BEKA BA574C, Manual

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1. DESCRIPTION
The BA574C is a 4/20mA loop powered
temperature transmitter incorporating a large easy
to read display. The instrument may be
programmed on-site to accept most common
thermocouples and resistance thermometers, and
will provide a linear 4/20mA output proportional to
temperature, plus a display in
o
C or
o
F. Voltage
inputs may be scaled allowing the BA574C to
display variables other than temperature.
Optional alarms provide two galvanically isolated
solid state outputs which may be independently
programmed as high or low trips. For installations
in poorly illuminated areas an optional display
backlight is available.
The BA574C transmitter is available in a glass
reinforced polyester (GRP), or an epoxy painted
aluminium enclosure, both provide IP66 protection.
Fig 1 Simplified block diagram
2. OPERATION
Fig 1 shows a simplified block diagram of the
transmitter. The input signal, which may be from a
thermocouple, resistance thermometer or a dc
voltage, is digitised and transferred to the
instrument processor via an optical isolator. The
processor scales the signal and for temperature
measurement applies linearisation using look-up
tables stored in permanent memory. The resulting
temperature is shown on the internal display and
controls the 4/20mA output current. The
transmitter and the optional alarms are powered
from the 4/20mA current loop, but the optional
display backlight requires a separate supply.
Each time power is applied to the instrument,
initialisation is performed. After a short delay the
following display sequence occurs:
-1.8.8.8.8 Display test in which all
segments of the display
are activated for 2.5
seconds.
. . . . For 1 second
0 For less than 0.5
seconds.
Input signal Using calibration
displayed information stored in
instrument memory.
2.1 Controls
All functions of the transmitter can be programmed
on-site via four push-buttons which are located
behind the enclosure cover - see Fig 3. In the
display mode i.e. when the transmitter is displaying
the input signal, these push-buttons have the
following functions. The 4/20mA output current is
not affected by operating these push-buttons, and
when released, the input signal will again be
displayed.
Button Function
Down While this button is pushed the
transmitter will show the display
corresponding to a 4mA output.
Up While this button is pushed the
transmitter will show the display
corresponding to a 20mA output.
For transmitters fitted with alarms
E + Up While these buttons are pushed the
transmitter will display setpoint 1.
E + Down While these buttons are pushed the
transmitter will display setpoint 2.
It is also possible to adjust the two alarm setpoints
from the display mode - see section 10.4
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