Communication for new device?

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ilr's Avatar (by Gravatar)ilr posted on
August 6, 2006, 9:17 pm
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Hi

Firstly I am new to control and have more of an IT background so if my
questions seem fundamental or are on the wrong track please excuse me.

I am involved with the development of a new sensor that will be used in
industrial environments. We are at the stage where we are deciding how to
communicate with this device that will ulimately be used for control
purposes.

I have a few questions that I would answers to or some direction on the
types of things we should consider.

1. Should such a device communicate via modbus or are their other
alternatives that should be considered?
2. Modubs RTU or TCP/IP?
3. How are modbus devices communicated with before they are programmed with
a modbus address (eg. is there a standard for programming the modbus ID on
such devices or is it device specific)?
4. Are there other considerations in relation to communication we should be
investigating?

I'm sure I will have are other questions that will come to mind or in
response to any answers but would appreciate any assistance or help with the
direction I should be looking.

Regards
ilr




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pieter steenekamp's Avatar (by Gravatar)pieter steenekamp posted on
August 7, 2006, 4:18 am
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Re: Communication for new device?



Factors like the type of industry you're targeting will influence the
best solution:

a) If you target the process industries, you might want to consider a
Fieldbus Foundation (http://www.fieldbus.org/ ) interface.

b) For other industries it might be worthwhile to consider other
fieldbusses like Profibus.

c) A simple 4 - 20 mA interface would easily connect you to any PLC or
DCS.

d) I don't think modbus or direct TCP/IP are good options to interface
to a single sensor, and if you have a system, the more modern approach
is probably to use OPC (http://www.opcfoundation.org/ ).

Pieter

ilr wrote:


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ilr's Avatar (by Gravatar)ilr posted on
August 7, 2006, 9:27 pm
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Re: Communication for new device?



Thank You Pieter

I really appreciate you advice

a,b) At this stage the device is for use in wineries.  I will have a look at
fieldbus and profibus to see what they offer.

c) 4-20mA was considered but other information is required from the sensor
other than just the analogue output as well as a requirement to store
calibration information.  Are their devices that can be used to control from
an output such as modubs/fieldbus or profibus rather than using PC hardware
to control?

d) Ultimately their will be multiple devices throughout the winery for
measurement and control.

Regards
ilr






Cameron Dorrough's Avatar (by Gravatar)Cameron Dorrough posted on
August 7, 2006, 11:27 pm
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Re: Communication for new device?




For the application you have described, I would suggest you look seriously
at Profibus www.profibus.com/pb/ - specifically Profibus DP.

If you don't want to use PC hardware, Siemens (Vipa and others) sell small
footprint PLCs that can communicate using Profibus and control other analog
and digital devices at the same time.  This equipment is already in common
use in wineries and breweries world-wide and likely some of your clients
already use it.

Good luck.

Cameron:-)



pieter steenekamp's Avatar (by Gravatar)pieter steenekamp posted on
August 8, 2006, 6:16 am
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Re: Communication for new device?



A typical winery probably already has a PLC and you just want to
interface to existing PLCs.

If you want to go the fieldbus route, there is probably general bias
towards Profibus and Foundation Fieldbus (FF) in Europe and US
respectively.

I know many people will disagree with me, but if all other factors are
ignored, and you consider just the pure technical specs, then FF is in
my view better than Profibus. But then, Profibus will probably not only
meet, but exceed the minimum requirements, so other factors could
influence the best choice in your specific case. If I were you I would
ask a couple of your potential customers what brand PLC they use and
then contact those PLC manufacturers for their preferred or recommended
interfacing standard.

Pieter


Cameron Dorrough wrote:


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ilr's Avatar (by Gravatar)ilr posted on
August 9, 2006, 2:38 am
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Re: Communication for new device?



Thanks to both of you for your assistance.

Sorry for my ignorance but could you clear something up for me.

I know that PLC's in general take an analogue or digital signal (on/off)
from some kind of sensor or device and then do something based on that
signal.  Is it common for PLC's to also take a signal from sensors or
devices that talk modbus, fieldbus, profibus etc. and do something based on
that value eg PID control (the signal is neither analogue or digital but a
numerical value)?  Does the PLC act as a "master" device polling the sensor
at regular intervals or the other way around.  Are these kind of PLC's
common or am I on the wrong track?

Thanks in advance










ilr's Avatar (by Gravatar)ilr posted on
August 9, 2006, 2:48 am
Permalink

Re: Communication for new device?



Thanks to both of you for your assistance.

Sorry for my ignorance but could you clear something up for me.

I know that PLC's in general take an analogue or digital signal (on/off)
from some kind of sensor or device and then do something based on that
signal.  Is it common for PLC's to also take a signal from sensors or
devices that talk modbus, fieldbus, profibus etc. and do something based on
that value eg PID control (the signal is neither analogue or digital but a
numerical value)?  Does the PLC act as a "master" device polling the sensor
at regular intervals or the other way around.  Are these kind of PLC's
common or am I on the wrong track?

Thanks in advance










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