Why would AB Clocktime Reset on download

I'm using a GSV to get the time from a Contrologix plc.

I noticed duplicate data in my SQL database.

We calculate a Julian date from the PLC clock for dates in a barcode and those clock dates got reset somehow. The timestamp(from SQL) of the reset was within minutes of a download I did to the line.

Can a download affect the PLC clock?

I know I did an upload seconds before I made a small servo config change, and redownloaded... but that does not explain why the PLC clock would change.

I fixed it using the Clock tool and am considering putting it in the startup of our local server. I didn't actually change code to fix this problem. The clock tool put the code back on track.

Thanks for any help.

P.S. I know PLC clocks are inaccurate. We use it for days not seconds. I am fully aware of many pitfalls involving PLC clocks... except of course for this one.

What was the date/time at the start of the download?
What was the date/time after the download?
Did any data get logged during the download?
Does the database read the PLC for data, or does the PLC write the data?

Basically, "reset" doesn't tell us what happened.

JeremyAdair87 said:

I'm using a GSV to get the time from a Contrologix plc. ....

Can a download affect the PLC clock?

Click to expand...

No. Downloading does not affect the clock. However...... if your program uses an SSV to set the time, then downloading could download old tag data which when the SSV runs could load old data into the clock.

OG

If you honestly want your data to by timesynched, pick a source and ONLY use that. For if you are using SQL timestamps, just use the timestamp from SQL. Select GetDate() will return the current SQL timestamp. Select GETUTCDATE() will return the GMT date time.

JeremyAdair87 said:

I'm using a GSV to get the time from a Contrologix plc.

I noticed duplicate data in my SQL database.

We calculate a Julian date from the PLC clock for dates in a barcode and those clock dates got reset somehow. The timestamp(from SQL) of the reset was within minutes of a download I did to the line.

Can a download affect the PLC clock?

Click to expand...

Firmware updates reset the clock to whatever the default is. I think ControlLogix is sometime in 1990.

Just uploading the PLC program and flipping to run doesn't do that on my ControlLogix system. We are running V27 on the L71 and L73s, V20 on the L61 and L63s.

I disagree with bad times from PLC clocks. I use a time server with a GPS input to broadcast NNTP on a dedicated subnet. An EWEB card receives that info and is the time master of the GPS ControlLogix rack. The 1756-L61 in that rack is time-synced to it. And the L61 is in turn the time master on our internal programming network. All 12 ControlLogix PLCs and 10 pairs of DeltaV controllers are subscribed to that time master and are within a few ms of each other.

We use time stamps to figure out what went down first between our PLCs in different buildings, ground fault info from our load center metering, transfer trip info from our substation metering, etc. It's cumbersome and takes a while, but the data is there if you want to dig it out.

Making PLC clocks accurate is *VERY* expensive, but so is down-time!