Andrew Evenson
Member
Hi guys!
I need your expert opinions on a problem of mine. Here's the story:
We have a solution tank in with we control the level. The level transmitter is analog, and is wired up in to the local rack. Lately, I seen a lot of shift calls stating that the HMI screen "freezes" up.
What has been happening is instrumentation has just been powering down and powering up the plc. The level now is unfrozen, and represent the true level in the tank.
I raised a stink about thier practices on resolving the problem, but wasnever around until yesterday to see what is really happening.
So, yesterday, the level froze again. I got instrumentation to check their instrument, it was reading 25% level in the tank. the PLc was reading 62% tank level. The analog output out of the level transmitter was approx. 8mA, so the istrument was OK.
What I did find though was the block transfer instruction for this analog card was not excecuting. I could write to the analog point for the level and it would accept my edit. i didnt see the ERR bit come on though...strange.
Now, we did power down the plc, and reseated the card. The problem went away, obviously, because the block transfer was reinitalized when the plc was re-powered up. Now I understand why instrumentation thought resetting the PLC "fixed" the problem.
I talking to the ex-line specialist, he indicated that they have had this problem since the plc went in(approx. 6-7 yrs ago.). They have also had problem with sensors in another tank, which just happen to input to the slot next the one that faulted yesterday. They had swapped out the susspected faulty card with another known good one in the rack already, and the problem still/has occured. I suspect the Rack/backplane to be fualty, and think it should be replaced. That is the one thing they haven't tried yet. Now, I should also state that the PLC itself does not freeze, it is still running when this problem occurs. What do u think???
Any input would be sppriciated.
Andrew Evenson
I need your expert opinions on a problem of mine. Here's the story:
We have a solution tank in with we control the level. The level transmitter is analog, and is wired up in to the local rack. Lately, I seen a lot of shift calls stating that the HMI screen "freezes" up.
What has been happening is instrumentation has just been powering down and powering up the plc. The level now is unfrozen, and represent the true level in the tank.
I raised a stink about thier practices on resolving the problem, but wasnever around until yesterday to see what is really happening.
So, yesterday, the level froze again. I got instrumentation to check their instrument, it was reading 25% level in the tank. the PLc was reading 62% tank level. The analog output out of the level transmitter was approx. 8mA, so the istrument was OK.
What I did find though was the block transfer instruction for this analog card was not excecuting. I could write to the analog point for the level and it would accept my edit. i didnt see the ERR bit come on though...strange.
Now, we did power down the plc, and reseated the card. The problem went away, obviously, because the block transfer was reinitalized when the plc was re-powered up. Now I understand why instrumentation thought resetting the PLC "fixed" the problem.
I talking to the ex-line specialist, he indicated that they have had this problem since the plc went in(approx. 6-7 yrs ago.). They have also had problem with sensors in another tank, which just happen to input to the slot next the one that faulted yesterday. They had swapped out the susspected faulty card with another known good one in the rack already, and the problem still/has occured. I suspect the Rack/backplane to be fualty, and think it should be replaced. That is the one thing they haven't tried yet. Now, I should also state that the PLC itself does not freeze, it is still running when this problem occurs. What do u think???
Any input would be sppriciated.
Andrew Evenson