Existing CAN project to buy / modify

[James Newtons Massmind]

I was asked to post this for a buddy, but it is serious money, if the quote
is accepted. Please reply offlist to me? Thank you!

Basically, he wants to find an ready to roll CAN bus project with EVERYTHING
needed to read a few sensors in a car, do some processing on those reading
with some microcontroller (PIC? MSP430? AVR? Whatever) and then post out
messages to some device on the bus that will do something with the
information. Yeah... not a great spec, but the point is to just find a
development system that already has the standard stuff in it for working
with things you find in a car so we don't have to burn all the cycles
required to come up to speed on it.

Here are the details we have so far:

PROJECT #1:  Automotive Sensor System  (HOT!--RFQ response due this
coming Monday, Product by mid-March)

Basic requirements are for an automotive environment (with ALL that
implies for temperature, shock, vibration, MTBF, etc.!) sensor/signal
conditioner/CAN transceiver module.  We already have the sensor suite
and signal conditioners as COTS products which will require minimal
modification.  We are looking for a recommended chip set and
benchmark design that provides the ADC and CAN interface and
processor.  The sensor suite will provide several (typically 2, but
potentially up to 8) analog signals which will need to be digitized,
and processed through a 2-3 element polynomial equation to generate a
temperature compensated and linearized output value for each
sensor.  It may also be possible to move the processing to the
control module and merely report measured values if there are
significant savings in cost or space. Overall accuracy can be met
with a 12-bit ADC, although higher resolution is MUCH preferred.

Although we have not yet seen the customer's CAN specification, it is
believed to meet normal American and European automotive
requirements, and have a relatively simple command/response
set.  Evenutally the system will require EU, CE, FCC, and other
approvals.  ROHS is also required.

Power availability is not an issue, although there is an overall
limit to about 2-5 watts, and a very clean power bus is
anticipated.  HOWEVER, there is a requirement for operation in a
Class-I, Div-1 or Div-2 explosive environment.  i.e. intrinsic safety
is mandatory, which implies low voltage and low power requirements,
along with high immunity to EMI, ESD, and gross over-voltage
conditions.  Energy storage devices such as inductors and capacitors
must be minimized almost to the point of non-existence compared to
normal consumer applications, which can create issues for
bypassing  and filtering electronic noise ;-).

Full galvanic isolation of the sensors and processor from the CAN bus
may be an additional requirement imposed by the sensors.  There are
several good digital isolation solutions available, and we do not
anticipate problems here.

Although this requirement is being driven by a specific customer, we
want to end up with a "generic" system that can be easily adapted to
different sensor suites and applications in the future.


James Newton: PICList webmaster/Admin
mailto:jamesnewton@...  1-619-652-0593 phone
http://www.piclist.com/member/JMN-EFP-786
PIC/PICList FAQ: http://www.piclist.com


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[Xiaofan Chen]

On 1/4/08, James Newton <jamesnewton@...> wrote:
> PROJECT #1:  Automotive Sensor System  (HOT!--RFQ response
> due this coming Monday, Product by mid-March)

This does not correlate well with the followed requirement of
IS (intrinsic safety) which is a long process and not many
people are in this field. You need a standard expert to guide
you on the design.

> Power availability is not an issue, although there is an overall
> limit to about 2-5 watts, and a very clean power bus is
> anticipated.  HOWEVER, there is a requirement for operation in a
> Class-I, Div-1 or Div-2 explosive environment.  i.e. intrinsic safety
> is mandatory, which implies low voltage and low power requirements,
> along with high immunity to EMI, ESD, and gross over-voltage
> conditions.  Energy storage devices such as inductors and capacitors
> must be minimized almost to the point of non-existence compared to
> normal consumer applications, which can create issues for
> bypassing  and filtering electronic noise ;-).
>

I have only done two projects with EEx ia (Intrinisic safety) so
I am not an expert. But I know that the domain knowledge of
intrinsic safety is very specific. The certification can take a long
time. Certification related testing can be quite long as well.

By the way, Pepperl+Fuchs (my previous employer) is the
leading Intrinsic Safety vendor along with MTL (a UK company).

Xiaofan
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[YAP-2]

You may use some useful stuff here http://www.vscp.org

Cheers
/Ake

On Jan 4, 2008 4:48 AM, James Newton <jamesnewton@...> wrote:

> I was asked to post this for a buddy, but it is serious money, if the quote
> is accepted. Please reply offlist to me? Thank you!
>
> Basically, he wants to find an ready to roll CAN bus project with EVERYTHING
> needed to read a few sensors in a car, do some processing on those reading
> with some microcontroller (PIC? MSP430? AVR? Whatever) and then post out
> messages to some device on the bus that will do something with the
> information. Yeah... not a great spec, but the point is to just find a
> development system that already has the standard stuff in it for working
> with things you find in a car so we don't have to burn all the cycles
> required to come up to speed on it.
>
> Here are the details we have so far:
>
> PROJECT #1:  Automotive Sensor System  (HOT!--RFQ response due this
> coming Monday, Product by mid-March)
>
> Basic requirements are for an automotive environment (with ALL that
> implies for temperature, shock, vibration, MTBF, etc.!) sensor/signal
> conditioner/CAN transceiver module.  We already have the sensor suite
> and signal conditioners as COTS products which will require minimal
> modification.  We are looking for a recommended chip set and
> benchmark design that provides the ADC and CAN interface and
> processor.  The sensor suite will provide several (typically 2, but
> potentially up to 8) analog signals which will need to be digitized,
> and processed through a 2-3 element polynomial equation to generate a
> temperature compensated and linearized output value for each
> sensor.  It may also be possible to move the processing to the
> control module and merely report measured values if there are
> significant savings in cost or space. Overall accuracy can be met
> with a 12-bit ADC, although higher resolution is MUCH preferred.
>
> Although we have not yet seen the customer's CAN specification, it is
> believed to meet normal American and European automotive
> requirements, and have a relatively simple command/response
> set.  Evenutally the system will require EU, CE, FCC, and other
> approvals.  ROHS is also required.
>
> Power availability is not an issue, although there is an overall
> limit to about 2-5 watts, and a very clean power bus is
> anticipated.  HOWEVER, there is a requirement for operation in a
> Class-I, Div-1 or Div-2 explosive environment.  i.e. intrinsic safety
> is mandatory, which implies low voltage and low power requirements,
> along with high immunity to EMI, ESD, and gross over-voltage
> conditions.  Energy storage devices such as inductors and capacitors
> must be minimized almost to the point of non-existence compared to
> normal consumer applications, which can create issues for
> bypassing  and filtering electronic noise ;-).
>
> Full galvanic isolation of the sensors and processor from the CAN bus
> may be an additional requirement imposed by the sensors.  There are
> several good digital isolation solutions available, and we do not
> anticipate problems here.
>
> Although this requirement is being driven by a specific customer, we
> want to end up with a "generic" system that can be easily adapted to
> different sensor suites and applications in the future.
>
>
> James Newton: PICList webmaster/Admin
> mailto:jamesnewton@...  1-619-652-0593 phone
> http://www.piclist.com/member/JMN-EFP-786
> PIC/PICList FAQ: http://www.piclist.com
>
>
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[Ruben Jönsson]

About intrinsic safety:

Keep the energy storing components to low values (capacitors and inductors) and
keep the voltage and current low for the sensor part (the one in hazardous
area) and you can use a comercial, ready made, approved, shunt barrier
(isolated or not) for the associated apparatus. Also make sure that there can't
be any hot surface with the maximum current and power from the shunt barriers
with any combinations of up to two faults.

The part in the hazardous area (behind the barrier) still has to be reviewed by
a notified body (unless it is a simple apparatus, like a thermistor or switch)
but that could be rather easy, compared to the barrier part.

I know that 'low' value and 'hot' surface are very vague terms but they depends
on the requirements (explosive type of gas/air mixture or dust) and has to be
looked up.

In any way, if intrinsic safety is going to be considered, take a look at the
requirements at first and keep that in mind when doing the design instead of
redoing it once again when the prototype is done and working. But I guess that
goes for everything.

/Ruben

> On 1/4/08, James Newton <jamesnewton@...> wrote:
> > PROJECT #1:  Automotive Sensor System  (HOT!--RFQ response
> > due this coming Monday, Product by mid-March)
>
> This does not correlate well with the followed requirement of
> IS (intrinsic safety) which is a long process and not many
> people are in this field. You need a standard expert to guide
> you on the design.
>
> > Power availability is not an issue, although there is an overall
> > limit to about 2-5 watts, and a very clean power bus is
> > anticipated.  HOWEVER, there is a requirement for operation in a
> > Class-I, Div-1 or Div-2 explosive environment.  i.e. intrinsic safety
> > is mandatory, which implies low voltage and low power requirements,
> > along with high immunity to EMI, ESD, and gross over-voltage
> > conditions.  Energy storage devices such as inductors and capacitors
> > must be minimized almost to the point of non-existence compared to
> > normal consumer applications, which can create issues for
> > bypassing  and filtering electronic noise ;-).
> >
>
> I have only done two projects with EEx ia (Intrinisic safety) so
> I am not an expert. But I know that the domain knowledge of
> intrinsic safety is very specific. The certification can take a long
> time. Certification related testing can be quite long as well.
>
> By the way, Pepperl+Fuchs (my previous employer) is the
> leading Intrinsic Safety vendor along with MTL (a UK company).
>
> Xiaofan
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==============================
Ruben Jönsson
AB Liros Electronic
Box 9124, 200 39 Malmö, Sweden
TEL INT [phone]
FAX INT [phone]
ruben@...
==============================
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[Olin Lathrop]

James Newton wrote:
> I was asked to post this for a buddy, but it is serious money,

It's good to see you understand this is serious money.  Anyone that says
they'll do this for a few $K doesn't understand what they're getting into.

However, I'd still want to know how this is funded.  Is this a new project
from a existing company, or someone trying to get their own idea going and
funding it out of pocket?  While you may think the money should be the same,
this distinction makes a big difference in project management and other
expectations.

> Basically, he wants to find an ready to roll CAN bus project with
> EVERYTHING needed to read a few sensors in a car, do some processing on
> those reading with some microcontroller (PIC? MSP430? AVR? Whatever)
> and then post out messages to some device on the bus that will do
> something with the information.

On what bus?  Talk back on the CAN bus or some other private data connection
to elsewhere?  In other words, is this strictly a CAN bus device, or a
bridge between the CAN bus and some other digital system?

> Yeah... not a great spec, but the point
> is to just find a development system that already has the standard
> stuff in it for working with things you find in a car so we don't have
> to burn all the cycles required to come up to speed on it.

Does this include the mechanicals?  The mechanicals aren't trivial in a
harsh environment like a car.  "Development system" sounds more like a
working board is all you need.  It will be used to develop the real system,
which will eventually include the mechanicals once the system is shown to
work with the development board.  Is this correct?

> PROJECT #1:  Automotive Sensor System  (HOT!--RFQ response due this
> coming Monday, Product by mid-March)

That's in 3 days.  Not a lot of time for several rounds of back and forth
questions and clarification, and a few passes over the spec until everyone
agrees on exactly what they are buying and delivering.  You're asking for a
fixed price quote (at least that's what it seems), so anyone that knows what
they're doing is going to insist on a clear spec so that they know exactly
what they're promising to do for the fixed price, and just as importantly,
what they're not promising to do.  By the same token, you need to know
exactly what you're getting and not getting for your money.

The most critical part of this project is the spec.  Once you have a quality
spec, most reasonably competent engineers can implement it.  But a vague or
incomplete spec will be a endless source of problem for the duration of the
project.  The spec is also your contract that tells you exactly what you're
going to get for your money.  You don't want to skimp on this part in the
interest of the schedule.  Doing so will cost a lot more schedule slippage
in the end.  If the schedule is already so tight that development can't
possibly be finished in time if the spec is done right, then the project is
already guaranteed to slip.  Understand that now and don't make is worse by
trying to economize on the spec.

> Basic requirements are for an automotive environment (with ALL that
> implies for temperature, shock, vibration, MTBF, etc.!) sensor/signal
> conditioner/CAN transceiver module.  We already have the sensor suite
> and signal conditioners as COTS products which will require minimal
> modification.

So conditioned signals will enter the unit, or your COTS conditioners are
expected to be integrated into the unit?

> We are looking for a recommended chip set and
> benchmark design that provides the ADC and CAN interface and
> processor.  The sensor suite will provide several (typically 2, but
> potentially up to 8) analog signals which will need to be digitized,
> and processed through a 2-3 element polynomial equation to generate a
> temperature compensated and linearized output value for each
> sensor.

What is the maximum sample rate per channel?  At what rate must new fully
compensated measurement values be available per channel?

> It may also be possible to move the processing to the
> control module and merely report measured values if there are
> significant savings in cost or space.

What control module?  How does this control module relate to the unit you
are asking to have designed?  You need to clarify the overall architecture.

> Overall accuracy can be met
> with a 12-bit ADC, although higher resolution is MUCH preferred.

I assume you've thought about this, but this is rather surprising.  Without
knowing the people at the other end of this request, my first knee jerk
reaction is that someone doesn't really understand their requirements.  I'd
want to hear more about what these sensors are to do a sanity check on the
accuracy and resolution requirements, and maybe come up with other ways of
addressing the real requirements.  This and the speed requirement together
will have a major influence on the overall architecture and choice of
processor(s), and therefore cost of development.

> Power availability is not an issue, although there is an overall
> limit to about 2-5 watts, and a very clean power bus is
> anticipated.

You mean you expect the unit to generate a clean power bus internally, or
that you will provide a clean power bus.  Normally I would expect rather
dirty "12V" power in for automotive environments.  I would expect to deal
with this in the unit, but then I don't understand what you mean by a "very
clean power bus is anticipated".  What am I missing?

> HOWEVER, there is a requirement for operation in a
> Class-I, Div-1 or Div-2 explosive environment.

So is this going anywhere worse than under the hood of a car, or are you
just using these specs to ensure under-hood operation will not be a problem?
And who has the liability?  That will make a VERY big difference to the
price of the quote and whether a quote will even be offered in many cases.

> i.e. intrinsic safety
> is mandatory, which implies low voltage and low power requirements,
> along with high immunity to EMI, ESD, and gross over-voltage
> conditions.

This is more what I expect in a car.  Now I'm really confused by the "very
clean power bus anticipated" statement.

> Energy storage devices such as inductors and capacitors
> must be minimized almost to the point of non-existence compared to
> normal consumer applications, which can create issues for
> bypassing  and filtering electronic noise ;-).

I can understand certain types of capacitors, but what do you have against
small inductors?  These are very reliable and safe, since they are basically
rolled up wire and a chunk of reasonably inert magnetic material.  A well
designed switching power supply on the input seems to me the safest choice.
The reduced need for cooling alone will simplify and safefy (;-)) things
compared to alternatives.

> Full galvanic isolation of the sensors and processor from the CAN bus
> may be an additional requirement imposed by the sensors.

You need to decide the "may" part.  As I'm sure you understand, that makes
quite a difference in the design.

> There are
> several good digital isolation solutions available, and we do not
> anticipate problems here.

Not so fast.  12 bit accuracy accross galvanic isolation means shipping
power to the isolated side, converting there, and shipping digital values
back.  While this is all doable, it does take power, parts, board space, and
$$.

> Although this requirement is being driven by a specific customer, we
> want to end up with a "generic" system that can be easily adapted to
> different sensor suites and applications in the future.

That makes sense given the overall "development board" flavor.  You think
you want is a platform for testing concepts and proving viability and as a
reference design for resulting products.  This unit is not intended to be
the product?

To get to a real spec there will need to be some serious interactive
discussion with the people that truly understand the requirements and are in
a position to make tradeoffs when choices are presented.  Often these people
know that they want, but don't realize all the ways the results could be
achieved and how seemingly small changes in the requirements can make big
differences to the implementation.  A interactive discussion between those
that know what they want and a engineer that knows the implementation
tradeoffs is necessary for a good result for everyone.  You need to provide
a phone number and a good time to call.


********************************************************************
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[phone].  Gold level PIC consultants since 2000.
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[Xiaofan Chen]

On Jan 4, 2008 8:53 PM, Ruben Jönsson <ruben@...> wrote:

> About intrinsic safety:
>
> Keep the energy storing components to low values (capacitors and inductors) and
> keep the voltage and current low for the sensor part (the one in hazardous
> area) and you can use a comercial, ready made, approved, shunt barrier
> (isolated or not) for the associated apparatus. Also make sure that there can't
> be any hot surface with the maximum current and power from the shunt barriers
> with any combinations of up to two faults.
>
> The part in the hazardous area (behind the barrier) still has to be reviewed by
> a notified body (unless it is a simple apparatus, like a thermistor or switch)
> but that could be rather easy, compared to the barrier part.
>

I understand that you have extensive experience with EEx.

In this case the requirement is not that clear to me.

Anyway, just quote the original post.
>> We already have the sensor suite and signal conditioners as
>> COTS products which will require minimal modification.

This may or may not be true when Intrinsic Safety comes to
play. I've done two IS project. One of them is a Namur
level sensor and the other is Namur sensor interface module.
It is certainly quite different if they are for non-Ex COTS product.

>> We are looking for a recommended chip set and benchmark
>> design that provides the ADC and CAN interface and
>> processor.  The sensor suite will provide several (typically 2, but
>> potentially up to 8) analog signals which will need to be digitized,
>> and processed through a 2-3 element polynomial equation to generate
>> a temperature compensated and linearized output value for each
>> sensor.  It may also be possible to move the processing to the
>> control module and merely report measured values if there are
>> significant savings in cost or space. Overall accuracy can be met
>> with a 12-bit ADC, although higher resolution is MUCH preferred.

>From the requirement, the sensor will reside in Division 1. If the
interface needs to be also in Division 1, it is not easy at all. If the
interface need only to be in Division 2, it will be easier. In fact, of all the
I/O families here in the company (No 1 USA PLC vendor, No 2 PLC
vendor worldwide after Siemens), there is only one family which is
good for Div 1. And incidently this family is developed by
Pepperl+Fuchs. Most other families will be good for Class 1 Div 2.


Xiaofan

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[Spehro Pefhany]

Quoting Olin Lathrop <olin_piclist@...>:

> James Newton wrote:
>> I was asked to post this for a buddy, but it is serious money,
>
> It's good to see you understand this is serious money.  Anyone that says
> they'll do this for a few $K doesn't understand what they're getting into.
<massive snippage>

>> Energy storage devices such as inductors and capacitors
>> must be minimized almost to the point of non-existence compared to
>> normal consumer applications, which can create issues for
>> bypassing  and filtering electronic noise ;-).
>
> I can understand certain types of capacitors, but what do you have against
> small inductors?  These are very reliable and safe, since they are basically
> rolled up wire and a chunk of reasonably inert magnetic material.  A well
> designed switching power supply on the input seems to me the safest choice.
> The reduced need for cooling alone will simplify and safefy (;-)) things
> compared to alternatives.

Capacitors and inductors (and batteries, and certain other components)
STORE ENERGY. If they CAN store enough energy
to cause an EXPLOSION they cannot be included in a device that is
"intrinsically safe". It may be safe, or it may be "safe", but it
cannot be "intrinsically safe" because intrinsically there is enough
energy storage to possibly cause the thing to explode in the hazardous  
environment of interest. It requires a great deal more analysis to  
determine safety if it is not intrinsically safe. Even *wire* is not  
completely safe- enough of it can store enough energy in the  
inductance to cause a spark which
will ignite a highly explosive gas (eg. acetylene, which IIRC is even
worse than hydrogen). Eg. CSA C22.2 covers this kind of product.

Often it's impossible (or impossibly difficult) to make all the
equipment intrinsically safe, so the sensors (for example) and/or some
other signal processing equipment may be intrinsically safe, and
the rest (eg. a powerful embedded computer) may be located OUTSIDE
the hazardous zone, and connected through an intrinsic safety
barrier of the type that Xiaofan's company produces. It's nothing more
than a set of fuses and TVS/zener diodes, but has enough approvals and
testing done to prove that (when it is used according to design)
nothing (within reason) that happens on the non-hazardous side (eg.  
direct connection to 120VAC) gets through the barrier with enough  
energy to cause Kaboom! on the other side.

Another possibility is to use an appropriately rated explosion-proof  
housing and provide safeguards (eg. positive pressure) to prevent  
problems.

>> Full galvanic isolation of the sensors and processor from the CAN bus
>> may be an additional requirement imposed by the sensors.
>
> You need to decide the "may" part.  As I'm sure you understand, that makes
> quite a difference in the design.
>
>> There are
>> several good digital isolation solutions available, and we do not
>> anticipate problems here.
>
> Not so fast.  12 bit accuracy accross galvanic isolation means shipping
> power to the isolated side, converting there, and shipping digital values
> back.  While this is all doable, it does take power, parts, board space, and
> $$.
>
>> Although this requirement is being driven by a specific customer, we
>> want to end up with a "generic" system that can be easily adapted to
>> different sensor suites and applications in the future.
>
> That makes sense given the overall "development board" flavor.  You think
> you want is a platform for testing concepts and proving viability and as a
> reference design for resulting products.  This unit is not intended to be
> the product?
>
> To get to a real spec there will need to be some serious interactive
> discussion with the people that truly understand the requirements and are in
> a position to make tradeoffs when choices are presented.  Often these people
> know that they want, but don't realize all the ways the results could be
> achieved and how seemingly small changes in the requirements can make big
> differences to the implementation.  A interactive discussion between those
> that know what they want and a engineer that knows the implementation
> tradeoffs is necessary for a good result for everyone.  You need to provide
> a phone number and a good time to call.

It's always a bit difficult to discuss a project such as this in public,
as you can neither say too much nor too little. Perhaps an NDA will
be required. Unfortunately, I'm way too busy atm to consider something like
this for short delivery time, despite having a fair bit of related
experience, but it does sound like a really interesting project.

BTW, I do not think that Class I div 1 is achievable with CAN, but
Class I div 2 is, so this requirement should probably be fixed a priori.

I agree with Xiaofan that you need someone with relevant process  
control experience.. the rest of it is stuff that pretty much any  
competent engineer with component-level process instrumentation  
experience should be able to handle expeditiously.

Best regards,
Spehro Pefhany
Sr. Member Instrument Society of America blah blah.
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[Xiaofan Chen]

On Jan 4, 2008 10:09 PM, Olin Lathrop <olin_piclist@...> wrote:
> > HOWEVER, there is a requirement for operation in a
> > Class-I, Div-1 or Div-2 explosive environment.
>
> So is this going anywhere worse than under the hood of a car, or are you
> just using these specs to ensure under-hood operation will not be a problem?
> And who has the liability?  That will make a VERY big difference to the
> price of the quote and whether a quote will even be offered in many cases.

You may want to read what is Ex and what is Class 1 Div 1/Div 2.

> > i.e. intrinsic safety
> > is mandatory, which implies low voltage and low power requirements,
> > along with high immunity to EMI, ESD, and gross over-voltage
> > conditions.
>
> This is more what I expect in a car.  Now I'm really confused by the "very
> clean power bus anticipated" statement.

Say this vehicle is for transporting oil/gas or other explosive goods.

> > Energy storage devices such as inductors and capacitors
> > must be minimized almost to the point of non-existence compared to
> > normal consumer applications, which can create issues for
> > bypassing  and filtering electronic noise ;-).
>
> I can understand certain types of capacitors, but what do you have against
> small inductors?  These are very reliable and safe, since they are basically
> rolled up wire and a chunk of reasonably inert magnetic material.  A well
> designed switching power supply on the input seems to me the safest choice.
> The reduced need for cooling alone will simplify and safefy (;-)) things
> compared to alternatives.

Again you need to understand what is intrinsic safety.

> > Full galvanic isolation of the sensors and processor from the CAN bus
> > may be an additional requirement imposed by the sensors.
>
> You need to decide the "may" part.  As I'm sure you understand, that makes
> quite a difference in the design.
>
> > There are several good digital isolation solutions available, and we do not
> > anticipate problems here.
>
> Not so fast.  12 bit accuracy accross galvanic isolation means shipping
> power to the isolated side, converting there, and shipping digital values
> back.  While this is all doable, it does take power, parts, board space, and
> $$.

This will depend where is the isolation.
1) analog isolation using speciallized analog interface card : not cheap
and 12 bit accuracy across galvanic isolation might be able to be done
not cheap.

2) ADC on board of the sensor with CAN interface. The sensors and
the interace will communicate through CAN interface. Isolation will be
easier. It seems from the OP that this is the route they have in mind.
However the sensor in Div 1 will be more difficult. In fact I do not
know of any CAN based Intrinsic Safe sensor in Div 1.

Xiaofan
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[Russell McMahon]

>> Energy storage devices such as inductors and capacitors
>> must be minimized almost to the point of non-existence
>> compared to
>> normal consumer applications, which can create issues for
>> bypassing  and filtering electronic noise ;-).

> I can understand certain types of capacitors, but what do
> you have against
> small inductors?  These are very reliable and safe, since
> they are basically
> rolled up wire and a chunk of reasonably inert magnetic
> material.  A well
> designed switching power supply on the input seems to me
> the safest choice.
> The reduced need for cooling alone will simplify and
> safefy (;-)) things
> compared to alternatives.

I'd guess it was related to the intrinsically safe
requirement - no energy stored in circuit elements inside
the barrier.


        Russell




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[Xiaofan Chen]

On Jan 4, 2008 10:46 PM, Spehro Pefhany <speff@...> wrote:
> Often it's impossible (or impossibly difficult) to make all the
> equipment intrinsically safe, so the sensors (for example) and/or some
> other signal processing equipment may be intrinsically safe, and
> the rest (eg. a powerful embedded computer) may be located OUTSIDE
> the hazardous zone, and connected through an intrinsic safety
> barrier of the type that Xiaofan's company produces.

Pepperl+Fuchs is my previous employer.

> It's nothing more than a set of fuses and TVS/zener diodes, but has
> enough approvals and testing done to prove that (when it is used according
> to design) nothing (within reason) that happens on the non-hazardous side (eg.
> direct connection to 120VAC) gets through the barrier with enough
> energy to cause Kaboom! on the other side.

Some of the zener barrier are simply fuse/resistor/zeners. Some of them
are so called transformer isolated interface cards which are much more
complicated. One side is connected to safe area and the other side
is connected to the hazardous area.

>
> Another possibility is to use an appropriately rated explosion-proof
> housing and provide safeguards (eg. positive pressure) to prevent
> problems.

That is not intrinsic safe (EEx ia or ib).

> It's always a bit difficult to discuss a project such as this in public,
> as you can neither say too much nor too little. Perhaps an NDA will
> be required. Unfortunately, I'm way too busy atm to consider something like
> this for short delivery time, despite having a fair bit of related
> experience, but it does sound like a really interesting project.

The interface part can be done with off-the-shelf components from
companies like Pepperl+Fuchs. Actually P+F used to offer a
CAN based I/O system called RPI but it is no longer promoted
now.

> BTW, I do not think that Class I div 1 is achievable with CAN, but
> Class I div 2 is, so this requirement should probably be fixed a priori.

That is my impression as well. This is a serious issue and may
not have a solution if the customer insists on Div 1 for the sensor
(which is justified due to the possibility of close proximity to
the explosive environment).

> I agree with Xiaofan that you need someone with relevant process
> control experience.. the rest of it is stuff that pretty much any
> competent engineer with component-level process instrumentation
> experience should be able to handle expeditiously.

I agree with you. But the main problem seems that the originator
of the project under-estimate the efforts of the project and want
a quick yet customized solution.

Xiaofan
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[Alan Smith-10]

Olin speaks from experiance, as do many of us who has ever been roped (only takes a a few times) into a project that becomes hell after a short time.
   
  Too many questions...too little time, even if it is $$$$.  Sounds like a mil type contract for handling explosives and such maybe, but who knows...
   
   
   
  OK...so, little primer on IS look at
   
  grouper.ieee.org/groups/1451/6/Documents/IS%20Overview.ppt
   
  I;ve done some IS projects, but its been easy as I used COTS barriers and enclosures.  My application was underground coal mines.
   
   
  One thing to consider is to use DeviceNet, that is based on CAN.  The reason I say this is that its an industrial standard and as such there are some vendors that make IS DeviceNet sensors.  Makes the whole job easier that way.  Then stick your electronics inside a rated enclosure.  Getting in and out use zener barriers from Gem or someone like that.
   
  But it all gets back to what sensors, etc
   
  *IF* I was quoting this....Olin is correct....the spec needs to be clear and concise, and everything spelled out in detail.  What is expected (proof of concept or production ready), etc
   
  I just hate working with clients that have zero clue on what it takes to actually design, build and get something into production.  The costs involved. The time it takes. The issues. Oh well...

       
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[Olin Lathrop]

Spehro Pefhany wrote:
> I agree with Xiaofan that you need someone with relevant process
> control experience.. the rest of it is stuff that pretty much any
> competent engineer with component-level process instrumentation
> experience should be able to handle expeditiously.

I was thinking that you'd get a specialist to do/advise on the intrinsic
safety part.  It's not clear at this point whether the customer has such a
person and whether they are available to the project and how much of the
intrinsically safe part they are expecting the vendor to own.  If they are
pushing it onto the vendor, then that will *greatly* decrease the number of
bids they will get.  It's also not clear yet whether this intrisically safe
spec is really deliberate or something that somebody checked off without
realizing the implications.  If this is for a car, which is all James has
said so far, then it doesn't make sense that intrinsically safe is
necessary.  Perhaps it is for other reasons, but this is one of several
things that need to be clarified.

There are enough red flags in the original message that I'd be unlikely to
bid on this myself, and if I'm supposed to own the intrinsically safe
certification I wouldn't go anywhere near it.  I've only watched that
process once from a distance, and probably couldn't find the right person
with the right experience in the very short time allotted, and would want to
take on the associated liability issues in any case.

However, I don't agree that just anybody can do a good job on the rest.  You
have to think carefully about ground currents, offset voltages, noise, etc,
for greater than 12 bit accuracy.  This is again why I think separate people
with different expertise is needed.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
[phone].  Gold level PIC consultants since 2000.
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[James Newtons Massmind]

So what I'm hearing is that the CAN bus stuff is no big deal, or at least
that there are some off the shelf resources available for it, but the
"Intrinsic Safe" part is a real killer.

There are two parts to that, as far as I can see:

1. The design has to be I.S.

2. The design has to be certified I.S.

Is the first part something that can be reasonable accomplished for a few
grand? And then the second part costs the big bucks? Or is it that an I.S.
design is going to have to be guided by top dollar people and/or use top
dollar parts?

--
James.

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[Alan Smith-10]

*if* you can use off the shelf IS barriers and sensors, then the cert may not be all that bad.  If your going to design it all, then the time and costs could be pretty big.  I'm not sure who can even certify....my project was thru MSHA but it was long ago and im sure things have changed.
   
  Its like UL...if all your components are certified, and your just building a system, then its just the system that needs certification, rather than each individual part.
   
 

James Newton <jamesnewton@...> wrote:
  So what I'm hearing is that the CAN bus stuff is no big deal, or at least
that there are some off the shelf resources available for it, but the
"Intrinsic Safe" part is a real killer.

There are two parts to that, as far as I can see:

1. The design has to be I.S.

2. The design has to be certified I.S.

Is the first part something that can be reasonable accomplished for a few
grand? And then the second part costs the big bucks? Or is it that an I.S.
design is going to have to be guided by top dollar people and/or use top
dollar parts?

--
James.

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[Xiaofan Chen]

On Jan 5, 2008 4:49 AM, James Newton <jamesnewton@...> wrote:
> So what I'm hearing is that the CAN bus stuff is no big deal, or at least
> that there are some off the shelf resources available for it, but the
> "Intrinsic Safe" part is a real killer.

The first big deal is that the specification is not clear. The CAN bus
stuff can be a big deal if the customer insist of using the sensor
on Class 1 Div 1 with CAN interface. There used to be some discussion
to have Instrinsic Safe DeviceNet but so far it has not been achieved.
http://www.cpac.washington.edu/NeSSI/21_CPAC_Spring_2003/DeviceNet_OverviewV2.ppt

> There are two parts to that, as far as I can see:
>
> 1. The design has to be I.S.
>
> 2. The design has to be certified I.S.
>
> Is the first part something that can be reasonable accomplished for a few
> grand? And then the second part costs the big bucks? Or is it that an I.S.
> design is going to have to be guided by top dollar people and/or use top
> dollar parts?
>

If this design is to be done with off-the-shelf components, I think it
is possible
to use 4-20mA sensors/transmiters from some vendors in Class 1 Div 1,
Pepperl+Fuchs Barrier as the interface between Div 1 and Div 2, Allen-Bradley
Analog Point I/O (based on DeviceNet) in Div 2 as the interface to convert
analog signal and the PLC, Allen Bradley CompactLogix as the PLC to control
the system. You can of course choose the vendors you prefer.

If the design is to modify the existing sensor and interface, then the work
is quite significant. A few grand for the first task is just to get to know
the requirement and a few hours of consultation with an IS expert. The
testing part can be as long as months. Basically I think if the originator
has no idea of IS, it is not easy at all without serious involvement of
an IS expert which can cost top dollars.

The second part is also depending on the project. I believe a few 10s
of grand is at least necessary.

Xiaofan
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[Ruben Jönsson]

In order to get a product Ex certified and to produce this product, the
production facility and routines also has to follow a quality standard which
will be reviewed at least once a year. This is true for Europe and for the
toughest environments (zones, classes) and I guess it is true for US as well.

But I guess this is common practice also for UL listed, non Ex products.

Never the less, it is something to think about if your production facilities
isn't already quality assured.

There is a standard, EN 13980, which specifically addresses application of
quality systems regarding products for explosive atmospheres and the different
protection methods, including IS.

/Ruben

> So what I'm hearing is that the CAN bus stuff is no big deal, or at least
> that there are some off the shelf resources available for it, but the
> "Intrinsic Safe" part is a real killer.
>
> There are two parts to that, as far as I can see:
>
> 1. The design has to be I.S.
>
> 2. The design has to be certified I.S.
>
> Is the first part something that can be reasonable accomplished for a few
> grand? And then the second part costs the big bucks? Or is it that an I.S.
> design is going to have to be guided by top dollar people and/or use top
> dollar parts?
>
> --
> James.
>

==============================
Ruben Jönsson
AB Liros Electronic
Box 9124, 200 39 Malmö, Sweden
TEL INT [phone]
FAX INT [phone]
ruben@...
==============================
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[Xiaofan Chen]

On Jan 4, 2008 10:55 PM, Apptech <apptech@...> wrote:
> >> Energy storage devices such as inductors and capacitors
> >> must be minimized almost to the point of non-existence
> >> compared to normal consumer applications, which can create
> >> issues for
> >> bypassing  and filtering electronic noise ;-).
>
> I'd guess it was related to the intrinsically safe
> requirement - no energy stored in circuit elements inside
> the barrier.

Alan Smith has posted this primer:
http://grouper.ieee.org/groups/1451/6/Documents/IS%20Overview.ppt

Another one:
http://www.iaei.org/subscriber/magazine/02_f/babiarz.htm

You can have energy stored in the circuit elements inside the
IS barrier (in Div 1 or Div 2 or so called Zone 1 and Zone 2 in
Europe). But you need to limit the energy to go to the field
(typically through triple-redudant zener/crowbar or at least double
redudant zener/crowbar to limit the voltage, metal film resistor or fuse
to limit the current

You can even have some energy storage elements inside
the IS sensors in Div 1 (or Zone 0). In fact, the Namur
sensor I designed have a push-pull converter inside. But
it takes some efforts in the front end to mitigate the
capacitors and inductance inside the circuit.


Xiaofan
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