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MC-PSTX02
對(duì)于需要對(duì)加熱和/或冷卻進(jìn)行雙位置控制的單區(qū)系統(tǒng)（例如，具有直接膨脹冷卻的燃?xì)馕蓓敊C(jī)組），建議采用雙位置負(fù)荷的時(shí)間比例控制。對(duì)于電加熱控制，尤其是底板電加熱，也建議采用時(shí)間比例控制。對(duì)于時(shí)間比例控制，必須小心避免控制設(shè)備的循環(huán)頻率超過(guò)設(shè)備制造商的建議。步進(jìn)控制步進(jìn)控制器按順序操作開(kāi)關(guān)或繼電器，以啟用或禁用兩位設(shè)備（如電加熱器或往復(fù)式制冷壓縮機(jī)）的多個(gè)輸出或級(jí)。階躍控制使用模擬信號(hào)嘗試從設(shè)備獲得模擬輸出，該設(shè)備通常處于打開(kāi)或關(guān)閉狀態(tài)。圖26和圖27顯示，各級(jí)可布置為在有或無(wú)運(yùn)行（開(kāi)/關(guān)）差速器重疊的情況下運(yùn)行。在任何一種情況下，典型的兩個(gè)位置差仍然存在，但總輸出是成比例的。74關(guān)-開(kāi)-關(guān)-開(kāi)-關(guān)-開(kāi)-關(guān)-開(kāi)-關(guān)-開(kāi)5 4 3 2 1差動(dòng)節(jié)流范圍空間溫度（°F）72 0%負(fù)載100%

Time proportioning control of two-position loads is recommended for applications such as single-zone systems that require two-position control of heating and/or cooling (e.g., a gas-fired rooftop unit with direct-expansion cooling). Time proportioning control is also recommended for electric heat control, particularly for baseboard electric heat. With time proportioning control, care must be used to avoid cycling the controlled equipment more frequently than recommended by the equipment manufacturer. STEP CONTROL Step controllers operate switches or relays in sequence to enable or disable multiple outputs, or stages, of two-position devices such as electric heaters or reciprocating refrigeration compressors. Step control uses an analog signal to attempt to obtain an analog output from equipment that is typically either on or off. Figures 26 and 27 show that the stages may be arranged to operate with or without overlap of the operating (on/off) differentials. In either case, the typical two-position differentials still exist but the total output is proportioned. 74 OFF ON OFF ON OFF ON OFF ON OFF ON 5 4 3 2 1 DIFFERENTIAL THROTTLING RANGE SPACE TEMPERATURE (°F) 72 0% LOAD 100%