Emerson Rosemount 248 Reference Manual page 40

Configuration
May 2019
• The low saturation level must be between the low alarm value plus 0.1 mA and 3.9 mA.
Example: The low alarm value has been set to 3.7 mA. Therefore, the low saturation level,
S, must be 3.8 ≤ S ≤ 3.9 mA.
• The high saturation level must be between 20.5 mA and the high alarm value minus 0.1
mA.
Example: The high alarm value has been set to 20.8 mA. Therefore, the low saturation
level, S, must be 20.5 ≤ S ≤ 20.7 mA.
See Failure mode
Rerange
Reranging the transmitter sets the measurement range to the limits of expected readings
which maximizes transmitter performance; the readings are is most accurate when the
transmitter is operated within the expected temperature range for the application.
PV range values
The PV URV and PV LRV commands, found on the PV Range Values menu screen, allow
the user to set the transmitter's lower and upper range values using limits of expected
readings. The range of expected readings is defined by the Lower Range Value (LRV) and
Upper Range Value (URV). The transmitter range values can be reset as often as necessary
to reflect changing process conditions. From the PV Range Values screen select 1 PV LRV
to change the lower range value and 2 PV URV to change the upper range value.
Note
The rerange functions should not be confused with the trim functions. Although the
rerange command matches a sensor input to a 4–20 mA output, as in conventional
calibration, it does not affect the transmitter's interpretation of the input.
Intermittent sensor detect (advanced feature)
The Intermittent Sensor Detect feature guards against process temperature readings
caused by intermittent open sensor conditions (an intermittent sensor condition is an
open sensor condition that lasts less than one update). By default, the transmitter is
shipped with the intermittent sensor detect feature switched ON and the threshold value
set to 0.2 percent of sensor limits. The Intermittent Sensor Detect feature can be switched
or OFF and the threshold value can be changed to any value between 0 and 100
ON
percent of the sensor limits with a Field Communicator.
Transmitter behavior with intermittent sensor detect ON
When the Intermittent Sensor Detect feature is switched ON , the transmitter can eliminate
the output pulse caused by intermittent open sensor conditions. Process temperature
changes (ΔT) within the threshold value are tracked normally by the transmitter's output.
A ΔT greater than the threshold value activates the intermittent sensor algorithm. True
open sensor conditions cause the transmitter to go into alarm.
The threshold value of the Rosemount 248 should be set at a level allowing for normal
range of process temperature fluctuations; too high and the algorithm will not be able to
filter out intermittent conditions; too low and the algorithm will be activated
unnecessarily. The default threshold value is 0.2 percent of the sensor limits.
40
for Failure Mode considerations.
Rosemount 248 Temperature Transmitter Reference Manual
Reference Manual
00809-0100-4825