Direct Logic 06

First Post. I am an AB guy, recently came to work at a place that uses Direct Logic series micro PLCs. I have run into some irritating nuances with the DL06. None as bad as an issue I had with a Stepper Motor that places a lid on a can.

The DL06 apparently sets it Processor using an internal bit, and the stepper logic is also controlled by structured V memory locations (hardware driven).

My first day here, our maintenance manager asked me to tie into the main stepper motor PLC to obtain an output he wanted on a PFM. For more than month the output worked fine, but we began to get signal degradation from the stepper motor and it's accuracy became an issue. I've tried reading up on what exactly happened, but I'm getting nowhere. I was wondering if anyone else has run into this issue.

BTW, I tied into a the stepper motor PLCs expansion slot output card and directly into the input of another PLC we have on the floor. The reason behind this, the PLC we were reading the input from is on our network. This enables me to read the input to our Red Lion red box to display on the PFM.

Which output on the stepper card did you tie in to?

How long is the wire from the Stepper card to the input of the PLC?


BTW, in case you did not know, ADC tech support is free. Monday through Friday 9am to 6pm Eastern time. 1(800) 633-0405 or email .

Y116 in Main PLC to X16 on our 'Vision' PLC. The wire running to our Vision PLC is probably 25 ft. maybe 30.

I should clarify that it's not the output that I'm getting a degradation on, it worked fine. The stepper motor itself is losing pulses and hamming up. It would come too far back or counter clockwise and place the lid too far back on the can. Once I disconnected the wire, it cleared up.

I've contacted AD support and gone into this in length with them. They have not been able to give me a straight answer. I actually got an 'I don't know.'

Also, I was thinking maybe it's an issue with ground potential difference or a polarity issue, but that's not the case.

I am assuming that you ran two wires to the other PLC, both the signal wire and a common wire. Is this correct?

Also, what voltage is the signal, 120vac or 24vdc or ???

If the signal is 24vdc is this fed from the same PS that feeds the stepper?

Two wires. Signal and common. 24vdc.

The stepper motor is fed off of a different power supply entirely.

This is where I'm drawing a blank. I only tied in an output and I'm losing my pulse count. I used an entirely seperate output from anything used.

Actually, let me correct that. I ran one wire. AD told me NOT to tie in a common. I'm not sure if they were thinking that I was running one output from an expansion slot to the input on the same micro plc or what. This could have been my problem...

So you are connecting the common of the signal to the common of the inputs on the vision PLC and the signal to X16. Are you sure that the common for X16 is also the negative of the DC power supply for the vision system?

Are the commons for the two power supplies tied to ground or are they floating?

The commons are tied to ground but the X16 isn't negative.

Is the common (C3) for X16 on the vision PLC negative and have you verified this?

Each bank of inputs can be either sinking or sourcing and have a different common potential.

When X16 fired I read 24vdc

That still is not what I asked.

I want to know if the wire that feeds the C3 terminal of the input terminal strip on the vision PLC is wired to the negative of the power supply that feeds the inputs of the vision PLC or not.

Yes it is wired to the negative

If both negatives are grounded, then by connecting the two negative commons together you are forming a ground loop between the two PLC's which is feeding back and "hamming" up the stepper.