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6.2.7 To ensure a rise in retransmit signal with rising input pressure signal, the top and bottom wires on the feedback potentiometer must be reversed in the connector located on the circuit. The central wire does not change.
6.2.8 Undo the changeover block central screw and rotate it by a quarter turn and replace and tighten screw. The changeover block is marked 'A' and 'C' which refers to 'anti-clockwise' and 'clockwise' respectively. Ensure the required letter is placed opposite the arrow marked on the top of the valve block.
6.3 Zero and Range Adjustment (refer to Figure 7).
Setting of the mechanical zero and range for the positioner with an angle retransmit is the same as described in section 4.2. The retransmit circuit must also be set for zero and range which is described below.
6.3.1 Set the circuit zero adjustment to the central position and connect a 4-20ma electrical source via the DIN plug or terminal block.
6.3.2 Set the positioner to zero degrees or the input pressure to 3 psi (0.2 Bar)
6.3.3 Slacken the two screws which clamp the potentiometer to the retransmit plate but do not remove. Rotate the potentiometer slowly using finger pressure until the electrical display shows 4ma.
6.3.4 Increase the air signal pressure to 15 psi (1 Bar) to set the positioner at 90 degrees. Adjust the Span potentiometer to read 20ma.
6.3.5 Repeat steps 6.3.2 to 6.3.4 until the desired readings are obtained at both ends of the stroke. The fine zero potentiometer can be used to obtain a more precise reading at the zero position.
6.3.6 Tighten the two potentiometer clamp screws.
6.4 Change of Direction for Rising Signal (discrete units).
6.4.1 Move actuator as in Section 6.2.1.
6.4.2 Remove positioner cover and undo the three M4 screws retaining the red retransmit plate, release the two wires onthe terminal block connected to the DIN plug (if fitted), as shown in figure 7. Loosen the central coupling screw sufficiently to pull the coupling complete with the retransmit assembly off the actuator connection.
6.4.3 Release the potentiometer strap from the slot in the lower coupling, as shown in Figure 8, remove the internal indicator from the coupling and withdraw the coupling from the retransmit plate.
6.4.4 Pull the two halves of the coupling apart sufficiently to allow the cam to be withdrawn from its location peg. Flip the cam over and push it back into the slot between the two coupling halves and locate it back on the peg.
6.4.5 Refit the coupling to the retransmit plate and slide the internal indicator over the top of the coupling and refit the potentiometer strap into one of the two marked slots of the lower coupling (marked 'A' and 'C' for anticlockwise and clockwise movement respectively).
6.4.6 If when the coupling was removed, the collet was left behind on the actuator connection, remove the collet from the connection and push it into the lower half of the coupling ensuring that it locates in the semicircular 'pip' and tighten the clamping screw by two turns. Place the coupling and retransmit plate back on the actuator connection so that the cam follower is approximately half way up the rise of the cam whilst holding back the two retransmit wires and pull back the spring lever with the other hand and tighten the coupling clamping screw. Re-tighten the retransmit plate retaining screws and refit the retransmit wires to the terminal block.
6.4.7 The internal changeover block is not effective with a discrete positioner. The changeover of the air flow path is achieved by swapping over the external connections. It may also be preferred to turn the positioner through 180 degrees to simplify the external pipe runs.
6.4.8 The adjustment of zero and range is completed as in section 6.3.
6.5 Change of Angle Retransmit Direction Without Changing Positioner Direction If a non-standard rise in retransmit signal is required without a change in positioner direction, then this can be achieved by the following procedure.