School Temperature Project SNAFU

I recently was tasked with recording the temperature over spring break and placing the values, along with a timestamp. I ran several tests over night for a few days and had no issues, and also changed the limit test value to the minute and the equal to statements to seconds, allowing me to test the program through a full run. The tests all went fine, however when I set up the program to run over spring break week, my program collected no data and I cannot figure out why. The only fault I had was minor one, Code 3 Type 93, which another group had as well, but there program was able to collect the data. The fault is an issue with asking for data from that analog module faster than it can produce it, as I understand it. I'm sure there must a stupid mistake somewhere or a legitmate reason why it didn't work, but I can't figure it out and it's driving me crazy. The only difference between the test runs and the final run, was during the final one, I unplugged the PLC from power, with a working battery, carried it over to its location and plugged it back in. Thanks for any insights offered.

first off, you ran a successful test.

what did you change? you added the minutes and seconds parameter.

so then, modify the code for minutes only and run test.
when it is successful, add the seconds, although this one may be hit or miss depending on the cpu speed.

question, why didn't you run a test after you modified the program for minutes and seconds to confirm it works?

in the plc world, NEVER assume it works! you must test your code each and every time.


since you didn't tell us the plc type and i/o configuration, i'm not much help.

regards,
james

The PLC is a 1769-L23E-QB1 with the expansion thermocouple input being a 1769-IT6/A, using rev 20.I tested the program with all the changes, and it ran fine, both using minutes and seconds, and when i was using the day and minutes as the test values. There were no issues with the data being collected through testing and the analog module configuration worked fine throughtout, the only change ever made without testing was unplugging the PLC and plugging it back in. I know the program was retained because when I retrieved it and connected, I was able to go online without being asked to upload or download a program, instead of the warning saying the programs did not match.

check if the file is still open,

Wish I could, it was kind of a one shot deal, my teacher checked and couldn't locate an issue, and then another class had to use our training PLCs. At this point, it is just about figuring out what happened and why for my own curiosity. If the power was cycled, the school has been having brief power troubles, would the first scan bit be reset, or would the battery retain the one shot condition.

the first scan bit is set on two occasions.

#1 when you go from program to run mode. true for one scan

#2 when the system powers up and enters the run mode for the first scan. one scan only

someone may correct me on the 2nd point, i'm still learning
the 5000.

regards,
james

Why do you have a limit on the days? Only going to work between day 9 and 15. At day 27 when you saved.

Also, you're first rung one shot isn't going to work. After the first time, Bit_First_Scan_One_Shot will be on forever. The OTE instruction is simply writing a 1 to that memory location. Next time you run the program it's already sitting at one, so the XIO evaluates as false and the Bit_First_Scan bit never comes on. The act of power cycle or going to program mode DOES NOT CLEAR any memory bits.

The period of time we were collecting data was midnight on the 9th to 11:30 PM on the 15th.

The first scan bit was intended only to clear out old data upon the program being redownloaded, just so it was clear that the data present reflects the current program.

The program was still in the PLC and the GSV instruction was placing the correct present time in the day/time array, which tells me that the battery worked as intended.The only way I think I would get the results I am seeing, which is 0s for all the data locations, and 0 in the counter's accumulated value, is if the first scan bit went TRUE again upon the power being cycled when I unplugged my PLC,brought it back to my desk, and plugged it in. I am testing this at the moment, using the same first scan bit logic, to see if the First_Scan_One_Shot retains it's true state when power is cycled, I will be using a counter incremented by the First_Scan_Bit to determine if it increments with every power cycle.