Automation Direct DL250 Analog Drift

WE HAVE HAD A DIRECT LOGIC 205- DL250-1 PLC FOR 8 YEARS. NO PROBLEMS. LAST WEEK WE HAD A SHUTDOWN AND AFTER WE TURNED POWER BACK ON WE HAVE NOTICED OUR ANALOG INPUT AND OUTPUT (4-20Ma) SIGNALS ARE AROUND 50% HIGHER THAN USUAL. THE 24V POWER SUPPLY HASNT CHANGED,STILL STEADY AT 24V.
THE CARDS ARE FD-O8AD-1/FD-08DA-1 . NEITHER CAN BE CALIBRATED. DO YOU THINK WE HAVE A BAD PROCESSOR?

Hello,

Is the A/O that is wrong Dependent on the A/I that is wrong?

Have you checked the actual mA reading coming into the input to see if it is what you expect it to be or if it is 50% higher than what you would expect it to be?

Both the input and output signal are independent of each other. We are going to check the counts tomorrow. Its very strange both cards are reading high . I am sure its the processor ?

Don't check the counts, check the currents.

Highland Controls said:

Don't check the counts, check the currents.

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I agree, see what you're getting from the device. I'm only an electrician and am just getting started in PLC's, but from my little bit of experience it seems 9 times out of 10, it's the device or cabling that causes issues.

phil hughes said:

AFTER WE TURNED POWER BACK ON WE HAVE NOTICED OUR ANALOG INPUT AND OUTPUT (4-20Ma) SIGNALS ARE AROUND 50% HIGHER THAN USUAL.

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You don't say what the field sensors are. It would be highly unusual for multiple field sensors to fail in the same fashion simultaneously. But they could be reporting the truth depending on what the app is. For instance, if they're pH in an equalizing batch tank, the contents might very well have doubled in pH after an outage.

phil hughes said:

THE 24V POWER SUPPLY HASNT CHANGED,STILL STEADY AT 24V.

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4-20mA field devices are current regulators so a higher than normal (but still within tolerance) power supply voltage will be compensated for by the field device(s). A power supply lower than required will result in a failure to drive the loop load resistance, appearing as a failure achieve a 17 or 18 or 19 or 20 mA value, depending on what the loop resistance is and what the power supply voltage is. So it's not the power supply.

phil hughes said:

THE CARDS ARE FD-O8AD-1/FD-08DA-1 . NEITHER CAN BE CALIBRATED. DO YOU THINK WE HAVE A BAD PROCESSOR?

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Usually the AI card converts the analog signal to a digital word format that the CPU uses. So the first suspicious component is the AI card. I'd replace the AI card before replacing the CPU.

Let us know what you find.