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DAVID W SPITZER'S E-ZINE (June 2021)

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Differential Pressure Flowmeters (Part 4 of 4) by David W Spitzer

Differential pressure flow transmitters generate an electrical signal that represents the differential pressure at its ports. Of importance is how well the differential pressure flow transmitter performs this function. Because performance is the prime concern in many applications, the technology used to effect the measurement is typically a secondary or tertiary matter. The following sections provide brief explanations of the principles used in differential pressure flow transmitter designs.

Capacitance
In a capacitance design, the differential pressure at the ports causes the wetted diaphragm to move an internal diaphragm located between two fixed plates. The movement of the internal diaphragm causes a capacitance change that can be converted into a signal that is proportional to the applied differential pressure.

Differential Transformer
In a differential transformer design, the differential pressure at the ports causes the wetted diaphragm (or bellows) to move the magnetic core in a transformer. The movement of the core causes an electrical imbalance that can be converted into a signal that is proportional to the applied differential pressure.

Force Balance
In a force balance design, the differential pressure at the ports causes the wetted bellows to create a force that is counteracted by a force generated by an electromagnet (or perhaps a servomotor). A measurement of the generated counteractive force can be converted into a signal that is proportional to the applied differential pressure.

Piezoelectric
In a piezoelectric design, the differential pressure at the ports causes the wetted diaphragm to apply force on a crystal. This force causes an electric signal to be generated that can be converted into a signal that is proportional to the applied differential pressure.

Potentiometer
In a potentiometer design, the differential pressure at the ports causes the wetted diaphragm (or bellows) to move the wiper of a variable resistor (potentiometer). The movement of the wiper causes a resistance change that can be converted into a signal that is proportional to the applied differential pressure.

Silicon Resonance
A silicon resonance sensor is a micro-machined semi-conductor structure fabricated on a silicon crystal. The structure is shaped such that it can oscillate and resonate at high frequencies. When a differential pressure is applied, part of the structure is under compression while another part of the structure is in tension. The compression and tension forces change the resonant frequency of the structure in a manner proportional to the applied differential pressure.

Strain Gage
In a strain gage design, the differential pressure at the ports causes the wetted diaphragm to apply a force on a strain gage. This force stretches the strain gage and causes the resistance of the strain gage to change. The resistance change causes an electric signal to be generated that can be converted into a signal that is proportional to the applied differential pressure.

Excerpted from The Consumer Guide to Differential Pressure Flow Transmitters

Flowmeter Billing Errors by David W Spitzer

Large legal cases are usually more complex, more challenging and more interesting than small and medium cases because large cases often involve multiple issues across multiple disciplines that need to be considered in a legal environment where access to information can be limited. All of this can be made more difficult because the potential monetary awards can reach tens of millions of dollars. In this environment, one oversight can cost millions of dollars.

Energy Savings of Operating a Pump at Reduced Speed by David W Spitzer

Approximately how much energy is saved by operating a pump motor at 85% speed as compared to operating the pump motor at full speed to provide the same liquid flow rate?

ABOUT SPITZER AND BOYES, LLC

In addition to over 40 years of experience as an instrument user, consultant and expert witness, David W Spitzer has written over 10 books and 500 articles about flow measurement, level measurement, instrumentation and process control. David teaches his flow measurement seminars in both English and Portuguese.

Spitzer and Boyes, LLC provides engineering, technical writing, training seminars, strategic marketing consulting and expert witness services worldwide.