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2.3 Pneumatic and Electrical Connections.
2.3.1 Air Supply
Connect main air supply (pressure between 3.5 and 7 bar or 50 and 100psi) to the supply port indicated in figure 3. Also connect signal air supply (pressure between 0.2 bar and 1 bar or 3 psi and 15 psi) to the inlet of the diaphragm housing. It is important that the air is clean, dry and oil free. Quality class 6.4.4 (taken from ISO standard 8573.2001) is adequate. This implies 5 micron max. Particle size, 3 deg. C dew point max. and 5mg per cubic metre max. oil content.
2.3.2 Angle Retransmit Option Supply.
The optional angle retransmit circuit is loop powered, requiring 8 to 30 volts to drive the 4-20mA current through it. Th current which passes is linearly in proportion to the shaft angle. The cable entry has the option of a cable gland fitting or 4-way DIN plug. With the cable gland entry the wires are directly connected to the internal Connector Block. An internal earth connection is provided if required. If the DIN plug option is
fitted then the internal connections have already been made as shown in Figure 3. An external earth connection is also provided if this is required.
2.3.3 External Actuator Ports.
For positioners not fitted directly onto Kinetrol Positioner type Actuators, two external ports are provided for connecting the positioner outlets to the actuator. The size of the ports is dependant on the positioner ordering code. These ports can also be used for fitting pressure gauges if desired.
3. DESCRIPTION OF OPERATION.
The AP Positioner works using the principal of a 'force balance' spool system with mechanical cam feedback. The air input signal (normally 3-15psi) is applied to a diaphragm which produces a force on the force balance lever which is proportional to the signal pressure. The resulting torque on the lever is balanced by the force produced from the feedback spring which is also joined to the lever.
A proportional flow spool valve is the third element attached to the lever. This is positioned at its central closed position when the lever is at the mid-stroke position which occurs when the actuator is at the desired angle. Several different versions of this valve are available with different flow capacities designed to give optimum performance when fitted to the range of Kinetrol actuators.
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.