Changing Positioner Action - Fisher 3570 Instruction Manual

3570 Positioners
September 2015
6. For positioners with two relays (3570, 3570C, 3570P, 3570PC, and 3571 positioners), observe the relay output
pressures. If the cylinder gauges are present as shown in figure 4, read the cylinder top and cylinder bottom gauges
or use clip‐on test pressure gauges. The two relay output pressures should be approximately equal [within 0.3 bar (5
psig)] and should be approximately 75 percent of the supply pressure. For example, if the supply pressure is 7 bar
(100 psig), the two relay output pressures should be within 0.3 bar (5 psig) of each other, and should be
approximately 5.2 bar (75 psig).
CAUTION
The relays in the 3570C and 3570PC positioners use a locknut (key 29P, figure 10) on the nozzle (key 29Q). If the nozzle is
rotated when the locknut is tight, damage to the relay diaphragm might result. Always use a wrench on the nozzle to
prevent it from turning while loosening or tightening the locknut.
If the relay output pressures are not at the values mentioned, adjust the nozzles. Counterclockwise rotation of either
nozzle will move the nozzle closer to the beam and will increase relay output pressure.
For all 3570 positioners, examine the end of the beam near the bias spring (see figure 2). The beam should be
approximately centered between the two E‐ring travel stops. Observing the caution above for 3570C and 3570PC
positioners, rotate the nozzle(s) to center the beam between the E‐rings. For positioners with two relays, the relay
output pressures must be approximately equal [within 0.3 bar (5 psig)] and approximately 75 percent of supply
pressure after the beam is centered.
7. Apply an input signal equal to the low value of the input signal range [0.2 bar (3 psig) in this example]. Adjust the
bias spring (see figure 2) up or down until the valve travel is at the starting point.
8. Loosen the spring lock (see figure 2) and slowly increase the input signal toward the high end of the input signal
range [1.0 bar (15 psig) in this example]. If the valve travel is less than its expected range, increase the travel by
adjusting the range spring counterclockwise. If the valve travel reaches the end of its expected range with an input
signal less than the high value of the input signal range, decrease the travel by adjusting the range spring clockwise.
9. Repeat steps 7 and 8 until the valve plug or travel indicator action corresponds to the input signal requirements of
the application [0.2 to 1.0 bar (3 to 15 psig) in this example].
10. Lock the range spring and the bias spring seat in position. The positioner is then ready for operation.
11. If the positioner is unstable and adjustment does not correct the problem, it might be due to unwanted fluctuations
in the input signal. A restrictor assembly (key 47, figure 10) can be installed in the input signal circuit to dampen
these fluctuations. The restrictor might help to minimize instability. To take the restrictor out of service, exchange
the location of the restrictor with that of the bellows mounting screw (key 46, figure 10).
12. Replace the cover (key 39) on the positioner.

Changing Positioner Action

The instructions given below are to be used after the springs have been changed or if no spring change is required.
Numbered parts mentioned in this section are shown in figure 5 unless otherwise noted.
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Instruction Manual
D200137X012