Siemens 7ML19985AB01 Flow Calculation, Display, Absolute vs. ratiometric, = constant

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FLOW CALCULATION

Absolute vs. ratiometric

The OCM-3 can be programmed to use either of two methods (P4) for calculating flow from the head measurement: absolute or ratiometric. The result is the same regardless of the method used. The principal difference is the information that must be entered in order for the OCM-3 to carry out the calculation. The user’s choice of method may ultimately be based upon the information which is at hand. Refer to U parameters for the primary element selected for a listing of the information required.

For the ratiometric method, it is usually sufficient that the user know the flow rate (Qcal) which occurs at maximum head (hcal).

On the other hand, absolute calculations require that the user enter information such as: the physical dimensions of the primary element and the constant relating to units of measure for both linear dimensions and flow rates.

e.g.

the general formula for flow through a single exponent primary element is:

Q = KHx

the specific formula for flow through a 45° V-notch weir is:

cfs = 1.03H2.5

thus:	Q = flow in cubic feet per second
	K = constant of 1.03
	H = head in feet

The absolute method is not applicable to the following:

Palmer Bowlus flume

H flume

DISPLAY

The normal display during operation is the Flow and Total Display (F2).

flow rate field

relay / "no echo" field

totalizer field

status field

7ML19985AB01

OCM III

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Contents Open channel Unit Repair and Excluded Liability Contact Smpi Technical Publications at the following addressTable of Contents General Keypad Initial Start Up Fundamental Checks Start UPOperation Maintenance Error Codes 100 Communications 101 7ML19985AB01 AppendicesOCM Short About thisIf you want to know about Read Product OCM Specifications » range 20 or 4-20 mA » resolution» 20 to 50 C -5 to 122 F IP65 enclosureProgrammer » CE *, FM, CSA NRTL/CTransducer Temperature SensorCabling Auxiliary Input Communication SoftwareOutput » Belden Installing the OCM-3 InstallationOutline and Mounting OCM-3 Layout OCM-3 System DiagramCustomer device Installing the Transducer Installing the Temperature SensorGround shield at OCM-3 only Basic Wiring Temperature Sensor Ground shield at OCM-3 onlyMA Output RelaysSynchronization AC Power Power ConnectionsDC Power Installing the Memory BACK-UP Battery Installing the ProgrammerDisconnect power before installing or replacing the battery Communicating VIA ComputerGeneral Start UPKeypad Initial Start UP OCM-3 is asking which language you prefer to communicateLanguage EnglishP0 language English P1 dimensional units Centimeters F13 auto zero calibration 160 Completed 7ML19985AB011141 24-hr. time114100 Enter new time F5 ddmmyyyy date October 12Fundamental Checks OCM Operation MemorySecurity UnitsFlow Calculation DisplayAbsolute vs. ratiometric = constantFor battery operation, set display lighting to off or auto DampingFor battery operation, have relays energizing on alarm Example For relay» 20 mA » P6 * flow rateFlow Rate and Totalizing FAIL-SAFEFlow rate Logging CapacityViewing the data log Blanking TemperatureTime and Date Emulation Mode ResetFlow Velocity Input Auxiliary Head InputVoltage Input Current Input As normal 7ML19985AB01DC Output Diagnostic Aids100% head 4 m, enter 5 m Security access required ‘D’ Parameter ListingVelocity Nominal target rangeOCM ‘F’ Parameter Listing Enter security code Emulation modeKeypad to mA output OCM Linear Velocity ‘P’ Parameter Listing= centimetres Flowrate Volume = absolute = ratiometric Flow rate unitsGallons = imperial million gallons per dayOCM = 4-20 mA = 0-20 mA 7ML19985AB01 OCM OCM Variable condition FixedUnits OCM ‘U’ Parameters for P3 Primary Element OCM Reference U0 = exponent U1 = k factor P4 = 0 only= constant factor U1 = head Typical SHARP-CRESTED Weirs Typical Weir ProfilesKhafagi Venturi Typical Parshall Flume Typical Leopold Lagco ‘U’ parameters required ‘U’ parameters calculated BS-3680 Rectangular Flume = crest width = Cv = crest height = Cd = crest length = a BS-3680 Round Nose Horizontal Crest Weir Cv = velocity coefficient ¤ Refer to Operation \ Flow Calculation 7ML19985AB01BS-3680 Trapezoidal Flume BS-3680 U-Flume, P3 = BS-3680 U-FLUME = crest width = C = crest height = Cp = crest length = head H and p applied to CBS-3680 Finite Crest Weir = Ce x 2⁄3 ⎯⎯√2⎯g x be x he1.5 Where q = flow rate = approach width = Ce = crest width = K b = crest height= gravitational acceleration = crest width He = effective head h + Kh = head Kh = 1 mmBS-3680 Thin Plate Rectangular Weir U0 = notch angle Alpha U1 = Ce BS-3680 Thin Plate V-NOTCH Weir U0 = crest width b Rectangular Weir Contracted Based on the Manning Formula = hydraulic radius = slope of hydraulic gradientRound Pipe U0 = maximum flume width, hmax PALMER-BOWLUS Flume U0 = maximum listed head, hmax Flume Universal Head vs FLOW, P3 = U0 = number of data points n, 4 toFlow, point A13 Head, point A14 Flow, point A15 Head, point A16Flow, point A17 Head, point A18 Flow, point A19U0 = channel width B U1 = area h Rectangular Area X Velocity = head, cm = flow velocity, cm/sec Trapezoidal Area X Velocity For h ≥ d = B b/d Where q = flow rate, l/s= channel top width, cm = head, cm = channel base width, cm Modified Trapezoidal Area X Velocity U0 = base diameter D U1 = area h Channel Area x Velocity U0 = conduit diameter U1 = area h Circular Area X Velocity GULL-WING Area X VELOCITY, P3 = Gull Wing Area X Velocity EGG-SHAPED Area X VELOCITY, P3 = EGG-SHAPED Area X Velocity Universal Area X VELOCITY, P3 = Typical open channelArea Head Universal Area X VelocityA10 = OCM Maintenance Error Codes Computer Customer’sSerial printer Protocol for the OCM-3 is as follows Baud rate 102DB-9 connector DB-25 connectorBipolar Current Refer to Cvcc InstructionP35 = 7, print interval set for 7 minutes Date104 Remote OCM-3 display Local display Utilities Software Programmer Remote OCM-3 programming105 106 Typical OCM-3 Display value00.000000 99.12399.123000 7ML19985AB01 107# = 0 through Content of P5 ResponseStop data log down load Start data log down load109 DB-25 connector 7ML19985AB01 Standard modemCable Computer Telephone lines Remote modemConnect Establishing Communication111 Ending Communication 112Rev