RPM sensor for sprocket teeth

Greg640 · Nov 2, 2008

Hello,

Is there anyone out there with experience getting an RPM signal off sprocket teeth and into an LG Master-K120S PLC?

I have hall-effect sensors picking up pulses from sprocket teeth. I have set the high-speed counter function in the PLC to the RPM function, with all the inputs and settings per the manual. But, no worky.

The Input Specification is 24VDC (7ma), with on voltage of 20.4-28.8VDC and off voltage of 6VDC. Do I need some kind of gizmo to get the hall-effect sensor signal up to the proper input voltages?

Thank you for any advise that may help.

hpl · Nov 2, 2008

which sensors do u use? something thats designed for the job or custom electronics? i searched hours last week for the right smd sensor for an electronics project couse i had to recognise the most smd sensors are only sensoring for ~40µs then have a wait cycle for 50-80ms before continuing sensing and are useless for fast signals.

Greg640 · Nov 3, 2008

The sensors were sold to me by a technician who says they are more than capable. I have a feeling that I need to amplify the voltage from the sensors before connecting to the PLC. But, I don't know how to do that. I would really appreciate a suggestion from anyone having experience with this sort of thing.

krk · Nov 3, 2008

For gear teeth sensing we've always used a magnetic sensor....

Red lion magnetic pickups

briancr · Nov 3, 2008

As hpl mentioned it depends on the rpm.

We use a standard inductive proximity switch, as our machines are low rpm, max 300 rpm.

Greg640 · Nov 3, 2008

Thank you! Will look into it.

JesperMP · Nov 3, 2008

I repeat hpl's question:

hpl said:
which sensors do u use?

And what is the frequency of the pulses ?
To ask in another way, how many teeth on the sprocket and how fast does the sprocket rotate ?
With this information it is possible to give advice.

bkottaras · Nov 3, 2008

krk said:
For gear teeth sensing we've always used a magnetic sensor....

Red lion magnetic pickups

I 2nd this one.
Stricktly for picking up teeth on a sprocket.
Then speed may become an issue.
More info would be great.

BITS N BYTES · Nov 3, 2008

For sensing sprocket teeth a standard 18mm shielded proximity sensor should work just fine.
For sensing gear teeth a gear tooth sensor is required.

http://www.cherrycorp.com/english/sensors/pdf/GS1001-GS1002_Series.pdf

jcallis2669 · Nov 3, 2008

Hall effect sensors require the use of a magnet to conduct. A sprocket tooth does not produce a magnetic field, therefore a hall effect sensor will "no-worky". BITS AND BYTES has the right idea. A standard inductive proximity sensor should work just fine for your application.

BITS N BYTES · Nov 3, 2008

jcallis2669 said:
Hall effect sensors require the use of a magnet to conduct. A sprocket tooth does not produce a magnetic field, therefore a hall effect sensor will "no-worky". BITS AND BYTES has the right idea. A standard inductive proximity sensor should work just fine for your application.

Not true, the Hall-Effect sensor details I posted DO NOT require a magnetic field. They are designed to work with Gear Teeth.

jcallis2669 · Nov 3, 2008

Never heard of that, but I will take your word for it. Every sensor I have ever used using the hall effect principle needed a magnetic field to excite the sensor. What is the difference in the one you detailed and an inductive proximity sensor??

jcallis2669 · Nov 3, 2008

It seams from the schematic, there is an internal magnet inside the sensor housing. I guess a ferrous metal interrupts the internal magnets lines of flux to in turn allow current flow. Man its amazing the gadgets they come up with these days.

Sparkz · Nov 4, 2008

There's a slight chance Greg is using an analogue sensor that can be connected directly to a speedometer.

But in fact, he's leaving us hanging... Please specify type and brand, Greg!

Greg640 · Nov 16, 2008

Thank you all! You're great! But no worky.

Thank you all for the great posts. I have the Red Lion magnetic pickups installed, per the manuals. 180 teeth per revolution and 1000 RPM is well within the frequency range specifications on the sensor and PLC. Still, no worky. I think my problem is that I can't quite figure out the LS Master-K 120 PLC High Speed Counter function. Anyone out there familiar with this PLC and function?

RPM sensor for sprocket teeth

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