Siemens RTD temperature sub zero

mass89

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M
Join Date
Oct 2017
Location
England
Posts
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Hi,
I have siemens SM1231 RTD module, the temperature I need to read is sub zero. The input is 15 bit plus sign, anyone can suggest the easiest way to convert input word to signed integer?
Thanks
 
From the manual:
The SM 1231 RTD analog signal module measures the value of resistance connected to the
module inputs. The measurement type can be selected as either "Resistor" or "Thermal
resistor".
● "Resistor": The nominal range full scale value will be decimal 27648.
● "Thermal resistor": The value will be reported in degrees multiplied by ten (for example,
25.3 degrees will be reported as decimal 253). The climatic range values will be reported
in degrees multiplied by one hundred (for example, 25.34 degrees will be reported as
decimal 2534).
Click to expand...
So it depends on what you have the module set to output. I would suggest that Thermal Resistor would be the way to go, then you just need to convert to Real and divide by 10 or 100.
 
BryanG said:
From the manual:
So it depends on what you have the module set to output. I would suggest that Thermal Resistor would be the way to go, then you just need to convert to Real and divide by 10 or 100.
Click to expand...

TIA, S7-1215, LAD, FBD or SCL, thermal resistor

I understand what you say and yes its true to just divide the input word by 10 and the result is in Celsius, as long as the temperature is > 0
When the temperature is less than 0 for example minus 10, one bit of the word represents the sign (being minus), and so the result is an input word 62000 for example which doesn't mean anything.

I ask if anyone knows easy way to take the input word of 62000 for example which would be a sub zero C temperature and convert to signed value
 

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