Micro Motion RFT9709 Instrukcja Obsługi Pobierz pdf (Strona 100)

Using ProLink

Software with Micro Motion

Transmitters

Configure Menu: Characterize

continued

Pressure compensation with RFT9739

8.7 Pressure compensation

with RFT9739

A Version 2 or Version 3 RFT9739 can compensate for the effect of

pressure on sensor flow tubes. Pressure effect is defined as the change

in sensor flow sensitivity due to process pressure change away from

calibration pressure. Sensors that are affected by pressure are listed in

Table 8-4

, page 87.

In applications where the operating pressure varies significantly from the

pressure at which the flowmeter was calibrated, the user can establish

pressure compensation. Pressure effect can be corrected in one of two

ways:

• For real-time compensation, by entering pressure correction factors

and connecting an external pressure transmitter

• For relatively stable operating pressures, by adjusting the calibration

factors for flow and density

Real-time compensation

For real-time pressure compensation, two pressure compensation

factors must be entered, one for flow and one for density. In the FlowFact

and/or DensFact text boxes, enter the appropriate values from

Table 8-4

, then click OK.

• The pressure correction factor for flow is the percent change in the

flow rate per psi.

• The pressure correction factor for density is the grams per cubic

centimeter change in density per psi.

The user should also enter the calibration pressure for real-time

pressure compensation. In the FlowCal Pressure text box, enter the

appropriate value in psi, then click OK. (At the factory, Micro Motion

sensors are calibrated for flow at 20 psig.)

In addition, real-time pressure compensation requires either gauge

pressure or analog pressure input. (To select an input for pressure

compensation, see

Section 11.3

, page 122.)

Gauge pressure input

If a pressure transmitter connected to a host controller measures gauge

pressure at the sensor input, the RFT9739 can use flow and density

signals from the sensor, and pressure signals from the host controller, to

compensate for the pressure effect on the sensor.

• In a HART-compatible network, the RFT9739 functions as a primary

or secondary master while polling the host controller.

• In a Modbus-compatible network, the host controller downloads

pressure values to register 40007 or register pair 20257-20258.

Analog pressure input

The RFT9739 can be connected to an analog pressure transmitter that

produces a 4-20 mA input signal representing pressure. The RFT9739

or an external source can power the pressure transmitter.

• To connect a pressure transmitter to the RFT9739, see the RFT9739

instruction manual.

• If a sensor is ordered for an application requiring pressure

compensation, the pressure input is configured at the factory.

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