Data conversion process from field instruments to DCS
Thread Content
The data conversion process from field instruments to the DCS, as found online: 1. The transmitter outputs a 4–20mA signal. 2. The explosion-proof junction box contains only terminal blocks; it does not perform any signal conversion, so the signal remains 4–20mA. 3. In the cabinet area, there are terminal block cabinets that reorganize the different signals before connecting them to the corresponding safety barriers (in the case of an intrinsically safe design); at this stage, the signal is still an analog 4–20mA signal. 4. The DCS I/O cards convert the analog signal into a digital signal, through an A/D conversion process. 5. The CPU reads the digital information. 6. The digital information is displayed on the operator station via the network. Can it be understood in this way: if the measurement range of the field flow meter is 0–50 t/h and the actual flow rate is 20 t/h, then the transmitter outputs a 10.4mA signal. After a series of conversions, before the value is displayed on the DCS screen, the percentage of the digital signal is multiplied by the range specified in the meter’s configuration settings to obtain the displayed value. So if the range value in the configuration information is entered incorrectly as 0-100 t/h, will the DCS display 40 t/h?
There is no need for taking a square root. Yes, in the case of a differential pressure gauge connected to a DCS, what is transmitted is the differential pressure current
Without considering the square root, that’s what it means. To correct that: it’s not a digital signal, but an analog signal
For differential pressure flowmeters, the issue of square rooting needs to be taken into account. There are two types of square rooting: square rooting of the gauge reading and square rooting of the system parameters. You are referring to the case of square rooting the gauge reading.