33
…5.10.1 Heat/Cool Control Page
Manual Reset (cool output)
Set the required proportional band offset, between 0.0 and 100.0% of the
engineering range span in 0.1% increments.
Derivative Action Time
Set the required time between 0.1 and 999.9 in 0.1 second increments (999.9
seconds = 16.67 minutes). 'OFF' is selected below 0.1.
Approach Band
Set the required value between 0.1 and 3.0 in 0.1 increments. (Set 1.0 initially).
Crossover Output Value
Set the required value between 0.0 and 100.0% of the P.I.D. output, in 0.1%
increments – see Section 5.10.2.
Transition Bandwidth
Set the required value between 0.0 and 100.0% of the P.I.D. output, in 0.1%
increments – see Section 5.10.3.
Output Off Hysteresis Band
Set the required value which prevents oscillation of control changes, between
0.0 and 25.0% of the P.I.D. output, in 0.1% increments.
MrESEt
PAGE
OFF
ContrL
c 50.0
dErIV
APPb
CrSOUr
t–bANdt–bANd
OFFHYS
c 100.0
c 0.0
0.1
OFF
3.0
0.1
100.0
0.0
100.0
0.0
25.0
0.0
999.0
50.0
1.0
10.0
25.0
Integral
Off
Derivative
Off
5.10.2 Calculating the Crossover Value – Fig. 5.18
The crossover value is calculated from the expression:
Crossover Value =
100
Gh/Gc + 1
Where Gh/Gc is the ratio of the two output driver gains.
The most common method for determining the Gh/Gc term is
by using 'nameplate' values from the heat/cool device(s).
If a heat/cool application can produce a maximum of 1.5kW
and absorb 0.75kW:
Output Gain Ratio =
1.5
0.75
= 2
Crossover Value =
100
2 + 1
= 33.3%
5.10.3 Calculating the Transition
Bandwidth Value – Fig 5.18
The Transition Bandwidth is the percentage difference of the
proportional band settings.
Example – if the proportional band settings for the heat output
is 20% and for the cool output is 25%:
Transition Bandwidth (%) =
25 – 20
25
x 100
Transition Bandwidth = 20%
If the proportional band settings for both outputs are equal, the
bandwidth is 0%. As a general rule, the Transition Bandwidth
should not exceed 30%.
5 CONTROL OPERATION
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