ABB Johnson Controls AYK550-UH, User Manual

Page: 219 / 348

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550-UH User’s Manual 1-219
Embedded fieldbus
Scaling drive feedback values
Feedback values are provided with units of percent, where 0% and 100%
correspond to the range of the sensor being used to measure the control variable.
These points have default units in Hz. If other units are required:
• Unbundle these points with appropriate slopes and intercepts.
• The new intercept equals the lowest value of the desired range.
• Calculate the new slope as follows:
Example – You are controlling water temperature from a cooling tower using the
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<.
550 to control a fan. The temperature sensor has a range of 30 to 250 degrees
Fahrenheit.
To unbundle the set point (INPUT REF 2), for commanding in degrees Fahrenheit,
where 0…60 Hz is equal to 30…250
°
F:
To unbundle the feedback (PRC PID FBCK) for monitoring in degrees Fahrenheit:
Loop gains
PRC PID GAIN (Point 50) and PRC PID ITIM (Point 51) are PID parameters similar
to the P and I gains in the APOGEE TECs. Because the
JCI
PI loop and the
Siemens loop are structured differently, there is no a one-to-one correspondence
between the gains. The following formulas allow translation from
JCI
gains to
Siemens gains and vice versa:
85 LAI AO 2 ACTUAL
FLN External PID Report
Point
Subpoint Name Data
# Type
New Slope =
(Desired Range, i.e. high - low values) x (Slope of Existing Point)
Range of Existing Point
=
(60 Hz - 0 Hz) x (0.01)
100% - 0%
= 0.006
New Slope =
(Desired Range) x (Slope of Existing Point)
Range of Existing Point
=
(250
°
F - 30
°
F) x (0.1)
100% - 0%
= 0.22
New Intercept = 30 (the temperature that corresponds to 0%)
New Slope =
(Desired Range) x (Slope of Existing Point)
Range of Existing Point
=
(250
°
F - 30
°
F) x (0.01)
100% - 0%
= 0.022
New Intercept = 30