Elster Instromet 2000, Инструкция по эксплуатации

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Model 2000 Flow Computer Instruction Manual
2.0 GENERAL DESCRIPTION
Model 2000 issue 21 Page No
22
2.4. INPUT SIGNALS
It is possible to configure the Model 2000 to accept either flow measuring inputs from a pulse generating turbine meter
(paragraphs 2.4.1 apply) or as a direct digital reading from an Ultrasonic meter (paragraphs 2.4.2 apply) or using differential
pressure measurement across an orifice plate or Venturi (paragraphs 2.4.3 apply) or using a Coriolis meter (paragraphs
2.4.4 apply)
2.4.1. TURBINE METER
If the M2000 is configured to accept turbine pulse inputs then these will be of the form of one or two periodic input signals
with the following parameters.
Current input: 10mA.
Frequency range: Up to 5kHz.
One input is defined as the reference frequency input (rf), low frequency input (lf) or monitor input and the other as the high
frequency input (hf) or meter input. The high frequency input is used to calculate all of the total flows. The reference
frequency input is used for blade failure checking, an uncorrected volume is also obtained from this input. The calculation of
total flow continues down to zero turbine frequency as input pulse counting techniques are used.
If Turbine Meters with low frequency relay contact outputs i.e. less than 20Hz are intended to be used then an input de-
bounce circuit should be selected (See Section 4.3 for link settings).
2.4.1.1. MINIMUM INPUT FREQUENCY
The minimum input frequency that is used to calculate flow rate and is used to indicate an alarm condition can be selected to
be between 0.004 Hz and 1 Hz by entering a value for f min. The value of f min used determines the time elapsed before a
loss of a turbine meter input signal, this time is equal to 1/f min. in seconds.
2.4.1.2. TURBINE METER LINEARISATION
A facility is provided which gives the option of linearise the turbine meter input which is connected to the high frequency
input. The options available are:-
off No correction.
20 pnt Linearity correction using 20 point interpolation.
The meter is characterised by entering up to twenty co-ordinates for flow and corresponding error values which are stored in
the Model 2000 memory. A linearity correction applied to the corrected flows by interpolating between the co-ordinate points.
Correction is applied to the uncorrected flow rates, uncorrected and corrected total flows.
The value entered into the %Qmax n data location is in % of maximum flow (Q max.) of the meter, this figure can range from
– Qmax to + Qmax to allow for different linearity in the opposite flow direction and the value entered in the corresponding
%Er.rd n location is the % error of reading. If the output from the meter is less than the actual flow through the meter then
the error is entered as a negative value.
%Er.rd n = the % error in reading of the meter flow rate at %Qmax n flow rate. n is an integer between 0 and 19
The lowest value of flow in this case nearest to –Qmax (or nearest to zero flow if the flow is only in the +ve direction) must be
entered at the position n = 0. The rest of the data points must be entered in ascending value of Q up to the top point. If it is
required to enter less than the maximum 20 points then any unused data positions must be set to invalid data by entering a –
sign with no numbers.
2.4.1.3. BI-DIRECTION METER OPERATION
The Model 2000 can be configured to operate from a Flow Meter that can produce a pulse output for flow in both the forward
or + direction and the reverse or – direction. If the unit is set to operate in this way the flow Totals are shown as separate
positive totals for the forward direction and negative totals for the reverse direction. Flow rates are shown with the
appropriate sign. Flow direction is set by a Digital status input, Status input 3 is reserved for this function. The input is set
Open or Off for Forward or + flow and Closed or On for Reverse or negative flow.