Differential pressure transducer output

Figure 4. Differential pressure transducer output, as a function of time, during a typical experiment at atmospheric pressure.

Pressure measurements are made with four differential pressure transducers which produce a 0- to 5-VDC output signal from an unregulated 24-VDC Input. The range of three of the transducers 1s 0 to 500 psi and the other 1s 0 to 320 psl. The signal from these transducers 1s connected to an analog Input card 1n the HP 3497. 

The basic component in this system is a sensitive differential pressure transducer (A) with one side measuring atmospheric pressure and the other the internal reactor pressure. The computer monitors the transducer output, and when a slight pressure differential (about a half inch of water) is detected because of the gas uptake in the reactor, the pulse valve (B) is opened to introduce a known volume of gas into the reactor. The size of this pulse is dependent on the gas pressure at the pulse valve and the time it remains open. These factors are adjusted to provide calibrated pulses of near one half cc of reactor gas. The selection valve (S) provides a simple means of using different reaction gases. This apparatus can also be used to study reactions in which a gas is produced. 

Opening controlled by output from differential pressure transducer... 

The polymer solutions with concentrations between 0.2 and 1.0 weight percent were injected by a dosing pump equipped with a variable speed drive. The polymer used was polyacrylamide SEPARAN AP45 (M = 4-5 xlO ). The pressure differences between pressure taps were measured with Philips differential pressure transducers (Model PD2), the outputs of which were connected to a computer (Hewlett Packard 1000) to enable direct analysis of the experimental data. 

Flow meters have traditionally been classified as either electrical or mechanical depending on the nature of the output signal, power requirements, or both. However, improvement in electrical transducer technology has blurred the distinction between these categories. Many flow meters previously classified as mechanical are now used with electrical transducers. Some common examples are the electrical shaft encoders on positive displacement meters, the electrical (strain) sensing of differential pressure, and the ultrasonic sensing of weir or flume levels. 

Sample solution is introduced into the solvent flow stream from a sample loop via a sample injection valve. The solvent flow pushes the sample solution through the analytical capillary vdiere the viscosity of the sample is detected. The AP signal from each pressure transducer is fed to a differential logarithmic amplifier as shown in the Figure. The viscometer output is the In signal of the sample solution. A pump is used to... 

All of these pressure transducers offer frequency response characteristics acceptable for most or all respiratory applications. In situations requiring the measurement of a single pressure (for example, the pressure at the mouth during breathing), one of the two input ports to the transducer is left open to atmospheric pressure. In other situations requiring the measurement of a pressure differential (for example, measuring the output of a pressure-drop flow sensor), the two ports of the transducer are attached to the two taps of the sensor. 

Linearizing the output of the transmitter if necessary (e.g., square root extraction of the differential pressure for a head-type flow transducer) can be done within the instrument instead of within the control system. 

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