Speed Adjustment; Orifice; Pilot Valve Stroke Adjustment - ABB AV1 Operating Instructions Manual

CALIBRATION

Speed Adjustment

GAIN AND SPEED ADJUSTMENTS
4 - 6
Speed adjustment is not normally required when calibrating a
positioner. Type AV positioners come from the factory adjusted for
maximum operating speed. However, the speed of operation can
be reduced in two ways. Speed control orifices can be used to
slow positioner operation or a speed adjustment can be made
internal to the positioner to change operating speed.
When the system involves only a single actuator, a high position-
ing speed is usually an advantage. However, in a complex control
system, it is generally desirable to operate all power devices at the
same speed in order to avoid interaction between units and con-
sequently undesirable process conditions.

ORIFICE

If it is necessary to reduce the speed of operation, 1.02-millimeter
(0.04-inch) speed control orifices are available as an option from
ABB. These orifices are installed directly into the output ports (01
and 02) of the positioner and have ¼-NPT ports for connecting
tubing from the actuator. If these orifices are too small (causing
the actuator to respond too slowly) they may be drilled out to
obtain desired speed control. Blank orifices are also available.
Refer to Table 1-9 for orifice part numbers.

PILOT VALVE STROKE ADJUSTMENT

If it is necessary to reduce the speed of operation, a pilot valve
stroke adjustment can reduce the speed and does not require
additional hardware. This adjustment limits the pilot valve stroke.
The pilot valve stroke is measured by the movement (displace-
ment) of the pilot valve stem, as shown in Figure 4-5. Figure
shows the maximum stroke length that is also the maximum
speed of operation and is how the positioner comes from the fac-
tory. Use the following procedure to reduce the speed of opera-
tion:
NOTE: Never adjust the pilot valve for a stroke greater than
0.762 millimeters (0.030 inches) in either direction. A greater
stroke will reduce the performance of the positioners.
⁄
1. Use a -inch Allen wrench to turn the top adjustment screw
3
32
⁄
clockwise -turn to reduce stroke time (Fig. 4-6). ABB suggests
1
8
⁄
-turn increments. Take note of the number of turns. In total, do
1
8
not exceed one full turn (clockwise) from the factory setting (Fig.
4-5). This adjustment controls the amount of air going to port 01.
4-5