real time application

Hello,

i want to use plc for switching an output at different times in a day. on and time(24 hour format) will be set seperately on mmi
can anybody help.

regards
sridhar

fist of all this has misleading topic, this has nothing to do with "real time".

also there is no mention of used hardware or software so any help will be very general and you will have to figure out how to implement it.

how do you do turn if off once that has been turned on? do you just keep it on and turning off is manual or so?

finally what is this for? i hope you are not planing to automatically start some sort of meat grinder machine based on shift start time that has been set on hmi.

about the help:
just compare current time with hmi set time. of course formats have to be the same and you would have to compare hours with hours, minutes with minutes...

Most PLCs have a real time clock that you can read to hours, minutes, and seconds. It isn't usually difficult to use compare statements to start and stop activities based on the time of day, but the details vary so drasticly form platform to platform that, as Panic said, you aren't going to get specific help without identifying the actual PLC and HMI brand and model.

General Pseudocode for it:

Output :=
((Current_Hour > On_Hour) and (Current_Hour < Off_Hour))
Or
((Current_Hour = On_Hour) and (Current_Minute >= On_Minute))
OR
((Current_Hour = Off_Hour) and (Current_Minute < Off_Minute))

thanks for reply,

what i actually need is for example the pump should swithch on at 18:30 and switch off at 3:00. these on and off times will be set from HMI.
hope the above will explain the req.

Best regards
sridhar

ANY PLC and HMI/MMI/SCADA application should be able to satisfy that requirement. If that's all you need, you might consider automationdirect - heck, go find the cheapest package. You might use an integrated PLC/display. Come back with implementation questions when you know what you'll be using - or if your requirements change.

spink2 said:

thanks for reply,

what i actually need is for example the pump should swithch on at 18:30 and switch off at 3:00. these on and off times will be set from HMI.
hope the above will explain the req.

Best regards
sridhar

Click to expand...

spink2 said:

thanks for reply,

what i actually need is for example the pump should swithch on at 18:30 and switch off at 3:00. these on and off times will be set from HMI.
hope the above will explain the req.

Best regards
sridhar

Click to expand...

So far, you have asked a general question, so you have received general answers.

You've been given several very good, though generic suggestions, including pseudo-code!, for doing what you want -- we can give you no more information without you giving us some information!

This is really not that hard, but HOW you work with a real time clock varies a lot from brand to brand (Siemens -vs- AB -vs- ...), even between models within the same brand (ControlLogix -vs- PLC5 or SLC500). If you want us to tell you how to do it, you have to tell us what you're wanting to do it with.

Hopefully, it's a PLC that does have a built in real time clock. You really don't want to have to count on an interfaced PC to provide your time for this -- the PC has always been the weakest link in automation (blue screens, anybody!) and I personally will NOT put a PC in control of anything important in my plants. A PC is for viewing INTO the process, not controlling it.

What kind of PLC sold these days doesn't include a clock? Of course interfacing with a PC for the time in that kind of application would be asinine.

Your rant about the place of the PC seems random in this thread, but I share the sentiment. In theory a PC could be a better, cheaper PLC. In practice, Windows boxes running plant controls has made many bad days. I agree with OZEE - much better idea to keep the PLC in control of safety and operation. I don't oppose the idea of using PCs to write setpoints, send start/stop signal, etc, though. The key is to NOT have PLC operation be dependent on the PC running. The degree obviously depends on your requirements in terms of: uptime, safety, and your needs (which a PLC alone may not be able to provide).

Oh yeah, OP, you're not winning any awards on providing the most detailed info. I'd be surprised if you get any more useful replies based on what you've given. In fact, I'm surprised you've received so much for your vague question.

OZEE said:

This is really not that hard, but HOW you work with a real time clock varies a lot from brand to brand (Siemens -vs- AB -vs- ...), even between models within the same brand (ControlLogix -vs- PLC5 or SLC500). If you want us to tell you how to do it, you have to tell us what you're wanting to do it with.

Hopefully, it's a PLC that does have a built in real time clock. You really don't want to have to count on an interfaced PC to provide your time for this -- the PC has always been the weakest link in automation (blue screens, anybody!) and I personally will NOT put a PC in control of anything important in my plants. A PC is for viewing INTO the process, not controlling it.

Click to expand...

My rant about the place of the PC was based on hoping he wouldn't try to take the RTC out of the HMI and try to somehow use it. Yes, technologically it's possible, but Spink hasn't given us enough information to know what he's wanting to try to do.

Good call. I agree.

OZEE said:

My rant about the place of the PC was based on hoping he wouldn't try to take the RTC out of the HMI and try to somehow use it. Yes, technologically it's possible, but Spink hasn't given us enough information to know what he's wanting to try to do.

Click to expand...

If you provide accurate information, you will get accurate answers. But you still have not said what PLC hardware are you using? The commands and locations of data are different for different vendors and different hardware.

To get a good answer, you've got to properly ask the question.

Thanks guys for having interest in my query.
i will try the pseudo code. but, here is the complete picture. sorry for keeping you guys guessing...
1. I have a PLC (ABB, AC31) and MMI(hakko make). Both have RTC inside.
2. I have configured UHR block in PLC which is used for setting PLC clock and using that clock i needed to operate a pump every day for some hours. starting lets say at 9:30 and stop at 18:30.
hoping this time i am clear.