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Ask an Expert Industrial Sensors - Episode 1

Ask an Expert about Industrial Sensors

Are you an engineer? Technical support person? Responsible for plant maintenance? Then you know that there are thousands of possible sensing solutions available. How do you choose? What's your decision process when you think you should be using a photoelectric sensor, but then again, perhaps an ultrasonic sensor might be a better option? What are the advantages of using either a Light On vs. Dark On mode on a photoelectric sensor?
When confronted with all these possibilities, you can always rely on our product experts to help you. Welcome to our first episode of Ask an Expert, the weekly series where questions from customers just like you are answered! Feel free to ask us your sensing questions, and we'll do our best to reply with the whys and hows of a particular solution.

In this week's episode, we cover questions on photoelectric sensors and ultrasonic sensors...


John: Welcome to Ask an Expert. Hi, this is John Appleson, Marketing Manager with Pepperl+Fuchs. Today I'm joined by Casey Sutton. Casey works as an Application Engineer here at Pepperl+Fuchs. So, welcome Casey, and thanks for being here.

Casey: Hi John, thanks for asking me.

John: Ok Casey, let's get started. The first question asks about placing two RLK series photoelectric sensors side-by-side and using one large reflector, rather than two small reflectors. Casey, is this a good idea?

Casey: Not in this case. While it is true that you can use two retroreflective sensors with one reflector, you want to make sure that the sensors have cross-talk protection. If they don't, you have the possibility of the target being in front of one sensor, but the sensor not activating because it's receiving reflective light from the other sensor. With cross-talk protection, the sensors only sense their own emitted light.

John: Here's a question about an application where they are using a UBR250 ultrasonic sensor. This ultrasonic sensor was designed for space-restricted applications. It has a minimal deadband with a sensing range of 0 mm to 250 mm. Does that mean it can actually detect objects up to the face of the sensor?

Casey: Yes! The UBR250 Series reflex sensor was designed to work as a retroreflective sensor where it needs a reflector to function. The sensor is taught-in to the position of the reflector, and any target that comes between the sensor and the reflector activates the sensor.

John: In addition to the sensing range, this sensor has an adjustment range. Casey, what is an adjustment range?

Casey: An adjustment range is the range you have to adjust where the sensor sees the target. In the case of the UBR250 Series reflex ultrasonic sensor, the adjustment range refers to where you can place the reflector.

John: Another question about this ultrasonic sensor, Casey - The UBR250 sensor is a retroreflective mode sensor. Would it be a good selection when there is a background that needs to be suppressed?

Casey: That depends. If you have the ability and space in the application to install a reflector, then anything past this reflector would not be sensed. If mounting a reflector is not an option, then another one of our ultrasonic sensors would have to be used.

John: Well, if mounting a reflector is not an option, which ultrasonic sensor would you recommend?

Casey: Another one of our ultrasonic sensors, such as the UB100 Series, would sense the target up to a pre-defined, taught-in distance and suppress anything beyond that distance.

John: Well that concludes this segment of Ask an Expert. I want to thank Casey for joining me today, and thank our audience as well!

Protect your Industrial Cables and Cable Connectors!

Protect your industrial cables!

Pepperl+Fuchs' standard 22 AWG cordsets are rated for 4 A. But most main enclosures have a power supply that is much larger than the rating of individual industrial cables and devices.

So, what if there's a situation where an output overloads, pulling 10 A or 20 A through a 4 A rated cable? The wires will start to heat up, the voltage will drop, and the cable connectors may get damaged. The worst case scenario could be a fire.

To protect the end devices, fuses or breakers are used to open the circuit in the event of cable or device failure. To do it right, you really have to fuse every sensor or fuse groups of sensors so the current limit to the cables is below the 4 A limit.

Overload or short-circuit protection must also be considered with industrial bus systems. AS-Interface is an industrial bus that provides power and communication to modules on the network. This network is designed to be completely field mountable so the use of fuses or breakers for every bus drop may not be convenient. If a power supply that is rated 4 A or less is used to power the entire bus, then no problems exist. The drop cables can’t be overloaded because the power supply can’t provide that much current.

Alternatively, what if you use an 8 A AS-Interface power supply and a 12 A auxiliary power supply? We have an auxiliary power cable with larger 13 AWG conductors that are rated for 12 A. It is possible for the drop cables off the AS-Interface trunk to be overloaded. What to do? You can’t put fuses in all the drop lines; there's nowhere to put them. And the fuse itself may interfere with AS-Interface communication. You could just mount everything to the trunk line so no drop cables are used at all, but that isn’t convenient or practical.

A simple solution comes with our series of PTC-protected drop connectors.
The idea is to limit the current that is delivered to the drop in order to protect the cable. With these cable connectors, the current is limited to 1.6 A, which is far below the 4 A cable limit. Once the short is removed or the end device is repaired, the drop cable will function normally and your network will come back up and run. LED indication on these protective devices will tell you where the short is so the problem can be easily resolved.

These drops are IP69K, washdown rated for use in the harshest conditions, and feature a 1 m pigtail with a straight M12 connector. They are available in an AS-Interface version and an AS-Interface/auxiliary version. Depending on quantity, we can provide additional versions with different connector styles and drop cable lengths.

This Valve Position Sensor Is Rugged and Outdoorsy

Valve sensor for outdoor use

Most valve position sensors on the market today are designed for process valve automation applications and environments where limit switch boxes with mechanical, magnetic, or inductive contacts are typically used to detect the position of the valve in valve actuators.

Industrial Sensors: Differences between No-load Supply Current and Load Current

Industrial Sensors and current consumption

The current consumption of an industrial sensor is a very important consideration. Knowing the current consumption of all your devices on a machine allows you to size wire properly and pick the right power supply for the application.

Moving from Wired HART Communication to WirelessHART

HART Communication

In a previous blog post, "General Characteristics of HART Communication", I went over the important aspects of HART, which is a wired communication technology that has been in existence since the 1980s. Naturally, technology does progress, and just like telephones moving from land lines to wireless, wired HART is moving to WirelessHART. Let's explore what you should know about WirelessHART, and what improvements it can offer to your plant communication.


Photoelectric Sensors Are at Home on the Automotive Factory Floor

Photoelectric sensors for automotive assembly

I recently had the opportunity to tour the body shop of an automotive assembly plant. Working for a company that makes sensors for this industry, I was looking forward to seeing our "heavy-duty, weld-slag resistant sensors with magnetic-field immune electronics that stand up to the rigors of the robotic welding cell."

6 Steps to Selecting a Fiber Optic Cable

6 Steps to Selecting Fiber Optic Cables

When selecting a fiber-optic cable, it is not as simple as “What fiber cable goes with this sensor?”  There are multiple factors that contribute to selecting the appropriate fiber-optic cable for your application. 

Why the Incredible G10 Housing is an AS-Interface Game Changer

G10 Module is a Game Changer for AS-Interface

AS-Interface is all about simplifying the designs of a control system, reducing the complexity of the wiring,cutting the cost of the installation, improving diagnostics, and making automation more productive.


General Characteristics of HART Communication

HART communication uses the BELL 202 telephone communication standard

Highway Addressable Remote Transducer

HART is a digital signal that rides on a standard 4 mA ... 20 mA process control loop. In the field of process automation, the 4 mA ... 20 mA loop is very steady. You may hear of it being referred to as “quasi-static,” as it doesn't change much. Field devices like mass flow, temperature, pressure transmitters, or valve positioners use this 4 mA ... 20 mA signal. HART information is extra information that you get back from your field instruments.
Historically, HART communication uses the BELL 202 telephone communication standard, which telephone land lines still use today. This standard was introduced in the early 1980s and uses Frequency Shift Keying (FSK) technology. FSK simply means that the information is keyed or coded into the frequency, which is how the data communicates back and forth. HART layers its digital communication signals on top of the 4 mA ... 20 mA control signal.

A drawback based on today's standards is the speed of HART communication, which is rather slow. HART is limited to 1200 bits/second and ranges from 1200 Hz to 2200 Hz. Information (1, 0) is represented by different frequencies. The HART signal creates 0s and 1s. A logic 1 is represented by 1200 Hz. A logic 0 is represented by 2200 Hz. On the plus side, HART communication doesn't interrupt the 4 mA ... 20 mA signal, and it allows a host application (master) to get up to three digital updates per second from a field device.

Back in the day when this technology was introduced, 1200 baud was screaming fast, but now it is painfully slow and just doesn't measure up to our expectations. As an example, a LAN (Local Area Network), in common use today, perks along at 100 Mbits/second. That's 1000 times faster than the BELL 202!

If the communication speeds are so slow, why do we continue to use HART communication for field instruments and devices? Well, the 4 mA ... 20 mA control signals with FSK are reliable and have been in use for decades. There is a large installed base of devices. By our estimates, there are at least 30 million HART-compatible field devices in use worldwide.  

Also, the HART information is easily extracted without interfering with the 4 mA … 20 mA signal used by the host system. Host systems are most commonly a distributed control system (DCS), programmable logic controller (PLC), asset management system, safety system, or a handheld device. HART enables two-way field communication to take place and makes it possible for additional information beyond the normal process variable to be communicated to or from a smart field instrument.

Interested in learning more about HART communication and solutions? Download our brochure:


What in the World are Cyber-Physical Systems?

What are cyber physical systems?

If you scan the Internet for the term Cyber-Physical Systems (or CPS) you will find many contributions discussing topics from mobile phones to time-aware software. CPS are objects that bring the physical (i.e., hardware) together with the computational world. In that sense, a modern car is an application of a CPS.

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