MC-TSTX03
对于需要对加热和/或冷却进行双位置控制的单区系统（例如，具有直接膨胀冷却的燃气屋顶机组），建议采用双位置负荷的时间比例控制。对于电加热控制，尤其是底板电加热，也建议采用时间比例控制。对于时间比例控制，必须小心避免控制设备的循环频率超过设备制造商的建议。步进控制步进控制器按顺序操作开关或继电器，以启用或禁用两位设备（如电加热器或往复式制冷压缩机）的多个输出或级。阶跃控制使用模拟信号尝试从设备获得模拟输出，该设备通常处于打开或关闭状态。图26和图27显示，各级可布置为在有或无运行（开/关）差速器重叠的情况下运行。在任何一种情况下，典型的两个位置差仍然存在，但总输出是成比例的。74关-开-关-开-关-开-关-开-关-开5 4 3 2 1差动节流范围空间温度（°F）72 0%负载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%