9/9/2019 8:22 AM | |
Posts: 7 Rating: (0) |
Hi guys Im using a 6ES7 134-6JD00-0CA1 analog card on a 1512SP-1 PN PLC,for a J type thermocouple. the values that i am reading are way of by 20-30 °C . I tried to do a manual calibration, but I failed , I always read the status message "the value supplied by the user deviates too much from the required value" On my hardware configuration i have set my measurement time as j type,see on attachment. on the manual it says that i get the values as a decimal and i must divide by 10 to get the degree Celsius value but it is way out. what else can i check for? Thank you for your reply in advance. ------------------------------------------------------------------------------------------ |
Last edited by: Jen_Moderator at: 09/09/2019 13:49:19New subject after splitting |
|
9/9/2019 8:26 AM | |
Posts: 7 Rating: (0) |
I've also attached more information with regards to calibration The measuring range of my thermocouple is -20-500°C. |
9/13/2019 1:34 PM | |
Posts: 6 Rating: (1) |
I’m jn the same boat as danw, I’m familiar with instrumentation, but not Siemens PLC hardware. Danw has identified the problem. This configuration is using a fixed cold junction reference value of 0 Deg C but the reality is that the temperature of terminals is not 0 Deg C; it’s something between 20 and 30 Deg C, which is the indicated error. On the configuration screenshot in post #1 it shows the selection of cold junction reference as: Reference junction = fixed reference junction Fixed reference temperature = 0 Degrees C The manual at this link shows On page 18 pdf the selections for the reference junction and notes that the default setting is “fixed reference junction”. The reference junction selections are defined on page 20 pdf in table 4-3. It appears that the internal reference temperature is associated with a base unit, whatever that is (I don’t know Siemens hardware). Most analog input modules have an thermistor or RTD used to determine the cold junction reference temperature of the wiring terminals. But that “internal” cold junction reference is apparently in the base unit, not the AI card itself ? ? ? My granfather used “fixed reference 80-90 years ago in the steel mills when they’d bury the physical thermocouple reference junctions 2 meters in the earth where there was constant reference temperature. The instruments of that era had an adjustment to compensate for the difference between the fixed reference temperature and 0 Deg C (part of the calibration routine). But this the first time I’ve run into fixed temp reference used as a default, because nobody nowadays buries their reference junctions in the earth. Group reference temperature is sometimes used where remote terminal assemblies are used, where the thermocouple wire or extension wire transitions to copper wire in a marshalling panel. That is where the cold junction reference temperature needs to be measured, not at the AI card terminals. So an RTD is used to measure the remote terminal temperature and the RTD temperature value is used as the reference temperature for a group of thermocouples connected to that remote terminal block. I suspect this hardware use falls into that category. If your base unit has an internal reference then select and enable it. Attachmentet200sp_ai_4xtc_hs_manual_en-US_en-US.pdf (216 Downloads) |
Last edited by: Jen_Moderator at: 09/16/2019 09:40:53Added PDF file as an attachment. |
|
Follow us on