SM1231 Analog Input - High Limited Exceeded

How about putting a delay timer on your main low voltage power and use the output of that delay timer to power these 4-20mA sensors with this overflow problem.

You could do this with a simple hardware switch to prove the point. 

Power up the plc, and once it starts scanning logic, flip the switch to power these sensors.  Now wait for the sensors to stabilize and see if the readings at the analog inputs are happy, or are they 32767?

If they are 32767, you want to reverse this and power these sensors before the plc gets power.

If it were me, I would contact Siemens support via My requests and create a new request with this issue.  You can test these ideas while waiting for them to answer you (tomorrow).

Send your project, and screenshot of your schematics and ask what you need to change as part of your request so they can give the most help.

Eli_Dias

Hi,

I'm using a SM1231 input module with a 1214C CPU (V4.2). It is reading pressure from 2-wires sensors (4-20mA).

I desabled broken wire and overflow diagnostic funtions, but whenever there is a power failure, once the PLC gets back to run mode the analog input reads 32767.

When this happens, an error of high limit exceeded is shown in the alarm buffer, but the PLC doesn't go to stop mode, since the diagnostic funtions were desabled.

The reading is only reestablished when I unplug the cable that comes from the sensor to the input module and plug it again.

Can anyone give a clue?

What ended up solving the problem? 

Eli_Dias

Thank you for your help!

Common mode errors are so difficult to find and get rid of. 

Eli_Dias

Hi!

At first I used your idea to use a relay, so the plant wouldn't get stuck anymore.

After a few tries, Siemens came up with the suggestion to use a 10k resistor in parallel with the analog input, and it worked! Apparently, there was a transient condition that was causing the analog module to "read" overflow and not leaving this condition once in steady state.

Thank you again!

How long has the system been in operation that is now seeing temperature and displacement analog inputs fail?

Are all analog input's in use?  Are any AI not used?  If there are, for each unused analog input, are they configured for voltage with jumper across input terminals, or not jumpered and configured for current input?

What type of temperature sensor is connected?  Are you using a TC or RTD AI module for the temperature input(s)?

For the other analog inputs, what size and type 24VDC supply is used?  Switching or linear?

Ken007actronics

HI, What it reaally happened? i have the same faiture for a temperature sensor and a displacment sensor input? please help