Moore 535 PROFILER, Руководство пользователя

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535-PROF User's Manual Chapter 7
107
Applications
compensate for disturbances (i.e., load changes), but it cannot compensate
for process noise. Attempting to do this will result in degraded controller
performance. The Noise Band is the distance the process deviates from the
setpoint due to noise in percentage of full scale.
Figure 7.14 shows a typical process variable response in a steady-state
situation. In this example, the process noise is within a band of about 0.5%
of full scale.
A noise band that is too small will result in tuning parameter values based on
noise rather than the effects of load (and setpoint) changes. If the noise band
is set too small, then Adaptive Tune will attempt to retune the controller too
often. This may result in the controller tuning cycling between desirable
system tuning and overly sluggish tuning. While the result may be better
than that achieved with a non-adaptive controller, this frequent retuning is
not desirable.
If the noise band is set too large, the process variable will remain within the
noise band, and the controller will not retune itself. With too large a noise
band, important disturbances will be ignored, and the controller will be
indifferent to sluggish and oscillatory behavior.
Noise band settings are generally between 0.1% and 1.0%, with most common
settings of 0.2% or 0.3%.
Figure 7.15 shows the conversion of peak-to-peak
noise to an appropriate noise band for each T/C type & RTD.
Figure 7.15
Noise Band Values for Temperature
Inputs
Figure 7.14
Noise Band Calculation Example
P
eak to P
eak Noise ˚F
INPUT TYPE
0
1
2
3
4
5
6
7
8
9
10
B
0.1
0.1
0.1
0.1
0.1
0.2
0.2
0.2
0.2
0.2
0.2
E
0.1
0.1
0.1
0.2
0.2
0.2
0.3
0.3
0.4
0.4
0.4
J
0.1
0.1
0.1
0.2
0.2
0.2
0.3
0.3
0.4
0.4
0.4
K
0.1
0.1
0.1
0.1
0.1
0.2
0.2
0.2
0.3
0.3
0.3
N
0.1
0.1
0.1
0.1
0.1
0.2
0.2
0.3
0.3
0.3
0.4
R/S
0.1
0.1
0.1
0.1
0.1
0.2
0.2
0.2
0.3
0.3
0.3
T
0.1
0.1
0.2
0.3
0.4
0.5
0.6
0.6
0.7
0.8
0.9
W/WS
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.2
0.2
0.2
0.2
PLATINEL
0.1
0.1
0.1
0.2
0.2
0.2
0.3
0.3
0.4
0.4
0.4
RTD
0.1
0.1
0.1
0.2
0.2
0.3
0.3
0.4
0.4
0.5
0.5
0.1˚RTD
0.1
0.1
0.2
0.3
0.5
0.6
0.7
0.8
0.9
1.0
1.1
–328
400
401
402
403
404
405
752
0
40 80 120 160 200 240
406
407
408
409
PROCESS
VARIABLE
Type T
Thermocouple
Range
–328
°
F TO 752
°
F
NOISE BAND =
(407 – 402)
[ 752 – (–352) ]
X 100 =
.5%
TIME (SECONDS)