Carrier 30GN040-420 Example 5B Ð 4 to 20 mA and Internally or, Externally Powered Reset

Example 5B Ð 4 to 20 mA and Internally or

Externally Powered Reset

In this example, the unit set point is reset from full load at 4 mA to a maximum reset value of 10 F (5.5 C) at 20 mA. Internally powered 4 to 20 mA option is used in this example.

NOTE: To use externally powered reset, when CRTYP

appears, press so CRTYP 4 appears in the

display. The remainder of the information in the fol- lowing example applies to either type of reset.

KEYPAD	DISPLAY	COMMENTS
ENTRY	RESPONSE
	FLD CFG
	CRTYP 0	Scroll past to reset type
	CRTYP 1	Internally powered reset
		selected
	RESET
	CRT1 0	Reset at 20 mA is 0
	CRT1 10	Reset at 20 mA is 10

Example 5C Ð Using Return Fluid

Temperature Reset

KEYPAD	DISPLAY	COMMENTS
ENTRY	RESPONSE
		Field con®guration
	FLD CFG	subfunction of
		service function
	CSPTYP X	Scroll past single/dual
	CRTYP 0	Display shows no reset
		type has been selected
	CRTYP 3	Return ¯uid temperature
		is selected and activated
	RESET	Reset set points

Temperature Reset Based on External Temperature Ð If de- sired, temperature reset can be based on an external tem- perature, such as space or outdoor-air temperature. This re- quires a thermistor (T10, Part No. 30GB660002) located in the space or outdoor air and wired to terminals as follows (also see Field Wiring section on page 69 and Fig. 6):

4 in/4 out Module Ð J7-15 and J7-16.

At the ®eld con®guration step, enter set points as de- scribed in Examples 5A-5C on pages 39 and 40. Then

select external temperature reset by entering when

CRTYP 0 appears. See Fig. 7.

Temperature Reset Based on 4-20 mA SignalÐ If desired, temperature reset can be based on a 4-20 mA signal. For proper connections, refer to Field Wiring section on page 69 and Fig. 8.

At the ®eld con®guration step, select 4-20 mA reset by

entering (internally powered) or (externally pow-

ered) when CRTYP 0 appears. Then enter set points as de- scribed previously in Examples 5A-C. See Fig. 8.

Subfunction displays demand limit set points.

Demand Limit, 2-Stage Switch Control Ð This control has been designed to accept demand limit signals from a build- ing load shedding control. The demand limit function pro- vides for 2 capacity steps. The keypad is used to set the 2 demand limit set points, which range from 100 to 0% of ca- pacity. Capacity steps are controlled by 2 ®eld-supplied re- lay contacts connected to the designated chiller terminals. (See Field Wiring section on page 69 and Fig. 7.)

Fig. 5 Ð Cooling Return Fluid Reset

40