Siemens s7-314 analogue problems

[bob.southall]

Hi all

I have a cpu314c with a 5ai/2ao unit, I can’t get any reading within my program.
I have tried with the simulator and the program works, but I can’t get a reading from the sensor (load cell, 0-10v)
I also canno get a reading when I put 9v onto the terminals (2&4) for ai0. I have also tried ai 1 and ai2.
My iw for ai0 is iw256. I have monitored this with a watch table but no reading in there either.
Do you have to turn on the configuration somewhere? Or can it be turned off somehow?

Regards, Bob

 

[Mike_RH]

How big is the process image?
Try PIW256

 

[JesperMP]

Is it a load cell with a resistance bridge, 4-wires or 6-wires connection, and 0-10V excitation ?
If so, you cannot really use a regular 0-10V analog input.
The load cell voltage value is very very small. That is why a either an PLC card for loadcells, or a loadcell signal converter (to 4-20 mA or 0-10V for example) is typically used.

 

[bob.southall]

I have attached a screen shot of where it is in the program....

The load cell has a 0-10v signal converter attached.

It has been working for 3 months without fault.

However, I cannot see the analogue signal representation in the program...

 

[JesperMP]

Try Mikre_RHs suggestion.

edit: and what do you mean by the "It has been working for 3 months without fault" ?

 

[bob.southall]

The machine has been installed for 3 months in this format, the load cell was a retrofit to give an even press to all products.

Yesterday the machine failed to stop when pressing and while trying to find the cause I saw that I had no value in the corresponding analogue input (%iw256).

I thought by giving the analogue input 9V it would alter this value and prove that the plc hardware was ok?

But I dont know enough about Siemens to confidently say that it is the analogue input card....

 

[JesperMP]

Repeat: try Mike_RHs suggestion.

 

[bob.southall]

Ok will try and report back. Thanks for help.

 

[RClem]

I would also confirm the address in the hardware configuration.