Reference Manual
00809-0100-4148, Rev BA
July 2010
Rosemount 148
3-4
At the time which the damping time constant is set, the transmitter output is at
63% of the input changes and it continues to approach the input according to
the damping equation above.
After one damping time constant following a sensor input step change, the
transmitter output will be 63.2% of that change. The output will continue to
approach the input according to the damping equation above.
For example, as illustrated in *, if the temperature undergoes a step change
from 100 ° to 100 °, and the damping is set to 5.0 seconds, the transmitter
calculates and reports a new reading using the damping equation. At 5.0
seconds, the transmitter outputs 106.3 °, or 63.2% of the input change, and
the output continues to approach the input curve according to the above
equation.
Figure 3-1. Change in Input vs.
Change in Output with Damping
Set to Five Seconds
Alarm and Saturation
Alarm Direction, Low Alarm Level, High Alarm Level, Low Saturation, and
High Saturation values can be set here. Rosemount and NAMUR standard
values can be found on Table A-1 * or user-configured values may be entered.
The guidelines are as follows:
• Low Alarm value must be between 3.50 and 3.75 mA
• High Alarm value must be between 21.0 and 23.0 mA
• 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, so the Low Saturation level (S) must be 3.8 - 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, so the Low Saturation level (S) must be 20.5 - 20.7 mA.
See “Failure Mode”* for Failure Mode considerations.
50/60 Hz Selection
The 50/60 Hz Selection sets the transmitter electronic filter to reject the
frequency of the AC power supply in the plant.