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5.8 Calibration of the 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
5.9.2
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 rate display at 20mA, press the Up
button which will cause the instrument to display
'SPAn'. Pressing P again will reveal the existing
full scale rate 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 can only be
adjusted by rolling-over the previous digit. When all
the digits have been adjusted press E to return to
the 'SPAn' prompt, followed by E to return to the
main menu.
5.9 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. To minimise the possibility of accidental
adjustment these functions are contained in a
protected sub-menu. To gain access to this 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'. 'S' is entered as '5'. Pressing E will then
give access to the sub-menu.
5.9.1 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.
5.9.2 Calibration of internal references:
rEF
The BA558C contains two references representing
4 and 20mA. These are used in the 'SEt' function
that 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 display 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 7.4
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
BA385C 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.
5.10 Resetting grand total: CLr. Gtot
The grand total is a separate sixteen digit counter
which duplicates the total display, but is not zeroed
when the total display is reset to zero. The grand
total may be viewed in the display mode in two
eight digit sections as described in section 2.1 of
this manual.
