Micro Motion RFT9709 Instrukcja Obsługi Strona 117

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Using ProLink
®
Software with Micro Motion
®
Transmitters
103
Configure Menu: Transmitter Variables
continued
Flow cutoffs
Configure Menu:
Transmitter Outputs
Configure Menu:
Transmitter Information
Configure Menu: EventsView Menu: Status
Configure Menu:
Characterize
Configure Menu:
Transmitter Variables
If the transmitter is an RFT9739 measuring viscosity, the flow cutoff
should be greater than the flow rate at which the process achieves the
maximum turndown pressure drop specified for the DP cell (the
minimum pressure drop that the DP cell can accurately measure). For
maximum turndown ratings of individual DP cells, refer to manufacturer's
specifications.
Milliamp outputs have their own flow cutoffs, which remain unaffected by
the flow cutoffs established for the frequency/pulse output and internal
totalizers.
Section 10.3
(page 112) explains how to set flow cutoffs for
milliamp outputs.
If the transmitter is a Version 3 RFT9739, the ProLink program provides
a "live zero" display, which enables the user to read the mass flow rate
when it drops below the cutoff that is set for mass flow.
Section 15.4
(page 158) describes how live zero can be used in the diagnostic
process.
Example:
Given:
The RFT9739 is configured to calculate viscosity in centistokes.
The maximum pressure drop measurable by the DP cell is 33 psid, at a
mass flow rate of 160 grams per second (g/sec). The maximum
turndown specified for the DP cell is 40:1. To minimize measurement
error, the flow cutoff is set to the flow rate that corresponds to a DP
turndown of 20:1.
Problem:
The frequency/pulse output should indicate zero flow when
the mass flow rate drops below 5% of 160 g/sec.
Solution:
Mass flow cutoff = 0.05 * 160 g/sec = 8 g/sec
Enter 8 into the Mass Flow Cutoff text box in the Configure Transmitter
Variables dialog box.
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