Siemens CA 333 Series Spezifikationen PDF herunterladen (Seite 9)

SD74

CAUTION

Synthetic compressor lubricants in the air stream at the instrument may cause it to fail.

The requirements for a quality instrument air supply can be found in the Instrument Society of America's "Quality

Standard for Instrument Air" (ISA-S7.3). Basically, this standard calls for the following:

Particle Size — Maximum particle size in the air stream at the instrument should be no larger than 3 microns.

Dew Point — The 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-condensable, should not exceed 1 ppm

under normal operating conditions.

2.3 VALVE POSITIONER

Single-Acting

When used as a single-acting valve positioner, the Model 74 uses one output connection. If the VALVE 2

connection is used, an increase in output must increase range spring (feedback) tension. If the VALVE 1 connection

is used, an increase in output must decrease range spring (feedback) tension. In either case, the connection not

chosen must be plugged.

Double-Acting

When used as a double-acting valve positioner, the Model 74 uses both the VALVE 1 and VALVE 2 connections.

In this case, an increase in output must increase range spring (feedback) tension.

2.4 MOTION TRANSMITTER

When used as a motion transmitter, the VALVE 1 connection is the transmitter output; plug the VALVE 2

connection. To use the Model 74S as a motion transmitter, order the P/N 14411-7 restriction fitting and install as

shown in Figure 4-2. For input motions greater than 12" and an output line that is less than 50 feet, install a volume

chamber in the output line to insure stable operation.

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Siemens CA 333 Series Spezifikationen Seite 9