Figure 5 Strain Gauge Used in a Bridge Circuit

Figure 4 Strain Gauge Pressure Transducer

Instrumentation and Control Volume 1 of 2
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PRESSURE DETECTION CIRCUITRY Pressure Detectors An increase in pressure at the inlet of the bellows causes the bellows to expand. The expansion of the bellows moves a flexible beam to which a strain gauge has been attached. The movement of the beam causes the resistance of the strain gauge to change. The temperature compensating gauge compensates for the heat produced by current flowing through the fine wire of the strain gauge. Strain gauges, which are nothing more than resistors, are used with bridge circuits as shown in Figure 5. Figure 5 Strain Gauge Used in a Bridge Circuit Alternating current is provided by an exciter that is used in place of a battery to eliminate the need for a galvanometer. When a change in resistance in the strain gauge causes an unbalanced condition, an error signal enters the amplifier and actuates the balancing motor. The balancing motor moves the slider along the slidewire, restoring the bridge to a balanced condition. The slider’s position is noted on a scale marked in units of pressure. IC-02 Page 8 Rev. 0

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