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'[EE] PLC interface.'
2005\09\06@184012 by Carlos Marcano

picon face
Hi folks.

 I am doing a CO2 fire extinguishing system using a PLC. The idea is
to protect 5 big potentially flammable machines with a CO2 system. I
have managed pretty much all the things but I need to monitor if the
lines that carry the triggering signals (termic contacts, manual
trigger) are opened (as in a broken wire). Do I need special input
modules? I am planning to use Allen-Bradley or Siemens PLC. I cant use
microcontrollers. Thanks for the help and sorry for the english.

Regards,
*Carlos Marcano*
-Guri, Venezuela-

2005\09\06@201430 by Chen Xiao Fan

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Normally you can detect the current. I have not used an
PLC but the sensor to PLC transformer isolated barrier
modules I developed is using this simple method.

The module is powering NAMUR sensors or simple switches in the
field with a 8.2V supply with 1kOhm internal impedance.
If the current is below 50uA, we will suppose the line is
broken (lead breakage or LB detection). If the current is above
6.2mA, we will suppose the line is short circuited
(short-circuit or SC detection).

The current is detected using the 200R resistor which is
part of the 1K Ohm internal resistance (another one is 820R).

In case of a mechanical switch connection, use a 10k Ohm
resistor to be in parallel with the switch and then
add a 1K Ohm (400R to 2k Ohm) resistor in series. So you can
still have LB and SC monitoring features.

However, you are dealing with flammable environment. In case you
need certain approval, I will recommend you to use Pepperl+Fuchs
K-card. They are EEx ia IIc approved and can be used in Zone 2.
The sensors can be put in Zone 0 and the PLC can be put in the
safe area. Pepperl+Fuchs Process Automation division is the
world leader in Intrinsic Safety (IS) and other explosion proof
product.

The interface modules will take care of the lead breakage
detection and the short circuit detection for you. Since you
are using a binary switch, I think SR2 (KFD2-SR2-Ex2.W and
other SR2 family product) is a good choice to you. The output is
relay. If you want transistor output, SOT2 and ST2 family are
what you want to use.

Go to http://www.pepperl-fuchs.com (English / German) or
http://www.am.pepperl-fuchs.com (US English) and type in
KFD2-SR2 (DC supply) or KFA5-SR2 or KFA6-SR2 (AC supply) in
the search box and you will find the datasheet and approval
information of the SR2 family. P+F should have representatives
which will speak your language.

Regards,
Xiaofan

----------------------------------------------
Xiaofan Chen
R&D Engineer, Photoelectric Sensor Development
Pepperl+Fuchs Singapore
http://www.pepperl-fuchs.com
Signals for the world of automation
--------------------------------------------

{Original Message removed}

2005\09\06@203942 by Carlos A. Marcano V.

picon face
Thanks a lot, Xiaofan. I will take a look at this info.

Regards,
*Carlos Marcano*
-Guri, Venezuela-


Chen Xiao Fan escribió:

>Normally you can detect the current. I have not used an
>PLC but the sensor to PLC transformer isolated barrier
>modules I developed is using this simple method.
>
>  
>
-- HUGE SNIP --

>Go to http://www.pepperl-fuchs.com (English / German) or
>http://www.am.pepperl-fuchs.com (US English) and type in
>KFD2-SR2 (DC supply) or KFA5-SR2 or KFA6-SR2 (AC supply) in
>the search box and you will find the datasheet and approval
>information of the SR2 family. P+F should have representatives
>which will speak your language.
>
>Regards,
>Xiaofan
>  
>

2005\09\07@131405 by Carlos A. Marcano V.

picon face
Thanks a lot, Xiaofan. I will take a look at this info.

Regards,
*Carlos Marcano*
-Guri, Venezuela-


Chen Xiao Fan escribió:

>Normally you can detect the current. I have not used an
>PLC but the sensor to PLC transformer isolated barrier
>modules I developed is using this simple method.
>
>  
>
-- HUGE SNIP --

{Quote hidden}

2005\09\07@133530 by Mchipguru

picon face
Often the use of 4-20 ma control loops for the actuators are good for this type of application. There can be alarms or failsafes in the event there is no current flow in the system.
Larry


{Quote hidden}

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