Post by thread:[EE] PLC interface.

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-

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}

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 > >

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}>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 > >

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}> > From: Carlos Marcano <spam_OUTc.marcanoTakeThisOuTgmail.com> > Date: 2005/09/06 Tue PM 06:40:11 EDT > To: "Microcontroller discussion list - Public." <.....piclistKILLspam@spam@mit.edu> > Subject: [EE] PLC interface. > > 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- > > --