Carrier 48MPD Control Loop Checkout, 48/50MP Units SMG, SCV and MLG Recommended Starting Values

Control Loop Checkout

The checkout and adjustment of control loops should only be done by certi®ed 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 Ð 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) and ECON (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 Ð 48/50MP Units SMG, SCV and MLG Recommended Starting Values

		SERVICE		GAIN VALUE
	FUNCTION/GAIN OR SCV	SUBFUNCTION
		(HSIO)	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 ²	11	1.0		1.0
	SMG ²	11	5.0		5.0
	Heating Coil
	MLG	7	1.0		1.0
	SMG	7	7.5		7.5
	SCV	7	50		50
	Humidi®er
	MLG	17	1.0		1.0
	SMG	17	7.5		7.5
	SCV	17	50		50
*Factory setting; differs from new control setting.
²48MP only.
	LEGEND
CV	Ð Constant Volume
MLG	Ð Master Loop Gain
SCV	Ð Submaster Center Value
SMG Ð Submaster Loop Gain
VAV	Ð Variable Air Volume

41