Hi speed DC outputs on ML1400

Hello all,
Could someone please tell me what I have to do to disable the PWM/PTO function on high speed outputs 2,3,4 of a Micrologix 1400. I am just trying to use them as standard outputs.

Thanks in advance,
Roy

Just don't configure or create a PTO or PWM function involving those outputs, and they'll run just like normal outputs do.

Are the outputs not functioning the way you expect, are you getting an error message in RSLogix 500, or are you just curious about how the configuration works ?

I'm not getting any error messages on the PLC. This application is for a new piece of equipment not yet in production. When we force the output, the display shows the output on and the voltage toggles between 1.4(force off) and 1.8 (force on) DC volts. The programmer/installer wasn't even aware that there were 3 fast and 3 normal outputs in the group so I'm quite sure he just programmed the outputs as normal. That is why I thought you might have to do something to get the normal output function. One thing I did notice was that there was no wire going to the Com terminal for group two which is the one in question. Last week, when the three outs didn't work. He assumed it was the PLC and ordered a replacement. This machine is set for a trial run in the morning so I certainly appreciate the help.

You need to get a wire onto the second com.

On a ML1400 they can be grouped to switch different voltages, or polarity, that means each group uses a separate com.

When you get a new ML1400 there is a manual that show this.

I understand that each group has it's own common. In group two on this 1400, 2,3,4 are the fast outs and 5,6,7 are the regular. In group two there are actually two terminals that are "common" to the group: VDC2 and COM2. I obviously have 24+ going to VDC2 and tried 0VDC and nothing at all on the COM2 terminal. 5,6,7 work fine in either config. But I can't get anything out of 2,3,4.

By the way Ken, I double checked the program this morning and there is no set up for PTO/PWM. There just written like normal outs. ONLY THEY DONT WORK!!!!! AHHHHHHHH

Are you measuring with the terminal open or is it attached to its load?

Hi Bernie,
When we couldn't get the starters to pull in, we disconnected the output wires so the voltages read were without the load.

With a load connected and 0VDC to the COM2 can you force and measure? Make sure the laod is within the current specs of the output.

Bernie,
I'm not currently at work so I'll have to do that measurement tomorrow. In the mean time, could you explain to me how and why the fast outputs should have to be wired differently than the regular outputs in that same group (group 2). In the AB documentation, all 6 outs in group two are listed as FET. Are fast outputs and FET two different things?

BTW: the load for all 3 outs in just a small Ormron 24VDC cube relay.

Thanks for the help,
Roy

rrparker07 said:

BTW: the load for all 3 outs in just a small Ormron 24VDC cube relay.

Click to expand...

I saw this reply, and it jogged my memory. A while back there was someone using some 24 volt relays that had built in suppression.

This is the thread
http://www.plctalk.net/qanda/showthread.php?t=43592&highlight=socket+diode

The problem was he had the polarity wrong and the diode was pulling down the power supply.

Have you checked your relays for polarity?

Thanks for the thought Vaughn, but my problem is I can't get the outputs to show voltage even with the load disconnected.

Re: Fast vs non-Fast FETs, without a detailed schematic it would be a pure guess as to what differentiates them. Though possibly a difference in protection circuitry around the FET may account for speed and characteristics of measured voltages.

Thanks to all whom offered their input.

WHO WOULD'VE BELIEVED that Allen Bradley would make two 1400's with the exact same defect. After the third processor arrived this morning by express courier, we hooked it up and it ran just fine the way it was originally wired.

When the second PLC had the same problem, I assumed it was something on our end. I should have remembered what my Dad said when you ***-u-me something.

Thanks again,
Roy