ch_client = “kb123″; ch_width = 300; ch_height = 250; ch_type = “mpu”; ch_sid = “Chitika Default”; ch_backfill = 1; ch_color_site_link = “#0000CC”; ch_color_title = “#0000CC”; ch_color_border = “#FFFFFF”; ch_color_text = “#000000″; ch_color_bg = “#FFFFFF”; Bridge Circuit Construction Figure 8 shows a basic bridge circuit which consists of three known resistances, R1, R2, and R3 (variable), [...]
Bridge Circuit Operation The bridge operates by placing Rx in the circuit, as shown in Figure 8, and then adjusting R3 so that all current flows through the arms of the bridge circuit. When this condition exists, there is no current flow through the ammeter, and the bridge is said to be balanced. When the [...]
Temperature Detection Circuit Figure 11 is a block diagram of a typical temperature detection circuit. This represents a balanced bridge temperature detection circuit that has been modified to eliminate the galvanometer. The block consists of a temperature detector (RTD) that measures the temperature. The detector is felt as resistance to the bridge network. The bridge [...]
Bellows-Type Detectors The need for a pressure sensing element that was extremely sensitive to low pressures and provided power for activating recording and indicating mechanisms resulted in the development of the metallic bellows pressure sensing element. The metallic bellows is most accurate when measuring pressures from 0.5 to 75 psig. However, when used in conjunction [...]
Bourdon Tube-Type Detectors The bourdon tube pressure instrument is one of the oldest pressure sensing instruments in use today. The bourdon tube (refer to Figure 2) consists of a thin-walled tube that is flattened diametrically on opposite sides to produce a cross-sectional area elliptical in shape, having two long flat sides and two short round [...]
Pressure Detector Functions Although the pressures that are monitored vary slightly depending on the details of facility design, all pressure detectors are used to provide up to three basic functions: indication, alarm, and control. Since the fluid system may operate at both saturation and subcooled conditions, accurate pressure indication must be available to maintain proper [...]
Resistance-Type Transducers Included in this category of transducers are strain gauges and moving contacts (slidewire variable resistors). Figure 3 illustrates a simple strain gauge. A strain gauge measures the external force (pressure) applied to a fine wire. The fine wire is usually arranged in the form of a grid. The pressure change causes a resistance [...]
Inductance-Type Transducers The inductance-type transducer consists of three parts: a coil, a movable magnetic core, and a pressure sensing element. The element is attached to the core, and, as pressure varies, the element causes the core to move inside the coil. An AC voltage is applied to the coil, and, as the core moves, the [...]
Capacitive-Type Transducers Capacitive-type transducers, illustrated in Figure 9, consist of two flexible conductive plates and a dielectric. In this case, the dielectric is the fluid. As pressure increases, the flexible conductive plates will move farther apart, changing the capacitance of the transducer. This change in capacitance is measurable and is proportional to the change in [...]
Detection Circuitry Figure 10 shows a block diagram of a typical pressure detection circuit. The sensing element senses the pressure of the monitored system and converts the pressure to a mechanical signal. The sensing element supplies the mechanical signal to a transducer, as discussed above. The transducer converts the mechanical signal to an electrical signal [...]
[Online Article is proudly powered by WordPress.]