Starting Point And Reference Variable; Adjustment After Mounting The Positioner On The Valve; Setting The Air Delivery (Volume Restriction Q) And Proportional Band Xp - Samson 4763 Mounting And Operating Instructions

Operating the positioner
6.2 Starting point and refer-
ence variable
The attached lever and the installed range
spring of the positioner are assigned to the
values of rated valve travel and the reference
variable as in Table 1.
In normal operation, the reference variable
span is 100 % = 16 mA. A smaller span of,
for example 50 % = 8 mA is only required
for split-range operation (Fig. 12).
The span can be changed by exchanging the
range spring (section 6.4). On making
adjustments to the positioner, the travel must
be adapted to the reference variable and
vice versa.
With a reference variable, for example 4 to
20 mA, the valve must move through its
entire travel range from 0 to 100 %. The
starting point then is 4 mA and the upper
range value 20 mA.
In split-range operation, the controller output
signal is used to control two control valves,
dividing it such that the valves move through
their entire travel range at half the input
signal range each (e.g. first valve set to 4 to
12 mA, second valve set to 12 to 20 mA). To
avoid overlapping, allow for a dead band of
± 0.5 mA as shown in Fig. 12.
The starting point (zero) is adjusted at the
screw (4); the reference variable span, i.e.
the upper range value, is adjusted at the pin
(2).
30
6.3 Adjustment after mounting
the positioner on the valve
Î Connect an ammeter to the control signal
input at the terminals 11 (+) and 12 (–).
Î Connect the supply air to the supply in-
put (supply 9).
6.3.1 Setting the air delivery
(volume restriction Q) and
proportional band Xp
1. Close the volume restriction (14) as far
as the required positioning speed per-
mits.
Check the positioning speed by pushing
the range spring (6) as far it will go.
2. Adjust the reference variable at the input
to approx. 50 % of its range. Then, turn
the zero adjustment screw (4) until the
valve is at approximately 50 % valve
travel.
On setting the Xp restriction, observe the
relationship with the supply air pressure as
indicated in Fig. 13. The preset value of Xp
should be approximately 3 %.
3. Check the plug stem's tendency to oscil-
late by pressing the range spring (6)
briefly as far as it will go.
The Xp value is to be adjusted to be as
small as possible, without considerable
overshooting occurring.
Additional points that apply concerning ad-
justment:
Î Always adjust the Xp restriction before
setting the starting point.
EB 8359-2 EN