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6.8 Calibration of rate display using internal
references: SEt
This function enables the zero and span of the rate
display to be adjusted without the need for an
accurate external current source, or for
disconnection from the 4/20mA loop.
The accuracy of this method depends upon the
accuracy of the internal references which should
be regularly calibrated as described in section
6.9.2
To calibrate the rate display select 'SEt' from the
main menu and press
P.
The instrument will
display 'ZErO', pressing
P
again will reveal the
current display at 4mA. For flow applications this
will usually be zero. Each digit of the rate display
can be changed by pressing the
Up
or
Down
buttons. When the first digit is correct pressing
P
will transfer control to the next digit. When the
least significant digit has been adjusted, press
E
to
return to the 'ZErO' prompt which completes the
adjustment.
To adjust the display at 20mA, press the
Up
button
which will cause the instrument to display 'SPAn'.
Pressing
P
again will reveal the indicator display.
Each digit can be changed by pressing the
Up
or
Down
buttons. When the first digit is correct,
pressing
P
will transfer control to the next digit.
The most significant digit, which can be 1 or 2, is
set by rolling-over the previous digit. When all the
digits have been adjusted press
E t
o return to the
'SPAn' prompt, followed by
E
to return to the main
menu.
6.9 Conditioning sub-menu: Cond
This sub-menu allows the mains (line) frequency at
which the instrument has maximum ac rejection to
be selected and the two internal references to be
calibrated. These functions are contained in a
protected sub-menu to minimise the possibility of
accidental adjustment. To gain access to the sub-
menu select 'Cond' from the main menu and press
P
which will cause the instrument to display '0000'.
Using the
Up
, and
Down
buttons and the
P
button
to move to the next digit enter the password 'SurE'.
Pressing
E
will then give access to the sub-menu.
Note 'S' is entered as '5'.
6.9.1 AC rejection: FrE
WARNING
If the mains filter frequency is
changed, the rate display and the
internal references (if used) must be
recalibrated.
To provide maximum low frequency rejection the
internal digital filter may be set to operate at 50 or
60Hz to correspond with the local mains (line)
frequency. To change the frequency select 'FrE'
from the 'Cond' sub-menu and press
P
which will
reveal the current setting. The setting can be
changed by pressing the
Up
or
Down
buttons
followed by the
E
button to return to the sub-menu.
6.9.2 Calibration of internal references: rEF
The BA354ND contains two references
representing 4 and 20mA. These are used in the
'SEt' function which enables the rate display to be
calibrated without an external current calibrator.
They are also used in the 'C--P' function when the
P
push-button is programmed to display the input
current in the operating mode. If either of these
two functions are used, the internal references
should be routinely calibrated against an external
4/20mA calibrator connected to the input terminals
of the instrument. See section 8.4
To calibrate the internal references select 'rEF'
from the sub-menu and press
P
which will result in
a '.004A' prompt being displayed. Adjust the
external current calibrator to 4.000mA and again
press
P
. The instrument will display 'Ent' while the
4mA reference is being updated and will then
return to the '.004A' prompt.
To re-calibrate the 20mA internal reference, press
the
Up
button which will cause the instrument to
display '.020A'. Adjust the external current
calibrator to 20.000mA and again press
P.
The
instrument will display 'Ent' while the 20mA
reference is being updated and will then return to
the '.020A' prompt. This completes calibration of
the internal references, two operations of the
E
button will return the instrument to the 'Cond'
prompt in the main menu.
