Rockwell Automation 1734sc-IE4CH E+H Instruments via HART to PlantPAx User Manual - Manual (Page 104)

104 Rockwell Automation Publication PROCES-UM002A-EN-P - July 2014
Appendix E Prosonic M Ultrasonic Level
The sensor of the Prosonic M transmits ultrasonic pulses in the direction of the
product surface. There, they are reflected back and received by the sensor. The
Prosonic M measures the time t between pulse transmission and reception. The
instrument uses the time t (and the velocity of sound c) to calculate the distance
D between the sensor membrane and the product surface:
D = c · t/2
As the device knows the empty distance E from a user entry, it can calculate the
level as follows:
L = E - D
An integrated temperature sensor compensates for changes in the velocity of
sound caused by temperature changes. The interference echo suppression feature
on the Prosonic M ensures that interference echos (e.g. from edges, welded joints
and installations) are not interpreted as a level echo. Enter the empty distance E
and the span F to calibrate the device. Span F may not extend into the blocking
distance BD. Level echos from the blocking distance cannot be evaluated due to
the transient characteristics of the sensor.
Measured Variables
The distance D between the sensor membrane and the product surface is
measured. Using the linearization function, the device uses D to calculate the
following:
• Level L in any units
• Volume V in any units
• Flow Q across measuring weirs or open channels in any units
Signals from Instrument to Control System
Signal Details
Current Output 4...20 mA with HART protocol (Minimum load for HART communication: 250
Ω)
Frequency Output FMU40 - approx. 70 kHz
FMU41 - approx. 50 kHz
FMU42 - approx. 42 kHz
FMU43 - approx. 35 kHz
FMU44 - approx. 30 kHz
Output Damping Freely selectable, 0...225 s