Hello Guest it is May 14, 2021, 06:45:58 PM

Author Topic: PMDX expansion I/O survey  (Read 2203 times)

0 Members and 1 Guest are viewing this topic.

PMDX expansion I/O survey
« on: January 23, 2016, 05:07:54 PM »
PMDX is in the process of designing an I/O expansion board
to work with our SmartBOB series controllers for Mach4. We
would like to know what mix of features makes the most sense.

If we set the number of I/O points as 24, how many should
be inputs and how many should be outputs? These would be
fully conditioned signals, so doing both on the same pin
is not practical cost wise.

We are expecting to have inputs that are more or less universal.
They would work with contact closures, 5 volt logic signals,
and sinking (NPN) or sourcing (PNP) sensors.

The output signals will be more dedicated in nature. The types
under consideration are:

1) Electronic sinking only and rated for 5 VDC to 25 VDC with
   a current rating of 500 milliAmperes.

2) Electronic sourcing only and rated for 5 VDC to 25 VDC with
   a current rating of 250 milliAmperes.

3) Electronic with selectable sinking (NPN) or sourcing (PNP)
   that work with 5 to 25 volts DC with a current rating of
   250 milliAmperes.

4) Relay outputs with normally open contacts rated at 5 amperes.

5) Relay outputs with SPDT contacts rated at 5 amperes.

6) Light duty Solid State Relay outputs rated for 100 mA AC or DC.

7) Medium duty Solid State Relay outputs rated for 2 amperes AC only.

The output styles above are listed more or less in order of increasing
cost to implement. In general, outputs are more expensive than inputs.

How important are signals that are isolated from each other as well
as from the controller? This will require two terminals per signal and
will therefore increase costs. Are signals that are isolated from each
other more important for outputs than for inputs?

Would it be better to keep this I/O expander simple and offer a different one
that is an adapter to connect to Opto22 style module racks to accommodate
more diverse needs?

Comments on other considerations not mentioned above are also welcome.

Your feedback and the reasoning for it will be appreciated.

Steve Stallings
www.PMDX.com

PS - The snow here is NOT delightful. Over 21" and still coming!
Steve Stallings
www.PMDX.com
For PMDX product support, please use PMDX forum or direct email for quickest response. We do not use this forum as our primary product support site.
Re: PMDX expansion I/O survey
« Reply #1 on: January 23, 2016, 05:35:54 PM »
My personal feeling coming from the PLC world is solid state outputs to 24vdc sinking or sourcing as I always try to protect the computer I/O from the real world with easily replaced plugin relays.  In my world lightning is a fact of life and and isolation is really important.  I'd much rather blow a discrete module in or out than a whole I/O board or the CPU. I like the I/O to do billions of cycles and then select the discrete solid state I/O or relays to match the actual load driven. Of course discrete costs more, but less than being down when bad stuff happens.

Offline poppabear

*
  • *
  •  2,233 2,233
  • Briceville, TN, USA
    • View Profile
    • S S Systems, LLC
Re: PMDX expansion I/O survey
« Reply #2 on: January 27, 2016, 08:54:04 AM »
Thoughts embedded:

If we set the number of I/O points as 24, how many should
be inputs and how many should be outputs? These would be
fully conditioned signals, so doing both on the same pin
is not practical cost wise.
>>>I guess do a 1/3, 2/3 split, i.e. 8 outputs and 16 inputs
>>>But, since you dealing with a processor, can't you do a native 32 I/O?


We are expecting to have inputs that are more or less universal.
They would work with contact closures, 5 volt logic signals,
and sinking (NPN) or sourcing (PNP) sensors.
>>>Can you make the inputs volt range from 5-30 or so, to cover a 24v system?
>>>It is kind of a PIA to do a split DC system, i.e. a 5v side and a 24v side.


The output signals will be more dedicated in nature. The types
under consideration are:

5) Relay outputs with SPDT contacts rated at 5 amperes.
>>>I personally like this one the best, it give the MOST flexibility.
>>>The user does NOT have to understand sinking/sourcing concepts,
>>>You can control AC or DC, in a N/O, N/C (or both) per Output point.
>>>IF you need to switch MORE than 5a, then you can go to a secondary
>>>relay for that point


The output styles above are listed more or less in order of increasing
cost to implement. In general, outputs are more expensive than inputs.

How important are signals that are isolated from each other as well
as from the controller? This will require two terminals per signal and
will therefore increase costs. Are signals that are isolated from each
other more important for outputs than for inputs?
>>>Can't you just run a an opto-isolator IC chip for each block of 8,
>>>and have those IC's in a IC socket so if you blow one, you can just
>>>order a replacement chip that the user can just swap it out.
>>>I think you should have isolation on both the input and output side.
>>>Really an Iso chip is what, less than a dollar, and to put it into your
>>>board your not really adding that much board size/cost,
>>>and other opto conditioning circuits would not add that much.


Would it be better to keep this I/O expander simple and offer a different one
that is an adapter to connect to Opto22 style module racks to accommodate
more diverse needs?
>>>Offer BOTH, the above native board, and an optional Opto22 style adapter board.
>>>Opto22 is EXPENSIVE and not a lot of bang for the buck.
>>>The person that wants to use Opto22, is in reality getting away for "Hobby" level pricing.


Comments on other considerations not mentioned above are also welcome.
>>>PLEASE offer an "Adapter" or "Mounting" system in where we can mount
>>>Your smart bob, and your other products on to a DIN rail system!


Your feedback and the reasoning for it will be appreciated.
>>>No.......... THANK YOU for your fantastic products and community involvement!

Steve Stallings
www.PMDX.com
« Last Edit: January 27, 2016, 08:55:50 AM by poppabear »
Commercial Mach3 & Mach 4, Design/Build/Retrofit CNC and Industrial machines.
http://www.ss-systems-llc.com/
Re: PMDX expansion I/O survey
« Reply #3 on: January 29, 2016, 11:06:14 AM »
Greetings.

I'm very happy to hear about a pure IO board. Trying to create a pendant or more complex IO has been a challenge.

If you have 24 I/O, I would say that the 16 IN, 8 Out split is standard. However, as poppabear mentioned, a 16 In, 16 Output would also be welcome.

I'm approaching this from two angles, 1. A general I/O board that would drive machine outputs, coolant pumps, solenoids, etc. The second would be something that I could embed in a pendant that is using mostly switches and lit pushbuttons.

For the pendant, LED pushbuttons @24 volts are around 25-30 mA. Even the incandescent ones are usually < 100mA. For those types of loads, one of the direct sync/source options would work. For machine outputs, while I like the idea of using sink/source outputs and sizing cube relays/contactors for the output loads, it may be simpler to provide a relay output. Driving an inductive load requires protection that some people may not put in. I've seen blown output drivers from a non-protected inductive load dumping itself back into the driver. (But, I've also seen fused relay contacts from the same thing.)

I'm leaning towards a sink/source output board with inductive load protections on board. That would save the outputs from people hooking relays/contactors up directly without putting the freewheeling diode in. It would allow a small board for driving pushbuttons and other pendant type I/O. However, I do like the idea of an expansion board for the diversity. But rather then doing an opto22 style expansion, perhaps a stacked board with just the relays. The board stacks with standoffs and a simple header type connection to the board itself. (if you do a 16 in/16 out, then you could bank the outputs and support 8 relays on an expansion board, and stack 0, 1, or 2 to get the outputs you need. Sorry, I'm digressing.)

I'm also voting for the inputs to support 5-30 volt inputs directly. (I believe that is what you were mentioning, but I just wanted to confirm.)

I also wanted to say thanks for the products and all your work. Great stuff coming out of your shop.

And ya, the snow sucked. I'm up in MD, and we're still digging out.

Jim

Re: PMDX expansion I/O survey
« Reply #4 on: January 31, 2016, 03:53:29 PM »
Responses mixed with quotes below:

>>My personal feeling coming from the PLC world is solid state outputs
to 24vdc sinking or sourcing

Solid state outputs are going to be available. The choice that we are
left with is to also offer a relay version.

The solid state outputs will be capable of operating as sourcing or sinking,
with an interface voltage range from 5 volts DC to 25 volts DC.

Another choice is how important it is to choose sourcing/sinking for a bank of
outputs, or to allow individual selection. The latter requires more connectors.

>>Can you make the inputs volt range from 5-30 or so, to cover a 24v system?

As stated above, the sourcing and sinking outputs will have a normal operating
range of as low as 5 volts and high as 24 volts nominal.

>>I personally like this one (relays) the best, it give the MOST flexibility.

We will try to offer relays as an optional configuration.

>>Can't you just run a an opto-isolator IC chip for each block of 8,
>>and have those IC's in a IC socket so if you blow one, you can just
>>order a replacement chip that the user can just swap it out.

The reasonably priced driver chips that can handle both sink or source up to
24 volts come in surface mount packages. Also, sockets introduce reliability
and cost issues.

>>I think you should have isolation on both the input and output side.

That is a given.

>>Opto22 is EXPENSIVE and not a lot of bang for the buck.

Support for Opto 22 would likely be a different board. We expect it to be used
mainly for retrofits where the Opto 22 racks and modules are already in the machine.

>>PLEASE offer an "Adapter" or "Mounting" system in where we can mount
>>Your smart bob, and your other products on to a DIN rail system!

DIN rail trays will be offered for the expansion board as well as for the PMDX-426
that it is designed to work with.

>>Trying to create a pendant or more complex IO has been a challenge.

The board being considered is for industrial I/O and is probably not a good fit for
a human interface device like a pendant. If an off the self pendant is not acceptable
to you, then a device like the PoKeys model 57 would offer more (non-isolated) I/O
for the price. Pendants should not need isolation and 24 volt capability. Mach4 can
readily run a mixture of devices and plugins at the same time, so long as only one
of them provides axis motion outputs.

>>I'm leaning towards a sink/source output board with inductive load protections on board.

We are hoping to use a driver that can handle up to 50 milliJoules of kick back
energy internally and may add external clamp diodes if we can be sure that they
do not otherwise degrade the performance.

>>.... to avoid confusion about usage...

The expansion board that we are discussing is a slave device to a PMDX-426 or
other PMDX controller board. It does not talk directly to the host computer.

>>.... on being all things to all people...

We are not expecting much in the way of sales volume for a product like this and
trying to cover all bases will just make it more expensive and less likely to sell.
Our goal is to provide a good basic set of features and let people with special
needs pursue add-ons from more specialized vendors.

>>.... why 24 I/O points...

Because that is a popular size interface chip to the serial bus used to talk to
the processor on the card hosting the expander board. If more I/O is needed, it
will be possible to use multiple expansion boards.


The feedback that we have received is much appreciated.

Steve Stallings
www.PMDX.com

Steve Stallings
www.PMDX.com
For PMDX product support, please use PMDX forum or direct email for quickest response. We do not use this forum as our primary product support site.