TAILIEUCHUNG - flame safeguard control phần 7

Đối với BKample, một ngọn lửa màu đỏ có thể được sử dụng 10 thí điểm IHE delecl, và một C7012E tự kiểm tra hoặc ngọn lửa F Deleclor tia cực tím có thể được sử dụng cho ngọn lửa ghi chính. Vì tất cả các bộ khuếch đại là plug-in, IHE phát hiện RJ '\ C: lClI3'can được thay đổi bất cứ lúc nào sau khi | tlmtts. Contrpil i lg jjE -fthd Interlocks ẠỊ w and make R to B when the controlled variable falls to the set point minus the differential. A Controller with an additive differential operates similarly except that the set point is at the ow end of the differential Instead of at the high end. A controller with manual reset also called lockout can be used as a limit to 1 shut down the System if it breaks a circuit or 2 operate an alarm ft makes a circuit. On most controllers with manual reset lockout occurs at the set point but on a tew models it occurs at the set point plus or minus the differential. The circuit will stay locked out until the temperature returns to normal lockout point plus or minus the differential and the operator depresses a manual reset lever or button Fig. 2 or 48 . If the lever or button has a trip-free feature operation will not be returned to CONTROLLERS. normal until the manual reset lever or button Is released. This prevents the controller from resetting automatically even if the manual reset lever or button is tied down or held in by tape wire Of some other device. Manual reset makes sure someone is going to notice something is wrong. A good service technician will correct the problem before resetting the switch. proportioning range The proportioning range also called throttling range usually extends above the set point Fig. 9 although on some controllers it extends on both sides of I he set point. Pressure or temperature variations cause the bellows or diaphragm to move causing the potentiometer wiper R terminal to move across its windings. This varies the re sistance between R and B and R and w. The resulting circuit unbalance drives a modulating motor or modulating valve actuator and regulates the firing rate. For a detailed explanation of this operation refer to the Flame Safeguard Reference on Firing Rate Controls form 70-8117. As the Controlled variable rises the wiper will move toward the w end erf the potentiometer driving the .

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