brown out protection

Is there some way to switch off the outputs in a pre-defined sequence when the power to the PLC fails ?
Right now, I see that when the power supply voltage falls down to about 50%, all the outputs are turned off simultaneously. Therefore, I can't go through a safe shutdown sequence.

I am using SLC 5/03.

Thanks

kps

Since the PLC is helpless after the power goes out (or drops below a minimum voltage), you'll need a UPS or battery to keep the PLC powered for a short period.

Then it's simply a matter of using one input on the PLC to detect loss of the mains supply (ahead of the UPS). Use that input to trigger an orderly shutdown.

I'd be more concerned as to why you're experiencing brownouts... utoh

beerchug

-Eric

If you pass the mains voltage directly to one of the PLC inputs, then the signal may change at some stage that is too late.
To catch a brownout earlier, you could pass the signal over a voltage monitoring relay.

I am curious

In what scenario would the PLC lose power or a 50% reduction and the main power not have problem?

How could you perform a sequential shutdown if there isnt power for the devices the outputs control?

I agree that a UPS could be used to maintain the plc but if you are getting brownouts that lower ALL the voltage then you wont be able to perform any type of shutdown.

I agree with Eric, determine WHY, if you determine its a power company issue then you may want to learn about gensets and transfer switches.

You probably cannot make a controlled shutdown.
But you CAN halt the program to continue if there is a brownout.

In the interval between where the i/o will start to behave strangely (maybe allready at 85% nominal voltage), and where the PLC will shutdown (maybe at 70% nominal voltage), some potentially dangerous situations can occur.
I actually have had an application where a customer specified voltage monitoring relays, to cover for just that situation.