Beginner PLC and Application Questions

Hi, so I am just getting into PLC's for a project and am looking at using the Allen Bradley 2711C PanelView C600 in combination with a Micrologix 1200 PLC.

The plan is to have the panelview be the menu for the system which allows what specific tests will be run. This is communicated with the PLC via the serial connection and the PLC will then pulse a Motor Driver in order to set the correct motor directions/speed etc.

Basically, the motor driver is a 2 axis driver, it has a few different inputs (clock, direction, speed) etc that need to be pulsed with 5v signals.

I want to make sure the PLC, using relay outputs, can supply these pulses to the driver?

Also, is what I have detailed possible with this system? I am a little confused about how to go about all of this using only ladder logic but I'm assuming its possible. I appreciate any suggestions/comments

Thanks!

No, you need transistor outputs to drive a step signal. Preferably high speed outputs (aka PTO). There is no reason you can't get an expansion card for this on the ML1200.

Wow.. well big mistake on my part. I really hope Allen Bradley will let me exchange PLC's :\

I was under the assumption relay outputs would work for both DC/AC signals so I could just supply a DC 5v and turn on/off the outputs to create a pulse generator.

I'm looking over the choices here, how do i determine if i want sink/source or fet?

mike64b said:

Wow.. well big mistake on my part. I really hope Allen Bradley will let me exchange PLC's :\

I was under the assumption relay outputs would work for both DC/AC signals so I could just supply a DC 5v and turn on/off the outputs to create a pulse generator.

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Relay Outputs take time to cycle On-Off-On. Say something like 300 ms, so you aren't going to be moving anything too fast. Mechanical Contacts can also have bounce. As Damian said, Solid State is the way to go. Several of the MicroLogix Line have dedicated Inputs for Encoders, and Outputs for PTO and PWM. That is what you should be looking at.

Wow.. well big mistake on my part. I really hope Allen Bradley will let me exchange PLC's

Click to expand...

If you haven't opened the box, they should exchange the PLC.

I'm looking over the choices here, how do i determine if i want sink/source or fet?

Click to expand...

That will depend on what you are driving with the Outputs. Check the documentation and see what it requires.

Stu....

So looking over things I would probably want Sourcing outputs then?

EDIT: Nevermind, saw your response thanks..


Also very unfortunate to say... the box was opened to inspect it but PLC never used. :[

mike64b said:

So looking over things I would probably want Sourcing outputs then?

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The most common in PLCs is Sourcing Outputs and Sinking Inputs. However, when interfacing with other Electronics, it could be anything. Without information on what you are driving there is no way to know.

Stu....

So I looked at the different plc lines again, I require 15 of these sourcing outputs for a three axis motor driver which means in any case, I would've needed a 1200 PLC + expansion card anyways.. So I will have to get a 1762-OB16 module

So I will have to get a 1762-OB16 module

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I would check the AB Catalog to make sure that this will for you.

What you need to remember is when selecting a PLC and expandsion cards, that a Sinking card is whatever you connect to it (relay coil) to Ground of your power supply and a Sourcing card and provide posiive voltage to whatever you connect to it.

Mike, your distributor should be able to help you out with choosing the correct material. That is what they are for.

Right, from what I've verified, I need a sourcing card with atleast 15 outputs and this is compatible with my MicroLogix 1200.

Now, my next issue is the interfacing of the Allen Bradley PanelView and Micrologix. I see the panelview is programmed with an inbrowser programmer while the AllenBradley uses RSLogix.. Are there any documents on how the two communicate with each other? None of this seems very straightforward..

Thanks
Mike

Your assumptions may be leading you astray a little.

Performing motion control with Step/Direction is not usually a general-purpose function of a general-purpose PLC. The pulses required to drive a Step/Direction motion controller are very fast (often several kHz) and need to be very precise, so they can't be generated by ordinary ladder logic routines.

This is why the MicroLogix and many other small controllers have dedicated high-speed output circuitry that is meant to run Pulse Train Output and Pulse Width Modulated functions. These are usually only a few outputs per controller, built into the base I/O. Expansion I/O doesn't have these kind of functions.

The MicroLogix 1200 has only one of these fast outputs; the MicroLogix 1100 has two, the MicroLogix 1400 has three.

In addition (and this is probably what led you to the relay idea) these outputs need to be available for general-purpose use as well, so they're 24V DC, not 5V DC. You could use a step-down circuit involving a Zener diode for this, but it's not ideal.

I don't know any of the details about your motion controllers or the motion functions that you might need to perform, so I can't give much more advice than that.

When multiple axes of simple motion control need to be connected to a MicroLogix family controller, the go-to company is AMCI. They have a 1762-series module that can connect to the MicroLogix 1200:

http://amci.com/plc-modules/plcmodules-1762-micrologix-stepper-servo-controller.asp