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6.4 Electronic.  Electronic devices are also known as capacitance devices.
In an electronic device, the dp is transmitted through an isolating diaphragm
to a hermetically sealed sensing diaphragm in the center of the device
(Figure 5-10).  The sensing diaphragm is surrounded by silicone oil contained
between capacitors.  As the sensing diaphragm deflects in proportion to the
dp, the position of the diaphragm is detected by capacitor plates on each side
of the diaphragm.  The differential capacitance between the plates and the
diaphragm is converted electronically to a 2-wire, 4-20 mA or 0-10 volt data
transmission signal.  Electronic devices are available in both square root and
linear function models. Solid state, plug-in components simplify
6.5 Calibration. Static calibration should be performed on all dp devices at
least every 6 months.
6.6 Data Transmission. Readings from various dp devices must often be
transmitted to remote data collection and recording sites.  This is because
the dp device may be too remote to warrant onsite reading.  Data transmission
may also be necessary because there may be many widely dispersed devices to be
read and it would be uneconomical to have each one read onsite; or a central
data management point has been set up to collect, record, plot, reduce, and
analyze all flow data. All the taps for dp will accommodate remote
transmission fittings along with the various dp devices.
6.6.1 Pneumatic. All the dp devices, except electronic, can have the
readings transmitted to a remote site by pneumatic lines.
6.6.2 Electrical. Rather than pneumatically, the recommended means of data
transmission is to have the dp electronically converted to an analog signal
and transmitted electrically to a data collection center.


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