Step 10 Return to the display mode
With the 'CAL' prompt displayed, press
E
to store the conditioning and
calibration information and return to the
operating mode. All the display
decimal points will be activated while
the information is being stored. This
completes the calibration of the
transmitter using the internal
references.
The following steps explain how, using the Trim
Menu, the BA374C transmitter may be calibrated
against an external reference, such as a voltage
source or temperature calibrator. Alternatively, the
complete loop including the primary element may
be calibrated by cooling and heating the
thermocouple to -10 and +240
o
C. This is the
preferred method for routine calibration.
Step 11 Entering the trim menu
Enter the trim menu by simultaneously
pressing the
P
and
Down
buttons - see
Fig 9. The transmitter will respond by
displaying 'COdE' . Press
P
to clear
this prompt and set the display to the
security code 1209 using the
Up
,
Down
and
P
push-buttons. Pressing
E
will
enter the code. After a few seconds
during which all the decimal points will
be activated, the first parameter 'ZEro'
will be displayed.
Step 12 Zero adjustment
This adjustment trims the display to
read exactly -10.0
o
C and the output
current to be exactly 4.000mA when the
type J thermocouple is at -10
o
C. This
can be achieved by cooling the
thermocouple to -10
o
C or by inputting
the voltage which the thermocouple
should theoretically produce. If a
voltage is used the transmitter cold
junction compensation (see section
6.3.4) should be turned off during the
calibration, or the input voltage should
be corrected for ambient temperature,
although this may be less accurate.
With the transmitter displaying the
'ZEro' prompt and the correct input
connected to the transmitter, push
P
which will cause the transmitter to
display the thermocouple temperature.
Adjust the display with the
Up
and
Down
buttons until it is -10.0
Note: Immediately the
Up
or
Down
button is operated the annunicator in
the top left hand corner of the display
will be activated to warn that any
change in the input signal will be
ignored while this display correction is
being made.
Operating the
P
push-button will lock
the transmitter display at -10.0
and
allow the output current to be trimmed
using the
Up
or
Down
button. When
the output current measured by a DVM
is 4.000mA, the
E
push-button should
be operated to return the transmitter to
the 'ZEro' prompt.
This completes calibration at -10.0
o
C.
Step 13 Span adjustment
With the transmitter displaying the
'ZEro' prompt select 'SPAn' by pressing
the
Up
or
Down
button. With the
thermocouple heated to 240
o
C, or an
equivalent voltage input, push
P
which
will cause the transmitter to display the
thermocouple temperature. Adjust the
display with the
Up
and
Down
buttons
until it is 240.0
Note: Immediately the
Up
or
Down
button is operated the annunicator in
the top left hand corner of the display
will be activated to warn that any
change in the input signal will be
ignored while this display correction is
being made.
Operating the
P
push-button will lock
the transmitter display at 240.0
and
allow the output current to be trimmed
using the
Up
or
Down
button. When
the output current measured by a DVM
is 20.000mA, the
E
push-button should
be operated to return the transmitter to
the 'SPAn' prompt.
This completes calibration at 240.0
o
C.
Pressing the
E
push-button again will
return the transmitter to the display
mode.
20
Summary of Contents for BA374C
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