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jcwelch111
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RVDT

11/18/2013 1:51 PM

I have a 120 ppr resolution rotary pulse generator with NPN output. With the current configuration and speed of the index motor, the output signal frequency is ~60 Hz (varies with changing roll diameter). The PLC I/O accepts PNP input only. This application is really slow in comparison to high-speed counter capabilities. Is there an inexpensive counter module that would accept NPN input and provide PNP output?
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jcwelch111
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#1

Re: RVDT

11/18/2013 2:14 PM

Additionally, the pulse generator delivers a fixed 50µs ± 20% output pulse at the leading and trailing edge of a passing slot.
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JohnDG
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#2

Re: RVDT

11/18/2013 3:04 PM

What PLC are you using? Can't see it from here.

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jcwelch111
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#3
In reply to #2

Re: RVDT

11/18/2013 3:11 PM

Festo CPX w/ CoDeSys controller
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jcwelch111
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#4
In reply to #2

Re: RVDT

11/18/2013 3:31 PM

Here is a data sheet for the I/O module:

https://www.festo.com/cat/en-us_us/products_CPX_E_1
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JohnDG
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#7
In reply to #4

Re: RVDT

11/21/2013 7:58 AM

That link goes to a list of products. Which I/O module do you have?

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jcwelch111
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#8
In reply to #7

Re: RVDT

11/21/2013 8:24 AM

Sorry John. Part #:526257 CPX-8DE-8DA
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JohnDG
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#9
In reply to #8

Re: RVDT

11/21/2013 9:05 AM

What is the make/part no. of the rotary pulse generator? (Or better, please give a link to the datasheet!)

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jhhassociates
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#5

Re: RVDT

11/19/2013 4:57 AM

Schneider Electric (their Pheonix Contact Ltd range) Part No 2964319 £11.64 (approx $19) packaged as a DIN rail terminal. Available in Europe from RS Components Ltd. Elsewhere from Schneider stockholders.
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jcwelch111
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#6

Re: RVDT

11/21/2013 7:42 AM

Status update: I had already purchased a Keyence OP-5148 NPN to PNP converter. Procured an oscilloscope to analyze the waveform of the rotary pulse generator at the operating speed of the drive motor to which it is attached. Testing before and after the signal converter revealed no losses through the conversion. The actual output pulse was longer than the 40-60µs specified on the data sheet. Oscilloscope readings ranged from 80-98µs duration for the output pulse. The frequency of the signal at the given speed was 27-38Hz. The lowest debounce time for the I/O is 0.1ms. Decided to go with a lower resolution encoder that will provide 50/50 on/off rather than the fixed pulse output. I'll update again when the new encoder arrives.
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JohnDG
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#10
In reply to #6

Re: RVDT

11/21/2013 9:36 AM

IMHO the pulse generator is a stange choice - an incremental encoder would have given you the 50/50 square wave on each of the 2 outputs, provided immunity to false counting when stationary, and given directional information if needed. Still, if that's what you're stuck with it sounds like you're going in the right direction.

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Shyam
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#11
In reply to #10

Re: RVDT

11/23/2013 11:10 PM

John is right. To use these encoders you need D-F/F configuration in PLC to sample the direction for UP/DOWN counting along with PPR counts which is maximum 120 PPS here. Pulse counters in PLC normally accept 10kHz pulse rate and you never use switch or relay input for high speed pulse counting or position encoding.

As far as NPN to PNP interface change is concerned, that can be easily altered using a proper converter interface. See http://cr4.globalspec.com/comment/939010/Re-Replacing-an-NPN-Sensor-with-a-PNP-Sensor

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