SD73
Dew Point — Dew point at line pressure should be at least 10°C (18°F) below the minimum temperature to which
any part of the instrument air system is exposed at any season of the year. Under no circumstances should the dew
point at line pressure exceed 2°C (35.6°F).
Oil Content — Maximum total oil or hydrocarbon content, exclusive of non-condensables, should not exceed 1 ppm
under normal operating conditions.
CAUTION
Exceeding the specified ambient temperature limits can adversely affect performance and
may cause damage.
ADJUSTMENT
The only adjustment that can be made on the positioner is a zero adjustment. The zero adjusting screw is located
under the positioner top cover.
To adjust the zero, set the instrument pressure to the midpoint of its span, and turn the zero adjustment until the
valve is at the mid-point of its stroke.
In some cases, valve shut-off or opening may be required at a specific instrument pressure. To zero the positioner at
this point, set the instrument pressure at the specific pressure and turn the zero adjustment screw until the valve
reaches the required position.
A slight change of the instrument pressure should start to move the valve.
The valve stroke for a given span may also be suppressed or shifted to the desired range by means of the zero
adjusting screw.
RANGE SPRING SELECTION
Range springs for the positioner are selected from the table in Figure 2. Color coding of the range springs is given
by the table in Figure 3.
To find the proper spring, select the stroke listed which most nearly agrees with the desired stroke, and the pressure
span which most nearly agrees with the desired span. The proper spring will be found at the intersection of these two
columns.
Series 4090 and 12395 range springs are available for stroke range tolerances of ±10%. Series 12388 range springs
are available, at extra cost, for stroke range tolerances of ±5%.
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