Answer / vivek

A Valve positioner is employed to accurately position the
control valve at the proposed opening or closing position

Answer / welcome4ujd

Summary - Positioners
1. A positioner ensures that there is a linear relationship
between the signal input pressure from the control system
and the position of the control valve. This means that for
a given input signal, the valve will always attempt to
maintain the same position regardless of changes in valve
differential pressure, stem friction, diaphragm hysteresis
and so on.

2. A positioner may be used as a signal amplifier or
booster. It accepts a low pressure air control signal and,
by using its own higher pressure input, multiplies this to
provide a higher pressure output air signal to the actuator
diaphragm, if required, to ensure that the valve reaches
the desired position.

3. Some positioners incorporate an electropneumatic
converter so that an electrical input (typically 4 - 20 mA)
can be used to control a pneumatic valve.

4. Some positioners can also act as basic controllers,
accepting input from sensors.

A frequently asked question is, ‘When should a positioner
be fitted?’
A positioner should be considered in the following
circumstances:

1. When accurate valve positioning is required.

2. To speed up the valve response. The positioner uses
higher pressure and greater air flow to adjust the valve
position.

3. To increase the pressure that a particular actuator and
valve can close against. (To act as an amplifier).

4. Where friction in the valve (especially the packing)
would cause unacceptable hysteresis.

5. To linearise a non-linear actuator.

6. Where varying differential pressures within the fluid
would cause the plug position to vary.

To ensure that the full valve differential pressure can be
accepted, it is important to adjust the positioner zero
setting so that no air pressure opposes the spring force
when the valve is seating.

Answer / nabakishore biswal

Positioner is an transducer which gives the proper position
of the final control element.

Answer / aby

Positoner makes the control action very smooth. The usually
getting o\p is 3-15 psi. but it is not the exact pressure
required for the valve to operate it may be above this. so
we have to convert this standard pressure to a pressure
that is needed for the valve. this is done by the
positioner. Also by applying the signal to diaphragm only
it takes more time for the control action. so the
positioner makes a connetion with the step and the make the
action simple.

Answer / raghuram

1) positioner name it self indicate as for accurate valve
positioning means for opening or closing for example: can
you please assume operator given 30% from HIS, of D.C.S,
WITH positioner accurately we can control valve position at
30% exactly ,with out positioner linearity is not posible.
2) At the time of calibration we will make linear 4 to 20
ma to .2 to 1k.g for I/P, but in case of positioner we will
check position(valve open close) with I/P, with valve
percentage for ex:
ma position(%)
4 0
8 25
12 50
16 75
20 100

Answer / cipriano

A valve Positioner is a device used to increase or decrease
the air pressure operating the actuator until the valve stem
reaches the position called for by the instrument controller.

Answer / anu

Positioner is for
1. amplification of 3-15 psi pneumatic signal from I/P
comvertor and the amplified signal ( eg. .2 - 1 kg/m2
range) is the i/p for the actuator.
2. feed back

Answer / praveen kumar

Positioner is used to Control valve for controlling the
final element, and where the signal is feeded to positioner
only the link is connected to Valve stem for opening &
closing.

Answer / aallam

positioner convert 4-20 mA to 3-15 psi and by 3-15 psi control the supply air to the valve to open or close with help by feedback arm to correct the supply air to the vave

Answer / mr.rao

It is doing sharing the signal(actual level)to Controller.

give classification of transducer based on type of application

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