Flowserve AF-17 Electronic Positioner - Manual (Page 4)

4 AF-17 Electronic Positioner: Installation, Operation and Maintenance WCAIM2031
1.2 Environmental Considerations
CAUTION: The AF-17 Electronic Positioner is sensitive to electrical noise on signal or supply lines and in the environment.
For maximum sensitivity, the electrical noise level should not exceed 10mV. Follow installation, calibration and adjustment
guidelines carefully and use shielded wire as stated in paragraph 1.2.4.
Flowserve recommends that all products that must be stored prior to installation be stored indoors, in an environment
suitable for human occupancy. Do not store product in areas where exposure to relative humidity above 85%, acid or alkali
fumes, radiation above normal background, ultraviolet light, or temperatures above 120°F or below 40°F may occur. Do not
store within 50 feet of any source of ozone.
Temperature and humidity are the two most important factors that determine the usefulness and life of electronic equipment.
1.2.1 Temperature
Operating solid-state electronic equipment near or beyond its high temperature ratings is the primary cause for most
failures. It is, therefore, very important that the user be aware of and take into consideration, factors that affect the
temperature at which the electronic circuits will operate.
Operating an electronic device at or below its low temperature rating generally results in a unit operating poorly or not at all,
but it will usually resume normal operation as soon as rated operating temperatures are reached. Low temperature
problems can be easily cured by addition of a thermostatically controlled heater to the unit’s housing.
At high temperatures, some components will destruct completely when their maximum temperature is exceeded; others will
cease operation at temperatures above ratings and will return to operation at normal ratings, but may have been
permanently changed in one or another parameter, causing a device to operate poorly, and may also cause greatly reduced
component life.
1.2.2 Positioner Temperature Considerations
The Worcester AF-17 Electronic Positioner is rated for operation between -40°F and 160°F. When using the positioner inside
the Worcester 75 Series actuators, a maximum ambient temperature of 115°F is required to ensure the circuit board
maximum temperature of 160°F is not exceeded.
1.2.3 Humidity
Most electronic equipment has a reasonable degree of inherent humidity protection and additional protection is supplied by
the manufacturer, in the form of moisture proofing and fungicidal coatings.
Such protection, and the 3 to 4 watts of heat generated by the circuit board assembly will generally suffice for environments
where the average relative humidity is in the area of 80% or less and ambient temperatures are in the order of 70°F average
with only occasional short term exposure to temperatures up to 90°F. Where relative humidity is consistently 80 to 90% and
the ambient temperature is high or subject to large variations, consideration should be given to installing a heater and
thermostat option in the enclosure. The heater should not increase the enclosure temperature to the point where the circuit
board assembly’s temperature rating of 160°F is exceeded.
In those instances where the internal heater would bring the circuit board’s operating temperature near or above its
maximum rating, the user might consider purging the enclosure with a cool, dry gas. The initial costs can usually be paid
off quickly in the form of greatly extended equipment life, low maintenance needs, and much less process downtime.
1.2.4 Input Circuit Noise Protection
Shielded wiring should be used for all signal input circuit wiring regardless of length.
With separately housed positioners, the wiring from the feedback potentiometer to remote positioner, would be considered
as signal input wiring and should also be shielded wire.
The shields should never be used in place of one of the input wires, and the shields normally should be grounded to
equipment housings at one end of the wiring run only. Grounding both ends of shielding can eliminate the shielding benefits
because of current ground loops. If two or more shielded cables come to the positioner from different locations, ground the
shields at the positioner.
Flow Control Division
Worcester Controls