Want to read value from PT100

Hello, I want to read value from PT100, and I am using FC105 block.

Measuring value is different on OUTPUT FC105 from the manual thermometer.

Do I need to use some constant or what?

Thanks for your help.

------------------------------------------------------------------------------------------
Split from Pt 100 temperature measurement.

Zlatko.p

Hello, I want to read value from PT100, and I am using FC105 block.

Measuring value is different on OUTPUT FC105 from the manual thermometer.

Do I need to use some constant or what?

Thanks for your help.

------------------------------------------------------------------------------------------
Split from Pt 100 temperature measurement.

 Use the forum search with PT100, then you will get your answers.

Hello Zlatko;

If you provide more precise information, we might be able to provide more precise answers.

What is your CPU, what version of Step 7 are you using, which analog input module do you have to read the PT 100, how have you wired it to the PT 100 (2-, 3-, or 4-wire connection)?

How far is the output of the SCALE FC from the manual thermometer? Please give us a screeshot if the FC, in Online mode if possible.

Hope this helps,

Daniel Chartier 

I am using jumo 0-150C  temperature sensor with transmiter 4-20mA analog signal which is connect to moeller analog card T-XN-1AI-I(0/4-20MA) with CPU 315-2DP.

Difference between sensor and manual thermometer is 10cm.

MD20 is always higher approximately 14% then temperature on manul thermometer.

I check temperature with two difference thermometer.

Hi there,

If i look at specs of:

• The analog Moeller card then i notice that is converts values from 4 .. 20 mA to 0 .. 32767
• The Siemens FC105 block then i notice that it internally converts values in a range of 0 ... 27648

So the values send by the analog Moeller card does not match with FC105. Think you need an other function to do this or create your own function.

Nice to know : Within S7-1200 you can use SCALE_X and NORM_X.

Link to analog Moeller card: https://www.eaton.com/content/dam/eaton/technicaldocumentation/mn/MN05002011Z_EN.pdf

Hello Zlatko;

The example provided as attachment is based on this FAQ, modified to take into account the numerical range of the K_Moeller analog input module:

How can you standardize and destandardize analog values with STEP 7 V5.5?

https://support.industry.siemens.com/cs/ww/en/view/24624928

Note that you must convert the numerical reading you get from the analog module (which is in integer format) to a REAL value (floating-point) if you want to use floating-point calculations. If you are doing this in LAD, use MUL_R, DIV_R ... instructions in your program.

Hope this helps,

Daniel Chartier