Analog input broken wire

Hi all.

I use S7-1200 CPU for one project.

Also I have sensor 4-20mA.

How to detect broken wire for that input?

I know that I must check Enable wire broken diagnostic, and include OB82 in project.

But how to know which bit or variable I should check for broken wire?

Hello Friend 

It is an instrumentation issue any way it is the reason of 4-20 mA standard. Why we are using 4-20 mA not 0-20 mA and we know bot of them are standard? 

The answer is simple because in 0-20 mA we can not see the difference between open loop or wire broken and the 0 mA

But if you use 4-20 mA and the feed back was 0 It means absolutely an open loop or broken wire....

MAZENJER

Hello Friend 

It is an instrumentation issue any way it is the reason of 4-20 mA standard. Why we are using 4-20 mA not 0-20 mA and we know bot of them are standard? 

The answer is simple because in 0-20 mA we can not see the difference between open loop or wire broken and the 0 mA

But if you use 4-20 mA and the feed back was 0 It means absolutely an open loop or broken wire....

 Thank's a lot. That's clear for me, but I want to know how to use OB82, and check codes to recognize wire break, and other errors

I found this: IOstate

How to know exact IOstate bits status, for example, analog input wire break?

Hello Milosh;

Look at the following screenshots, taken from the S7-1200 System Manual:

SIMATIC S7 S7-1200 Programmable controller

https://support.industry.siemens.com/cs/ww/en/view/109478121

You can use OB82 on analog output modules, and also on RTD/TC temperature input modules (check the manual Appendix A.8 and A.9 for more details).

For analog input modules, you must rely on the 4-20 mA undercurrent reading for broken wire diagnostics in your program, as explained earlier by Mazenjer.

Hope this helps,

Daniel Chartier

dchartier

For analog input modules, you must rely on the 4-20 mA undercurrent reading for broken wire diagnostics in your program, as explained earlier by Mazenjer.

 Hi Daniel,

I am a bit confused. So, if wire is broken, I should get 0 mA (which corresponds to the integer -6912).

But what if I get 32767?  

Look at the picture attached here, please. Upper values are raw integers, lower values are temperatures in range 0...50°C, except the first one, which is -50...50°C).

Please, ignore the first two sensors, they are connected wrong!

Sensor is QAA2071. Values are scaled according to the For an S7-1200/S7-1500 controller in STEP 7 (TIA Portal), how do you scale integer values in real numbers and vice versa for analog inputs and outputs?

I am using Analog Input module (6ES7 231-4HF32-0XB0), each input is configured as 4-20 mA.

My question is: why for disconnected sensors I do not get 0, only 32767?

Hi,

Not going into details, I can only say that you will get 32767 for 4-20mA signal, if there is an open circuit (wire break). (if you have 4-20mA configured in your analogue card in the HW config)

In your analogue scaling logic you can add a condition to inhibit scaling (e.g. make signal to equal 0) if the raw input value is 32767.

Regards,

Tom

Hello,

so for signal 4-20mA, how you can distinguish between open loop and overflow with 22,96mA, where you get 32767 too?

AutoGen_7492078

Hello,

so for signal 4-20mA, how you can distinguish between open loop and overflow with 22,96mA, where you get 32767 too?

 Read the I/O modules manual, there is usually description what value represents what situation.