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Product description
5
PRODUCT DESCRIPTION
5.1
General description
The Type 8791 positioner is a digital electro-pneumatic positioner for pneumatically actuated continuous
valves. The device contains the main functional groups
- Position sensor
- Pilot valve system (electro-pneumatic actuating system)
- Microprocessor electronics
The position sensor measures the current positions of the continuous valve.
The microprocessor electronics continuously compare the current position (actual value) with a position set-
point value prescribed by the standard signal input and supply the positioner with the result.
If there is a control difference, the pilot valve system corrects the actual position.
5.1.1
Characteristics
•
Variant
The positioner is available with position control function.
The position of the actuator is controlled according to the position set-point value. The position set-point
value is specified by an external standard signal (or via fieldbus).
•
Position sensor
- Internal high-resolution conductive plastic potentiometer or
- External contactless wear-free position sensor (remote).
•
Microprocessor-controlled electronics assembly
for signal processing, closed-loop control and valve control.
•
Control module
The device is controlled with two keys and four DIP switches.
Two LEDs (one RGB-LED for the device status and one green LED for the status of the communication
interface) enable different device statuses to be displayed.
•
Pilot valve system
The actuating system consists of two solenoid valves and four diaphragm amplifiers. For single-acting
actuators, working port 2 must be sealed with a threaded plug.
•
Position feedback
The position of the valve can be transferred either via 2 proximity switches or via a 0/4...20 mA output
(variant without fieldbus communication) or transferred digitally via a fieldbus communication (for
example, büS, IO-Link) to the PLC. The proximity switches or basic positions can be changed by the user
using control vanes.
•
Pneumatic interfaces
Internal thread G1/4“
•
Electrical interfaces
(circular plug-in connector or cable gland)
•
Communication interface
To exchange process data and for configuration and parameterisation
•
Housing
Plastic-coated aluminium housing with hinged cover and captive screws.
The housing of the positioner is protected against internal pressure that is too high, for example following
leakages, by a pressure limiting valve.
Type 8791, REV.2
english
Summary of Contents for 8791 REV.2
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