15
stored in memory, and will then return to the
'SPAn' prompt. Finally press E again to
return to the main menu.
This function may also be used when
calibrating a complete loop including the flow
meter.
6.8 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 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 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.
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. 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.
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 BA358C 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 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 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.
6.10 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
