Micro Motion RFT9709 Manual de Instruções descarregar pdf (Página 116)

102

Using ProLink

Software with Micro Motion

Transmitters

Configure Menu: Transmitter Variables

continued

Temperature and pressure units

If a density unit other than degrees API is selected, the RFT9739

calculates gross volume at line conditions. Any standard engineering

units for gross volume can be selected for standard volume.

Accuracy of standard volume measurement is dependent on the

accuracy of the following factors:

• Mass flow rate measurement

• Operating density measurement

• Temperature measurement

• Transmitter correlation to API tables

The accuracy of each factor varies based on process operating

conditions and the fluid being measured. For most Generalized

Petroleum Products, standard volume will be accurate within ±0.5% of

the flow rate. Because the temperature correction correlations for

density are based on API equations, the standard volume output applies

only to Generalized Petroleum Products or materials that exhibit the

same thermal expansion characteristics as Generalized Petroleum

Products.

9.4 Temperature and pressure

units

The transmitter can measure and indicate temperature in any of the

standard units listed in

Table 9-5

, page 95. After selecting the

temperature unit of measure, continue using the same units to configure

outputs, process limits, calibration factors, and characterization factors.

A Version 2 or 3.0 RFT9739 can measure and indicate pressure and

viscosity in any of the standard units listed in

Table 9-3

, page 94, and

Table 9-8

, page 96. After selecting the pressure and/or viscosity units of

measure, continue using the same units to configure outputs, process

limits, calibration factors, and characterization factors.

9.5 Flow cutoffs

Enter mass or volume flow cutoffs into the Cutoff text boxes under Mass

Flow or Volume Flow.

In some sensor installations, process conditions may cause the

transmitter to read slightly nonzero values when the process is at a

no-flow state. Flow cutoffs allow the user to filter out noise by defining

the measured value below which the transmitter frequency/pulse and

digital outputs indicate zero flow.

A flow cutoff is the lowest flow rate at which the transmitter produces a

nonzero digital flow reading and frequency/pulse output. If the flow

signal drops below the flow cutoff:

• The transmitter frequency/pulse output goes to 0 Hz

• The transmitter internal totalizers stop counting

• The transmitter indicates zero flow during polling from a host

controller

A default flow cutoff is entered into the transmitter at the factory. This

number can be adjusted by the customer, using the ProLink program, to

achieve the filter effect described above.

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