1. On Professional control boards (with LCD display), the negative pole of the analogue opening-command signal must be jumpered to the actuator's internal M earth. With direct terminal-board connection (X3.2 terminals 14 and 15) short terminals 15 and 18; with the round-plug connection (XK pins 11 and 12) short pin 12 to pin 6. See the wiring diagram.
Note: on newer boards (with two additional status LEDs — see page 9 of the control-board description in the December 2003 or April 2004 Chinese manual) the jumper is provided internally and no external link is needed. For older boards not fully wired, remind the user of the jumper.
2. If the negative poles of the DCS analogue input module (AI, carrying the command signal to the actuator) and the analogue output module (AO, carrying the position feedback) are at the same potential, no analogue isolator is needed in the loops of a SIPOS 5 FLASH actuator. If a potential difference exists, an analogue isolator must be inserted in the feedback path to the DCS input channel. If both float to earth, note that the signal negative pole also floats internally (M) inside the actuator — wiring then ties three floating earths together, and voltage fluctuations cause short-circuit currents. If the DCS AI/AO channels are not isolated from each other either, the situation is more complicated still and both loops may need isolators. In the SIPOS 5 FLASH the negative poles of the setpoint signal and the feedback signal are internally common (see note 1). If a potential difference exists on the DCS side, connecting the actuator lets even a tiny voltage difference drive a large short-circuit current that can damage DCS modules (and possibly the actuator control board). And if the note-1 jumper is missing, the resistor in the actuator analogue input path will burn out, causing an analogue input fault, possibly damaging DCS cards as well.
In short: this situation is dangerous — take care.
Furthermore: if the DCS command and feedback module negatives are at one potential but the actuator is another make, an analogue isolator is mandatory, because in that make the two signal negatives may not be common inside the actuator.
3. The analogue feedback signal at the DCS must be wired so that the DCS does not power the loop: the signal is already powered by the actuator. Wrong wiring burns the actuator control board — in severe cases, combined with the situations above, both power board and control board.
4. Needless to say, analogue signals must use screened cable with the screen reliably earthed.
