Control Loop Checkout - Carrier 48FP Controls Operation And Troubleshooting

Control Loop Checkout

The checkout and adjustment of control loops should only
be done by certified Carrier Comfort Network (CCN) tech-
nicians. 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 PIC units come with pre-
set default values. However, it may be necessary to adjust sev-
eral of these values to achieve stabled control. These values
are submaster loop gain (SMG), submaster loop center 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 Comfort-
WORKS® 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
disable all routines.
3. Verify that all forced values have been removed.
4. Table 53 indicates recommended starting values for
MLG and SMG for 48/50FB,FP,JB,JP units. Verify
that these values have been entered by checking the
service function.
Table 53 — 48/50FB,FP,JB,JP Units SMG, SCV and MLG Recommended Starting Values
FUNCTION/GAIN OR SCV
Cooling Control
MLG
Economizer
MLG
SMG
SCV
Duct Pressure (VFD)
MLG
SMG
SCV
Building Pressure
MLG
SMG
SCV
Staged Heat
MLG†
SMG†
Heating Coil
MLG
SMG
SCV
Humidifier
MLG
SMG
SCV
LEGEND
— Constant Volume
CV
— Master Loop Gain
MLG
— Submaster Center Value
SCV
— Submaster Loop Gain
SMG
VAV — Variable Air Volume
SERVICE SUBFUNCTION
(HSIO)
8
10
10
10
9
9
9
18
18
18
11
11
7
7
7
17
17
17
60
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 responds to a change in the temperature in
small increments, then increase the SMG in small
amounts until the output steadies.
NOTE: Do not be alarmed if the submaster sensor
stabilizes 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
minimum. 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 IGV and
VFD) loops and increased for CC (cooling control)
and ECON (economizer) loops.
GAIN VALUE
CV Application
1.0
1.0
–7.5
50
N/A
N/A 5.0 (034-078), 2.0 (088,104)*
N/A
1.0
–5.0
50
1.0
5.0
1.0
7.5
50
1.0
7.5
50
*Factory setting; differs from replacement control default setting.
†48FP,JP or 50FP,JP with optional or accessory electric heat-
ers only.
VAV Application
1.0
1.0
–7.5
50
1.0
50 (034-078), 35 (088,104)*
1.0
–5.0
50
1.0
5.0
1.0
7.5
50
1.0
7.5
50