Posted: 9/3/2014 8:41:45 PM EDT
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OK, I am (slowly!) learning automation and PLCs.
I am playing with a pneumatic cylinder that has a feedback reporting to a servo-proportional valve. I have checked and double checked the wiring and it is right (now anyway). What is happening is the sensor isn't reading until the last half inch of the cylinder movement. It goes the full range of 0-10V, but there is 6" of stroke and it only changes in the last little bit. What have I done wrong? What should I check? I am wondering if something has come loose in the cylinder, but it is brand new, unused. Any suggestions would help. |
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Is the position sensor integral to the cylinder, or is it a separate component? There are a number of styles of sensors, can you post a pic?
You may try putting a meter on the leads for the sensor, and measuring the resistance while extending and retracting the cylinder. It should increase and decrease steadily over the entire travel of the cylinder. |
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Sounds like you have signal power and ground mixed up. Do like Joker says and look at the resistance between all three wires as you extend and retract the cylinder.
Or the PLC card for the feedback isn't set properly or you have a bad cylinder. Either way divide and triumph. |
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Hmmm... OK. I would do like I said before, and run the cylinder in and out with a meter on the sensor connections. It should change resistance proportional to the amount you move it (this is actually a handy situation for an old analog multimeter... its easier to track the needle than watch numbers change on a digital display). If resistance only changes in the last bit of travel (where it begins registering position), then you probably have a bum sensor in the cylinder.
Hope this helps! |
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It really depends on if it's just a proximity switch reading the end of stroke (which it usually is) unless there is an encoder of some sort reading the whole position.
ETA, it really depend on the application. You can use a cylinder to run something with say a recirculating ball screw that would have an encoder on the end of it to give exact positioning, or a simple cylinder stroke position which would normally just be proximity. |
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Ok,
Three wires; Brown, Blue, Black Blue to Brown Gives a constant resistance. Blue to black gives a resistance that climbs as the cylinder is compressed Black to brown gives a resistance that drops as the cylinder is compressed Both numbers go to ~0 and up to ~6.3kOhm So I know some things now, but Im not sure how to figure from that which ones are the feeback, power and ground. Ill think through it, but I made a C in circuits years ago and was happy with that! So I know it is a wiring issue, the cylinder is reporting right (or so it seems). |
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Quoted:
It really depends on if it's just a proximity switch reading the end of stroke (which it usually is) unless there is an encoder of some sort reading the whole position. ETA, it really depend on the application. You can use a cylinder to run something with say a recirculating ball screw that would have an encoder on the end of it to give exact positioning, or a simple cylinder stroke position which would normally just be proximity. It is supposed to be a full length encoder (I would say LVDT, but I don't know if that is what is in there.) |
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Quoted:
Ok, Three wires; Brown, Blue, Black Blue to Brown Gives a constant resistance. Blue to black gives a resistance that climbs as the cylinder is compressed Black to brown gives a resistance that drops as the cylinder is compressed Both numbers go to ~0 and up to ~6.3kOhm So I know some things now, but Im not sure how to figure from that which ones are the feeback, power and ground. Ill think through it, but I made a C in circuits years ago and was happy with that! So I know it is a wiring issue, the cylinder is reporting right (or so it seems). Are you getting linear feedback the whole length of travel? |
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Ok, this makes me believe that the blue and brown are my power and ground for the sensor. Leaving black for the feedback.
I think that was how I had it wired too, but I am not sure. I may have had one swapped. How far off am I? Like I said, circuits was a long time ago |
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Quoted:
Are you getting linear feedback the whole length of travel? Quoted:
Quoted:
Ok, Three wires; Brown, Blue, Black Blue to Brown Gives a constant resistance. Blue to black gives a resistance that climbs as the cylinder is compressed Black to brown gives a resistance that drops as the cylinder is compressed Both numbers go to ~0 and up to ~6.3kOhm So I know some things now, but Im not sure how to figure from that which ones are the feeback, power and ground. Ill think through it, but I made a C in circuits years ago and was happy with that! So I know it is a wiring issue, the cylinder is reporting right (or so it seems). Are you getting linear feedback the whole length of travel? Yes, so far as I can tell. |
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Quoted:
Does it have an ALE (absolute linear encoder) ? If I was sure what one was, I could try and tell you! 
I don't have a lot of documentation on the cylinder, but a good bit for the valve. I can call tomorrow for info, but I am at my show now, and I figured that ARFCOM had people that could help. Im gonna go try that new wiring order. |
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Quoted:
If I was sure what one was, I could try and tell you!
I don't have a lot of documentation on the cylinder, but a good bit for the valve. I can call tomorrow for info, but I am at my show now, and I figured that ARFCOM had people that could help. Im gonna go try that new wiring order. Quoted:
Quoted:
Does it have an ALE (absolute linear encoder) ? If I was sure what one was, I could try and tell you!
I don't have a lot of documentation on the cylinder, but a good bit for the valve. I can call tomorrow for info, but I am at my show now, and I figured that ARFCOM had people that could help. Im gonna go try that new wiring order. Google it.  The more I read your post, the more I'm thinking it does.
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Quoted:
Ok, Three wires; Brown, Blue, Black Blue to Brown Gives a constant resistance. Blue to black gives a resistance that climbs as the cylinder is compressed Black to brown gives a resistance that drops as the cylinder is compressed Both numbers go to ~0 and up to ~6.3kOhm So I know some things now, but Im not sure how to figure from that which ones are the feeback, power and ground. Ill think through it, but I made a C in circuits years ago and was happy with that! So I know it is a wiring issue, the cylinder is reporting right (or so it seems). It sounds like the feedback sensor is a potentiometer and black is the moving contact (wiper) while blue and brown are the energizing connections (one ground, one 5V or whatever the system expects). But the thing you haven't clarified, and this is Very Important is just what kind of sensor type is used for the position feedback. You can't always tell from the ohm readings, even though I guessed at it above. It might be analog (potentiometer), analog (magnetorestrictive), digital of one or other flavor, or even LVDT like someone else mentioned. These sensors are all VERY different as to what they need for a supply, and what kind of signal they return. We really need to know the actual part and MFR of the cylinder you're using to say for sure. ETA: the link to the Bimba cylinder doesn't clarify. It sounds like a potentiometer feedback, but you do need to be sure. Black seems to be the feedback though. |
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Quoted: NPN or PNP sensors? OP, does the card input supply +10 volts that the resistance of the cylinder sensor pulls down, or is it passive and expects the sensor to supply a voltage of 0-10V to it? If you post the part number of the cylinder and input card we could all look them up online and probably give you real helpful information. |
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Quoted: Sounds to me like it is only a prox switch. Did a lot of work with SMC pneumatic cylinders and quite a few had integral prox switches. Did you see where he said "servo proportioning valve"... The spongiest servo ever imagined but for some applications they work. |
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OK, Success!
Yall were right on with the wiring being swapped. Got it done like said above and it started giving readings in the middle of the stroke, but not changing on the ends (All of this has been done through the Servo valve software, Enfield S2 is the valve). The cylinder came from the supplier of the valve with no documentation or info or even model or maker markings on the cylinder. I can find that out tomorrow though. After I got the wiring right, the valve wouldn't move, but I could hear a small leak out one of the exhausts. Turns out the translation speed is set to near zero as a factory default, so when I got it move up, off she went! Still some tuning and tweaking to do, along with calibrating the stop locations, but I am very happy to have it working. Thanks to all who replied! Yall helped a whole lot. This is what happens when Mechanical Engineers try and play electrician... 
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