Dc Power Supply; Analog Output; Hart Communications; Grounding - ABB LST300 Operating Instruction

c b
Figure 19 Termination introduction
a Positive polarity of power supply (+)
b Negative polarity of power supply (-)
c Extend meter, shorted with negative polarity for normal use (Ext)

DC power supply

The LST300 operates from a DC power supply that is connected
to the terminals shown in Fig . 15 .
• Open the blind cover first to connect the cable .
• The power supply voltage is 12 to 42 V DC without surge
protection, and 14 to 42 V with surge protection when the -
and Ext Meter terminals are shorted .
• It is recommended to use twisted pair cables for better
resistance to electrical disturbance .

Analog output

LST300 has a 4 to 20 mA analog output to transmit
measurements and alarms .
• The 4 to 20 mA output and power supply input share the same
wires .
• The output current is the process variable during normal
conditions . It can also be a fixed value as a failsafe or to
indicate alarm conditions .
• The current output range of a valid signal is 4 to 20 mA .
• The Low Alarm value is configurable in the range of 3 .5 mA to
3 .6 mA .
• The High Alarm value is configurable in the range of 21 mA to
22 .6 mA .
• The refresh frequency of the 4 to 20 mA output is 0 .2 second .
L S T 3 0 0 | C O M PA C T U LT R A S O N I C L E V E L T R A N S M I T T E R | L S T 3 0 0 – E N R E V. E
a

HART communications

The HART protocol is used for digital communication between a
process control system / PC, a handheld terminal, and LST300 .
It can be used to send all device and measuring point
parameters from the transmitter to the process control system
or PC . Conversely, it also provides a means of reconfiguring the
transmitter . Digital communication utilizes an alternating
current superimposed on the analog output (4 to 20 mA) that
does not affect any meters connected to the output .
• The HART communication shares the cable with the power
supply . No additional wires are required .
• An extra resistor is needed for HART communication . The
minimum value of resistor is 250 ohm . The resistor in power
line causes voltage drop, and should be considered to ensure
the power supply to the LST300 remains above the minimum
rated input voltage .
• The baud rate of the HART communication is 1200 .

Grounding

The LST300 requires a ground connection to the terminal as
shown in Fig . 16 .
• The LST300 provides two connectors for ground (PE) . An
effective ground connection is needed for optimum EMC
protection .
• All grounding must comply with anti-explosion regulations if
the LST300 transmitter is to be used in hazardous
environments (Zone 1 Div 1 and Zone 1 Div 2) .
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