Flowserve MX HART Field Unit - Manual (Page 50)

MX/QX HART Field Unit FCD LMENIM2340-00 – 1/14
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Enter the new URV value and click on the Set button.
3.7.3 Analog Signal to Primary Variable Process Flow
The following Figure 3.2 shows the process flow used to convert the analog input signal to a positions setpoint target
value for the PV.
1. The analog signal is read by the ADC and converted to a digital value
2. The digital value is assigned an equivalent mA value based on fixed internal values
3. The loop current value is now scaled between the zero and gain trim points
a. The gain trim value can be set from the DD menu Device Setup->Wired HART Board->Calibration
b. The zero trim value can be set from the DD menu Device Setup->Wired HART Board->Calibration
c. The loop current value can be set to a fixed value for simulation from the DD menu Process Variables->
Wired HART Board
4. The loop current is checked for saturation and the appropriate alarms are set or cleared
a. The Field Device Status bit “Loop Current Saturated” will be set/cleared
5. The Upper and Lower Transducer limits (fixed) are used to do a linear transformation to convert the loop current
to position setpoint value in percent open. (4 mA = 0% PV – Lower Transducer Limit, 20 mA = 100% PV – Upper
Transducer Limit)
a. The analog channel level and percent range can be read using command 60 with channel number 0 (which is
the loop current)
6. The Upper and Lower Range scaling set by the customer is applied to the Primary Variable. This may reverse the
signal polarity, or limit the range.
a. The Upper Range Value can be set from the DD menu Device Setup->Wired HART Board->Calibration
b. The Lower Range Value can be set from the DD menu Device Setup->Wired HART Board->Calibration
c. The PV can be forced to a fixed value for simulation from the DD menu Process Variables->Wired HART
Board; it is also used to write the PV value when in Multi-drop mode
7. The PV value is checked for Out-of-Limits and the appropriate alarms are set or cleared
a. The Field Device Status bit “Primary Variable Out of Limits” will be set/cleared
b. The PV value will be limited to the Upper or Lower Range value if it is detected to be out of limits