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2.3.2 Main Electronics Module
The Main electronics module is the main controller for all the electronics functionality in
the SVI3 unit. It performs the functions including HART Communications, actuator
position control, valve diagnostics and power management. It also interfaces with
external control system (PLC, DCS...). Main module also has Hall Position Sensor, A/D,
D/A, Temperature sensor and HART Communication chip.
2.3.2.1 Magnetic Position Sensor
A Hall effect based position sensor uses magnetic field to measure the valve position
through the housing wall. It senses the rotation of a magnetic assembly directly mounted
on the end of a rotary valve shaft or by a turnbuckle and lever assembly connected to a
reciprocating valve shaft.
The output of the Hall sensor provides the position feedback signal to the position control
algorithm. The magnetic assembly is environmentally sealed and is entirely external to
the electronics housing. This sensor has a maximum travel range of up to 140° rotation.
2.3.2.2 Temperature Sensor
A temperature sensor is located in the electronics module and measures temperature
within the enclosure. This measurement is used to provide temperature compensation for
the position and pressure sensors and other internal electronic components. The
temperature sensor reading is used to provide warning of excessive ambient temperature
at the positioner.
2.3.3 Pneumatic Module
The pneumatic module consists of I/P Converter, Pneumatic Relay and Pneumatic
Electronics. The Pneumatic electronics board contains pressure sensors and mechanical
component compensation circuitry. This module also acts as pass through for display
module.
2.3.3.1 Pressure Sensor
There are four pressure sensors in the pneumatic electronics board. they are used for
measurement of Ambient, Pilot, Supply and Actuator pressure.
2.3.3.2 Current-to-Pressure Converter, I/P
The I/P converts a current signal to a pressure signal in the following manner. A fixed coil
creates a magnetic field proportional to the applied current. The field magnetically pulls a
flexure towards a nozzle to increase pressure on the flexure. The pressure on the flexure
increases in response to an increase in the coil current. Encapsulation of the coil provides
protection from the environment.
