SLC-50/4 Processor Fault wont clear

[sparkytex]

Hello all,

I noticed our "Airmaster" PLC which is a SLC 5/04 processor was in Fault when I connected to it via DH+. I cleared the fault and put the processor back into RUN mode and the fault happened again. and keeps repeating. I went to "go to error" and the description is as follows "a minor error bit is set at the end of the scan. Refer to S:5 minor error bits. When I look at the S:5 table S:5/0 = 1 (math overflow trap) and also S:1/13 = 1 (major error halt). I will attach the program to this post. If any one could help me I would greatly appreciate it.

cheers, Tex

 

[mscholz]

Look at I:4.0, it is so high that after it goes through the SCP it drives O:4.0 beyond 32767, causing a math overflow.

 

[Operaghost]

When a math operation causes an overflow as the SCP on Rung #57 is doing, it sets a bit called the Overflow (S:0/1) bit. That bit causes the Overflow Trap (S:5/0) bit to set. If the Overflow Trap bit is still set at the end of the scan, the controller faults with the error you are seeing.

Many programmers will add an additional rung at the very end of the logic to unlatch the Overflow Trap bit. This prevents the controller from faulting due to the math overflow. The logic COULD still use the Overflow bit to identify that there has been an overflow and take an action.

So the larger problem is that the SCP has identified that your input Discharge Air Pressure (ACFM) is supposed to range from 3277 - 16384. But the value as displayed is 24032. Why did that happen?

OG

 

[sparkytex]

ok, I'm having an instrument mechanic look into the pressure transmitter and possibly re-calibrate it. Hopefully that's the issue. I know they were working on it a while back, maybe they changed the range of the pressure transmitter and it no longer correlates with the logic.

 

[Operaghost]

Ideally we could add some error checking logic in there to prevent it from happening again. Just one possible example here. Although I would probably also want to add something to tell me when we are out of range again.

OG

 

[sparkytex]

awesome suggestion ghost, I programmed that and am at least able to put the processor back into run mode and I can clearly see the raw data from that analog channel (pressure transmitter) jumping all over the place from 6 to 23,000 raw data. The instrument mechanic is down at the transmitter checking it out. Thanks for your guy's help!

Cheers