Red Lion pulse generator help

Hey Guys

So, I have a micrologix 1500 and I'm trying to get the HSC to count pulses from a RPGC rotary pulse generator. It seems like a simple setup, +24, common, shield, and the pulse output. I'm only getting a max of .3v output from the encoder and I'm wondering if this is why the HSC will not see the pulses. It appears on the multimeter that the encoder is reaching "0" in the cycles so I dont think I need a pull up resistor . Is there a minimum voltage needed to trigger the input? Or maybe something else I'm missing.

Thanks

Unless it will conflict with your other inputs wire DC COM 0 to +24VDC. The encoder is indeed a "Pull Down' type output according to the manual.

If you must maintain the common at the low side then tie a 1 K ohm 1 watt resistor between the input terminal and +24 VDC as a pull-up.

Based on the manual I found, you will need a pull-up resistor on the output.

http://www.redlion.net/Products/Groups/ShaftEncoders/ZCG/Docs/11027.pdf

"The ZCG, ZFG, and ZGG series of sensors have open collector outputs. An open collector output brings the uncommitted collector of the encoder switching device to the external world. Because the collector element is not associated with the sensor supply voltage, the sensor output collector may be “pulled up” to external voltages (40 VDC max.) different than the encoder supply voltage. NPN open collector outputs are current sinking devices. An output signal will not be generated unless a pull-up resistor is connected from the open-collector to the positive side of an external supply. The same supply can be used for powering the unit and for the pull-up resistor."



-Eric

Hey Bernie,
As you suggested, I did have the COM 0 wired to +24VDC with no luck and I just tried again (just to be sure). It appears that the HSC 0 is indeed working as I tried with another higher voltage input and I got pulses.
It seems like even if I set the encoder to its highest output point at .35V and touch the input, it still wont trigger the counter.
Seeing how I am still very green to this technology, Is there a sensitivity setting for the HSC input that I never knew about to filter out lower voltages? Also, do you have any idea of what the output voltage should be for this generator? I couldn't tell from the documentation.

Thanks,
Vin

Hi Eric,

It seems you answered my questions before I could finish the last reply! Thanks, I will try it tomorrow when I get some resistors, you think the same 1 K ohm 1 watt resistor that Bernie suggested?

The pull-up will pull (hence the name) the voltage towards 24V when the encoder output is OFF. When the encoder output turns ON, the transistor will conduct, and pull the voltage towards zero.

It really shouldn't matter what voltage reference you tie the COM terminal to. If you tie it to 24, the input will 'see' the 0V pulses. If you tie it to zero, the input will 'see' the 24V pulses. The encoder output is simply going 24-0-24-0-24-0, but with a single output encoder, you probably don't care which state is considered as 'ON' by the PLC.

1K should be fine.



-Eric

@ Eric and Bernie,

The Pull up did the trick. It works great at any RPM. Hard to believe it works accurately at such high rate of pulses.

Thank you both.
Vin

Glad to hear it works. Thanks for the update!...



-Eric