PLC and Terminal block and Sensor wiring selection

[Lancie1]

I would then turn the plc outputs on accordingly to input the desired signal to the multiplexer which in turn, turn low-voltage output signals that will serve as inputs to electromagnetic relays. Is my undestanding correct?

Yes, the purpose is to allow using fewer PLC Inputs or Outputs to do a the same job. It is usually the Inputs that are the problem, as most PLC programs need about 2 or 3 times more inputs than outputs.

As for multiplexing analog I/O, I have only multiplexed analog inputs. The way I did that was to use 9 PLC digital relay outputs to consecutively switch one PLC analog input terminal (only 2 total available) to 9 different sets of physical analog input wires. So in my case, no "analog multiplexer" was required, only digital outputs.

 

[SergioB]

The way I did that was to use 9 PLC digital relay outputs to consecutively switch one PLC analog input terminal (only 2 total available) to 9 different sets of physical analog input wires. So in my case, no "analog multiplexer" was required, only digital outputs.

Cool, but you did use electromagnetic relays to switch on those analog input wires from the sensors, right? I ask this because the solid state relays in AB SLC-500 digital output cards are (as far as I know) solid state and as I understand, would modify the signal from the analog devices.

Thanks!

 

[DamianInRochester]

I almost bought them, but you're right, I have to make sure they are analog, otherwise what's the point, right?

By the way, I wanted to ask about the wiring of these multiplexers. It may be obvious to most of you, but since I'm a beginner, I wanted to make sure I understood it correctly.

MY UNDERSTANDING IS AS FOLLOWS: The purpose of using these multiplexers is to reduce the number of PLC outputs I need to use to turn relay on/off. So I need to step down the voltage from my 24vdc power supply accordingly so that I can connect the multoplexer chip. I would then turn the plc outputs on accordingly to input the desired signal to the multiplexer which in turn, turn low-voltage output signals that will serve as inputs to electromagnetic relays. Is my undestanding correct?

Thanks for all the good advise!

That is one purpose, but also just as important is that these devices are designed specifically to do this function. In principle they should save a lot of wiring and perform much better than a home grown multiplexer in both speed and attenuation.

turn low-voltage output signals that will serve as inputs to electromagnetic relays.

Maybe, but not necessarily.

 

[SergioB]

That is one purpose, but also just as important is that these devices are designed specifically to do this function. In principle they should save a lot of wiring and perform much better than a home grown multiplexer in both speed and attenuation.

Understood. Thanks a lot!

 

[Lancie1]

Cool, but you did use electromagnetic relays to switch on those analog input wires from the sensors, right? I ask this because the solid state relays in AB SLC-500 digital output cards are (as far as I know) solid state and as I understand, would modify the signal from the analog devices. Thanks!

I used PLC output relays (which were electromagnetic). Solid-state relays have the annoying characteristic of not being isolated (activation trigger is not isolated from the relay input or output).

 

[SergioB]

I used PLC output relays (which were electromagnetic). Solid-state relays have the annoying characteristic of not being isolated (activation trigger is not isolated from the relay input or output).

Mine are solid state, so I'm gonna have to use separate electromagnetic ones.
Thanks!

 

[james_plc]

Hi,
Does anyone know who uses Beckhoff technology in Alberta Canada?

Thanks in advance!