two-plc´s-again

Thanks for your feedbacks, Im using the same plc´s, they are 200feet
apart, and they have to share 1 DI, near plc#1.
Questions?
1) They must have a Master-Slave relationship?
2) The Modbus-protocol is called from the ladder logic?
3) At which scanning rate?
4) What about the simplest wiring and speed?
5) rs-232 ful duplex? two-wires-22 awg?
Thank You

The answers to your questions are dependent on the brand and model of each PLC, as different PLCs use different communications structures and protocols. You will need to provide the exact model and brand of each PLC.

MODEL

HI TOM
I HOPE YOU ARE BACK HERE,
MI TWO PLC´S ARE
MICRO 16 OF CONTROL MICROSYSTEMS
THANKS

ketal said:

Thanks for your feedbacks, Im using the same plc´s, they are 200feet
apart, and they have to share 1 DI, near plc#1.
Questions?
1) They must have a Master-Slave relationship?
2) The Modbus-protocol is called from the ladder logic?
3) At which scanning rate?
4) What about the simplest wiring and speed?
5) rs-232 ful duplex? two-wires-22 awg?
Thank You

Click to expand...

1. Yes. One PLC will be the master and the other the slave. Check to see if the PLCs can be configured to be in either master or slave mode.
2. Hopefully the MICRO 16 makes this easy. I have no idea.
On a Automation Direct this is easy. On a Mitsubishi FX this is very difficult. It depends on the PLC. Look at the documentation.
3. Normally I would send or poll the data contiuously. Any delays or timeouts are treated as a wire break and therefore an error condition. You should easily be able to send data at 19.2KB. Sometimes it is good for the master to increment a register in the slave just to let the slave that the data link is still active.
4. & 5. Use isolated RS-485 which must be used with a half duplex. DO NOT USE RS-232. The two wire 22 awg should be fine at the speeds you need.

Let's take a time out here!!

Am I missing something? You say that you have a situation where a signal from one sensor needs to get to two PLCs. The sensor is physically close to one of the PLCs, and the second PLC is about 200 feet away.

And you're thinking that the best way to accomplish this is over a serial communications link???

There is no doubt that when you have I/O that need to be shared among multiple PLCs, there comes a point at which it makes sense to use a remote I/O network. There is also no doubt in my mind that the I/O count at which that approach makes sense is a number somewhat larger than one.

Wire the sensor to both PLCs. Use an isolating relay if necessary.

Control MicroSystems is actually an RTU, with ladder logic capabilities, and they are optimized for communications. Either unit can be set up for master or slave, and they have at least two comm ports on each RTU. I don't have the details here (I am out of the office for the week) but they have good manuals, and if you contact the manufacturer they can help. I have found their tech support to be excellent.

simple is best

I agree with Steve... wire the sensor to a relay and use two contacts one to each PLC....Do not complicate a simple problem.

two PLCs

It will depend on what you are using the input for but the advice, from Steve, to wire the sensor to both PLCs is good advice.

If you are only sharing the sensors data with the second PLC and that data is not used for any control purpose and the absence or inaccuracy of the data will not have a profound affect on life or equipment, it will be a lot less expensive to share the data via remote link.

just two plc,s

Thank you all again
I´ll try to be more specific based on your answers
It happens I already have two RTU´s micro-16 of
Control Microsystems and two Modems which can be
adapted by radio-or-telephone-or-two wire direct.
Then I suppose that:
1) I must use the modems if the plc´s are 100 meters appart.
2) the simplest way is two wire half duplex

But I should suppose also that:
1) You can have only one master all the time?
2) The second PLC could also need a DI from PLC1(Master)
then cannot make its polling?
3) And if I have for hexample 8 anaog imputs near
by the slave do I need a PLC to colect and send them
to the master via modem?
4) The slave can have its own ladder secuences?
5) If I need all the field data to be presented in
a PC, is the PC taken as another slave?
6) Do I have to by a specific program from the manufacturer
to present this data, can´t I use simple basic commands.

Maibe you could help.
Thanks.