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Control Loop Checkout
The checkout and adjustment of control loops should
only be done by certified Carrier Comfort Network
(CCN) technicians. The following checkout procedure
is offered as a guide and presumes the user has obtained
basic knowledge of controls through CCN training.
TO CHECK OPERATION OF ANALOG OUTPUTS — The
control algorithms of the unit controls utilize the master/
submaster loop concept. The master loop monitors the
master sensor (the sensor which tries to maintain the desired
set point), and calculates the submaster reference required to
do so. The submaster loop monitors the submaster sensor
and controls the actual output to the controlled device.
These algorithms require the adjustment of a number of
gain values to function properly. The 48/50MP units come
with preset default values. However, it may be necessary to
adjust several of these values to achieve stable control. These
values are submaster loop gain (SMG), submaster loop cen-
ter value (SCV), and master loop gain (MLG). In addition,
proportional, integral, and derivative multiplier values can
be accessed through the Building Supervisor, Service Tool,
or ComfortWorks™ software.
To verify or adjust submaster default values, perform the
following for each controlled device (control loop):
1. Verify that the system is in the Occupied mode and the
supply-air fan is running.
2. Verify that the supply-air fan status indicates ON. If the
fan status is OFF, the unit control algorithms will dis-
able all routines.
3. Verify that all forced values have been removed.
4. Table 27 indicates recommended starting values for MLG
and SMG for 48/50MP units. Verify that these values
have been entered by checking the service function.
5. Verify/adjust the SMG. If the SMG is too large, the loop
will tend to oscillate (hunt). If it is too small, the loop
will react too slowly.
Verify or adjust the SMG as follows:
Using the HSIO keypad, force the submaster reference
of the control loop to a value above or below the actual
sensor reading. Verify that the actuator responds cor-
rectly. If the actuator drives in the wrong direction, go
to the submaster gain (SMG) for the control loop and
reverse the sign of the gain.
For example: If the submaster loop gain is 5.0, change
it to -5.0.
6. Observe the operation of the controlled device for a few
minutes. If the device oscillates every few seconds around
the forced value, then lower the SMG by small amounts
until the output steadies. If the output to the device re-
sponds to a change in the temperature in small incre-
ments, then increase the SMG in small amounts until
the output steadies.
NOTE: Do not be alarmed if the submaster sensor sta-
bilizes at a value greater or less than the forced value.
This is called the submaster droop offset and is normal.
7. It is not necessary to adjust the submaster loop center
value, as the master loop will adjust the submaster ref-
erence as required to satisfy its set point. However, it
may be desirable to keep the submaster droop to a mini-
mum. This is most often required for economizer loops.
If the submaster droop is too large, adjust the SCV as
follows:
If the submaster droop is positive (actual value greater
than reference value), the SCV should be decreased for
HCV (heating coil) and IGV (supply fan VFD) loops
and increased for CC (cooling control) andECON (econo-
mizer) loops.
If the submaster droop is negative (actual value less than
reference value), the SCV should be increased for HCV
and IGV loops and decreased for CC and ECON loops.
Table 27 — 48/50MP Units SMG, SCV and MLG Recommended Starting Values
FUNCTION/GAIN OR SCV
SERVICE
SUBFUNCTION
(HSIO)
GAIN VALUE
CV Application VAV Application
Cooling Control
MLG 8 1.0 1.0
Economizer
MLG 10 1.0 1.0
SMG 10 −7.5 −7.5
SCV 10 50 50
Duct Pressure (VFD)
MLG 9 N/A 1.0
SMG 9 N/A 2.0*
SCV 9 N/A 35*
Building Pressure
MLG 18 1.0 1.0
SMG 18 −5.0 −5.0
SCV 18 50 50
Staged Heat
MLG † 11 1.0 1.0
SMG † 11 5.0 5.0
Heating Coil
MLG 7 1.0 1.0
SMG 7 7.5 7.5
SCV 75050
Humidifier
MLG 17 1.0 1.0
SMG 17 7.5 7.5
SCV 17 50 50
*Factory setting; differs from new control setting.
†48MP only.
LEGEND
CV — Constant Volume
MLG — Master Loop Gain
SCV — Submaster Center Value
SMG — Submaster Loop Gain
VAV — Variable Air Volume
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