- Flow direction Uni/bidirectional Uni/bidirectional Communication Optional HART® Add-on modules, HART, Profibus PA & DP, MODBUS RTU, DeviceNet, Foundation Fieldbus H1 Display 3 lines 3 lines 20 characters 20 characters (optional without display) (optional without display) Meter uncertainty ±0.4% o.r. Enclosure IP67, IP20 IP67, IP20.
- Danfoss range of electro-magnetic flowmeters 2 MAG 5000 MAG 6000 Outputs 1 current output 1 current output 1digital output 1digital output 1 relay output 1 relay output Flow direction Uni/bidirectional Uni/bidirectional Communication Optional Add-on modules HART HART, DeviceNet, Profibus DP, Profibus PA, CANopen Display 3 lines 3 lines.
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Basic Elements
The purpose of this manual is to advise Danfoss users on generally accepted circuit arrangements, but it does not, and cannot, describe all possible circuits which may be appropriate for various applications. Transmission circuits are unique designs and must be developed and tested to ensure required performance and life. 4.2.5 29-5. Flow Confirmation 99 4.3 Application Set-up Examples 100 4.3.1 Submersible Pump Application 102 4.3.2 BASIC Cascade Controller 103 4.3.3 Pump Staging with Lead Pump Alternation 104 4.3.4 System Status and Operation 104 4.3.5 Cascade Controller Wiring Diagram 105 4.3.6 Fixed Variable Speed Pump Wiring Diagram 106.
Just like other flowmeters, differential pressure flowmeters consist of two elements. They are:
A primary element: This element causes a change in kinetic energy which results in the differential pressure in the pipe. The unit must be suitably matched to the
- pipe size,
- flow conditions, and
- the liquid's properties
Besides, the measurement accuracy of the element must be fine over a practical range.
A secondary element: The secondary element measures the differential pressure created by primary element and gives the signal or read-out which is in turn transformed to the actual flow value.
Types of Differential Pressure Flowmeters
Most widely used differential pressure flowmeters are:
- Orifice Plates
- Flow Nozzles
- Venturi Tubes
- Variable Area flowmeters, i.e. Rotameters
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Accuracy & Rangeability
Performance of a head-type flowmeter installation is a function of the
- precision of the flow element and
- the accuracy of the d/p cell
On average, flow element precision is expressed in percentage of actual reading terms, whereas d/p cell accuracy is stated as a percentage of calibrated span. A d/p cell typically provides accuracy of ±0.2% of the calibrated span. With no detrimental effect on accuracy, rangeability of a flowmeter can be extra enhanced by employing several d/p flowmeters in parallel runs.
Errors and Noise
Errors and Noise
In case of compressible fluids, the ratio of differential pressure divided by upstream pressure should not exceed 0.25 for reduction of error and correction of density. Metering errors caused due to wrong installation of the primary element can become considerable i.e. up to 10%. Following are the possible causes of these errors:
- the condition of the mating pipe sections
- insufficient straight pipe runs
- pressure tap and lead line design errors
In turbulent flow conditions, not more than 10% of the d/p signal could possibly be noise produced by disturbances from valves and fittings. These disturbances can be both up- and downstream of the element, and by the element itself. To sort out this noise, a damping is provided in d/p cells which prove to be adequate for majority of the applications. Rigorous noise can be diminished by applying two or more pressure taps connected in parallel on both sides of the d/p cell.
Sources
Danfoss Flow Meter User Manual Transfer Switch
OmegaTech
Engineering Toolbox
Danfoss Flow Meter User Manuals
Omega.literature
