Position Transmitter Principle
Indicates the valve opening with potentiometer and the resistance value is sent to DCS and the opening by step from 0%-100% can be read. : V = I(4-20mA) x R(resistance value), i.e. the variation of resistance value is made depending upon the current in case V (Voltage) is constant. Accordingly it’s mainly applied to modulating type to verify the position, and the routine verification and monitoring for the valve opening is available at DCS. For Smart type it can carry out the function of Position Transmitter at the same time, Limit Switch is normally built-in.
A signal of 4-20mA is transferred from main board to potentiometer then the resistance value of potentiometer is computerized at the main board, and the data(opening %) is transferred to DCS in case that the order value is surely carried out and the action value does not make an error. In case purchaser wants to read the actual feed-back value at DCS not the value computerized for the opening %, as an option the resistance value,- indicated by potentiometer connected to the feed-back module separately put in the positioner, is transferred to DCS. Operator can recognizes the accurate opening % at this time because it indicates the direct resistance of potentiometer, not computerized value. The voltage for this smart positioner is available with DC voltage (12V DC, 24V DC, 48V DC) only, but not available with AC voltage (110V AC, 220V AC).
Author - Stanley Park