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Pepperl+Fuchs Blog

Ask an Expert Industrial Sensors - Episode 8

Posted by John Appleson on Wed, Apr 15, 2015

This episode of Ask an Expert for industrial sensors examines and provides answers to interesting sensing questions we've received from customers just like you. We explore and answer these questions:

1. Magnetic sensor MB60-12GM50-E2: What is the performance of this sensor like if the sensing surface is less than 10 mm away from the sensor?

2. How does the magnetic field sensor 41FY1 work? Is it a two-part magnetic sensor?

3. What is the required target size for the inductive sensor NJ5-18GM-N-5M? Will a 1/8 in. wide keyway that is .03 in. deep on a 4 in. diameter shaft work?

4. I'm trying to connect an NBB5-12GM50-E0-V1 inductive sensor to a PLC, but I am unable to make the two work together correctly!

5. Do you have cable connectors? What about for specialty cable types?ask-an-expert-industrial-sensors-resized-600
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.

Transcript:

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

Tracy: Hi John, thanks for asking me.

John: The first question asks about the performance of the MB60-12GM50-E2 magnetic sensor, when the sensing surface is less than 10 mm away. Tracy, the customer states that they had one magnetic sensor show a spurious ON, then OFF, and ON again, when the sensing surface is about 3 mm away. The problem seemed to disappear when the sensor was pushed out to an 8 mm gap. Tracy, can you explain what's happening here?

Tracy: Yes, the sensing range specifications on the MB60-12GM50-E2 data sheet are based on this sensor's use with a specific magnet. It's our DM60 magnet. The size and strength of this - it activates the sensor when the gap is between 10 mm and 50 mm. So, if the magnet is closer or if it's farther away, the sensor's output may not be predictable, as the customer has discovered. That's why the 10 mm to 50 mm range is shown on the data sheet. Magnetic sensors also won't signal detection where the poles meet on a magnet, but if the customer uses a different magnet with the MB60-12GM50-E2 magnetic sensor, a magnet that is smaller or weaker than the DM60 magnet, they'll see a reduction in the uncertain part of the range when approaching either pole of the magnet. In fact, I've tested this sensor with a variety of magnet targets and found some for which the output stays on even if the target and sensor are touching. But we don't have any data that will allow us to predict the sensor's response based on size or strength of the magnetic field target. That's something that needs to be determined in the application, like the customer is doing.

John: Ok, this customer wants to know how the 41FY1 magnetic field sensor works, and if it's a two-part magnetic sensor.

Tracy: Well, first of all, the 41FY1 is not the sensor, it's the magnet target that serves as a matching actuator for the magnetic field sensors in the 40FY series. The sensor and magnet are in identical housings, except the sensor includes a cable for the purpose of electrical connection. So yes, this is a two-part device consisting of the sensor and the matching magnet. 40FY sensors and other similar devices require power - both to generate the detection field they emit and produce their solid-state switching output. When powered, and in the case of two-wire devices with an appropriate load in series, an electromagnetic field is generated from the sensing face, and when the target magnet enters this field, the sensor's output switches states, so that's how they work.

John: So we have a customer who is wondering what the required target size is for the NJ5-18GM-N-5M inductive sensor. And, if a keyway that is 1/8th inch wide and thirty-thousandths deep on a 4 inch diameter shaft would work. Could you share your thoughts on this?

Tracy: Sure! The customer's sensor is an inductive sensor, so it's activated by metal entering its detection field. Based on the customer's description, the 4 inch shaft, assuming it's made of metal, would be the actual target for the sensor. The keyway would then be a place where you might want the sensor's output to switch, signaling the absence of a target. However, such a small area would not be large enough for this sensor, which has a detection area as wide as its 18 mm sensing face, at a very short range, and doesn't get as small as 1/8th of an inch until nearly the far end of its range. Even if you were to manage to set the sensor at a place where the output would switch at the 1/8th inch keyway, as soon as the shaft was rotating with any speed, that small gap in the metal target would pass by too quickly for the sensor to switch there. The general recommendation for such an application is to have the target be at least as large as the sensing face - so, 18 mm in diameter in this case, and for any spaces between targets to be twice that size, which would be 36 mm in diameter. That equates to a nearly one and a half inch wide keyway. In addition, that keyway would need to be much deeper than the thirty-thousandths this customer proposes, in order to ensure that the metal that remains in the gap does not influence the sensor's operation. In this case, the keyway should be at least 15 mm deep, which is about 6/10ths of an inch.

John: Alright, in this next application, the customer has an E0 type output inductive sensor (NBB5-12GM50-E0-V1) that is connected to a PLC, but he can't seem to get them to work together. He states that when he is testing with a 24 V supply and a voltmeter, he's able to read about 22 V from the output. The black wire, however, when he's connected to the PLC, which is a 24 V system, the PLC input is not activating. What do you think the problem is?

Tracy: Well, since the sensor operates correctly when tested with a voltmeter and a bench, the problem most likely has to do with the wiring to the PLC input card. The voltage difference, 24 vs. 22, is probably not going to matter to the PLC, but because the sensor is an E0 type, that is a three-wire device with NPN or current-sinking output, and that means that the switching output on the sensor's third wire - the black wire, is internally pulled down to DC negative and needs an external source, typically the 24 VDC, at his PLC input. But if the customer's input card provides a current sink instead, the DC negative instead of a source, then this sensor won't work with it, and he'll need to switch to a sensor that has PNP or current-sourcing output. Those are the E2 types.  

John: Ok, last question, Tracy. This customer is using one of our quick-disconnect sensors on a valve assembly, but he has very specific requirements for the cable that he wants to use. Does he have to use one of our standard cordsets, or are there other alternatives?

Tracy: We have a variety of cordsets available for use with our sensors, but there are times when exactly what the customer wants is not available. In a case like this, we do have an alternative for wiring the sensor. The customer can find the raw cable that meets his particular requirements, and make his own cordset using one of the field-attachable connectors we offer.

John: Well that concludes this segment of Ask an Expert. I'd like to thank Tracy for joining me today, and thank our audience as well.
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Topics: Inductive Sensors, Cables/ Cordsets, Ask an Expert, Magnetic Sensors

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