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IO-Link: End to Analog Sensors

With most sensors now coming out with an IO-Link output, could this mean the end of using traditional analog sensors? IO-Link is the first IO technology standard (IEC 61131-9) for communications between sensors and actuators on the lower component level.

Analog sensors

A typical analog sensor detects an external parameter, such as pressure, sound or temperature, and provides an analog voltage or current output that is proportional to its measurement. The output values are then sent out of the measuring sensor to an analog card, which reads in the samples of the measurements and converts them to a digital binary representation which a PLC/controller can use. At both ends of the conversion, on the sensor side and the analog card side, however, the quality of the transmitted value can be affected. Unfortunately, noise and electrical interferences can affect the analog signals coming out of the sensor, degrading it over the long cable run. The longer the cable, the more prone to interference on the signal. Therefore, it’s always recommended to use shielded cables between the output of the analog sensor to the analog card for the conversion. The cable must be properly shielded and grounded, so no ground loops get induced.

Also, keep in mind the resolution on the analog card. The resolution is the number of bits the card uses to digitalize the analog samples it’s getting from the sensor. There are different analog cards that provide 10-, 12-, 14-, and 16-bit value representations of the analog signal. The more digital bits represented, the more precise the measurement value.

IO-Link sensor—less interference, less expensive and more diagnostic data

With IO-Link as the sensor output, the digital conversion happens at the sensor level, before transmission. The measured signal gets fed into the onboard IO-Link chipset on the sensor where it is converted to a digital output. The digital output signal is then sent via IO-Link directly to a gateway, with an IO-Link master chipset ready to receive the data. This is done using a standard, unshielded sensor cable, which is less expensive than equivalent shielded cables. And, now the resolution of the sensor is no longer dependent on the analog card. Since the conversion to digital happens on the sensor itself, the actual engineering units of the measured value is sent directly to the IO-Link master chipset of the gateway where it can be read directly from the PLC/controller.

Plus, any parameters and diagnostics information from the sensor can also be sent along that same IO-Link signal.

So, while analog sensors will never completely disappear on older networks, IO-Link provides good reasons for their use in newer networks and machines.

To learn about the variety of IO-Link measurement sensors available, read the Automation Insights post about ways measurement sensors solve common application challenges. For more information about IO-Link and measurement sensors, visit www.balluff.com.

Analog Inductive Sensors Enable Easy Double Blank Detection in Stamping

Double sheet detection, also known as double blank detection, is an essential step in stamping quality control processes, as failure to do so can cause costly damage and downtime. Analog inductive sensors can deliver a cost-effective and easy way to add this step to stamping processes.

Most people have experienced on a smaller scale what happens when the office printer accidentally feeds two sheets of paper; the machine jams and the clog must be manually removed. Beyond the annoyance of not getting the printout right away, this typically doesn’t cause any significant issues to the equipment. In the stamping world, two sheets being fed into a machine can severely affect productivity and quality.

When two metal sheets stick together and are fed into a machine together, the additional thickness can damage the stamping dies and other equipment like the robot loaders, which can cause the production line to shut down for repairs. Even if the tool fares better and does not get damaged, the stamped product will likely be defective. In today’s highly competitive and just-in-time market, machine downtime and rejected shipments due to quality can be very costly.

A simple solution to detect multiple sheets of metal is analog inductive sensing. This kind of sensor offers non-contact sensing with a 0…10V analog output, which can be used to determine when the thickness of the metallic material changes. As the material gets thicker, or as multiple sheets of metal stack on top of one another, the analog output from the sensor varies proportionally. These sensors can be used with ferrous or non-ferrous metals, but the operating range will be reduced for non-ferrous metals. As shown in the graph (Image 1), as the distance with the metallic target changes, the analog output increases from 0 to 10V.

The pictures above, shows the technology in action. With a single sheet of aluminum, the output from the sensor is 2.946V, and for two sheets, the output is 5.67V. The user can establish these values as a reference for when there is more than one sheet of metal being fed into the machine and stop the equipment from attempting to process the material before it is damaged. These sensors can be placed perpendicular or inline with the target material and are offered in various form factors so they can be integrated into a wide range of applications.

The Benefits of Guided Changeover in Packaging

Today’s consumer packaged goods (CPG) market is driving the need for greater agility and flexibility in packaging machinery. Shorter, more customized runs create more frequent machine changeover. Consequently, reducing planned and unplanned downtime at changeover is one of the key challenges CPG companies are working to improve.

Many packaging machine builders are now providing fully automated changeover, where motors move pieces into the correct position upon recipe change. This has proven to be a winning solution, however, not every application can accommodate motors, especially those on older machines.

Guided changeover represents an opportunity to modify or retrofit existing equipment to improve agility and flexibility on older machines that are not yet ready to be replaced.

An affordable intermediate step between fully manual and fully automated changeover:

A measurement sensor can be added to provide position feedback on parts that require repositioning for changeover. By using indicator lights, counters or displays at the point of use, the operator is provided with visual guidance to reposition the moving part. Only once all parts are in the correct position can the machine start up and run.

By utilizing this concept, CPG companies can realize several key benefits:

Reduced planned downtime: Adding guidance reduces the amount of time it takes to move parts into the correct position.
Reduced unplanned downtime: Providing operator guidance minimizes mistakes, avoiding jams and other problems caused by misalignment.
Reduced waste: Operators can “dial in” moving parts quickly and precisely. This allows the machine to be fully operational sooner, minimizing runoff and scrap.
Improved operator training: Providing operator guidance helps CPG companies deal with inevitable workforce attrition. New operators can be quickly trained on changeover procedures.

Selecting the correct sensor

A variety of sensor technologies can be used to create guide changeover; it’s really a matter of fit, form and function. Common technologies used in changeover position applications include linear positioning transducers and encoders. Other devices like inductive and photoelectric distance sensors can be used with some creativity to solve challenging applications.

Available mounting space and environmental conditions should be taken into consideration when selecting the correct device. Sensors with enhanced IP ratings are available for harsh environmental conditions and washdown.

Analog devices are commonly used to retrofit machines with older PLCs, while IO-Link can be used in place of analog for a fully digital solution, enabling bi-directional communication between the sensor and controller for condition monitoring, automatic device replacement and parameter changes.

IO-Link vs. Analog in Measurement Applications

IO-Link is well-suited for use in measurement applications that have traditionally used analog (0…10V or 4…20mA) signals. This is thanks in large part to the implementation of IO-Link v1.1, which provides faster data transmission and increased bandwidth compared to v1.0. Here are three areas where IO-Link v1.1 excels in comparison to analog.

Fewer data errors, at lower cost

By nature, analog signals are susceptible to interference caused by other electronics in and around the equipment, including motors, pumps, relays, and drives. Because of this, it’s almost always necessary to use high-quality, shielded cables to transmit the signals back to the controller. Shielded cables are expensive and can be difficult to work with. And even with them in place, signal interference is a common issue that is difficult to troubleshoot and resolve.

With IO-Link, measurements are converted into digital values at the sensor, before transmission. Compared to analog signals, these digital signals are far less susceptible to interference, even when using unshielded 4-wire cables which cost about half as much as equivalent shielded cables. The sensor and network master block (Ethernet/IP, for example) can be up to 20 meters apart. Using industry-standard connectors, the possibility for wiring errors is virtually eliminated.

Less sensor programming required

An analog position sensor expresses a change in position by changing its analog voltage or current output. However, a change of voltage or current does not directly represent a unit of measurement. Additional programming is required to apply a scaling factor to convert the change in voltage or current to a meaningful engineering unit like millimeters or feet.

It is often necessary to configure analog sensors when they are being installed, changing the default characteristics to suit the application. This is typically performed at the sensor itself and can be fairly cumbersome. When a sensor needs to be replaced, the custom configuration needs to be repeated for the replacement unit, which can prolong expensive machine downtime.

IO-Link sensors can also be custom configured. Like analog sensors, this can be done at the sensor, but configuration and parameterization can also be performed remotely, through the network. After configuration, these custom parameters are stored in the network master block and/or offline. When an IO-Link sensor is replaced, the custom parameter data can be automatically downloaded to the replacement sensor, maximizing machine uptime.

Diagnostic data included

A major limitation of traditional analog signals is that they provide process data (position, distance, pressure, etc.) without much detail about the device, the revision, the manufacturer, or fault codes. In fact, a reading of 0 volts in a 0-10VDC interface could mean zero position, or it could mean that the sensor has ceased to function. If a sensor has in fact failed, finding the source of the problem can be difficult.

With IO-Link, diagnostic information is available that can help resolve issues quickly. As an example, the following diagnostics are available in an IO-Link magnetostrictive linear position sensor: process variable range overrun, measurement range overrun, process variable range underrun, magnet number change, temperature (min and max), and more.

This sensor level diagnostic information is automatically transmitted and available to the network, allowing immediate identification of sensor faults without the need for time-consuming troubleshooting to identify the source of the problem.

Distance Measurement with Inductive Sensors

When we think about inductive sensors we automatically refer to discrete output offerings that detect the presence of ferrous materials. This can be a production part or an integrated part of the machine to simply determine position. Inductive sensors have been around for a long time, and there will always be a need for them in automated assembly lines, weld cells and stamping presses.

We often come across applications where we need an analog output at short range that needs to detect ferrous materials. This is an ideal application for an analog inductive proximity sensor that can offer an analog voltage or analog current output. This can reliably measure or error proof different product features such as varying shapes and sizes. Analog inductive sensors are pure analog devices that maintain a very good resolution with a high repeat accuracy. Similar to standard inductive sensors, they deal very well with vibration, commonly found in robust applications. Analog inductive proximity sensors are also offered in many form factors from M12-M30 tubular housings, rectangular block style and flat housings. They can also be selected to have flush or non-flush mounting features to accommodate specific operating distances needed in various applications.

Application Examples:

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For more specific information on analog inductive sensors visit www.balluff.com.

Solving the Analog Integration Conundrum

These days, there are several options to solve the integration problems with analog sensors such as measurement or temperature sensors. This blog explains the several options for analog integration and the “expected” benefits.

Before we describe the options, let’s get a few things cleared up. First, most controllers out there today do not understand analog at all: whenever a controller needs to record an analog value, an analog-to-digital converter is required. On the other end of the equation is the actual sensor measuring the physical property, such as distance, temperature, pressure, inclination, etc. This sensor, a transducer, converts the physical property into an analog signal. These days with the advanced technologies and with the cost of microprocessors going down, it is hard to find a pure analog device. This is because the piezo-electronics inside the sensor measures the true analog signal, but it is converted to a digital signal so that the microprocessor can synthesize it and convert it back to an analog signal. You can read more about this in a previous blog of mine “How Do I Make My Analog Sensor Less Complex?”

Now let’s review the options available:

The classical approach: an analog to digital converter card is installed inside the control cabinet next to the controller or a PLC. This card offers 2, 4, or even 8 channels of conversion from analog to digital so that the controller can process this information. The analog data can be a current measurement such as 0-20mA or 4-20mA, voltage measurement such as 0-10V, +5- -5V etc., or a temperature measurement such as PT100, PT1000, Type J, Type K and so on. Prior to networks or IO-Link, this was the only option available, so people did not realize the down-side of this implementation. The three major downsides are as follows:

Long sensor cable runs are required from the sensor all the way to the cabinet, and this required careful termination to ensure proper grounding and shielding.
There are no diagnostics available with this approach: it is always a brute-force method to determine whether the cable or the actual transducer/sensor has the issue. This causes longer down-times to troubleshoot problems and leads to a higher cost to maintain the architecture.
Every time a sensor needs to be replaced, the right tools have to be found (programming tools or a teaching sequence manual) to calibrate the new sensor before replacement. Again, this just added to the cost of downtime.

The network approach — As networks or fieldbuses gained popularity, the network-based analog modules emerged. The long cable runs became short double-ended pre-wired connectors, significantly reducing the wiring cost. But this solution added the cost of network node and an additional power drop. This approach did not solve the diagnostic problems (b) or the replacement problem above (c ). The cost of the network analog module was comparable to the analog card, so there was effectively no savings for end users in that area. As the number of power drops increase, in most cases, the power supply becomes bigger or more power supplies are required for the application.
The IO-Link sensor approach is a great approach to completely eliminate the analog hassle altogether. As I mentioned earlier, since the sensor already has a microprocessor that converts the signal to digital form for synthesis and signal stabilization, why not use that same digital data over a smarter communication to completely get rid of analog? In a nutshell, the data coming out of the sensor is no longer an analog value; instead it is a digital value of the actual result. So, now the controller can directly get the data in engineering units such as psi, bar, Celsius, Fahrenheit, meters, millimeters, and so on. NO MORE SCALING of data in the controller is necessary, there are no more worries of resolution, and best of all enhanced diagnostics are available with the sensor now. So, the sensor can alert the controller through IO-Link event data if it requires maintenance or if it is going out of commission soon. With this approach, the analog conversion card is replaced by the IO-Link gateway module which comes in 4-channels or 8 channels.

Just to recap about the IO-Link sensor:

IO-Link eliminated the analog cable hassle
IO-Link eliminated the resolution and scaling issue
IO-Link added enhanced diagnostics so that the end users can perform predictive maintenance instead of preventative maintenance.
The IO-Link gateway modules offers configuration and parameter server functionality that allows storing the sensor configuration data either at the IO-Link master port or in the controller so that when it is a time to replace the sensor, all that is required is finding the sensor with the same part number and plugging it in the same port — and the job is done! No more calibration required. Of course, don’t forget to turn on this functionality on the IO-Link master port.

Well, this raises two questions:

Where do I find IO-Link capable sensors? The answer is simple: the IO-Link consortium (www.IO-Link.com) has over 120 member companies that develop IO-Link devices. It is very likely that you will find the sensor in the IO-Link version. Want to use your existing sensor? Balluff offers some innovative solutions that will allow you bring your analog sensor over to IO-Link.
What is a cost adder for this approach? Well, IO-Link does a lot more than just eliminate your analog hassle. To find out more please visit my earlier blog “Is IO-Link only for Simplifying Sensor Integration?“

Balluff offers a broad portfolio of IO-Link that includes sensors, RFID, SmartLights, Valve connectors, I/O hubs, and the gateway modules for all the popular fieldbuses and networks. Learn more at www.balluff.com

Real-Time Optical Thickness Gauging for Hot Rolling Mills

An ever-present challenge in hot rolling operations is to ensure that the material being produced conforms to required dimensional specifications. Rather than contact-based measurement, it is preferred to measure the material optically from a standoff position.

Light band gauging station in hot strip rolling operation detects material thickness in real time.

In some instances, this has been accomplished using two ganged analog optical lasers, each detecting opposite sides of the material being measured. Through mathematical subtraction, the difference representing thickness could be determined. One difficulty of the approach is the need to put a sensor both above and below the material under inspection. The sensor mounted below could be subjected to falling dirt and debris. Further, only a single point on the surface could be measured.

A new approach uses a scanning laser to create a band of light that is used to directly measure the thickness of the material. An analog or digital IO-Link signal represents the measured thickness to a resolution of 0.01mm with a repeat accuracy between 10μm to 40μm depending on distance between emitter and receiver. What’s more, the measurement can be taken even on red-hot metals. The illustration above shows a flat slab but the concept works equally well or better on products with a round profile.

To learn more visit www.balluff.us

Back to Basics: Analog Signals

Industrial sensors used for continuous position or process measurement commonly provide output signals in the form of either an analog voltage or an analog current. Both are relatively simple interfaces, but there are things to consider when choosing between the two.

Industrial sensors with current output are typically available with output ranges of 0 to 20 mA, which can be converted to 0-10 VDC by using a 500 Ω resistor in parallel at the controller input. Output ranges of 4 to 20 mA, which can be converted to 1-5 VDC by using a 250 Ω resistor in parallel at the controller input. Although it requires a shielded cable, current output allows use of longer cable runs without signal loss as well as more immunity to electrical noise. It is also easily converted to voltage using a simple resistor. Most, but not all, industrial controllers are capable of accepting current signals.

Industrial sensors with voltage output are typically available with output ranges of:

0 to 10 VDC (most common)
-10 to +10 VDC
-5 to +5 VDC
0 to 5 VDC
1 to 5 VDC

One of the main advantages of voltage output is that it is simple to troubleshoot. The interface is very common and compatible with most industrial controllers. Additionally, voltage output is sometimes less expensive compared to current output. With that being said, compared to current signals, voltage signals are more susceptible to interference from electrical noise. To avoid signal loss, cable length must be limited. Voltage output also requires high impedance input and shielded cable.

To learn more about this topic visit our website at www.balluff.us.

How Do I Make My Analog Sensor Less Complex?

So, you have a (or many) analog sensor in your application or system and they could be 4-20mA signal or 0-10V or even -10- +10V signal strength. You probably know that installing these specialty sensors takes some effort. You need shielded cables for signal transmission, the sensor probably has some digital interface for set-point settings or configuration. In all, there are probably 6-8 at minimum terminations for this single sensor. Furthermore, these expensive cables need to be routed properly to ensure minimal electromagnetic interference (EMI) on the wire. To make matter more complex, when its time to diagnose problem with the sensor, it is always on the back of your mind that may be the cable is catching some interference and giving improper readings or errors.

On the other hand, the cost side also is little tricky. You have the state of the art sensor that requires expensive shielded cable and the expensive analog input card (which generally has 4 channels- even if you use single channel), plus some digital I/O to get this single sensor to communicate to your PLC/PAC or controller. You are absolutely right, that is why people are demanding to have this sensor directly on their network so that it eliminates all the expensive cables and cards and talks directly to the controller on express way– so to speak.

Recently, there has been an explosion of industrial communication networks and fieldbuses. To name a few: EtherNet/IP, DeviceNet, PROFINET, PROFIBUS, CC-Link, CC-Link IE, Powerlink, Sercos, and the list goes on. As a machine builder, you want to be open to any network of customer’s choice. So, if that is the case, having network node on the sensor itself would make that sensor more bulky and expensive than before — but not only that, now the manufacturers have to develop sensor connectivity to ALL the networks and maintain separate inventory of each type. As a machine builder, it does put lot more stress on you as well to maintain different Bills of Materials (BOMs) for different projects – most likely – different sourcing channels and so on.

So far what we discussed are two extremes; the way of the past with shielded cables and analog cards, and a wishful future where all devices are on the network. There is a middle ground that bridges yesterday’s method and the wishful future without adding any burden on manufacturers of the sensors or even the machine builders. The solution is IO-Link. IO-Link is the first standard (IEC 61131-9) sensor actuator communication technology. There are over 100+ members in the consortium that produce wide variety of sensors that can communicate over IO-Link.

If a sensor has IO-Link communication, denoted by , then you can connect a standard M12 prox cable — let me stress– UNSHIELDED, to connect the sensor to the IO-Link port on the IO-Link master device. That’s it! No need to terminate connections, or buy expensive hardware. The IO-Link master device typically has 4, 8 or 16 ports to connect various IO-Link devices including I/O hubs, RFID, Valve connectors and more. (see picture below)

All signal communication and configuration now occurs on standard 3 conductor cable that you are currently using for your discrete sensors. The IO-Link master in turn acts as a gateway to the network. So, the IO-Link master sits on the network or fieldbus and collects all the sensors or discrete I/O information from devices and sends it to the controller or the PLC of the customer choice.

When your customer demands a different network or the fieldbus, the only thing that changes in your question is the master that talks to a different protocol.

In my next blog we will discuss how you can eliminate shielded cables and expensive analog cards for your existing analog sensor. Let me give you a hint– again the solution is with IO-Link.

You can learn more about IO-Link at www.balluff.us.

What’s best for integrating Poka-yoke or Mistake Proofing sensors?

Teams considering poka-yoke or mistake proofing applications typically contact us with a problem in hand. “Can you help us detect this problem?”

We spend a lot of time:

talking about the product and the mistakes being made
identifying the error and how to contain it
and attempting to select the best sensing technology to solve the application.
- sometimes it is a vision solution for error proofing
- many times it is a sensor solution for error proofing

However this can sometimes be the easy part of the project. Many times a great sensor solution is identified but the proper controls inputs are not available or the control architecture doesn’t support analog inputs or network connections. The amount of time and dollar investments to integrate the sensor solution dramatically increases and sometimes the best poka-yoke solutions go un-implemented!”

“Sometimes the best poka-yoke solutions go un-implemented!”

Many of our customers are finding that the best controls architecture for their continuous improvement processes involves the use of IO-Link integrated with their existing architectures. It can be very quickly integrated into the existing controls and has a wide variety of technologies available. Both of these factors make it the best for integrating Poka-yoke or Mistake Proofing due to the great flexibility and easy integration.

Download this whitepaper and read about how a continuous improvement technician installed and integrated an error-proofing sensor in 20 minutes!

Tag: analog

IO-Link: End to Analog Sensors

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