need help interfacing inputs and outputs to Siemens S7-300 PLC

[fayyazali]

Hello, im a new student of PLC's and i wanted to know how u could connect npn and pnp sensors to a plc ... and also how to connect output to plcs using relays ???
thankyou

 

[girevik]

you have to use either "onboard" I/O on the PLC or Signal Modules like SM321 (inputs) and SM322 (outputs)

 

[fayyazali]

i already have a i/o module installed ... it is SM-334 .... but how to connwect npn and pnp sensors to the plc with an external power supply ???

 

[dchartier]

Hello Fay yazali;

A SM-334 is an analog In/Out card, 4 inputs/2 outputs; it cannot be used for digital signals (NPN and PNP connections are used for digital signals).
For more details, I suggest you go to Siemens' support website and search/download the pdf manual "Programmable Logic Controllers S7-300 Module Data". It will help you select the adequate modules for your application, and give you specs and wiring diagrams for all modules.
http://support.automation.siemens.com/WW/llisapi.dll?func=cslib.csinfo&changelang=true&aktprim=0&siteid=cseus&lang=en

Note that manufacturers will use different terms to designate the modules they produce. For Sioemens, PNP = source, NPN = sink. a module such as the 6ES7321-1BH50-0AA0 is designated Source Input, so it will accomodate PNP sensors (the terminal diagram is quite clear).

Hope this helps,
Daniel Chartier

 

[fayyazali]

Hello,
thnx for replying ... there is a digital i/o card available with the number similar to that u've written and ive been able to connect contact switches and it works ... but how to connect npn and pnp sensors to that module ... the problem is when i connect npn and pnp sensors to the module at the same time !!! ... To connect npn sensors we shud have +ve end of PLC and external power supply common ... but if we we want to connect pnp sensors we shud connect ground of plc and external power supply together ... if this is correct then plz tell me how to connect both npn and pnp sensors at the same time to the plc ???.... if im wrong then correct me
thankyou

 

[girevik]

you can't have SM334 with digital I/O

please provide the "order number" of your SM card..

and anyway I doubt you will have a succeses in connecting both pnp and npn to the same SM card...anyone please correct me if i'm wrong.

 

[PeterW]

If you want both to the same card it is impossible, you will have to connect the incorrect type via a relay, where you can wire the volt free to the way you require.

 

[Gambrinus]

If you want to connect, for example, NPN sensor to module intended for PNP sensors, this can be achieved by resistor if relay isn't suitable: one end to +24V, another end to sensor output. For example, SM321 (for PNP) module assumes -30V to 5V as 0, 13V to 30V as 1. Input current is 7 mA. Voltage drop on 720 Ohm resistor is 5V. We have 19V at module input (logical 1) when sensor output transistor is closed. When sensor output transistor is fully opened, voltage drop on it is small and we can ignore it. Current through sensor is less than 33 mA when 720 Ohm is used. If your sensor rated operational current is greater than that value - OK.

 

[fayyazali]

i have an npn module ... so how do i connect a pnp sensor to the module ???