11
be reduced from eight to six digits. The rate and
total annunciators will also be interchanged.
Pressing the
Up
and
Down
buttons simultaneously
will interchange the displays.
Note:
Both decimal points must be repositioned
after the displays have been interchanged.
5.7 Lower display: ‘dISPLAY.2’
This function turns the lower display on or off.
When turned off, the BA538C will only have one
eight digit display which may be programmed to
show total flow or rate of flow.
5.8 Rate scale factor: ‘SCALE-r’
Together with the instrument timebase, this
function defines the arithmetic relationship
between the pulse input frequency and the rate
display. When used with a flowmeter SCALE-r
should be set to the K-factor of the flowmeter i.e.
the number of pulses the flowmeter produces for a
unit of flow. e.g. 45.6 pulses per litre. See
section 6 for a worked example.
SCALE-r is a dividing factor that may be adjusted
between 0.001 and 99999999.
To check or change the total scale factor select
'SCALE-r' from the main menu and press
P
to
reveal the existing setting, one digit will be
flashing. The value of the flashing digit can be
changed by pressing the
Up
or
Down
buttons.
When this digit is correct pressing
P
will transfer
control to the next digit.
To position the decimal point in the rate scale
factor, move the flashing digit to the left hand side
of the required decimal point position and
simultaneously press the
Up
and
Down
buttons.
When the required rate scale factor has been
entered, press
E t
o store the number and return to
the main menu.
5.9 Timebase: ‘t-bASE’
The timebase multiplies the rate display by 1, 60
or 3,600 depending upon whether the BA538C is
required to display rate per second, per minute or
per hour. See Fig 5.
To check or change the timebase, select 't-
bASE' from the main menu and press
P
which will
reveal the current setting. Pressing the
Up
or
Down
button will index through the three options:
tb-1
for flow / second
tb-60
for flow / minute
tb-3600
for flow / hour
Select the required multiplier and press
E
to return
to the main menu.
5.10 Rate filter: ‘FILtEr’
This digital filter has two independent adjustable
parameters enabling the rate display frequency
response to be tailored for optimum performance.
The filter parameters are controlled by a two digit
number. The first digit defines the amount of
filtering applied to the display as shown below.
First digit
Filter time constant
seconds
0X
0
1X
1.3
2X
4.3
3X
6.5
4X
8.7
5X
11.3
6X
15.7
7X
20.9
8X
25.2
9X
31.5
The second digit defines the deviation from the
displayed rate at which the filter will be overridden
and the rate display will move rapidly to the new
value.
Second
digit
Magnitude of step
change which will
produce a rapid
response
X0
Off
X1
1%
X2
2%
X3
4%
X4
8%
X5
12%
X6
16%
X7
24%
X8
32%
X9
64%
By careful adjustment of the two parameters a
stable display with an acceptable step input
response can be obtained for most applications.
During commissioning it is recommend that
initially the second digit is set to 0 (off) and the
first digit is adjusted to provide acceptable rate
display stability. The second digit should then be
increased until the selected step size is greater
than the noise on the display signal, at which
setting the rate display will again become stable.
These will be the optimum filter parameters for
acceptable rate display stability and a fast
response to a large rate signal change.
Summary of Contents for BA538C
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