Samson 4763, Mounting And Operating Instructions

4.3.2 Setting actuator version

“Stem extends”

Note:

To ensure that the total closing force of the

actuator can be effective in the control valve,

the diaphragm chamber must be completely

vented at the lower range value of the refer-

ence variable (operating direction <<) and

at the upper range value (operating direc-

tion <>).

Therefore, set input signal to a slightly in-

creased starting point of 4.5 mA when the

operating direction is direct << and to a

slightly lowered starting point of 19.5 mA

when the operating direction is reverse <>.

This applies in particular to controllers and

control systems whose output signal is lim-

ited to a range of 4 to 20 mA.

Starting point (zero)

e.g. 4.5 mA

1. Turn the zero adjustment screw (4) until

the plug stem just begins to move from

the resting position (observe plug stem

with travel indicator).

2. Reduce the input signal on the ammeter

and increase again slowly. Check

whether the plug stem starts moving at a

starting point of 4.5 mA and, if neces-

sary, correct.

Upper range value (span)

e.g. 20 mA

3. After the starting point has been ad-

justed, increase the input signal. The plug

stem must be motionless at an upper

range value of exactly 20 mA and there-

fore already moved through 100 % of its

travel range (watch the travel indicator at

the valve!). If the upper range value is in-

correct, the pin (2) must be moved as fol-

lows in order to correct the signal:

4. Move pin to:

End of lever –> to increase travel

Pivot –>  to reduce travel
Whenever you correct the input signal,

re-adjust zero afterwards. Subsequently,

check the upper range value.

Repeat until the two values match.

4.3.3 Setting actuator version

“Stem retracts”

Note:

For actuator version "Actuator stem re-

tracts", the diaphragm chamber must be

loaded with a pressure that is capable of

tightly closing the control valve, even with

prevailing upstream pressure in the plant.

This concerns an upper range value of the

input signal corresponding to 20 mA (direct

operating direction <<) or a lower range

value corresponding to 4 mA (reverse oper-

ating direction <>).

The required signal pressure is indicated on

the adhesive label on the positioner or is

roughly estimated as in section 3.2.2.

Starting point (zero)

e.g. 20 mA

1. Adjust the input signal to a starting point

of 20 mA on the ammeter.

Turn the zero adjustment screw (4) until

the control valve just begins to move

from the initial position.

2. Increase the input signal and slowly re-

duce to a starting point of 20 mA again.

16

EB 8359-2 EN

Operation