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Required Transmitter Configuration
6.6.1
Configuring the process variable
Table 6-12 lists the process variables that can be assigned to the frequency output.
Table 6-12
Frequency output process variable assignments
Process variable
Mass flow
Volume flow
Note: The process variable assigned to the frequency output is always the TV (tertiary variable)
defined for HART communications. You can specify this process variable either by configuring the
frequency output or by configuring the TV (see Section 8.11.7). If you change the process variable
assigned to the frequency output, the TV assignment is changed automatically, and vice versa.
If your transmitter does not have a frequency output, the TV assignment must be configured directly
(see Section 8.11.7), and the value of the TV must be queried through a HART connection.
6.6.2
Configuring the output scale
The frequency output scale defines the relationship between output pulse and flow units. You can
select one of three output scale methods, as listed in Table 6-13.
Table 6-13
Frequency output scale methods and required parameters
Method
Description
Frequency = flow
• Frequency calculated from flow rate as described below
Pulses per unit
• A user-specified number of pulses represents one flow unit
Units per pulse
• A pulse represents a user-specified number of flow units
Frequency=flow
If you specify Frequency = Flow, you must also specify TV Frequency Factor and TV Rate Factor.
TV Rate Factor is defined as the maximum flowrate appropriate to your application. TV Frequency
Factor can then be calculated using the following formula:
where:
•
Rate = maximum appropriate flowrate (TV Rate Factor in configuration)
•
T = factor to convert selected flow time base to seconds
•
N = number of pulses per flow unit, as configured in the receiving device
Configuration and Use Manual
ProLink II code
Mass Flow
Vol Flow
Rate
×
----------- -
FrequencyFactor
=
N
T
Communicator
code
Display code
Mass flo
MFLOW
Vol flo
VFLOW
Required parameters
• TV frequency factor
• TV rate factor
• TV pulses/unit
• TV units/pulse
49
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