14
To re-calibrate the 20mA internal reference,
press the
Up
button which will cause the
indicator to display '.020A'. Adjust the external
current calibrator to 20.000mA and again press
P .
The indicator will display 'Ent' when the
20mA reference has been updated and will
then return to the '.020A' prompt.
Two
operations of the
E
button will return the
indicator display to 'Cond' in the main menu.
The accuracy of the internal references, and
hence the display accuracy, will depend upon
the accuracy of the external current source.
With a maximum span of 19999 the indicator
has a display resolution of 0.8µA, we therefore
recommend that the accuracy of the external
current source used for calibration is greater
than 0.4µA.
6.11 Function of the
P
push button:
C - - P
This parameter defines the function of the
P
push button when the indicator is in the display
mode. While the button is operated the digital
display will show the input current in milliamps,
or the input current as a percentage of the
span.
The analogue display continues to
operate normally while the
P
button is
operated.
To check or change the parameter select
'C - -P' from the main menu and press
P
to
reveal the current setting. Pressing the
Up
or
Down
button will toggle the setting between '4-
20' the current display and 'PC' the percentage
display.
When set as required press
E
to
return to the main menu.
Accuracy of the current display depends upon
the accuracy of the internal references which
should be periodically calibrated - see section
6.10.2
6.12 Null display function: null
This function enables the BA326C analogue
bargraph to operate as a deviation indicator
displaying the difference between the input
current and a specified reference.
To activate this function select 'null' from the
main menu and press
P
. Pressing the
Up
or
Down
button will toggle the function between
'OFF' and 'On', when set as required press
E
to return to the main menu.
To define the input about which deviation is to
be displayed the BA326C must be returned to
the display mode.
With the instrument
displaying the required input reference, press
the
Down
and
E
buttons simultaneously. The
BA326C will respond by displaying 'null' for a
few seconds, after which the reference input
will be automatically subtracted from both the
analogue and digital displays.
Starting at the reference point, the bargraph
will display a column extending upwards or
downwards to indicate the difference between
the input and the reference.
Fig 8 illustrates
the display resulting from a BA326C calibrated
to display 0 to 1000 when nulled at 500
(12mA) and 250 (8mA).
To prevent accidental or unauthorised access
the null function can only be used once. If the
reference point needs to be changed, the null
function must be turned off and then back on
from the main programme menu.
To prevent inadvertent alarm setpoint changes,
the null function can not be operated if either of
the optional alarms are enabled.
If alarms
are required, they must be enabled after the
null function has been used.
Fig 8 Effect of nulling at two different inputs
Summary of Contents for ba326c
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