Square Wave Problem With Micrologix

[seabiscuit101 0]

Hello all, this is my first post. I am using an AB Micrologix 1400 (1766-L32BXB Ser C FW 21). I was trying to generate a pulse train using the PTO instruction. I have modified PTOX funct. file. The ladder is just a simple XIO followed by PTO, (The Quick Start ladder from 1766-RM001). When I looked at the output waveform on my oscilloscope, I noticed that it wasn't a square wave. I decided to run it at several different frequencies to see how the wave form would change. At 10Hz i got a square wave. As I increased the frequency the falling edge became sloped and almost horizontal. Is this how the output should behave? The data sheet indicates a max frequency of 100kHz, but at frequencies over 150 Hz. The wave form looks like the output of SMPS. 

Edited 8 Jan 2019 by seabiscuit101

[jazzplayermark 2]

Did you connect the dc common to the comm2 terminal? Also do you any load on your output or are you just looking at it not connected?

 

[Fabianfe 0]

 

Hi. I have the same problem with the same PLC. But with the PWM function. As a load I put an R = 470 ohms. I am designing a circuit to convert that signal that the user manual says is PWM, but is not, to 0-10 volts DC. My English is pretty bad. Sorry

[panic mode 246]

what do you mean? what is the exact PLC you have? how exactly you wired the output and what did you use as program?

according to documentation this is only possible with BXB or BXBA unit, and only with embedded outputs, not expansion I/O. next, you cannot do this by only connecting resistor. PWM is analog in time domain. to get steady analog output PWM need to be filtered. so how exactly did you construct filter?