Differential Pressure Sensor with Pair of Strain Gauges

The following differential pressure sensor uses a matched pair of strain gauges. As the differential pressure increases, one strain gauge becomes compressed while the other becomes stretched. A voltmeter registers the bridge circuit’s imbalance and displays it as a pressure measurement:

Differential Pressure Sensor

Determine the following:

• Identify which port is the “high” pressure port
• Identify what the voltmeter will register if fixed resistor R1 fails open
• Identify a component fault that would drive the voltmeter full upscale (“peg” positive)
• Identify another component fault that would drive the voltmeter full upscale (“peg” positive)

Answer:

Which port is the “high” pressure port: Port “B”

What will happen if fixed resistor R1 fails open: Voltmeter will drive fully upscale (“peg” positive)

Identify a component fault that would drive the voltmeter full upscale (“peg” positive):  as follows below

• Strain gauge #1 fails shorted
• Strain gauge #2 fails open
• R1 fails open
• R2 fails shorted

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Credits: Tony Kuphaldt