Step 7
Cold junction compensation
In this example only one thermocouple
is connected so cold junction
compensation is required. Using the
Up
or
Down
button select 'CJC' from the
sub-menu and press
P
. The
Up
and
Down
buttons will turn the cold junction
'On' and 'OFF'. Select 'On' and press
E
to return to the sub-menu.
Step 8
Input open circuit drive
Using the
Up
or
Down
button select
'burn' from the sub-menu and press
P
to
reveal the current status. Select 'uP'
using the
Up
or
Down
button and press
E
three times to return to the 'InPut'
prompt via the 'burn' and 'tHC' prompts.
Step 9
Calibrating the 4/20mA output
'CAL' defines the display at which the
output current is 4mA and 20mA.
Select 'CAL' from the menu using the
Up
or
Down
push-button, and enter the
sub-menu by pushing
P
. The
transmitter will display a 'ZEro' prompt
requesting the display at which the
output is to be 4mA. Press
P
and
enter -10.0 using the
Up
,
Down
and
P
buttons. Press
E
to return to the 'ZEro'
prompt. Select 'SPAn' from the
sub-menu and press
P
. Enter 240.0
which is the display at which the output
current is to be 20mA and press E
twice to return to the 'CAL' prompt.
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
display 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 BA578C 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.
17
Содержание BA578C
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