Sterling 30RA010-055 manual A — 4- to 20-mADemand Limiting, B — Cooling Set Point 4 to 20 mA

	100								50% CAPACITY AT 20 mA
(%)
LOAD	80
ALLOWABLE.MAX	60
	40	100% CAPACITY AT 4 mA				75% CAPACITY AT 12 mA
	20
	0	0	2	4	6	8	10	12	14	16	18	20
						DEMAND LIMIT SIGNAL – 4 - 20 mA INPUT
					Fig. 21A — 4- to 20-mA Demand Limiting

Care should be taken when interfacing with other manufac- turer’s control systems, due to possible power supply differences, full wave bridge versus half wave rectification. The two different power supplies cannot be mixed. ComfortLink™ controls use half wave rectification. A sig- nal isolation device should be utilized if a full wave bridge signal generating device is used.

DEMAND LIMIT (SCN Loadshed Controlled) — To con- figure Demand Limit for SCN Loadshed control set the De- mand Limit Select (DMDC) [Configuration, RSET] to 3. Then configure the Loadshed Group Number (SHNM), Loadshed Demand Delta (SHDL), and Maximum Loadshed Time (SHTM) [Configuration, RSET]. See Table 27.

The Loadshed Group number is established by the SCN system designer. The ComfortLink control will respond to a Redline command from the Loadshed control. When the

Redline command is received, the current stage of capacity is set to the maximum stages available. Should the loadshed con- trol send a Loadshed command, the ComfortLink control will reduce the current stages by the value entered for Loadshed Demand delta. The Maximum Loadshed Time is the maximum length of time that a loadshed condition is allowed to exist. The control will disable the Redline/Loadshed command if no Can- cel command has been received within the configured maxi- mum loadshed time limit.

Cooling Set Point (4 to 20 mA) — A field supplied and generated, externally powered 4 to 20 mA signal can be used to provide the leaving fluid temperature set point. Connect the signal to TB6-3,5(+,–). See Table 27 for instructions to enable the function. Figure 21B shows how the 4 to 20 mA sig- nal is linearly calculated on an overall 10 F to 80 F range for fluid types (FLUD) 1 or 2 [Configuration, OPT1]. The set point will be limited by the fluid (FLUD) type. Be sure that the chilled water loop is protected at the lowest temperature.

	100
	(38)
	90
	(32)
	80
	(27)
	70
	(21)						MAXIMUM
							SET POINT
	60						70 F (21.1 C)
F (C)	(15)
	50
POINT,
	(10)
	40
SET
	(4.4)
				(FLUD = 1) MINIMUM
	30			SET POINT 38 F (3.3 C)
	(-1)
	20
	(-7)
	10	(FLUD = 2) MINIMUM
		SET POINT 14 F (-10 C)
	(-12)
	0
	(-17)
	4	6.3	8.6	10.9	13.1	15.4	17.7	20

4 TO 20 mA SIGNAL TO EMM

EMM — Energy Management Module

Fig. 21B — Cooling Set Point (4 to 20 mA)

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