HMI going blank even though supply is ON

Hi All

I am using SIEMEN's HMI with 24 VDC input ... Supply seems to be sufficient (rated 24V ... 3A...). Last week we connected one NPN
switch across PLC.. used pull up resistor after making all calculation on bennch and now Not sure but some how My HMI is acting up. Problem is not consistent .It just goes blank ....

1. I tried different HMI... same HMI will work outside once this happens and if you put it back it will work again.

2. Siemen's HMI-270 B has input polarity protection so if it sees short it goes blank... but in this case it will be functional many hours and then suddenly this will happen. I could not repeat the fault....

We have pressurized cabinet, regulator set to 1.5 PSI ; switch is set to 0.8 PSI ( It is vacuum switch..) Pull up resistor has been added across PLC have enough value and wattage rating...

Is this something related to pressure or connecting switch... it is 3 wire switch .. one connected to PLC input and other two connected to supply as manufacturer diagram states....

If any one can supply any comments on this that will be great help.. Appreciate...

Shot in the dark

Some HMIs have a configuration setting similar to a PC, after X amount of time not used they may hibernate (screen goes blank). May want to check the manual(s) etc to verify this is NOT an issue.

Yes Checked that one out. It is something else. I am suspecting
pressure switch with Pull up resistor( It is NPN sensor)

Sounds to me like you are mixing cause/effect issues.

OK... you introduced something.

I would dare say that you did some coding to handle that something.

I wonder... if you were to remove that coding, would the screen behave?

If so, then I would have to believe that the code is affecting the "paging".

That is, the coding cause a Blank Page to be called up.

Try removing or negating the code and see what happens.

If the screen returns to normal operation then you need to examine, very carefully, the new code, for it's affects on paging.

try isolating the issue... if you have a spare 24vdc power supply, wire it up and run only the HMI off it and see if it goes away. if problem goes away, then quadruple check the wiring and make sure nothing is shorting out, then try a bigger power supply.

that's my gut instinct without being able to see the actual setup.

Coding was just adding a logic for switch which is turning on and off based upon code .... so seems to be ok

Sounds good let me try that.

Ok finally found the problem.Had a bad CF card and it was causing HMI screen to go blank. Interesting....I kept on worrying about electrocnis
including new pressure switch, pull up resistor value etc etc...Thanks all
for help