Many of the automation systems that increasingly appear in our daily lives have a fundamental need to sense the presence and movement of human beings. Whether that system simply shuts off the lights to save energy at home or triggers an emergency response in a health care facility, accurate motion sensing is a crucial requirement.
Passive infrared (IR) sensors are a well-known, cost-effective motion sensing technology for these applications. Getting the most out of these sensors, however, requires some engineering expertise. In this post, we’ll examine some of most commonly asked questions about the capabilities of our passive IR sensors:
- How do IR motion sensors work? These sensors discern human movement by detecting incident IR radiation, which varies in proportion to the temperature difference between human body surfaces and the surrounding environment. The sensors, in essence, can distinguish the thermal signature emitted by a human being from the thermal signature emitted by walls, ceilings, floors and other inanimate objects.
- What infrared wavelengths are detected? Our most capable IR sensors detect infrared wavelengths 5 µm or longer. The human body emits 10 µm wavelengths.
- What do I need to know about ambient temperature? Pansonic IR Sensors operate in a wide ambient temperature range from –20 to 60ºC and are designed for indoor use only. Outside that operating temperature range, the sensor may output false detection signals. Keep in mind that changes in ambient temperature can also affect sensor performance. For example, detection can be more difficult in the summer because there tends to be a smaller difference between body and ambient temperatures than in the winter.
- Does clothing affect sensor performance? The amount and color of clothing can make a small difference in sensor performance. Because clothing affects the amount of IR radiation emitted by the human body, it changes the differential between human body and ambient temperatures. The effect of clothing, however, is minor compared to the influence of ambient temperature.
- What is the maximum sensing distance—and can it be adjusted? The best IR sensors have a nominal sensing distance that can range from 2 to 12 meters, depending on the model. This distance specification does not necessarily represent the farthest distance the sensor can detect. Instead, it’s the maximum distance at which sensing is guaranteed. IR motion sensors do not have an adjustable distance setting, but you can limit the sensor’s detection range by mounting it at an angle that blocks its field of view.
- How fast are IR motion sensors? IR sensors have a response time of about 0.5 seconds. The response time represents the interval between the actual movement and the detection of that movement. The duration of the sensor output signal after detection depends on the speed of movement and the magnitude of temperature difference. It usually averages to at least 10mS
- What types of applications should use IR motion sensing? This type of sensor is particularly well-suited to applications that require a wide detection area, even if that detection area that extends to walls and floors. IR motion sensors also excel at detecting even the slightest motions.
- And what applications should not? The broad detection area and sensitivity of IR sensors can also work against them in some applications. For example, these sensors do not offer adjustable distance settings required by some automation systems. They can also confuse humans and small animals. And their detection capabilities can be diminished in proximity to intense heat sources or materials that block IR radiation. In these cases, alternative sensing technologies, such as area reflective sensors, can be a good alternative.
- Are there different types of IR sensors for different tasks? Sensors come in different versions to meet specific detection requirements. At Panasonic, for example, our MP IR sensors come in seven versions. The standard standard sensor offers a wide horizontal detection ranges. Another sensor type specifically targets slight motion. The third type is a spot sensor which can limit the detection range—in small spaces, for example. The fourth offers a wide 12-meter detection area for use in large spaces. And the fifth version addresses battery-operated applications by offering power consumption as low as 1 µA. Two other low power models offer 2 and 6 µA, respectively.
If you’ve spent any time looking for the right connector to use in a smart phone or other mobile device, you might believe that all fine-pitch, low-profile connectors are created equal. But they’re not.
In spite of similarities in package size and pitch, at least on their datasheets, these connectors differ in subtle ways that can affect their reliability during the assembly process and in use. Here are the key technical factors to consider when looking for a reliable connector for use in mobile devices:
- Tolerates mechanical forces. The board-to-board and board-to-FPC connections within mobile devices have to withstand substantial forces–from insertion forces during assembly to shock and vibration forces in use. A robust contact geometry is the first line of defense against these forces.
- Contains the solder. The low-profile connectors used in mobile devices are susceptible to damage from solder rise. The best connectors will provide an integrated nickel barrier to keep the solder in its place.
- Resists corrosion. Corrosive gases generated during the assembly process can damage connectors, ultimately shortening their life. Look for connectors with an anti-corrosion surface treatment.
- Stays in alignment. Coplanarity of the connector pins may not be the most obvious product selection factor, but it directly affects insertion force and the connector’s ability to withstand repeated insertions. Look for connectors with the best coplanarity specs.
We’ve designed our fine-pitch connectors with all these technical factors in mind. Our Tough Contact construction is built around a metal bellows whose spring forces strike a balance between easy insertion and resistance to shock loads. The Tough Contact design also features a notched cross section to ensures a high-force, edge-to-edge contact between connector halves. This v-shaped notch has the side benefit of sealing out contamination from flux or other particulate. Our Tough Contact system also features an integrated nickel solder barrier and a proprietary anti-corrosive treatment. Our connectors also offer a best-of-class coplanarity of 0.08 maximum.
Our connector line for mobile devices includes board-to-board and board-to-FPC products starting as small as 0.35mm pitch to 0.8mm pitch and mated height of 0.6mm.
For help selecting a product for your application, contact one of our application engineers.
Not so long ago, all relays performed their switching duties through electromechanical means. Today, however, engineers can also opt for solid-state relays that use semiconductors to switch their output circuits. The choice between traditional electromechanical relays and the solid-state varieties comes often comes down to reliability and performance.
With no moving parts, solid-state relays avoid all the obvious mechanical failure modes associated with traditional relays. They also tend to offer desirable electrical characteristics and design advantages including:
- Low power consumption.
- Low leakage current.
- Stable on-resistance over lifetime.
- High reliability with extremely long life.
- Small size.
- Fast switching speeds.
- High vibration and shock resistance.
- No contact bounce or switching noise.
Keep in mind that solid-state are not created equal when it comes to these performance advantages. Optically-isolated relays, in particular, can outshine other solid-state devices that use electrical or magnetic operating principles.
To learn more about the operating principles of optically-isolated relays, how to apply them in different applications and how to maximize their long life cycles, download our white paper.
Engineers who specify electrical products for industrial equipment tend to have a good working knowledge of UL ratings. However, one rating that gives many engineers trouble is UL 1604, which certifies electrical components for use in hazardous environments.
We routinely field questions about UL 1604 and which products comply with it. Here are some answers.
What Is UL 1604? This rating applies to most types of electrical equipment, circuits and components operating in conditions that the National Electrical Code (NEC) defines as hazardous due to the presence of flammable gasses, combustible dust or ignitable fibers. The NEC categorizes these conditions as Class I for gasses, Class II for dust and Class III for fibers or flyings.
While referred to in North America as UL 1604, this standard has been supplanted by a global standard known as ANSI/ISA-12.12.01. The requirements are similar.
UL 1604 also addresses whether a flammable material is present as part of normal operating conditions or is present only during abnormal operations. The NEC refers to these two scenarios as Division 1 and Division 2, respectively.
Finally, UL 1604 considers different types of hazardous materials according to their NEC codes. Codes A, B, C and D segment different gasses and vapors according to their ignition temperatures. Codes E, F and G segment dusts according to ignition temperatures and conductivity.
Putting all the classes, divisions and codes together, UL 1604’s key provisions:
- Apply to equipment, circuits, and components designed specially for use in hazardous locations the NEC classifies as Class I and II, Division 2 and Class III, Divisions 1 and 2.
- Provide minimum requirements for the design, construction and marking of electrical equipment for use in these locations.
- Cover Class I, Division 2 equipment in which the circuits and components are incapable of causing ignition of a specified gas under normal operating conditions.
- Cover equipment constricted to reduce or exclude the entrance of dust in Class II and Class III locations.
- Apply under specific atmospheric conditions, including ambient temperature between 5 and 40 C, oxygen concentration no greater than 21% and nominal barometric pressure of 1 atmosphere.
- Apply to portable battery powered equipment, other than flashlights, in locations defined as Class I and II, Division 2 and Class III, Divisions 1 and 2.
UL 1604 has other provisions too and excludes some electrical equipment covered by other standards. If you’re in doubt whether a specific component or piece of equipment is compliant, it’s a good idea to contact one of our application engineers.
Which Products Comply? A wide variety of industrial equipment falls under the guidelines of UL 1604. So we’ve made the effort to develop and test a number of compliant electrical components. Among them are:
- DK Relays. 10 Amp Miniature polarized Power relays
- DS Relays. 2 Amp high switching Signal relay
- PA Relays. 1a 5A Slim Power relay for Interface
- PF Relays. 1a/1c 6A Slim Power relay
For more information on UL 1604 compliance, contact Jane Awittor.
Optically-isolated relays inherently have a long lifespan, thanks to their lack of moving parts and the robustness of their solid state electronics. You can, however, make them last even longer by accounting for LED power losses.
Keep in mind that LED power does not remain constant over time. Instead, all LEDs experience a power loss in proportion to the time that current is applied to them. With optically-isolated relays, including PhotoMOS, this loss of LED power affects the device’s operating characteristics and lifecycle.
Rising Currents. As LED power falls, the relay’s operating currents will rise accordingly. On a typical PhotoMOS relay, for example, LED power might drop by roughly 3% after a 5 mA input current has been applied for 100,000 hours. As a result, the relay’s operating (IFon) and turn off (IFoff) currents would rise from their initial value by 3%.
This change in the electrical characteristics of the PhotoMOS has lifecycle implications. As LED sensitivity degrades with continues usage, more current is needed to generate the same amount of light. This light is used to charge the gates of internal MOSFETs and ultimately turn the relay on.
Slower Turn On Time. The turn on time of optically-isolated relays slows as LED power falls. Going back to our example of a 3% degradation of LED power after 100,000 hours at 5mA, the turn-on time would likewise slow down by 3%. Put differently, a PhotoMOS with a turn-on time of 0.03mS out of the box will have a turn-on time of 0.0309 mS after 100,000 hours of use at 5 mA.
This slowdown occurs because light intensity diminishes, which reduces the voltage and current output of the photo diode array in the IC. So it takes more time to bias the MOSFET gates.
Elevated Temperature Effects. At elevated ambient temperatures, more LED current is needed to generate the same amount of lamination. This lamination will then be converted to produce the necessary electrical voltage and current to charge the gates of MOSFETs and maintain ON state.
Careful design is required to set up the series limiting resistance of the input LED to ensure proper operation of the relay across the operating range of the relay.
In many applications, the electrical change related to optically-isolated relays may not make a practical difference. Adding 3% to an already fast on-time, for instance, won’t matter in every application.
Yet even incremental changes in performance or lifecycle can be significant in cutting edge applications. Examples include high-speed test and measurement systems.
In these cases, the datasheet alone won’t tell you whether you have picked the right relay for the job. You will have to evaluate the relay based on the electrical characteristics that will emerge after an operating time horizon that corresponds to your application.
For more information on how LED power losses will affect your application, contact Aiman Kiwan.