change of shift

plcnewbie · Sep 1, 2006

I recently had an issue where the shift change occured but the PLC was powered off so the oneshot didnt go off at the correct time. I am currently using an equ instruction to know when to change shifts for data collection.

What do you use for this if the PLC is off when it happens to avoid this problem.
I was thinking of using a LIM. Would this be correct?

ChuckM · Sep 1, 2006

I assume you are using an SLC. Perhaps you can move the current hour somewhere with a one shot the goes true when where you move it doesn't equal the current hour. Then compare the last hour you recorded with the hour you see on the first scan next time the SLC powers up.

RSL · Sep 1, 2006

A LIM instruction for each shift would be a lot more reliable.

You just define the beginning and ending times of your shifts and use them in the limits and compare them to the current time. If the time is between the beginning and ending of a shift then it is "That" shift.

Using limits would not let it miss a shift change. Once the plc is powered up it would set the correct shift word or bit. The only thing that will throw it off is the plc's internal clock. It might be wise to update the plc's time from an HMI or other source regularly. The clocks do drift a little.

Be careful how you define your shift overlaps. It is possible to have two shifts or no shifts be "true" at the same time if you are not careful about defining the beginning and ending times.

RSL

rsdoran · Sep 1, 2006

I would consider a UPS.

geniusintraining · Sep 1, 2006

rsdoran said:
I would consider a UPS.

Ta da!!!! and the winner is

Ron got my vote.

plcnewbie · Sep 1, 2006

The clocks on our machines are all messaged from a main server as well as the HMIs so they are all pretty much the same.

Would I even use a UPS if I was powering down for cleaning or what not? I just got done putting in the LIM commands instead and I am pretty sure I got it right as far as the overlaps.

TimWilborne · Sep 1, 2006

This is what I use. It will execute your ons on power up after a shift change. A UPS is not a proper solution for this problem. Shutdowns and breakdowns can shut machines down longer than a UPS last

ControllerStatus.DateTime[3] = Hour
ControllerStatus.DateTime[4] = Minute
ESSV1PR1In[9] = 1st Shift Start Hour
ESSV1PR1In[10] = 1st Shift Start Minute
ESSV1PR1In[11] = 2nd Shift Start Hour
ESSV1PR1In[12] = 2nd Shift Start Minute

And yes I have it in RsLogix 500 too

TimWilborne · Sep 1, 2006

For some reason I can't get my other image to post but pretty much take the Running1stShift bit and put it in front of ONS, then the shift change code you wish to execute just like you normally would.

plcnewbie · Sep 1, 2006

TW,

Thanks that looks good.

geniusintraining · Sep 1, 2006

TWControls said:
A UPS is not a proper solution for this problem.

TW,

I don't know enough about bit shift's to give a good answer other wise...but are you saying that UPS are bad in general? and don't think they should be used? or that they would not be a good resolve for this?

I have several on UPS (for other reasons)

TimWilborne · Sep 1, 2006

geniusintraining said:
TW,

I don't know enough about bit shift's to give a good answer other wise...but are you saying that UPS are bad in general? and don't think they should be used? or that they would not be a good resolve for this?

I have several on UPS (for other reasons)

No GIT, UPS is a very good thing. I am saying that it is not good to rely on a UPS to keep data such as this from being lost.

TimWilborne · Sep 1, 2006

Here it is in RsLogix 500

RTC:0.HR = Hour
RTC:0.MIN = Minute
L20:9 = 1st Shift Start Hour
L20:10 = 1st Shift Start Minute
L20:11 = 2nd Shift Start Hour
L20:12 = 2nd Shift Start Minute

geniusintraining · Sep 1, 2006

Ok, Thanks

TimWilborne · Sep 1, 2006

The reason I don't like relying on a UPS in this instance is from previous problems I have had doing this. If you have a machine that is struggling but is still running and there is no danger in contining running it for now, are you going to shut it down now or wait till then end of the shift?

And of course the end of the shift always is about 10 minutes early which means the machine is down at the shift change time.

This always seems to end up being our long shutdown periods, this is why I don't like to rely on the UPS for this.

I like to use the UPS for our encoders to ride through short power outages and to report all fault information to our central diagnostics before they shut down. I can cut down the time it take for us to get them back up tremendously.

rsdoran · Sep 2, 2006

Ok I will bite. I am not sure what TW is saying exactly, if it is to send the data on next powerup after a shift change then I would agree.

I assumed the issue was with the machine being turned off 10-15 minutes prior to shift change. If that is the case then the plc can monitor that power is off within a specific time of shift change and will have time to send data or log the data for transfer at next powerup.

I was not refering to the UPS to be used for anything more than allowing the PLC to finish transfering or logging the data for transfer, if power is cut at wrong point it may not complete.

Personally I wonder why they are cutting power at a shift change? Are there just 2 shifts and 2nd powers off?

It mainly depends on how important the data is, I have had cases where the PLC had to be powered separately and was never, or rarely off.

change of shift

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