Questions about Yokogawa CS3000
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This post was last edited by jacob451 on 2011-3-17 at 12:50. I would like to ask: when a thermocouple (with an on-site transducer unit) generates a 4–20mA signal that is sent to the AI card, how does the program convert this 4–20mA signal into the corresponding temperature value? For example, in what way is the value %TT123 output to the PVIPVI function block used to display the current temperature? Is it related to the RAW value set during tuning in that function block?
The thermocouple is connected to an AI card through a temperature converter; this converter sets the range of the thermocouple, for example to 0–1000 degrees, with the corresponding current signal being 4–20 MA. The temperature converter first converts the thermocouple’s MV signal into a temperature value, and then transforms it into an MA signal that is sent to the DCS. The DCS already has configurations for these temperature values, and the range specified in those configurations must match that of the temperature converter. In this way, the 4–20 MA signal received from the temperature converter can be converted back into the corresponding temperature value. This is how I understand it; I’m not sure if you get it
It is recommended that the original poster learn about the basic principles of A/D conversion and D/A conversion. Then further understand the working principle of AI cards.
The explanation on the 2nd floor is very good: the range in the configuration must match the range of temperature variation; by paying attention to this point, the temperature will be properly corresponding. It has nothing to do with the RAW value.
After three linear conversions, 4-20mA is first converted to 1-5V, then 1-5V is converted to RAW values, and finally the RAW values are converted to values expressed in engineering units