Samson 3767 - Zero and Span

EB 8355-2 EN 5-21
Installation
Check the positioning speed by pushing
the diaphragm lever (3 in Fig.5-3) as far
it will go.
2. Adjust the set point at the input to ap-
prox.50%ofitsrange.Thenturntheze-
ro adjuster (6.2 in Fig.5-3) until the
valveisatapproximately50%valve
travel.
3. Use the adjuster (8 in Fig.5-3) to set the
proportional band X
p
to a value half way
(half turn).
4. Check the valve's tendency to hunt and
thepositioningspeedbybrieytapping
the diaphragm lever (3 in Fig.5-3). The
Xp value is to be adjusted to be as small
as possible, without considerable over-
shooting occurring.
Additional points that apply concerning ad-
justment:
Î Always adjust the Xp restriction before
setting the starting point.
Î Incaseofazeroshift(e.g.duetoasub-
sequent change in the restriction setting
orsupplypressure),checkthezeroset-
ting and readjust it.
− When the positioner is controlled by a
computer whose signal is limited, e.g.
between4to20mA,setthepositioner
totherangefrom4.5to20mA.Thisis
the only way to ensure that the actuator
is completely vented and the valve com-
pletely closed when the controller issues
a4mAsignal.Foroperatingdirection
<>,settherangeto4to19.5mA.
5.5.2 Zero and span
When setting the zero adjuster (6.2 in
Fig.5-3), check whether the actuator is re-
lieved of pressure. When the input signal is
4mA and the operating direction >> or the
input signal is 20mA and the operating di-
rection <>, the pressure gauge must indicate
0bar.
a) Actuator with "stem extends"
fail-safe action
To ensure that the total closing force of the
actuator acts on the valve, proceed as fol-
lowswhileadjustingthesetpoint:
Î Withoperatingdirectionincreasing/in-
creasing<<:adjuststartingpointto
4.5mA(slightlyraised).
Î Withoperatingdirectionincreasing/de-
creasing<>:adjuststartingpointto
19.5mA(slightlylowered).
Starting point (zero) e.g. 4mA
1. Turnthezeroadjuster(6.2inFig.5-3)
until the valve just starts to move from its
initial position.
2. Reducetheinputsignalto0mAand
slowly increase it again. Check whether
the valve starts to move at exactly
4.5mA.
Correctanydeviationatthezeroadjust-
er (6.2 in Fig.5-3).
Note