Among the list of problems, which may cause SVI to enter the FAIL SAFE MODE, inappropriate installa-
tion or configuration, loss of air supply or insufficient air supply can cause the position error and position
sensor error conditions. Other problems are more likely related to SVI hardware or software.
Timeout of hardware watchdog timer clamps output to fail-save condition and initiates CPU reset.
Timeout of software (microprocessor COP watchdog timer initiates CPU reset.
A position error occurs when the valve position differs from the requested position by more than the
Position Error Band for more than the position error Time 1. See Chapter 9: Configuration Mode.
However a position error does not cause SVI to enter the FAIL SAFE MODE unless the Time 2 is
enabled and the position error persists for more than the position error Time 2. The user should decide
if fail-to-safe mode is desirable for a position error for a specific application. If not, position error Time 2
should not be enabled. To avoid unnecessary position error, Position Error Band should not be config-
ured too small (2 to 10% is typical) and Time 1 and 2 should be larger than the time required to stroke
the valve from fully close to fully open and from fully open to fully close. If these parameters are set
appropriately, loss of air supply or insufficient air supply is probably the reason that causes a position
error.
The active range of a standard SVI position sensor is 120 degree. A position sensor error may occur
when the SVI position sensor is out of the active range. Check the SVI linkage and position sensor ori-
entation to make sure the installation is appropriate (see MASONEILAN SVI Instruction Manual).
Alternatively send the Clear Status and Read Status commands to check if the problem is corrected.
Exiting Failsafe Mode
Once the problem is found and solved, the SVI can be restarted by resetting the power to the SVI or
clicking the Manual button in the FAIL SAFE MODE window then clicking the reset button to reset the
SVI device.
If the problem is caused by inappropriate configuration parameters, click the Manual button in the FAIL
SAFE MODE window, then immediately clicking the Configure button in the Manual Mode window to
enter the configuration mode to change configuration parameters.
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