Converter: 24V from PLC to TTL devices

Feb 25, 2011 34 Replies
J

too.

24V

somewhere.

Ah, then, no wonder I was confused. I was talking about a simple way of interfacing two circuits with common grounds, while it appears you were, and are, talking about how the Peter Principle can manifest itself in a blue-collar world, something totally unrelated!
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J

On a sunny day (Tue, 01 Mar 2011 09:14:23 -0600) it happened John Fields wrote in :

numbers somewhere.

An important point to notice, is that in industrial, and he was talking ->PLC

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U

Unless you are designing a one off project and you are prepared to go to the other end of the world to install it, you really have to design your device in such a way that a hardly literate local worker can install it.

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S

A trip to another city, or even across town, can pay for an awful lot of prevention. And if you assume illiterate idiots, you won't be too far off a significant portion of the time. That portion can cost you all your profit as well all your reputation.

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J

numbers somewhere.

Yes, of course, and when the modifications are done they should be done by someone who has the competence, and documentation, to do it correctly instead of by some illiterate grunt who can't tell the difference between 240VAC and 24VDC. My solution fulfilled the OP's request for something simpler than an opto, and used under the conditions he specified should function satisfactorily and present no problems. Of course setting up straw men is your prerogative, but it has precious little to do with the OP's query.
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J

On a sunny day (Tue, 01 Mar 2011 13:19:58 -0600) it happened John Fields wrote in :

I thought John Larkin was your sparring partner?

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J

It's hardly within your bailiwick to comment on how I should prosecute a design, but in this instance I'm not designing a product. This is USENET, and I was posting advice to a querant who wanted an answer to a specific question. He was afforded that answer, and it should be one of a number of solutions to the problem he described and, arguably, the least expensive. Whether or not he chooses to use my solution is his decision to make, of course, but I'd be interested in your critique of my design bearing in mind the OP's request.
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J

When you argue like he does you also become fair game.
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J

"querant" ?? What is that, a gay ant ?:-)

snipped-for-privacy@downunder.com is rapidly approaching killfile status. ...Jim Thompson

| James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Remember: Once you go over the hill, you pick up speed
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S

His uncle's lesbian sister?

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J

Bwahahahaha ha! ROTFLMAO! ...Jim Thompson

| James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Remember: Once you go over the hill, you pick up speed
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M

Or his dad's lesbian brother?

You can't fix stupid. You can't even put a Band-Aid? on it, because it's Teflon coated.
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J

Bloviating ;-) ...Jim Thompson

| James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Remember: Once you go over the hill, you pick up speed
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F

If the OP is concerned about 24VDC outputs then chances are his PLC is a simple 'source only' output which pulls the output to the 24 supply for activation and shuts off with no pulldown for deactivation. In such a case the diode circuit will not work very well.

Please view in a fixed-width font such as Courier.

. . . . . Logic supply . . +5V . ----- . | . / . \ 1K . / . \ . | _____ . +------> INPUT . | . 10K c . 24VDC PLC 1/4W |/ . SOURCE OUTPUT >--+--/\/\--+-------+----b-| NPN . | | | |\ . / / --- e . \ 560 \ 1.2K / \ | . / 2W / 1/4W --- | . \ \ |1N4148 | . | | | | . | | | | . . . COMMON . . . . . He can juice things up with some nickel-dime low impedance stuff for both pulldown and PLC line crosscoupling attenuation and also some attenuation at the input for speedup and logic switching around mid- swing of the PLC output transition- no filtering or Schmitt triggers needed in most cases. The 50mA loading is winging it- it's up to the OP to find out what he's working at a more detailed level.

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