Bulletin hy14-1450-M1/us installation and Service Guide
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| Null Adjustment
If it is desired to have the actuator go in a preferred direction with electrical power off (electrical failure), a null offset adjustment can be made to make sure the actuator moves in the desired direction. To adjust the valve null, the following procedure should be used: 1. Remove the screw from the null adjust access hole in the valve cover. (See installation drawing for its location). 2. Make sure the actuator or motor is unobstructed in case it were to move its load fully in either direction. 3. Disconnect the electrical connector on the valve. 4. Apply the rated supply pressure to the valve. 5. Insert a non-ferrous 1/16 inch hex wrench into the access hole and engage the adjusting screw. (A ferrous metal wrench, such as steel, can be used but must be moved out of the hole after each adjustment to determine if the desired position has been achieved). The screw can be rotated in either direction until the desired result is obtained. (Actuator motion stops, retracts, etc.) The adjustment available is ±10 to 15% of full valve stroke through approximately ±4 turns of the screw. The screw is trapped on either end so it cannot come out; however, it should not be over tightened at the ends of its travel. The adjusting screw locking device offers resistance to turning or moving on its own. 6. After adjustment, replace the access hole sealing screw. Dither If the system resolution is not as precise as desired, it can sometimes be improved through the use of “dither”. A small amplitude signal at a relatively high (60-150 Hz) frequency is superimposed on the valve command signal. This signal will cycle the valve spool sufficiently to prevent valve silting and “stiction”. It should be noted, however, that if the amplitude is high enough, or the frequency low enough, the actuator could follow signal in such a way that would wear the seals rapidly. Therefore, care should be exercised in setting the frequency and amplitude of the dither. If dither does not solve the problem, the feedback device may be the limiting factor, or the servovalve may be sized too large for the accuracy desired. tải về 0.84 Mb. Chia sẻ với bạn bè của bạn:
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