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The feedback cam is retained by a coupling which, in the case of a Kinetrol direct mounted positioner, is held onto the vane square by a collet. For discrete versions, the coupling is retained in bearings and connected by either a male square or 'Namur' style connector.
The cam provides positional feedback via a unique four bar linkage which ensures a linear movement of the cam follower whether the cam is set for clockwise or anticlockwise movement for a rising signal. The lower part of the linkage is attached to the other end of the feedback spring which stretches the spring as the cam is rotated to produce the feedback force mentioned earlier. The standard cam produces a linear characteristic, but alternative profiles are available.
The common adjustments are split into zero and range. Both are achieved without the need for special tools and the actual adjustments are made using finger pressure only.
Air passages in the main body are provided with the capability of many options with a minimum of changes. External ports are provided on all models to allow for external connection to the actuator or for the fitting of pressure gauges if desired. Three main air flow options are available (as detailed in the AP literature). The two lower flow rate options (AP & MP) are affected by change of valve size and tapping size in the body. The largest flow rate option (HP) not only has a larger valve but also a different port plate with 3/8 tapping and external combination silencer/snubbers.
The mounting options are accommodated by three different channel plate designs. The channel plate is the plate fitted to the base of the unit. The smallest is dedicated to direct mounting on an 050 Actuator. The second is used for direct mounting on Actuators 070 to 140. The third is used for discrete models having a Namur mounting hole pattern.
An optional angle retransmit can be fitted within the positioner body and additional options of I/P controller and limit switch box can also be fitted allowing a wide range of switch options to be specified.
4. SETTINGS AND ADJUSTMENTS.
The positioner will have been factory set to the requirements given in the ordering code ( i.e. the direction of rotation for a rising pressure signal and the range and zero settings). However, if these settings need to be changed, the following section describes the procedure for achieving this.
4.1 Change of Direction for Rising Signal (direct mounting units only).
4.1.1 Move the actuator to approximately mid-position to avoid problems in correct orientation later. This is obviously not possible or necessary with spring return models because the position of the vane will be known. Reduce both main supply and signal pressures to zero.
4.1.2 Remove positioner cover and undo the two M4 screws retaining the red angle scale plate and remove, as shown in Figure 5. Loosen the central coupling screw sufficiently to draw the coupling off the actuator square.
4.1.3 Pull the two halves of the coupling apart sufficiently to allow the cam to be withdrawn from its location peg as shown in Figure 6. Flip the cam over and push it back into the slot between the two coupling halves and locate it back on the peg.
4.1.4 If when the coupling was removed, the collet was left behind on the actuator square, remove the collet from the square and push it into the lower half of the coupling ensuring that it locates in the semicircular 'pip'. Tighten the clamping screw by two turns before placing it back on the actuator square such that the cam follower is approximately half way up the rise of the cam and tighten the clamping screw. Replace the angle scale plate.
4.1.5 Undo the changeover block central screw and rotate it by a quarter turn and replace and tighten screw. For your convenience, the changeover block is marked 'A' and 'C' which refers to 'anticlockwise' and 'clockwise' respectively. Ensure the required letter is placed opposite the arrow marked on the top of the valve block.