Endress+Hauser iTEMP TMT84 - Page 77

TMT84 11 Operation using PROFIBUS
®
PA
Endress + Hauser 77
Failsafe mode
If an input or simulation value has the status BAD, the Analog Input function block uses the failsafe
mode defined in the "Failsafe mode" parameter. The "Failsafe mode" parameter (Page 84)
offers the following options:
!
Note!
Failsafe mode is also activated if the Analog Input function block is set to the "OUT OF SERVICE"
operating mode.
Limit values
You can set two warning limits and two alarm limits for monitoring your process. The status of the
measured value and the parameters of the limit-value alarms are indicative of the measured value's
relative situation. You also have the option of defining an alarm hysteresis in order to avoid frequent
changes of the limit-value flags and frequent switching between enabled and disabled alarm settings
(Page 83).
The limit values are based on the OUT output value. If the output value OUT exceeds or under-
shoots the defined limit values, an alarm is sent to the automation system via the limit value process
alarms.
Process alarms provide information on certain block states and events. The following process alarms
can be defined and generated in the Analog Input function block:
Limit value process alarms
If a limit value is violated, the specified priority of the limit value alarm is checked before the limit
value violation is communicated to the fieldbus host system.
Rescaling the input value
In the Analog Input function block the input value or input range can be scaled in accordance with
the automation requirements.
Example:
• The system unit in the Transducer Block is °C.
• The measurement range of the sensor is -200 to 850°C.
• The process relevant measurement range is 0 to 200°C.
• The output range to the process control system should be 0 to 100%.
The measured value from the Transducer Block (input value) is rescaled linearly via the input scaling
PV SCALE to the desired output range OUT SCALE:
Options in the FAILSAFE
TYPE parameter
(failsafe mode):
Failsafe mode:
FSAFE VALUE The value specified in the "Failsafe value" parameter is used for further processing.
LAST GOOD VALUE The last good value is used for further processing.
WRONG VALUE The current value is used for further processing, despite the BAD status.
! Note!
The factory setting is WRONG VALUE.
HI HI LIM Page 82 LO LO LIM Page 82
HI LIM Page 82 LO LIM Page 82
Parameter group PV SCALE (Page 81) Parameter group OUT SCALE (Page 81)
PV SCALE MIN
 0 OUT SCALE MIN  0
PV SCALE MAX
 200 OUT SCALE MAX 100
OUT UNIT
 %