare personnel who operate or rely on medical electronic equipment continue to indicate displeasure with the alarm signals on the devices, including concern with their loudness, distraction due to multiple signals, and recognition of the critical ones. These challenges, coupled with the demands of patient safety, mean additional regulation. It should come as no surprise then, that the alarms used in medical electronic equipment are also subject to relatively strict technical standards and guidelines in the form of the IEC Standard IEC 60601-1-8. In this blog, we will review the general outline of IEC 60601-1-8 and the key requirements given for audible alarms in medical equipment as well as providing example medical buzzer tones.
What is IEC 60601-1-8?
The International Electrotechnical Commission (IEC), a European-based standards organization, published the IEC 60601 international consensus technical standard covering all medical equipment requirements some time ago. A subset of the standard is IEC 60601-1-8, which deals with medical alarm systems. This portion of the standard is officially titled: General requirements, tests, and guidance for alarm systems in medical electrical equipment and medical electrical systems.
IEC 60601-1-8 Requirements for Audible Alarms in Medical Equipment
If you are a designer of electronic medical devices or systems, the alarm components you need to specify for patient and device monitoring are indeed critical, and the process may take a bit more planning than you thought. Fortunately, however, there is guidance in place to help you.
The IEC 60601-1-8 standard was developed and continues to be updated to help regulate alarm design and prevent confusion in medical settings where several alarms and ongoing signals may be sounding at the same time. It is a relatively lengthy technical document that sets a framework for the alarm sounds that medical electronic equipment should make in different healthcare situations. The standard addresses the design of the alarms that can be used in medical equipment by doing the following:
Defines the medical conditions that should trigger an alarm.
Classifies alarms as either low, medium, or high priority.
Defines the alarm pulse frequency range, pulse shape, rise/fall time, and signal burst pattern.
Prescribes alarm sound levels in decibels as they relate to priority.
Sets a maximum amplitude difference between the alarm pulses.
Separates physiological alarms, or those related to patient condition, from technical alarms, or those related to equipment status.
Discusses the temporary silencing (muting) of alarms by healthcare personnel.
Allows for specific melody alarm tones for certain applications, including general, cardiac, artificial perfusion, ventilation, oxygenation, temperature/energy delivery, fluid/drug delivery, and equipment or supply failure.
From a technical standpoint, and to give you an idea of how technically focused the document is, here are some of the specific metrics that the standard assigns to medical alarms:
The alarm frequency must be between 150 Hz to 1,000 Hz and must be one of four harmonics with the greatest sound level.
There must be a minimum of four frequency peaks between 150 Hz and 4,000 Hz.
The sound level of the greatest four frequency peaks between 150 Hz and 4,000 Hz must be within 15 dB of each other.
While specific in noting that all medical equipment must include at least one set of audible warning sounds that meet the requirements of the standard, it also allows for additional sound sets to be built into the equipment, including music, voice, or, outside of audio, visual alarms. The intent is that these alternate alarms may be easier to learn and identify by healthcare personnel. Voice alarms are frequently used in aircraft cockpit pilot warning systems.
Compliance with the IEC 60601-1-8 standard for medical equipment alarms is mandatory in the U.S., Canada, and the EU to promote evidence of device safety and performance.
A Word About Components Used in Medical Alarm Systems
Alarm system components for medical electronic equipment can range from buzzers, bells, or sirens for relatively uncomplicated situations, to audio speakers or transducers for voice or music tones, and to visual indicators to complement audio tones. Deciding what makes sense for your design will obviously hinge on the system you are designing for, the setting in which it will be used, the skill or learning ability of the potential operator personnel, and your budget.
There may also be a discussion among your design team about the complexity of the alarm system required by your device or system in order to get the desired response needed for a particular healthcare setting. For example, will a buzzer suffice in an operating room setting, or does it need to be coupled with a visual indicator?
The reality of designing alarms for medical applications is that you are not just doing device or systems engineering. You are working with information design and communication, along with accommodating the complex human factors that exist in the healthcare environment. Alarms not only have to be noticed, they also must be learned and recognized by the healthcare staff.
Using Electrical Buzzers as Medical Equipment Alarms
Electrical buzzers are straightforward audio signaling devices that are available in many configurations, footprints, frequency ranges, voltages, drive currents, sound pressure levels, and price points. They convert electrical signals into sound that, depending on the device, can vary by volume, tone, frequency, and pulse. Buzzers may also be called audio alarms, audio indicators, or sounders.
Generally powered by dc voltage, buzzers come in two types:
Electromechanical (or magnetic) – uses a magnet, oscillator, and vibrating diaphragm to generate sound.
Piezoelectric – uses ceramic piezo materials that deform when a current is applied, resulting in sound generation.
Electromechanical buzzers are traditional components in that they use a magnetic field produced by an electric current. They typically operate at lower voltages but higher drive currents than piezoelectric buzzers. Piezoelectric buzzers operate at larger frequency ranges than electromechanical types due to their more linear relationship between input frequency and output power level. Piezo buzzers also have larger sound pressure levels (SPL) and higher resonant frequencies than electromechanical buzzers.
Using a buzzer as an audible medical alarm can offer ease and elegance of design-in, high performance, low cost, and high reliability – as long as you comply with the guidelines of the IEC standard discussed. To make this aspect of medical alarm design simpler, manufacturers, such as CUI Devices, have created specific medical buzzers that meet those IEC 60601-1-8 guidelines.
These specialized buzzers create tones that correspond exactly to those requirements set out by the IEC standards for different applications, reducing the steps required by you as the designer in creating a system. As examples, these include the following tones as indicated by Table G.4 within the guidelines (click the links below to listen to the specific tones):
General tone: A more generic tone for non-specific applications.
Ventilation tone: An inhalation sound with a pause followed by an exhale.
Oxygen tone: An irregular sound with stylized dripping or saturation sounds.
Cardiovascular, ventilation, and oxygen tone waveforms (Image source: CUI Devices)
Using Speakers in Medical Equipment
IEC 60601-1-8 focuses a considerable amount of attention on the communication challenges, the required waveforms, and the environments in which medical equipment is found. However, it does not provide a significant amount of information on the actual physical equipment to be used in medical equipment applications. As such, while buzzers are an extremely popular option due to their low power requirements, high power to sound-level ratio, and general robustness, speakers can also be used in medical equipment.
Speakers may not be as power frugal as buzzers, but they make up for it with increased flexibility in what sounds they can reproduce and, in some cases, improved sound quality. For example, if the medical equipment should also provide some sort of spoken audio alert in addition to the alarm, a buzzer would be unable to recreate a human voice, thus making a speaker the appropriate choice.
You should be aware that speakers are more prone to “popping” noises when exposed to abrupt voltage changes and the IEC standards warn against these pops. This can be avoided with appropriate waveform shaping, careful software development, and hardware precautions against transients. As long as you follow these steps and select a speaker that can withstand anticipated environmental conditions, speakers are an excellent option for medical alarms. CUI Devices has created specific medical speakers designed to meet the IEC 60601-1-8 guidelines.
Conclusion
The use of audible alarms in medical equipment is expanding as both the number of alarms per device increases and the quantity of devices being used in healthcare settings expands. Audible medical alarms should help healthcare personnel easily identify the onset of an alarm condition, differentiate between a patient problem and an equipment problem, communicate the urgency of the response that may be needed, and easily indicate the location of the alarm signal.
This list of mandated requirements for an electronic alarm device is quite demanding, but also very necessary in a complex medical setting. The search for the avoidance of “sonic ambiguity” in medical alarms led to the development of the IEC 60601-1-8 technical standard. This guideline helped to spell out the requirements for the design and test of alarms in medical electronic equipment and continues to evolve to meet the requirements of a rapidly expanding field.
As mentioned, CUI Devices’ offers a range of medical buzzers compliant with the alarm signal requirements of IEC 60601-1-8. This family of piezo audio indicators produces low, medium, and high priority tones for general medical use as well as tones for specific medical applications, including ventilator, oxygen, and cardiovascular equipment. CUI Devices’ line of medical speakers is also designed to meet IEC 60601-1-8 to help simplify medical design integration.
More Info
Designers of medical electronic devices or systems can purchase the IEC 60601-1-8 document on the webstore page of the IEC website at www.iec.ch. Additional information on the standard and designing alarms in medical electronic equipment can also be located through the Association for the Advancement of Medical Instrumentation (AAMI), the National Center for Biotechnology Information’s National Library of Medicine, or the Journal of the Acoustical Society of America (ASA). CUI Devices’ line of medical speakers is also designed to meet IEC 60601-1-8 to help simplify medical design integration.
“CUI Devices’ focus and dedication to innovation fits right in with our modern, data-driven approach to sales”, said Kingsland Coombs, President of Control Sales. “With their extensive offering of electronic component products, CUI Devices can help a vast range of engineers. We look forward to working with them.”
CUI Devices is an electronic components manufacturer dedicated to nurturing the spirit of innovation by being more human—caring more than is expected, embracing evolution, taking a holistic approach, and having fun along away. The company specializes in an ever-expanding range of product technologies, including audio, interconnect, motion, capacitive encoders, sensors, and thermal management solutions.
Control Sales is pleased to introduce Diversified Plastics, Inc., a custom plastic-injection molder and additive manufacturer of high-precision, close-tolerance parts for medical devices, filtration, aerospace equipment, batteries, and a variety of other industrial devices. The company is a full-service contract manufacturer providing design for manufacturing assistance, mold construction and intricate molding as well as cleanroom assembly and packaging.
“We are thrilled to be working with the talented team Diversified Plastics.” said Kingsland Coombs, President of Control Sales. “Their commitment to innovative solutions, highest quality products and exceptional service will serve our OEM customers well.”
Diversified Plastics’ Acceleration Station®, powered by the Carbon DLS process, is 100 times faster than traditional 3D printing methods. The Acceleration Station produces high-quality plastic-production parts in days, not weeks, without tooling.
Mill-Max announces a new lineup of spring-loaded pins available with either pointed or flat tip plungers. These new pins expand our extensive offering of spring-loaded products, providing solutions for testing and other specialized connection requirements.
The LN Series of panel mounted Solid State Relays offer reliable back-to-back SCR switching up to 75 Amps at 528 VAC, coupled with a patented trigger circuit design which allows the SSR to switch resistive loads with minimal electromagnetic noise generated, ideal for use in commercial, residential and medical applications.
UL recognized and TUV certified, the LN series offers superior performance in applications that demand reliable switching and low emitted noise.
Additional features include:
Rating up to 75A @48-528 VAC
Zero Voltage Turn-On Switching
Conformance with IEC60947-4-3 Environment B for low voltage domestic, commercial and light industrial locations/installations
Mill-Max Manufacturing Corp., Inc. is proud to announce the development of new spring-loaded pins delivering high current carrying capacity in a small form factor. They are ideal for charging applications as well as for directly delivering power via cable or board to board interconnects. The reduced size makes them attractive for use in low profile and dense packaging designs.
This new product offering is available in three different termination styles: surface mount, through-hole, and solder cup. All three meet two of the most demanding requirements designers currently face: the need for more power and a reduction in overall device size.
Control Sales and Panasonic Industrial Devices Sales Company of America were proud to exhibit at the Arrow Technology Expo on Thursday, November 3rd, 2022 at the Stonegate Conference Center in Hoffman Estates, IL. A productive day of sharing new products and diving into the latest technologies. Thanks to Arrow for a great event!
