Imprecise encoder counting

Hi,

In a program I've successfully managed to recover the position of an engine using its encoder by counting edges and checking the left/right inputs for direction (in the program).

My encoder has channels A, A/, B and B/. 

My issue is, when I try to know the direction by checking B's state during A's edges, counting is erratic and incoherently slow compared to the first method.

I tried switching encoder channels with every possible combination (in case i made an error) and made a special small program to test (attached to this thread).

The encoder i use is 1,54kHz max (relative to the engine's max speed) and HTL (with 24v), i'm using a logo 8 24CE.

The program is as follow: inputs 11/12 allow to move left/right, encoder inputs are I3 and I4.

I3 is for edges and I4 for direction for the counter block B015, counter block B003 uses the original method of checking the direction with I11.

My message block shows B015's count and B003's count. When i try the program B015's count is about 2/3 of B003's, so it seems some edges for B015 are counting backward for some reason.

I'd like to know if this is a hardware issue, i've seen some threads stating that the logo is bad at handling encoders using two channels for direction, has anyone got specific informations on this?

Thanks,

Yann

Hi, thanks for your answer,

I highly doubt the encoder is flickering at 24rpm, that would be an exceptionnaly rare case.

I didn't know about EMC/EMV and looked it up, are you talking about the electronic part being screwed up? (again quite unlikely?)

I tried using the encoder at a very slow speed (by disengaging the rotor and rotating it manually) and everything works perfectly. Tried at max speed, everything's a mess (except for just counting edges which works fine).

Now, to me the most probable cause is, as you said, the Logo's time cycles messing things up. 

If I remember correctly it is 0.01s, which would explain the mess.