| 摘要 |
<p>A fail-safe, precision current-to-pressure converter for providing a regulated pneumatic output pressure proportional to an electrical control current (21) includes a main valve member (4) for regulating the pneumatic output pressure at outlet (3), operation of the valve member (4) being controlled by the pressure of control fluid contained in a chamber (11). The control fluid pressure is controlled by admitting control fluid into the chamber (1) via a continuously pulsed, electromagnetically actuated on/off reed valve (16) and simultaneously allowing control fluid continuously to exhaust to atmosphere via a fixed bleed orifice (17), the rate of admittance of control fluid into the chamber (11) relative to the exhaust rate from the orifice (17) being variable so that the desired, substantially constant output pressure, as dictated by the electrical current input (21) and as measured by a transducer (15) that produces a feed-back signal, will be attained. In the event that the input current (21) fails, the valve (16) remains closed and continued exhaust of control fluid from the chamber (11) causes the control fluid pressure, and therefore the output pressure at (3), to fall to atmospheric pressure, ie the converter fails to "zero" in such event. Because of its relatively simple design, a converter of the invention is somewhat more rugged and less expensive to manufacture than prior I/P converters. <IMAGE></p> |
