Emerson Rosemount 644 with HART Protocol, Справочное руководство

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22
Reference Manual
00809-0200-4728, Rev SA
Configuration
July 2018
Configuration
2.8.2 Damping
The damping function changes the response time of the transmitter to smooth variations in output
readings caused by rapid changes in input. Determine the appropriate damping setting based on the
necessary response time, signal stability, and other requirements of the loop dynamics of the system.
The default damping value is 5.0 seconds and can be reset to any value between 1 and 32 seconds.
The value chosen for damping affects the response time of the transmitter. When set to zero (disabled),
the damping function is off and the transmitter output reacts to changes in input as quickly as the
intermittent sensor algorithm allows. Increasing the damping value increases transmitter response time.
With damping enabled, if the temperature change is within 0.2 percent of the sensor limits, the
transmitter measures the change in input every 500 milliseconds (for a single sensor device) and outputs
values according to the following relationship:
P = previous damped value
N = new sensor value
T = damping time constant
U = update rate
At the value to which the damping time constant is set, the transmitter output is at 63 percent of the
input change and it continues to approach the input according to the damping equation above.
For example, as illustrated in Figure 2-14 , if the temperature undergoes a step change—within 0.2
percent of the sensor limits—from 100 degrees to 110 degrees, and the damping is set to 5.0 seconds,
the transmitter calculates and reports a new reading every 500 milliseconds using the damping
equation. At 5.0 seconds, the transmitter outputs 106.3 degrees, or 63 percent of the input change, and
the output continues to approach the input curve according to the equation above.
For information regarding the damping function when the input change is greater than 0.2 percent of
the sensor limits, refer to
“Intermittent sensor detection” on page 28 .
Figure 2-14. Change in Input vs. Change in Output with Damping Set to Five Seconds
Damped Value
N P
–
( )
2
T U
–
2
T U +
-----------------
 
 
×
P
+
=