10
We recommend, nevertheless, that you check zero after the actuator has been
attached to the valve. Proceed as described below:
1) Connect an ammeter to the control signal input and apply compressed air to the
input "Supply".
2) Loosen the fastening screw and move away the cover plate (3, fig.4).
3) Pull the jumper from the pins to deactivate the tight-closing function.
Zero is adjusted via the zero adjuster (4, fig.4) and the upper range value via the
potentiometer for span (1, fig.4).
Important:
Each modification of span results in zero shift. Zero must therefore
always be corrected after the span has been modified.
1.1 Adjusting actuators with close fail-safe action "Air to open"
Zero (starting point)
1) Use an ammeter to adjust the input signal to 4 mA.
2) Turn the zero adjuster (4, fig.4) until the plug stem just begins to leave its rest
position.
3) Switch off the input signal and then slowly increase it again. Check if the plug
stem begins to move at 4 (+0.1) mA.
4) Correct any deviations via the zero adjuster (4, fig.4).
Turning counterclockwise causes the valve to leave its rest position earlier,
whereas turning clockwise causes the valve to delay leaving of the rest position.
Upper range value
5) Having completed adjustment of the starting point, use the ammeter to increase
the input signal to 20 mA.
When reaching the upper range value of 20 (-0.1) mA, the plug stem must have
passed through its entire rated travel range of 100 %.
6) Adjust the potentiometer for span (1, fig.4) until the upper range value is correct.
Turning clockwise increases the travel, and turning counterclockwise reduces the
travel.
7) When the correction procedure is finished, switch off the input signal and slowly
increase it again.
First check the starting point (4 mA), afterwards the upper range value (20 mA).
8) Repeat the correction procedure until both values are correct.
9) Plug the jumper on the pins so that the tightclosing function will be activated.
