8
SH 8384-3 EN
Safety-related functions
3 Safety-related functions
1. Emergency venting over the i/p converter
(Fig. 1 path
)
In automatic operation, the PD controller (3) compares the actual value to the DC control
signal from 4 to 20 mA coming from the microcontroller. In case of a system deviation,
the activation of the i/p converter is changed so that the actuator (1) is either vented or
filled with air. Fail-safe action is triggered when no signal (0 mA) is applied to terminals
11/12 and, as a result, to the i/p converter.
2. Emergency venting over the optional solenoid valve
(Fig. 1 path
)
The solenoid valve (12) is energized by a 24 V DC voltage signal. Fail-safe action is trig-
gered when no signal (0 mA) is applied to terminals 81/82. This causes the solenoid
valve (12) to vent the output of the i/p converter to the atmosphere. The actuator is vent-
ed as well.
3. Safety-related end position monitoring over the optional inductive limit contact
(Fig. 1 path
)
The inductive limit contact SJ2-SN (NAMUR NC contact) indicates the adjusted end posi-
tion in a safety-instrumented system at terminals 41/42. See
u
EB 8384-3 for adjusting
the limit contacts.
Fail-safe action
Fail-safe action is triggered by the i/p converter or solenoid valve and upon supply air fail-
ure. The positioner fully discharges its pneumatic output to the atmosphere, causing the
mounted actuator to be vented. As a result, the valve moves to the fail-safe position. The fail-
safe position depends on how the springs are arranged in the pneumatic actuator (air-to-
close or air-to-open).
When the air supply fails and the optional solenoid valve is de-energized, all positioner
functions, except open/closed loop control, remain active (including diagnostics, HART
®
communication as well as position and status feedback).
The pneumatic output of the positioner can also be vented to the atmosphere over the
software, e.g. by entering a suitable set point. This procedure is not a safety-instrumented
function.
Protection against unauthorized changes to the configuration
A change to the configuration cannot affect the safety function nor cause it to be deactivated.
Note
Summary of Contents for TROVIS 3730-3
Page 16: ...16 SH 8384 3 EN...
